Five membered sulfur nitrogen ring compounds

(1)FIVE-MEMBERED SULFUR-NITROGEN RING COMPOUNDS Vit Matuska. A Thesis Submitted for the Degree of PhD at the University of St. Andrews. 2009. Full metadata for this item is available in Research@StAndrews:FullText at: http://research-repository.st-andrews.ac.uk/. Please use this identifier to cite or link to this item: http://hdl.handle.net/10023/828. This item is protected by original copyright.

(2) Five-Membered Sulfur-Nitrogen Ring Compounds A thesis submitted by. Vit Matuska In partial fullment for the award of Doctor of Philosophy of the University of St Andrews School of Chemistry, University of St Andrews North Haugh, St Andrews, Fife, KY16 9ST. 12 May 2009.

(3) Declarations I, Vit Matuska, hereby certify that this thesis, which is approximately 50,000 words in length, has been written by me, that it is the record of work carried out by me and that it has not been submitted in any previous application for a higher degree. Date:. Signature of candidate:. I was admitted as a research student in September, 2004 and as a candidate for the degree of Doctor of Philosophy in May, 2009; the higher study for which this is a record was carried out in the University of St Andrews between 2004 and 2009. Date:. Signature of candidate:. I hereby certify that the candidate has fullled the conditions of the Resolution and Regulations appropriate for the degree of Doctor of Philosophy in the University of St Andrews and that the candidate is qualied to submit this thesis in application for that degree. Date:. Signature of supervisor:. In submitting this thesis to the University of St Andrews we understand that we are giving permission for it to be made available for use in accordance with the regulations of the University Library for the time being in force, subject to any copyright vested in the work not being aected thereby. We also understand that the title and the abstract will be published, and that a copy of the work may be made and supplied to any bona de library or research worker, that my thesis will be electronically accessible for personal or research use unless exempt by award of an embargo as requested below, and that the library has the right to migrate my thesis into new electronic forms as required to ensure continued access to the thesis. We have obtained any third-party copyright permissions that may be required in order to allow such access and migration, or have requested the appropriate embargo below. The following is an agreed request by candidate and supervisor regarding the electronic publication of this thesis: embargo on both all or part of printed copy and electronic copy for the same xed period of 1 year on the following ground: publication would preclude future publication. Date:. Signature of candidate: Signature of supervisor:. 2.

(4) Acknowledgements I want to thank my Mum, Dad, Brother and my grandparents for a massive support throughout the studies. Without them I would have not been able to reach this point. I would like to dedicate this thesis to them. Special thanks to Stu Robertson and Richard Bond, who very patiently introduced me to the british culture and helped me to feel in Scotland like at home. My academic parents Gil Viana and Blerina Kellezi were always ready to cheer me up and for that I thank them a lot. I am indebted to Klára Mí£ková who helped me a lot in the very beginning. I am thankful to my landlords Mr and Mrs Gall, David and Gisele, Tom Lébl and Nathaniel for cosy rooms and to my atmates Mi²o, Alex, Gil, James and Lucia for creating a relaxed atmosphere at home. The Woollins, Slawin and Kilian groups - thank you folks for a really enjoyable time both in and outside the lab and also for the patience you had with me. Writing-up of this thesis was easier with LATEX 2ε and the KOMA - Script bundle. In addition to the authors I would like to thank Piotr for his help, tips and mainly Konwerter. Paul Waddell checked errors in some parts of this thesis. Grazie Poalo! I thank Dr. Tomá² Lébl and Melanja Smith for their very kind and instant help whenever needed downstairs in the NMR room. Many thanks to Dr. Joe Crayston (CV), Caroline (mass spec.), Sylvia (microanalysis), Marj, Bobby, Brian, Colin the storesman, Artur and Colin the glassblower. I am grateful to Dr. Petr Kilián who spent a lot of time bringing me up in the lab, showing me the equipment, its maintenance and explaining new techniques. A big thank is due to Prof. Alex Slawin who was always ready to measure my crystal structures knowing that they were going to be either S4 N4 , sulfur, Na2 SO4 or they would not diract at all. Finally, I would like to thank my supervisor, Prof. Derek Woollins, for all his help, support, advice, comments and corrections and for the patience he had with me during those years.. 3.

(5) Abstract A series of 1,3,2,4,5-dithiadiazarsoles with the general formula RAs(S2 N2 ) (R = Me, Et,. i Pr, t Bu,. Ph and Mes) have been prepared and characterised by multinuclear NMR, IR. and Raman spectroscopies and mass spectrometry. The X-ray structures of PhAs(S2 N2 ) and MesAs(S2 N2 ) were determined. The low temperature X-ray structures of the half-sandwich 5,1,3,2,4-metalladithiadiazoles Cp*M(S2 N2 ) (M = Co, Ir) were determined and Cp*Rh(S2 N2 ) was prepared. All three metalladithiadiazoles were characterised by multinuclear NMR, IR and Raman spectroscopies and mass spectrometry. The X-ray structures of complexes [Cp*RhCp*]Cl, [Cp*Rh(µ-S3 N2 )(µ-S2 O3 )RhCp*] and Cp*Ir[S2 N2 (IrCl2 Cp*)] obtained during this work were determined. The low temperature X-ray structure of Roesky's sulfoxide (S3 N2 O) is presented together with assignments of its vibrational spectra as suggested by theoretical calculations. The experimental structures of the metalladithiadiazoles and that of Roesky's sulfoxide are compared with calculated geometries. A limited amount of simple experiments have been carried out with selected title compounds to get an insight into their reactivity.. 4.

(6) Contents Declarations. 2. Acknowledgements. 3. Abstract. 4. List of Figures. 12. List of Tables. 14. Abbreviations. 16. General abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 16. NMR spectroscopy abbreviations . . . . . . . . . . . . . . . . . . . . . . . . .. 17. Vibrational spectroscopy abbreviations . . . . . . . . . . . . . . . . . . . . . .. 17. I. Introduction. 19. 1. General considerations. 20. 1.1. Preparation routes of sulfur-nitrogen heterocycles . . . . . . . . . . . . .. 20. 1.2. The multiplicity of S−N bonds. . . . . . . . . . . . . . . . . . . . . . . .. 22. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 24. 1.3.1. Geometry of a molecule . . . . . . . . . . . . . . . . . . . . . . .. 24. 1.3.2. Charges and bond orders . . . . . . . . . . . . . . . . . . . . . . .. 25. 1.3.3. Aromaticity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 25. 1.3.3.1. Aromaticity of sulfur-nitrogen compounds . . . . . . . .. 27. 1.4. General experimental conditions . . . . . . . . . . . . . . . . . . . . . . .. 28. 1.5. Experimental details of the key sulfur-nitrogen reagents syntheses . . . .. 29. 1.5.1. [S3 N2 Cl]Cl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 29. 1.5.2. [S4 N3 ]Cl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 30. 1.5.3. [ Bu2 Sn(S2 N2 )]2 . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 30. 1.3. Theoretical calculations. n. 5.

(7) Contents. II. Arsenic-Sulfur-Nitrogen Heterocycles. 32. 2. Introduction. 33. 2.1. The toxicity of arsenic . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 33. 2.1.1. Arsenic in the environment . . . . . . . . . . . . . . . . . . . . . .. 33. 2.1.2. Biotransformation of arsenic in nature . . . . . . . . . . . . . . .. 34. 2.1.3. Arsenic in the human body . . . . . . . . . . . . . . . . . . . . .. 35. 2.1.3.1. The principle of toxicity of arsenic . . . . . . . . . . . .. 35. 2.1.3.2. Metabolism of arsenic in the human body . . . . . . . .. 36. 2.2. Commercial availability of starting materials . . . . . . . . . . . . . . . .. 38. 2.3.. 75. As NMR as an analytical tool . . . . . . . . . . . . . . . . . . . . . . .. 38. 2.4. Methods of preparation of common starting materials . . . . . . . . . . .. 39. 2.4.1. Arsenic trihalogenides . . . . . . . . . . . . . . . . . . . . . . . .. 39. 2.4.2. Alkylarsonic acids . . . . . . . . . . . . . . . . . . . . . . . . . . .. 40. 2.4.3. Arylarsonic acids . . . . . . . . . . . . . . . . . . . . . . . . . . .. 41. 2.4.3.1. Rosenmund's method. . . . . . . . . . . . . . . . . . . .. 41. 2.4.3.2. Bart's reaction . . . . . . . . . . . . . . . . . . . . . . .. 41. 2.4.3.3. Modications of Bart's method . . . . . . . . . . . . . .. 46. 2.4.3.4. Béchamp's reaction . . . . . . . . . . . . . . . . . . . . .. 46. 2.4.4. Dialkyl- and diarylarsinic acids . . . . . . . . . . . . . . . . . . .. 47. 2.4.5. Organohalogenoarsines . . . . . . . . . . . . . . . . . . . . . . . .. 48. 2.4.5.1. From arsonic and arsinic acids . . . . . . . . . . . . . . .. 48. 2.4.5.2. From AsX3 and organometallic reagents . . . . . . . . .. 48. 2.4.5.3. Controlled substitution of halogens in AsX3 . . . . . . .. 50. 2.4.5.4. From AsX3 and organosilicon and organotin reagents . .. 52. 2.4.5.5. From AsX3 by aromatic electrophilic substitution . . . .. 54. 2.4.5.6. Special methods of RAsX2 preparation . . . . . . . . . .. 55. 2.4.5.7. Halogen exchange reactions of RAsX2. . . . . . . . . . .. 58. 2.5. Arsenic containing main-group ring compounds . . . . . . . . . . . . . .. 59. 2.5.1. Organoarsenic heterocycles . . . . . . . . . . . . . . . . . . . . . .. 59. 2.5.1.1. Five-membered heterocycles . . . . . . . . . . . . . . . .. 59. 2.5.1.2. Six-membered heterocycles. . . . . . . . . . . . . . . . .. 60. 2.5.2. Arsenic homocycles . . . . . . . . . . . . . . . . . . . . . . . . . .. 61. 2.5.2.1. Five-membered arsenic homocycles . . . . . . . . . . . .. 61. 2.5.2.2. Six-membered arsenic homocycles . . . . . . . . . . . . .. 62. 2.5.2.3. Arsafullerenes . . . . . . . . . . . . . . . . . . . . . . . .. 63. 2.5.3. Arsenic containing analogues of S4 N4 . . . . . . . . . . . . . . . .. 64. 2.5.3.1. Cyclotetrathiatetrarsocane . . . . . . . . . . . . . . . . .. 64. 6.

(8) Contents. 2.5.3.2. Cyclotetraarsazenes. . . . . . . . . . . . . . . . . . . . .. 66. 2.5.3.3. Cyclotetraarsazanes . . . . . . . . . . . . . . . . . . . .. 67. 2.5.3.4. Dithiatetrazadiarsocines . . . . . . . . . . . . . . . . . .. 69. 2.5.3.5. 1,5,2,4,6,8,3,7-dithiatetrazadiarsocanes . . . . . . . . . .. 72. 2.5.3.6. Other AsSN eight-membered heterocycles . . . . . . . .. 72. 2.5.4. Arsenic containing analogues of S2 N2 . . . . . . . . . . . . . . . .. 73. 2.5.4.1. As2 S2 . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 73. 2.5.4.2. As2 N2 . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 75. 2.5.5. Five- and six-membered arsenic-sulfur-nitrogen rings . . . . . . .. 77. 2.5.6. AsEN heterocycles (E = Se, Te) . . . . . . . . . . . . . . . . . . .. 77. 2.5.6.1. Eight-membered As4 E4 heterocycles (E = Se, Te) . . . .. 77. 2.5.6.2. Four-membered As2 E2 heterocycles (E = Se, Te) . . . .. 78. 2.6. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 79. 3. Results and Discussion. 80. 3.1. Comments on preparative procedures . . . . . . . . . . . . . . . . . . . .. 82. 3.1.1. Alkyl/aryldihalogenoarsines . . . . . . . . . . . . . . . . . . . . .. 82. 4 2. 3.1.2. 5-alkyl/aryl-1,3λ δ ,2,4,5-dithiadiazarsoles . . . . . . . . . . . . .. 87. 3.2. NMR spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 89. 3.2.1.. 1. 3.2.2.. 14. H and. 13. C NMR data . . . . . . . . . . . . . . . . . . . . . . . .. 89. N NMR data . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 92. 3.3. Mass spectrometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 94. 3.4. IR and Raman spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . .. 95. 3.4.1. The assignments and their discussion . . . . . . . . . . . . . . . .. 96. 3.5. X-ray structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 3.5.1. PhAs(S2 N2 ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 3.5.2. MesAs(S2 N2 ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 3.6. Cyclic voltammetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 3.7. Reactivity of PhAs(S2 N2 ) . . . . . . . . . . . . . . . . . . . . . . . . . . 110 3.8. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112. 4. Experimental. 114. 4.1. Preparation of AsCl3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 4.2. Preparation of CH3 AsI2 4.3. Preparation of EtAsI2. . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115. i. 4.4. Preparation of PrAsCl2 . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 4.5. Preparation of t BuAsCl2 . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 4.6. Preparation of PhAsCl2. . . . . . . . . . . . . . . . . . . . . . . . . . . . 118. 7.

(9) Contents. 4.7. Preparation of mixture of mesityldihalogenoarsines . . . . . . . . . . . . 119 4.8. Preparation of p-phenylenediarsonic acid by Bart's reaction . . . . . . . . 120 4.9. Reaction of MeAsI2 with [n Bu2 Sn(S2 N2 )]2 4.10. Reaction of EtAsI2 with 4.11. Reaction of 4.12. Reaction of 4.13. Reaction of 4.14. Reaction of. [n Bu. . . . . . . . . . . . . . . . . . 121. 2 Sn(S2 N2 )]2 . . . n 2 with [ Bu2 Sn(S2 N2 )]2 . . t BuAsCl with [n Bu Sn(S N )] 2 2 2 2 2 . n PhAsCl2 with [ Bu2 Sn(S2 N2 )]2 . . mesityldihalogenoarsines with [n Bu. i PrAsCl. . . . . . . . . . . . . . . . 122 . . . . . . . . . . . . . . . 123 . . . . . . . . . . . . . . . 124 . . . . . . . . . . . . . . . 125 2 Sn(S2 N2 )]2. . . . . . . . . 126. 4.15. Reaction of PhAs(S2 N2 ) with Pt(COD)Cl2 . . . . . . . . . . . . . . . . . 127 4.16. Methylation of PhAs(S2 N2 ) with CH3 I . . . . . . . . . . . . . . . . . . . 127 4.17. Reaction of PhAs(S2 N2 ) with [Mo(CO)4 (piperidine)2 ] . . . . . . . . . . . 128 4.18. Reaction of PhAs(S2 N2 ) with Cp2 Ti(CO)2 . . . . . . . . . . . . . . . . . 128 4.19. Reaction of PhAs(S2 N2 ) with Cp*Co(CO)2 . . . . . . . . . . . . . . . . . 128 4.20. Reaction of PhAs(S2 N2 ) with sulfur . . . . . . . . . . . . . . . . . . . . . 129. III. Transition Metal Sulfur-Nitrogen Ring Compounds 5. Introduction. 130 131. 5.1. Four-membered rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 5.2. Five-membered rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 5.2.1. M(S2 N2 ) complexes containing the (S2 N2 ) 2  anion . . . . . . . . 134 5.2.1.1. Preparation from S4 N4 or S2 N2 . . . . . . . . . . . . . . 134 5.2.1.2. Preparation from other SN rings . . . . . . . . . . . . . 135 5.2.1.3. Transmetallation reactions . . . . . . . . . . . . . . . . . 137 5.2.1.4. Deprotonation of M(S2 N2 H) complexes . . . . . . . . . . 137 5.2.1.5. Preparation from acyclic SN compounds . . . . . . . . . 138 5.2.2. M(S2 N2 ) complexes containing the (NSSN) moiety . . . . . . . . . 138 5.2.3. M(S2 N2 H) ring complexes . . . . . . . . . . . . . . . . . . . . . . 139 5.2.3.1. Preparation from S4 N4 . . . . . . . . . . . . . . . . . . . 139 5.2.3.2. Protonation of M(S2 N2 ) complexes . . . . . . . . . . . . 140 5.2.4. M(S3 N) ring complexes . . . . . . . . . . . . . . . . . . . . . . . . 140. 5.2.4.1. Preparation from [S7 N]  . . . . . . . . . . . . . . . . . . 140 5.2.4.2. Desulfuration of [S4 N]  . . . . . . . . . . . . . . . . . . 141 5.2.4.3. Preparation from other SN compounds . . . . . . . . . . 141. 5.2.5. Structure of the ve-membered MSN rings . . . . . . . . . . . . . 141 5.3. Six-membered rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 5.3.1. M(S3 N2 ) ring complexes . . . . . . . . . . . . . . . . . . . . . . . 142. 8.

(10) Contents. 5.3.2. M(S2 N3 ) ring complexes bearing the (S2 N3 )  anion . . . . . . . . 143. 5.3.3. M(S2 N3 ) ring complexes bearing the (S2 N3 ) 3  anion. . . . . . . . 143. 5.3.4. M(S2 N3 ) ring complexes bearing the [N2 S2 N(SO2 NH2 )] 2  anion . 144. 5.4. Seven-membered rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 5.5. Eight-membered rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 5.5.1. Complexes of the (S3 N4 ) 2  anion . . . . . . . . . . . . . . . . . . 145 5.5.2. Complexes of the (S4 N3 )  anion . . . . . . . . . . . . . . . . . . . 146 5.6. Nine-membered rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 5.6.1. Monocyclic nine-membered rings . . . . . . . . . . . . . . . . . . 146 5.6.2. Insertion of a metal centre in S4 N4 . . . . . . . . . . . . . . . . . 146 5.7. Half-sandwich M(S2 N2 ) complexes . . . . . . . . . . . . . . . . . . . . . . 148 5.8. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148. 6. Results and discussion. 149. 6.1. Syntheses of the complexes . . . . . . . . . . . . . . . . . . . . . . . . . . 149 6.1.1. Cp*Co(S2 N2 ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 6.1.2. Cp*Rh(S2 N2 ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 6.1.3. Cp*Ir(S2 N2 ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 6.2. The X-ray structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 6.2.1. Cp*M(S2 N2 ) (M = Co, Rh, Ir). . . . . . . . . . . . . . . . . . . . 152. 6.2.1.1. The inuence of M in CpM(S2 N2 ) and Cp*M(S2 N2 ) . . . 156 6.2.2. Cp*Rh(µ−S3 N2 )(µ−S2 O3 )RhCp* and [Cp*RhCp*]Cl . . . . . . . 158 6.2.3. Cp*Ir[S2 N2 (IrCl2 Cp*)] . . . . . . . . . . . . . . . . . . . . . . . . 160 6.3. NMR spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 6.3.1.. 14. N NMR spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . 164. 6.4. Mass spectrometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 6.5. IR and Raman spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . 165 6.6. Protonation of Cp*Co(S2 N2 ) . . . . . . . . . . . . . . . . . . . . . . . . . 165 6.7. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166. 7. Experimental. 168. 7.1. Preparation of [Cp*RhCl2 ]2 . . . . . . . . . . . . . . . . . . . . . . . . . 168 7.2. Preparation of Cp*Co(CO)2 . . . . . . . . . . . . . . . . . . . . . . . . . 169 7.3. Preparation of Cp*Co(S2 N2 ) . . . . . . . . . . . . . . . . . . . . . . . . . 169 7.4. Cp*Rh(S2 N2 ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 7.5. [Cp*RhCp*]Cl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 7.6. [Cp*Rh(µ-S3 N2 )(µ-S2 O3 )RhCp*]. . . . . . . . . . . . . . . . . . . . . . . 171. 7.7. Preparation of [Cp*Rh(S2 N2 H)]PF6 . . . . . . . . . . . . . . . . . . . . . 172. 9.

(11) Contents. 7.8. Cp*Ir(S2 N2 ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 7.9. Cp*Ir[S2 N2 (IrCl2 )]Cp* . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 7.10. Protonation of Cp*Co(S2 N2 ) with HBF4 . . . . . . . . . . . . . . . . . 174 7.11. Protonation of Cp*Co(S2 N2 ) with HCl . . . . . . . . . . . . . . . . . . 175 7.12. Computational details. . . . . . . . . . . . . . . . . . . . . . . . . . . . 175. IV. Roesky's Sulfoxide, S3N2O. 176. 8. Introduction. 177. 8.1. Synthesis of Roesky's sulfoxide . . . . . . . . . . . . . . . . . . . . . . . . 177 8.2. Structure and reactivity . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 8.3. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181. 9. Results and Discussion. 182. 9.1. The crystal structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 9.1.1. Aromaticity of Roesky's sulfoxide . . . . . . . . . . . . . . . . . . 184 9.2. Vibrational spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 9.3.. 14. N NMR spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185. 9.4. Cyclic voltammetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 9.5. Reactivity of Roesky's sulfoxide . . . . . . . . . . . . . . . . . . . . . . . 185 9.6. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188. 10.Experimental. 189. 10.1. Preparation of S3 N2 O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 10.2. Reaction of S3 N2 O with Cp*Co(CO)2 . . . . . . . . . . . . . . . . . . . . 189 10.3. Reaction of S3 N2 O with Cp2 Ti(CO)2 . . . . . . . . . . . . . . . . . . . . 190 10.4. Reaction of S3 N2 O and [(Ph3 P)Au(CH3 CN)][ClO4 ] . . . . . . . . . . . . 190 10.5. Protonation of S3 N2 O with HBF4 . . . . . . . . . . . . . . . . . . . . . . 191 10.6. Reaction of S3 N2 O with Woollins' Reagent . . . . . . . . . . . . . . . . . 191 10.7. Reaction of (S2 N2 )CO with Woollins' Reagent . . . . . . . . . . . . . . . 192 10.8. Computational details . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192. Conclusion. 193. Further work. 195. References. 196. 10.

(12) Contents. Appendices. 211. A. Crystallographic data. 212. 11.

(13) List of Figures 1.1. Selected S-N compounds with S-N bond lengths . . . . . . . . . . . . . .. 24. 2.1. Arsenobetaine, arsanilic acid and roxarsone . . . . . . . . . . . . . . . . .. 34. 2.2. The structures of syn - and anti - arenediazoates . . . . . . . . . . . . . .. 43. 2.3. Ball and stick model of the anion [As@Ni12 @As20 ] 3 . 64. . . . . . . . . . . .. 2.4. The structures of realgar (α-As4 S4 ), realgar As4 S4 (II) and their metal complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 66. 2.5. A schematic demonstration of the structural dierence between S4 N4 and dithiatetrazadiarsocines . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 70. 2.6. Possible conformations of the As2 S2 ring . . . . . . . . . . . . . . . . . .. 73.  2.7. A part cut out from the polymeric anion [NiAs4 S8 ] 2n . . . . . . . . . . . n. 74. 2.8. Mesomeric structures of bis(1,3,2-dithiarsolylium) dication . . . . . . . .. 75. 3.1. 1,4-bis(dichloroarsino)benzene, p -phenylenediarsonic acid and Atoxyl . .. 86. 3.2. Simulated and recorded 1H NMR spectrum of EtAs(S2 N2 ) . . . . . . . .. 91. i. 3.3. A general presentation of conformers for EtAsI2 , PrAsCl2 , EtAs(S2 N2 ) and i PrAs(S2 N2 ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 96. 3.4. The X-ray structure of PhAs(S2 N2 ) . . . . . . . . . . . . . . . . . . . . . 106 3.5. The stacking of PhAs(S2 N2 ) molecules in the crystal. . . . . . . . . . . . 107. 3.6. The X-ray structure of MesAs(S2 N2 ) . . . . . . . . . . . . . . . . . . . . 108 3.7. Cyclic voltammogram of PhAs(S2 N2 ) . . . . . . . . . . . . . . . . . . . . 110 5.1. Possible coordination modes of the N2 S and NS2 ligands onto a metal centre . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 5.2. The structure of [Cl2 Re(S2 N3 )(Cl3 ReSN3 )]22  . . . . . . . . . . . . . . . . 144 5.3. The structures of complexes [(PPh3 )(CO)IrCl(f ac-S4 N4 )] and [PPh4 ][Cl3 Pt(f ac-S4 N4 )] . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 5.4. The structures of complexes [(PPhMe2 )PtCl2 (mer-S4 N4 )] and [(PPhMe2 )PtCl2 (f ac-S4 N4 )] . . . . . . . . . . . . . . . . . . . . . . . . . 147 5.5. Numbering of the CpM(S2 N2 ) and Cp*M(S2 N2 ) complexes . . . . . . . . 148 6.1. The X-ray structure of Cp*Co(S2 N2 ) . . . . . . . . . . . . . . . . . . . . 153. 12.

(14) List of Figures. 6.2. The X-ray structure of Cp*Ir(S2 N2 ) . . . . . . . . . . . . . . . . . . . . . 156 6.3. The X-ray structure of Cp*Rh(µ−S3 N2 )(µ−S2 O3 )RhCp* . . . . . . . . . 158 6.4. A Newman projection of Cp*Rh(µ−S3 N2 )(µ−S2 O3 )RhCp* . . . . . . . . 160 6.5. The X-ray structure of [Cp*RhCp*]Cl · H2 O . . . . . . . . . . . . . . . . 160 6.6. The X-ray structure of Cp*Ir[S2 N2 (IrCl2 Cp*)] · n Bu2 SnCl2 . . . . . . . . 161 6.7. Cp*Ir[S2 N2 (IrCl2 Cp*)] and [Cp*Ir[S2 N2 (IrCl(PPh3 )Cp*)]][PF6 ] . . . . . . 163 9.1. The crystal structure of S3 N2 O . . . . . . . . . . . . . . . . . . . . . . . 183 9.2. The packing of S3 N2 O molecules in the crystal . . . . . . . . . . . . . . . 183 9.3. Cyclic voltammogram of S3 N2 O . . . . . . . . . . . . . . . . . . . . . . . 186 9.4. The structure of the complex Cp2 Ti(N3 )−O−Ti(N3 )Cp2 . . . . . . . . . 187. 13.

(15) List of Tables 3.1. Melting and boiling points of Me3 SiX and n Bu2 SnX2 . . . . . . . . . . .. 81. 3.2.. 1. 90. 3.3.. 1. H NMR data of RAsX2 . . . . . . . . . . . . . . . . . . . . . . . . . . . H NMR data of RAs(S2 N2 ) . . . . . . . . . . . . . . . . . . . . . . . . .. 91. 3.4.. 13. 92. 3.5.. 13. C NMR data of RAsX2 . . . . . . . . . . . . . . . . . . . . . . . . . . . C NMR data of RAs(S2 N2 ) . . . . . . . . . . . . . . . . . . . . . . . . .. 93. 3.6.. 14. N NMR data of RAs(S2 N2 ). . . . . . . . . . . . . . . . . . . . . . . . .. 93. 3.7. Selected IR and Raman wavenumbers of MeAsI2 and MeAs(S2 N2 ) . . . .. 98. 3.8. Selected IR and Raman wavenumbers of EtAsI2 and EtAs(S2 N2 ) . . . . .. 99. 3.9. Selected IR and Raman wavenumbers of i PrAsCl2 and i PrAs(S2 N2 ) . . . 100 3.10. Selected IR and Raman wavenumbers of t BuAsCl2 and t BuAs(S2 N2 ) . . . 101 3.11. Selected IR and Raman wavenumbers of PhAsCl2 and PhAs(S2 N2 ). . . . 103. 3.12. Selected IR and Raman wavenumbers of MesBr and MesAs(S2 N2 ) . . . . 105 3.13. Selected bond lengths and angles of PhAs(S2 N2 ) . . . . . . . . . . . . . . 106 3.14. Selected bond lengths and angles of MesAs(S2 N2 ) . . . . . . . . . . . . . 109 3.15. Experimental and simulated voltammetric data for PhAs(S2 N2 ) . . . . . 110 6.1. Selected bond lengths and angles of CpCo(S2 N2 ), Cp*Co(S2 N2 ) and Cp*Ir(S2 N2 ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 6.2. Selected calculated geometrical data for CpM(S2 N2 ) and Cp*M(S2 N2 ) . . 154 6.3. Calculated Wiberg bond orders for the most important bonds in CpM(S2 N2 ) and Cp*M(S2 N2 ) . . . . . . . . . . . . . . . . . . . . . . . 157 6.4. Selected bond lengths and angles for Cp*Rh(µ−S3 N2 )(µ−S2 O3 )RhCp* . 159 6.5. Selected bond lengths and angles for [Cp*RhCp*]Cl · H2 O . . . . . . . . . 160 6.6. Selected bond lengths and angles for Cp*Ir(S2 N2 ), Cp*Ir[S2 N2 (IrCl2 Cp*)] and [Cp*Ir[S2 N2 (IrCl(PPh3 )Cp*)]][PF6 ] . . . . . . . . . . . . . . . . . . . 162. H NMR data of compounds 47, 49, 51, 52, 53 and 54 . . . . . . . . . . 163. 6.7.. 1. 6.8.. 13. C NMR data of compounds 47, 49, 51, 52, 53 and 54 . . . . . . . . . 164. 9.1. The bond lengths and angles for S3 N2 O . . . . . . . . . . . . . . . . . . . 183 9.2. Selected IR and Raman wavenumbers of S3 N2 O . . . . . . . . . . . . . . 184 9.3. Voltammetric data for S3 N2 O . . . . . . . . . . . . . . . . . . . . . . . . 185. 14.

(16) List of Tables. A.1. Crystal data and structure renement for PhAs(S2 N2 ) . . . . . . . . . . . 212 A.2. Crystal data and structure renement for MesAs(S2 N2 ) . . . . . . . . . . 213 A.3. Crystal data and structure renement for Cp*Co(S2 N2 ) . . . . . . . . . . 214 A.4. Crystal data and structure renement for Cp*Ir(S2 N2 ) . . . . . . . . . . 215 A.5. Crystal data and structure renement for [Cp*Rh(µ−S3 N2 )(µ−SSO3 )RhCp*]·CH2 Cl2 . . . . . . . . . . . . . . . . . 216 A.6. Crystal data and structure renement for [Cp*RhCp*]Cl · H2 O . . . . . . 217 A.7. Crystal data and structure renement for Cp*Ir[S2 N2 (IrCl2 Cp*)] · n Bu2 SnCl2. . . . . . . . . . . . . . . . . . . . . . 218. A.8. Crystal data and structure renement for S3 N2 O . . . . . . . . . . . . . . 219. 15.

(17) Abbreviations General abbreviations ◦. degrees Celsius. Å. Ångström, 1 × 10−10 m. Ac. acetyl. approx.. approximately. b.p.. boiling point. n Bu. but-1-yl. t Bu. tertiary butyl, 2-methylprop-2-yl. calc.. calculated. CI. chemical ionisation. COD. cycloocta-1,5-diene. conc.. concentrated. Cp. cyclopentadienyl (C5 H5 ). C. Cp* Cp. 0. 1,2,3,4,5-pentamethylcyclopentadienyl (C5 Me5 ) methylcyclopentadienyl (C5 H4 Me). Cp×. 1-ethyl-2,3,4,5-tetramethylcyclopentadienyl (C5 Me4 Et). Cy. cyclohexyl. DBN. 1,5-diazabicyclo[4.3.0]non-5-ene. DBU. 1,8-diazabicyclo[5.4.0]undec-7-ene. decomp.. decomposition. DME. 1,2-dimethoxyethane. DMF. N,N -dimethylformamide. DMSO. dimethylsulfoxide. EI. electron impact. ES. electrospray. Et. ethyl. Fc. ferrocenyl. HOMO. Highest Occupied Molecular Orbital. hr, hrs. hour, hours. 16.

(18) Abbreviations. IR. infrared. LCAO. Linear Combination of Atomic Orbitals. LUMO. Lowest Unoccupied Molecular Orbital. m.p.. melting point. Me. methyl. Mes. mesityl, 2,4,6-trimethylphenyl. min.. minute, minutes. MS. mass spectrometry. NBS. N -bromosuccinimide. NMR. Nuclear Magnetic Resonance. Ph. phenyl. Phth. phthalimide. i Pr. iso -propyl, prop-2-yl. r.t.. room temperature. toil. oil bath temperature. THF. tetrahydrofuran. TOF. Time Of Flight. XRD. X-Ray Diraction. NMR spectroscopy abbreviations d. doublet. dd. doublet of doublet. m. multiplet. qqrt. quartet of quartet. qrt. quartet. quart.. quarternary (written as a subscript to an atom, e.g. Cquart. ). s. singlet. t. triplet. Vibrational spectroscopy abbreviations m. medium. ms. medium-strong. mw. medium-weak. 17.

(19) Abbreviations. s. strong. sh. shoulder. v. very. w. weak. β. bending (in-plane). γ δ ν ν number. bending (out-of-plane). ρ τ ω Qnumber. deformation stretch a fundamental frequency; also used for labelling vibrational mode corresponding to that frequency rocking twist wag a general label for a vibrational mode if description by commonly used greek letters cannot be used. 18.

(20) Part I. Introduction. 19.

(21) 1. General considerations This thesis concentrates on the preparation and characterisation of ve-membered sulfurnitrogen ring compounds with the emphasis on ve-membered heterocycles. Since particular projects involved in this thesis deal with elements from dierent areas of the Periodic System, it seemed better to compose the thesis along these lines. The rst part describes the syntheses of the key sulfur-nitrogen reagents used throughout the research period as well as denitions of basic terms in computational chemistry, which are used in the sebsequent parts. The focus of the second part is on 1,3,2,4,5-dithiadiazarsoles with the general formula RAs(S2 N2 ). The third part deals with half-sandwich 5,1,3,2,4-metalladithiadiazoles of the Group 9 metals (Co, Rh, Ir) and in the last part the structure and reactivity of Roesky's sulfoxide (S3 N2 O) is discussed. Every part has its own introduction, discussion of results and experimental section. The overall contribution described in the thesis is summarised in a nal conclusion, after which a short account on future work follows. References are listed at the end of the thesis followed by appendices.. 1.1. Preparation routes of sulfur-nitrogen heterocycles General synthetic routes leading to sulfur-nitrogen heterocycles have been thoroughly reviewed. 13 The most useful are the cyclocondensation reactions which start with cheap and commercially available acyclic materials and nish with ring compounds. These ring compounds can be further converted into other ring compounds with suitable reagents. 1,3 A number of methods will be described in the introductions of particular chapters. The routes leading to the most frequent suur-nitrogen reagents used during this work are described here. All syntheses started with S2 Cl2 , NH4 Cl and elemental sulfur, which react together in the absence of solvents at 150152 ◦C to give the air-sensitive ve-membered ring salt. 20.

(22) 1. General considerations. [S3 N2 Cl]Cl (eq. 1.1). 4 Cl 2 NH4Cl + 4 S2Cl2. S+. +S. N. reflux. S Cl. + 8 HCl + 5 S. N. S. (1.1). Although unpleasant and despite relatively low yields, this synthesis can be conveniently scaled-up to provide good amounts of the material. Interestingly, [S3 N2 Cl]Cl has not been used in many syntheses other than conversions to other purely SN rings. One such example is the preparation of [S4 N3 ]Cl (eq. 1.2). 4 Cl S+ 3. N S. S Cl. -. + S2Cl2. S. N. CCl4. 2. reflux. N S Cl + 3 SCl2. S N. N. S. (1.2). The bright yellow crystalline compound is also air-sensitive but can be stored for long time periods with only marginal decomposition. The conversion from [S3 N2 Cl]Cl to [S4 N3 ]Cl is nearly quantitative. [S4 N3 ]Cl became extremely popular over the years because it is a safe source of the. [S2 N2 ] 2  anion, which is the building block in a large number of metal-sulfur-nitrogen complexes (see Part III of this thesis). S4 N3 Cl reacts with liquid ammonia to form a complex mixture, which was thoroughly studied by. 14. N NMR spectroscopy. 5 The major. product was shown to be the [S3 N3 ]  anion (eq. 1.3), while [S2 N2 ] 2  was not detected. However, experiments preceding the NMR study conrmed the formation of metalladithiadiazoles (PR3 )2 M(S2 N2 ) (M = Pt, Pd) from Na[S3 N3 ] (eq. 5.10, page 136) 6 indicating that [S2 N2 ] 2  could be formed from [S3 N3 ]  . The role of the metal centre in the transformation of [S3 N3 ]  was not investigated but it was suggested that [S3 N3 ]  disproportionates to give S4 N4 and [S2 N2 ] 2  (eq. 1.4). 6. 9 [S3N3]- + H2S + 16 H+. 7 [S4N3]+ + 6 NH3 4 [S3N3]-. 2 S4N4 + 2 [S2N2]2-. (1.3) (1.4). Based on the results from previous works 7 it is very probable that the disproportionation of [S3 N3 ]  occurs also in the liquid ammonia reaction mixture. The generated [S2 N2 ] 2  anion can then be directly utilised in substitution reactions with organometallic dihalogenides to give various metalladithiadiazoles.. 21.

(23) 1. General considerations. One class of metalladithiadiazoles, namely the tin analogues dithiadiazastannoles (or stannadithiadiazoles) became versatile reagents in SN synthesis. [n Bu2 Sn(S2 N2 )]2 represents a good example of a versatile tin reagent prepared from n Bu2 SnCl2 and [S4 N3 ]Cl in liquid ammonia (eq. 1.5). 8. S. n. Bu. 18 nBu2SnCl2 + 28 S4N3Cl + 92 NH3. NH3 (l). 9. N S. N. n. Sn. Bu. N. S N. n. Bu. Sn S. +. n. Bu. + 18 S4N4 + 4 NH4SH + 64 NH4Cl. (1.5). The procedure is relatively time consuming (23 days) but this is mainly due to long purication period (Soxhlet extraction). The time is reasonable with respect to the quantities of the tin reagent obtained. Both the liquid ammonia method and the use of the tin reagent [n Bu2 Sn(S2 N2 )]2 have been frequently employed during this work. The experimental details of the syntheses of the above SN reagents are described at the end of this introductory part.. 1.2. The multiplicity of S−N bonds It is often important to know whether a chemical bond is single, double or triple. This can be formally decided on the basis of a bond order, which can be calculated according to the well known formula. b=. n−n∗ 2. ,. where b is the bond order, n is the number of electrons in bonding orbitals and n∗ is the number of electrons in antibonding orbitals. 9 Cystallographic methods showed that triple bonds are shorter than double, which are shorter than single bonds. Thus, it is possible to make an assessment of bond multiplicities of a novel compound on the basis of its X-ray structure. Organic molecules are excellent examples, in which the types of bonds correspond very well with their lengths. Is this also the case for sulfur-nitrogen compounds? Pauling's original covalent radii of singly bound nitrogen (0.70 Å) and other rst row elements were corrected by Schomaker and Stevenson (0.74 Å), who also provided the covalent radii for doubly and triply bound main group elements. 10 Pauling included these corrected values in the 3rd edition of his famous book about chemical bonds but. 22.

(24) 1. General considerations. recommended to use them only for the second period elements. 11 Thus, the covalent radii for singly, doubly and triply bound nitrogen are 0.74, 0.62 and 0.55 Å, respectively, and those of sulfur are 1.04, 0.94 and 0.87 Å, respectively.∗ For the calculation of the length of a single bond between atoms A and B, Pauling suggested to use Schomaker and Stevenson's equation. D(A−B) = rA + rB − c|xA − xB | , where rA and rB are Pauling's and - for the second period elements - Schomaker and Stevenson's covalent radii of the two elements, xA and xB are Pauling's electronegativities of the two elements and c is a correction coecient. Pauling suggested the coecient to be 0.08 Å for any bond involving one or two atoms from the second period of the Periodic System. This is the case for a S−N single bond, which should be 1.74 Å long. The theoretical S−N bond length calculated by the addition of the covalent radii for doubly bound nitrogen and sulfur 11 is 1.56 Å and the S−N length is 1.42 Å. The reality is not so straightforward. Classication of S−N bonds on the basis of their length is tricky, as the intervals for the lengths of particular bond types are very wide. For example the experimental values of a S−N single bond range from 1.74 to 1.61 Å (Fig. 1.1). 14,15 The experimental values of a S−N bond lie in the interval 1.561.46 Å (in INSNI and [S−N−S] + , respectively) 16,17 and the S− −N bond lengths were found from 1.46 to 1.42 Å (in NSPh3 and NSF3 , respectively). 1820 The overlap between the double and triple bond length interval is striking. On one hand it was emphasised that the valence description of [S−N−S] + most probably does not correspond to reality and that the S−N bonds in the cation have a signicant triple character. 17 Nevertheless, the form [S−N−S] + is still commonly used. On the other hand it was shown, that the length of a S−N bond depends on the charge of a S−N molecule,. i.e. the total number of electrons within the molecule. For example S4 N4 contains nearly equal S−N bonds with the length of 1.63 Å (mean value). 21 A withdrawal of one or two electrons from the antibonding HOMO orbitals results in a dramatic structural change and shortening of the bonds to 1.55 Å observed in the radical cation [S4 N4 ] ·+ and in the planar forms of the [S4 N4 ] 2+ cation, respectively. 22,23 If similar bond shortening by 0.08 Å is to be expected upon withdrawing electrons from the hypothetical thio-analogue ∗. Two recent studies brought a list of new single bond covalent radii for nearly all the elements. While the summary by Cordero et al. 12 is based on a vast amount of experimental values published in the Cambridge Structural Database, Pyykkö and Atsumi brought a more consistent set of radii based on experimental or calculated data of several model molecules, which were subsequently optimised by least-squares t. 13 For nitrogen, both Cordero et al. and Pyykkö and Atsumi published a covalent radius of 0.71 Å. The value is very close to the Pauling's original value but since Pauling himself adopted the corrected value of 0.74 Å, 0.74 Å will be used throughout this thesis. The new single bond covalent radius of sulfur was found to be 1.05 Å (Cordero) or 1.03 Å (Pyykkö). Pauling's original value (1.04 Å) oers an excellent compromise and will be used throughout this thesis.. 23.

(25) 1. General considerations O. 1.74 Å. O 1.61 Å. S. S. HN. N NH. 1.69 Å. S. S S. S. N. I 1.56 Å. S. S. 1.55 Å. N. S. (a). N. S. 1.58 Å. N I. N S 1.56 Å (1.53 Å). 1.60 Å (1.57 Å). (b). (c). Fig. 1.1. Selected S-N compounds with S-N bond lengths: (a) S6 (NH)2 (1,4isomer); (b) S4 N4 O2 ; (c) INSNI; the bond lengths in parentheses belong to another INSNI molecule in the unit cell.. of nitrogen dioxide radical (·NS2 ), then Pauling's S−N bond length (1.56 Å) will change to 1.48 Å, which is very close to the experimental value in the [S−N−S] + cation. 17 A signicant triple character then must be put in question. According to Parsons and Passmore, the formal bond order in [S−N−S] + is indeed 2. 24 Overall the determination whether a S−N bond is single or double is precarious. Similarly problematic is the commonly used term  a length between a single and a double. S−N bond  for molecules where π -electrons delocalisation is possible.. 1.3. Theoretical calculations Research in chemical synthesis has been for some time strongly supported by the use of computing techniques. Nowadays, there are only a few synthetic chemists who would refuse to benet from predictions of structure or electron arrangements within molecules of their interest. Since some compounds discussed in this thesis were thoroughly analysed by computational methods, a brief section is included about how structure, bonding and aromaticity can be described by the results obtained from theoretical calculations.. 1.3.1. Geometry of a molecule The structure of a molecule is given by a set of atoms arranged in certain manner in threedimensional space. A particular set-up of atoms will be stable only if the total energy of this set-up will be low. A correlation between energy of a particle and its position in a three-dimensional space is mathematically described by the Schrödinger equation. Once a mathematical description of a problem exists, calculations can be started to solve the problem. The geometry of a molecule is optimised in two steps. The rst step is usually ab. initio quantum mechanical calculations, the target of which is to nd a solution of the. 24.

(26) 1. General considerations. Schrödinger equation for a multiatomic system, i.e. the energies of atomic orbitals. 9 Because the Schrödinger equation cannot be precisely solved for more than a two-particle system, the equation used is simplied by several approximations. These approximations lead to inaccurate orbital energy values and therefore it is necessary to apply post-ab. initio  methods (e.g. DFT). The post-ab initio methods elaborate the ab initio results by taking into account circumstances neglected or averaged by the previously used approximations and as a result lower orbital energy values are obtained. 25 In the second step the ab initio geometry is subjected to molecular mechanics calculations (force eld calculations), which assess how distorted are particular structural parameters of the ab initio structure - i.e. bond lengths, bond angles, dihedral angles and non-bonding interactions - from ideal values given by agreed standards. 25 The higher the distorsion, the higher energy contribution and the higher the overall energy of the. ab initio geometry. The overall energy must correspond to a minimum on a Potential Energy Surface (PES) if the ab initio structure is to be considered as stable. During these molecular mechanics calculations the vibrational frequencies are also calculated. 25,26. 1.3.2. Charges and bond orders The atomic charges and bond orders are calculated by partitioning the total electron density in the regions of the atoms. For both the atomic charge calculation and the bond order calculation several concepts have been developed. The principles are complex. 26. 1.3.3. Aromaticity Aromaticity deserves to be regarded as something special chemistry has been endowed with. One cannot forget the rst lectures in organic chemistry where planar ring structure, fully conjugated system of multiple bonds and 4n+2 π -electrons were described as the basic criteria of aromaticity. 27 However, the concept of aromaticity has deeper roots. For complicated systems a more general approach must be opted for and that is where aromaticity starts to be even more interesting. The three known criteria for aromaticity need to be generalised and modied to give a set of ve new ones: 28,29. • (4n+2) π -electrons • Structural criteria • Energetic criteria • Electronic criteria • Magnetic criteria. 25.

(27) 1. General considerations. The origin of the Hückel's rule, (4n+2) π -electrons, is in quantum mechanics and the rule is a condition of aromaticity valid for both organic and inorganic compounds. 30 The term structural criteria refers predominantly to planarity and bond length equalisation in aromatic molecules. Thanks to the delocalisation of π -electrons, the experimentally found bond lenghts in aromatic molecules do not have values of localised single or double bonds but bear an average value between the two. 28 The delocalisation. energy represents another possible aromaticity criterion 28 since the delocalisation of the π -electrons brings lowering of the energy of aromatic systems in comparison with their non-delocalised analogues. 27 Electronic criteria refer to the description of the delocalised π -electronic system by electron population analysis. 31 The typically high chemical shift of aromatic protons in 1H NMR spectrum 27,32,33 points at the magnetic. properties of aromatic compounds which are of big signicance, especially in the area of theoretical calculations as is described in the next paragraph. It was shown that none of the ve criteria can serve as an indicator of aromaticity on its own. 28 The desire to dene a single quantity which would be directly connected with aromaticity became stronger and in 1968 a quantity called Diamagnetic Susceptibility Exaltation (Λ) was introduced as a unique criterion of aromaticity. 34 This quantity is dened as the dierence in magnetic susceptibilities between systems with delocalised and non-delocalised π -electrons:. Λ = χM − χM 0. (1.6). Since magnetic susceptibility is directly linked to the delocalised π -electrons in aromatic compounds, 35,36 diamagnetic susceptibility exaltation represents the best instrument of aromaticity description. 28,37 Unfortunately, despite being a single quantity describing aromaticity, diamagnetic susceptibility exaltation is not convenient for semi-empirical theoretical calculations, as its value  depends strongly on the ring size (area) and requires. suitable calibration standards . 38 Instead, it was suggested to calculate absolute magnetic shieldings at the centres of aromatic rings. The obtained values were named NucleusIndependent Chemical Shifts (NICS). 38 The precision of this method was later enhanced when functional groups attached to the parent aromatic hydrocarbons were taken into consideration. Dierent functional groups have dierent magnetic environments which inuence the overall environment within the resulting molecule. Therefore it was found more exact to calculate NICS at 1 Å above the ring plane. 39 For non-planar molecules least-squares plane through the ring must be calculated and in addition the use of NICS at 1 Å below the plane was proposed. 40 NICS is then denoted as NICS(1), NICS(0) and NICS(-1) for NICS 1 Å above, at the centre and 1 Å below the plane, respectively. 39,40 The convention says that negative NICS values denote aromaticity and the positive denote anti-aromaticity.. 26.

(28) 1. General considerations. 1.3.3.1. Aromaticity of sulfur-nitrogen compounds The Hückel's rule was originally postulated for benzene, i.e. a molecule with six equivalent atoms forming a ring with delocalised π -electrons. Inorganic analogues of benzene (e.g. borazine) are usually formed by dierent atoms. Dierent atoms bring inequivalent electronic environments to the molecule and therefore the solution of the quantum mechanical problem could oer results signicantly dierent to those obtained for benzene. 30 This could make Hückel's rule impossible to use for inorganic rings. However, since the semi-emprirical parameters used in the quantum mechanical calculations are very similar for certain heteroatoms, the Hückel's rule may be applied to some inorganic compounds. 30 In the case of binary sulfur-nitrogen rings, the Hückel's rule can be applied. The number of π -electrons can be easily counted according to the method of Banister: 41,42 every sulfur (6 valence electrons) and nitrogen (5 valence electrons) atom uses 2 electrons for the connection with their neighbours by σ bonds and every atom in the ring keeps 2 more electrons as a lone pair. Thus, sulfur has 2 and nitrogen 1 electron spare which can be used for π bonding. If the sum of the spare electrons within a SN cycle equals a (4n+2) number, then a high probability arises that the compound is aromatic to some extent. Additional assurance about aromaticity can be obtained by calculating Topological Resonance Energy (TRE)† , an analogue to delocalisation energy. If TRE > +0.01 β , a compound is aromatic, if +0.01 β > TRE > −0.01 β , a compound is nonaromatic and TRE values lower than −0.01 β indicate antiaromaticity. 30,43 It was shown that (4n+2) SN rings give TRE values in the aromatic range. Also, the preference of some (4n+2) SN rings to adopt nonplanar geometry was explained on the basis of the TRE values: nonplanar rings gave signicantly lower TRE values than the planar ones. 43 Also in case of inorganic rings, the calculation of NICS became very popular among theoretical chemists and is frequently used as an instrument of aromaticity determination. 31,40,4446 Except for the extremely useful tool for π -electron counting, Banister also revealed that the content of π -electrons in the SN rings is higher than in the aromatic hydrocarbons of the same ring size. 41 The explanation for this comes from the quantum mechanical (Hückel and Extended Hückel) calculations which showed that the energies of sulfur and nitrogen atomic orbitals contain lower coulombic repulsion contributions than those of carbon. 43 The energy of the molecular orbitals formed by the LCAO is thus lower than in aromatic hydrocarbons. 1,30,47 In addition, the gap between HOMO and LUMO was found to be smaller than in aromatic hydrocarbons. 1 As a result, the excessive π -electrons occupy nonbonding or antibonding π orbitals which are more accessible. 1,30,47 Since the †. TRE is given in units of resonance integral β , which is also a calculated quantity.. 27.

(29) 1. General considerations. number of electrons in bonding and antibonding orbitals determines the magnitude of a bond order, 9 the occupation of antibonding orbitals in SN aromatics brings lowering of the bond order. This is then reected in higher reactivity and lower thermal stability of SN aromatics in comparison with aromatic hydrocarbons. 1,47. 1.4. General experimental conditions The following general experimental details apply for all the following parts of the thesis. Unless otherwise stated, all reactions were carried out in an oxygen-free nitrogen atmosphere using standard Schlenk and syringe techniques. The term  high vacuum  corresponds to the pressure of 0.3 Torr. Dry solvents were used from the Solvent purication system MB-SPS-800 (MBraun GmbH). Less common solvents were dried, puried and stored according to common procedures. 48 1. H,. 13. C and. 31. P NMR spectra were recorded on a Jeol GSX spectrometer at the fre-. quencies of 270.2, 67.9 and 109.4 MHz, respectively. Chemical shifts δ were referenced to external tetramethylsilane and phosphoric acid, respectively.. 14. N NMR spectra were. recorded on a Bruker Avance II 400 spectrometer at 28.9 MHz with δ referenced to external liquid ammonia. All reasons. 13. C and. 31. 13. C and. 31. P NMR spectra are proton-decoupled; for practical. P descriptions will be used instead of. 13. C{ 1 H} and. 31. P{ 1 H}, respec-. tively. Mass spectrometry was performed by the University of St Andrews Mass Spectrometry Service and elemental analyses were performed by the St Andrews University School of Chemistry Service. Cyclic voltammetry was performed using an EcoChemie µAutolab apparatus controlled by GPES 4.2 software. Three-electrode system consisted of a glass-embedded platinum disc working electrode (area = 0.008 cm2 ), platinum wire counter electrode and Ag/AgCl reference electrode. Typically, 5 mm solutions of the analyte in dry CH3 CN were placed in an electrochemical cell of 10 ml capacity and were provided with 1.0 mmol of supporting electrolyte ([n Bu4 N][PF6 ]). A small amount (0.2 mg) of solid ferrocene was added as internal standard. The voltammograms were calibrated for the half-wave potential of the ferrocene/ferrocenium couple E1/2 = 0 V. Digital simulation of cyclic voltammograms was performed using the DigiSim software. IR spectra were recorded as pressed KBr discs (unless otherwise stated) on a PerkinElmer 2000 FT/IR/Raman spectrometer. Raman spectra were recorded in glass capillaries in the range 3500100 cm−1 using the same spectrometer.. 28.

(30) 1. General considerations. Single crystal X-ray structure data were collected on Rigaku MM007 confocal optics/Saturn or Mercury CCD diractometers using Mo-Kα radiation (confocal optic,. λ = 0.710 73 Å), and corrected for absorption. The structures were solved by direct methods and rened by full-matrix least-squares methods on F 2 values of all data. Renements were performed using SHELXTL (Version 6.1, Bruker-AXS, Madison WI, USA, 2001). Powder X-ray diraction patterns were recorded on a Stoe STADI/P diractometer using CuKα1 radiation.. 1.5. Experimental details of the key sulfur-nitrogen reagents syntheses 1.5.1. [S3N2 Cl]Cl 4 All joints were coated with teon sleeves or teon tape and slightly greased. Where teon coating could not be used, the joints were properly greased. [NH4 ]Cl (300 g, 5.61 mol) and sulfur owers (60.0 g, 0.230 mol) were placed in a 1 litre ask. S2 Cl2 (300 ml, 506 g, 3.75 mol) was quickly added, the mixture was mixed a little bit with a glass rod and the ask was covered with a lid. The lid was tted with an air condenser (3.5 cm outer diameter, 75 cm long) and the top of the condenser was tted with a drying outlet (anhydrous CaSO4 ). The top of the lid was insulated with glass wool and aluminium foil and the mixture was gently reuxed. The heating was adjusted so that the upper level of the condensing S2 Cl2 lies just within the bottom joint of the air condenser (150152 ◦C). The reaction is nished usually within 15 20 hours with the lower part of the condenser being covered with a layer of orange/brown crystals of [S3 N2 Cl]Cl. After cooling down to ambient temperature, the air condenser was transferred quickly on air onto an empty, predried and weighed 500 ml Schlenk ask with a nitrogen gas ow. The drying tube was removed, the top of the condenser was plugged with a well greased stopper and the apparatus was evacuated for 30 minutes to dry the product. The nitrogen gas was reintroduced and the dry product was scraped o the condenser walls with a spatula attached to a long metal rod. Yield 73 g (40 %, based on S2 Cl2 ). IR data: 1406 (mw), 1164 (mw), 1127 (vw), 1013 (ms), 960 (sh), 942 (vs), 705 (vs), 677 (sh), 581 (ms), 562 (sh), 472 (m), 458 (m), 432 (mw) cm−1 . Raman data: 1017 (m), 934 (w), 730 (m), 582 (m), 460 (w), 405 (s), 370 (ms), 351 (ms), 266 (vs), 175 (s) cm−1 .. 29.

(31) 1. General considerations. 1.5.2. [S4N3 ]Cl 4 All joints were coated with teon sleeves and slightly greased. In a 250 ml ask equipped with a stirring bar, dry CCl4 (50 ml) was cooled to -10 to -20 ◦C (acetone/dry ice) and under stirring S2 Cl2 (50 ml, 84.4 g, 0.630 mol) was added in one portion. The solution was cooled to -20 ◦C (acetone/dry ice) and [S3 N2 Cl]Cl (14.0 g, 0.072 mol) was added in one portion. The mixture was gently reuxed (toil = 96 ◦C) for 5 hours. Still warm, the mixture was ltered through a sinter and the canary yellow product was washed twice with 20 ml and 10 ml CCl4 respectively. The product was dried under high vacuum for 1 hour. Yield 7.0 g (71 %). IR data: 1262 (vw), 1165 (vs), 1130 (sh), 1001 (vs), 936 (sh), 794 (vw), 719 (vw), 683 (s), 639 (mw), 608 (m), 589 (sh), 565 (s), 527 (sh), 469 (vs), 454 (s) cm−1 . Raman data: 1173 (w), 1004 (w), 607 (mw), 568 (m), 447 (vs), 250 (s), 210 (ms) cm−1 .. 1.5.3. [n Bu2Sn(S2N2)]2 8 Ammonia (200 ml) was condensed at −78 ◦C (acetone/dry ice) in a predried 1 litre ask equipped with a stirring bar and [S4 N3 ]Cl (7.0 g, 0.034 mol) was added in three portions. The dark red mixture was stirred for 30 minutes at −78 ◦C after which time n Bu2 SnCl2 (20.0 g, 0.066 mol) was added in small portions over the period of 5 minutes. After a while the mixture thickened and changed colour from dark red to brown/orange. The mixture was stirred at −78 ◦C for 2.5 hours, then the cooling bath was removed and the mixture was allowed to warm up to room temperature overnight with the ammonia being evaporated. After the evaporation the mixture was evacuated for an hour to remove residual ammonia. The ask was then transferred to a glove box together with a Soxhlet apparatus. The crude solid was carefully scraped o the walls and was placed in a Soxhlet thimble, the thimble was placed into the apparatus and the apparatus was closed with stoppers. In this way protected crude [n Bu2 Sn(S2 N2 )]2 was moved back to a fume cupboard where the Soxhlet apparatus was attached to a 1 litre ask containing dry and degassed petroleum ether (650 ml). The Soxhlet apparatus was insulated with glass wool and aluminium foil and to the top a water condenser with an oil-bubbler was attached. The crude solid was extracted for 8.5 hours (toil = 7880 ◦C), at that point the extracts were nearly colourless. The extract was allowed to cool to room temperature, its volume was reduced to approx.. 1 2. and the concentrate was placed to freezer overnight,. where bright yellow precipitate separated. This was ltered o, washed twice with cold (−40 ◦C) degassed petroleum ether, dried under high vacuum for 1 hour and stored under argon. The ltrate was further reduced in volume and the resulting dark orange solution was placed in a freezer, where another portion of the material separated. This was isolated. 30.

(32) 1. General considerations. in the same way as the rst crop. The second crop showed less satisfactory elemental analyses. Overall yield 14.4 g (67 %). Microanalysis (rst crop): Found C, 29.5; H, 5.6; N, 7.8. Calc. for C8 H18 SnS2 N2 : C, 29.4; H, 5.6; N, 8.6 %.. 31.

(33) Part II. Arsenic-Sulfur-Nitrogen Heterocycles Abstract The introductory part starts with a brief summary of information on toxicity of arsenic and its compounds. Then, it seems appropriate to provide a small literature review on preparative methods of basic arsenicals, which are frequently used as starting materials but are not commercially available anymore. A short account on the participation of arsenic in ve- and six-membered main group heterocycles follows and the introductory part is ended with an overview of known arsenic-sulfur-nitrogen heterocycles with the emphasis on the analogues of S4 N4 and S2 N2 . Their reactivity is discussed and selenium and tellurium analogues are also described. Finally, new development within the area of AsSN heterocycles is presented in the form of a detailed discussion of the results of my research..

(34) 2. Introduction The chemistry of arsenic oers a lot of adventure. Generations of chemists have been investigating the chemical behaviour of arsenic in the hope that the amount of knowledge will at least match that of arsenic's lighter neighbours in Group 15, phosphorus and nitrogen. It seems correct to say that these expectations have only been fullled partly. Without any deep considerations three main reasons can be named which have hindered the chemical research of arsenic: toxicity, lack of commercially available starting materials and low applicability of arsenic NMR.. 2.1. The toxicity of arsenic Arsenic and its compounds are very often referred to as strong poisons and carcinogenic substances. The use and synthesis of arsenic compounds forms a substantial part of this thesis. To better understand where is the cause of arsenic's toxicity, a short literature survey is included in the following brief section.. 2.1.1. Arsenic in the environment Arsenic is the 20th most abundant element in the Earth's crust and is found in nature mainly in suldic ores. 49 Its spread into the environment can occur by natural means such as volcanic activity, wind erosion or the biological activity of microorganisms. The human population contributes considerably to the overall arsenic content in the environment through industrial activities such as mining or smelting, but also by burning fossil fuels or by the use of arsenic-based pesticides. 49 On the other hand, the possibilities of natural arsenic removal from the environment are very limited. The principle of arsenic elimination from water is the oxidation and subsequent coprecipitation with oxidised iron or manganese particles present in oxygen-rich surface water. The precipitate then forms sediments which are of high arsenic content. Furthermore, rainfall and dry deposition help to remove arsenic from the atmosphere. 49. 33.

(35) 2. Introduction. 2.1.2. Biotransformation of arsenic in nature Arsenic is present everywhere in the environment and all organisms are unwillingly exposed to it. Fortunately, every organism has a metabolic pathway in which its body is detoxied. For example fungi and molds methylate arsenicals and release the corresponding alkyl(aryl)arsines as the nal metabolic products. 49 It was also found that fungi in rotting wood, previously treated with arsenic-based preservatives, are able to transform these arsenicals into trimethylarsine. 50,51 The attitude of plants towards arsenicals is diverse. While some plants succumb to the eects of on purpose invented weed killers, other plants have an extraordinary tolerance to arsenic and can take up and concentrate arsenic from the environment (e.g. water hyacinth). 52 The high arsenic content in the ash of some plants (e.g. Douglas Fir) was even interpreted as a biogeochemical indicator of the presence of gold veins buried in the subsoil. 53 Fish and other water fauna metabolise arsenicals to arsenobetaine (Fig. 2.1). This O H3C H3C. OH As OH. O. OH As OH. OAs+ O. H3C. 1. NO2 NH2. OH. 2. 3. Fig. 2.1. Arsenobetaine (1), arsanilic acid (2) and roxarsone (3) 49. highly methylated organoarsenic compound is believed to be the nal product of the arsenic metabolism in sh. Analyses have shown that the amount of arsenic in marine sh is greater than in the freshwater sh. 49,54 The possible poisoning of people by the arsenic contained in sh and seafood is of no concern, since arsenobetaine is not metabolised in the human body and is excreted unchanged. 55 The arsenic tolerance of terrestrial animals is low. Much is known about the arsenic metabolism of mice, rats and rabbits as they are commonly used for toxicity testing. Arsenic in their bodies undergoes methylation and is excreted in urine. 56,57 Similar metabolites were observed in the urine of dogs, pigs and cows. 58 Poultry and pigs show increased weight gain by the addition of arsanilic acid (4-aminobenzenearsonic acid) and roxarsone (4-hydroxy-3-nitrobenzenearsonic acid) (Fig. 2.1) to their food but these are excreted unchanged. 59. 34.

(36) 2. Introduction. 2.1.3. Arsenic in the human body The fact that arsenic is toxic to humans is strongly backed up by a large volume of medical, toxicological and biochemical studies. It is predominantly the inorganic forms of arsenic to which people are nowadays exposed. The main routes of exposure are inhalation and ingestion. Similarly to other toxic substances, the consequences of exposure to arsenic depend on the scale of the dose and on the period during which the dose was taken up. Acute poisoning with huge doses of arsenic leads to a cardiovascular collapse and heavy brain damage with death coming within hours. 60 Smaller doses cause acute arsenic poisoning with slower progress. The rst responses come from the gastrointestinal tract and take hours to days. They are followed by cardiovascular system shock which takes from minutes to hours and already causes no small amount of deaths. The poisoning proceeds further with multiple organ failures (kidney failure, liver enlargement, lung oedem) and also bone marrow damage. Within a week, symptoms on the skin and brain start to develop. Typical for the skin is an increase of pigmentation, hyperkeratoses and dermatitis. Brain aection is distinguished by perplexity, convulsions or prolonged coma. 60 Even if acute arsenic poisoning is successfully warded o, the nal consquences including tumors and cancers may appear. These consequences are tricky because they always develop with a latency period and with no respect to the amount of arsenic one was exposed to. 60 Chronic arsenic poisoning develops during a prolonged exposure to arsenic. In the past, arsenic was frequently ingested as a medicine in the form of Fowler's solution (i.e. 1 % solution of potassium arsenate prepared by dissolving As2 O3 in aqueous KHCO3 ). 61,62 Nowadays it is predominantly people living in areas where drinking water is taken from wells sunk in arsenic-rich subsoils who suer from chronic arsenic poisoning. The most well known areas are e.g. Bangladesh, the West Bengal state in India, several regions in Argentina and Chile and the southwest coast of Taiwan. 61 The consequences of chronic arsenic poisoning are tumors and cancers of various tissues, dermatitis, gangrenes (Black Foot disease) and other complications. 61,63. 2.1.3.1. The principle of toxicity of arsenic There are nowadays two theories explaining the reason why arsenic is toxic to people. The rst and commonly accepted theory is based on the anity of arsenic to sulfur. In the human body, arsenic in both oxidation states As III and As V reacts with the free thiol groups of proteins, enzymes and cofactors. 56,64 This process was successfully simulated. It was shown that the interaction runs eciently at neutral pH according to equations. 35.

(37) 2. Introduction. 2.12.3. 64 RxAsO(OH)3-x + 2 R'SH RxAs(SR')2(OH)3-x RxAs(OH)3-x + (3-x) R'SH. RxAs(SR')2(OH)3-x + H2O. (2.1). RxAs(OH)3-x + R'SSR'. (2.2). RxAs(SR')3-x + (3-x) H2O. (2.3). The stability of the products is variable. While aliphatic As−S compounds are not so stable, As−S heterocycles are characterised by their increased stability. As expected, the ve- and six membered rings are the most stable. 65 The cofactors of the fundamental enzymes in cell metabolism provide the source of vicinal SH groups which react with arsenic to form stable heterocycles. The cofactor and thus the activity of the enzyme then become blocked, subsequent biochemical reactions are disrupted, cell metabolism collapses and the cell dies. 66 The second theory is based on the fact that inorganic As III compounds stimulate the production of H2 O2 in the human body. 67 In the presence of Fe 2+ , H2 O2 may dissociate in free hydroxyl radicals according to the Fenton reaction (eq. 2.4). 68 Fe3+ +. Fe2+ + H2O2. OH + OH-. (2.4). The radicals oxidise proteins and enzymes, as a consequence of which the cell metabolism collapses causing death of the cell. 66,69 This theory is currently under investigation but represents a strong challenge to the previously described thiol group theory. Arsenic in the oxidation state +5 has another toxic eect. Due to its similarity to phosphate ion, arsenate can enter the ATP formation process and can replace phosphate. The resulting compounds are unstable, hydrolyse spontaneously and thus cannot serve as energy reservoirs. 56,70. 2.1.3.2. Metabolism of arsenic in the human body Arsenic from all sorts of sources gets to the blood by which it is distributed through the whole body. Arsenicals are however quickly eliminated from blood and are redistributed into the organs. The organs most aected with arsenic poisoning are the liver, kidneys, bowel and spleen. 60 Also well known is the accumulation of arsenic in hair and nails, a feature frequently utilised in forensics. Hair and nails are skin derivatives composed of keratins, i.e. structural proteins with high ratio of aminoacids containing thiol groups. Arsenic carried to the hair by blood interacts with these thiol groups and remains stored. 71,72 The metabolism of inorganic arsenicals takes place in the kidney. 60 Arsenites are oxidatively methylated to give methylarsonic acid. Methylarsonic acid can be further reduced. 36.

(38) 2. Introduction. to methylarsonous acid and methylated again to dimethylarsinic acid. Inorganic arsenates must be rst reduced to arsenites so that they can undergo methylation. The methylated products are then excreted in urine. Scheme 2.1 summarises the metabolical process. 55,56,64 [AsVO4]32e-. 2e-. [MeAsIIIO2]2-. Me+. Me+. [AsIIIO3]3Me+. [Me2AsVO2]-. Me3AsVO. 2e-. [MeAsVO3]22e-. 2e-. [Me2AsIIIO]-. Me+. Me3AsIII. Scheme 2.1 Metabolism of inorganic arsenate in human body 64. During the oxidative methylation, a methyl group from a donor is enzymatically transferred onto the As III centre. The following reduction is also an enzymatic process and the source of electrons are thiols which at the same time are oxidised to disuldes in accordance with equations 2.1 and 2.2. 64,73,74 It was found that soon after the arsenic intake, the unmetabolised inorganic forms are excreted but after 16 hours it is already dimethylarsinic acid as the main metabolite. Also, during chronic arsenic poisoning the main metabolite is dimethylarsinic acid whereas for acute arsenic poisoning the excretion of methylarsonic acid is dominant. This is caused by the inhibition of the methylation by As III . 75 Despite the possibility of reducing dimethylarsinic acid to dimethylarsinous acid and continue the sequence up to trimethylarsine as suggested by Scheme 2.1, no trimethylated species have been detected in human urine. 55,57 An interesting recent discovery is that methylarsonous acid, an intermediate in human detoxication pathway, is more toxic than inorganic compounds of As III which were considered to be the most toxic arsenic substances to people. 73. 37.

(39) 2. Introduction. 2.2. Commercial availability of starting materials∗ The toxicity of arsenic and its compounds (especially inorganic) represents probably the toughest obstacle from both practical and organisational points of view. In the past arsenicals were used as chemical weapons and nowadays the risk of their misuse still persists, this time imposed by terrorist organisations. This forces commercial suppliers to introduce strict policies both for the production and distribution. On the industrial level, the companies producing arsenicals must have special governmental licences which must be regularly renewed for no small fees. Preparations of major amounts of arsenic compounds are subject to strict evidence and limits within both the production, stock holdings and dispatching. Waste disposal is strictly monitored and therefore there must be investment in technologies which can make the waste arsenic-free. The overall high nancial demand on the production of arsenicals adds a signicant amount to the prices of the nal products which are then dicult to sell (e.g. 250 g of AsCl3 for over ¿400). Only major companies can aord to produce arsenicals and the range of products is usually very narrow. Especially universities nd this inconvenient. Simple starting materials need to be prepared which is not necessarily dicult but it can be time consuming and it slows down the progress of the research. The cheapest available material is arsenic trioxide, As2 O3 , which can be purchased in large quantities. It is, however, not useful for synthesis since it is not soluble in common organic solvents and it is not particularly reactive at ambient temperatures. Arsonic and arsinic acids are usually poorly available with only phenylarsonic (C6 H5 As(O)(OH)2 ), arsanilic (Fig. 2.1 on page 34) and dimethylarsinic (Me2 As(O)(OH)) acids being the regular items in the stocks. Arsenic(III) chalcogenides As2 E3 (E = Se, Te) can be purchased but they nd application as semiconducting materials rather than starting materials in chemical synthesis. 76,77 Arsenic trihalides AsF3 , AsCl3 and AsI3 are available but the ratio quantity:price is not convenient. Mono- and dialkyl/aryl substituted halogenoarsines are not commercially produced due to their possible warfare use. Triphenylarsine is the only trisubstituted arsine available.. 2.3.. 75As. NMR as an analytical tool. The rapid development in phosphorus chemistry was signicantly helped by the magnetic properties of the element.. 31. P NMR enabled virtually immediate product or mixture. characterisation. Arsenic, similarly to phosphorus, is monoisotopic ( 75As) but its nu∗. The commercial availability data were taken from the internet catalogues of Sigma-Aldrich (http://www.sigmaaldrich.com), Alfa Aesar (http://www.alfa-chemcat.com) and Apollo Scientic (http://www.apolloscientic.co.uk), accessed during my research period.. 38.

(40) 2. Introduction. clear spin of. 3 2. and make. 75. molecules.. 78,79. and relatively high quadrupolar moment result in broad lines in spectra. As NMR impossible to use for characterisation of other than symmetrical. 2.4. Methods of preparation of common starting materials The term common starting materials relates to simple inorganic and organoarsenic compounds, which were described in vast majority of the studied literature as starting materials for particular syntheses. They can be sorted in 4 classes:. • Arsenic trihalogenides • Arsonic acids • Arsinic acids • Organohalogenoarsines. 2.4.1. Arsenic trihalogenides The most convenient laboratory preparations of arsenic trihalogenides on a medium scale use arsenic trioxide and follow similar procedures. AsF3 and AsI3 are prepared by the. treatment of As2 O3 with suitable halogenating agent (CaF2 , KI) in concentrated acid: 80,81 As2O3 + 3 CaF2 + 3 H2SO4 As2O3 + 6 KI + 6 HCl. 2 AsF3 + 3 CaSO4 + 3 H2O. (2.5). 2 AsI3 + 6 KCl + 3 H2O. (2.6). The preparation of AsF3 is carried out in a combined apparatus where a still head with a water condenser is attached to the reaction ask from the beginning. The mixture requires gentle heating in a water bath. The reaction starts at 30 ◦C and at 65 ◦C the colourless product distills to the collection ask. AsF3 can be puried from small amounts of HF by the addition of dried NaF which is usually placed in the collection ask. Subsequent distillation to a metal storage cylinder aords suciently pure AsF3 as a colourless, air-sensitive liquid. 80,82,83. Solid AsI3 precipitates when mixture of As2 O3 and conc. HCl is carefully added to an. aqueous solution of KI (eq. 2.6). 81 AsI3 is ltered o and puried by recrystallisation from CS2 81 or diethyl ether. 84 AsI3 is an orange/red crystalline solid at room temperature. 81. 39.

(41) 2. Introduction. AsBr3 can be prepared within a couple of hours when As2 O3 is allowed to react with. conc. HBr at 120 ◦C in the absence of any solvents (eq. 2.7). 85 As2O3 + 6 HBr. 4 AsBr3 + 3 H2O. (2.7). HBr is used in excess which shifts the equilibrium to the right. AsBr3 crystallises out of the solution after cooling, is isolated and puried by extraction with hexane. At room temperature, AsBr3 is a colourless, crystalline and volatile substance. 85 AsCl3 is best prepared from As2 O3 and SOCl2 : 86,87. 2 AsCl3 + 3 SO2. As2O3 + 3 SOCl2. (2.8). SOCl2 is used in excess as it fullls also the role of a solvent. The reaction proceeds smoothly over the period of 2 days, excess SOCl2 is then separated from AsCl3 by fractionation distillation using a Vigreux column and the crude product is distilled under nitrogen at atm. pressure to give pure AsCl3 as a clear and colourless, air-sensitive liquid. This preparation route gives good yields of AsCl3 , leaves minimum waste and the distilled SOCl2 may be used for another preparation. 87. 2.4.2. Alkylarsonic acids In 1883 Meyer observed that iodomethane oxidises sodium arsenite to sodium methylarsonate at 75 ◦C. Sucient amount of alcohol had to be added to ensure mixing of the inorganic aqueous phase with CH3 I (eq. 2.9 and 2.10). 88 2 Na3AsO3 + 3 H2O. As2O3 + 6 NaOH. (2.9). O Na3AsO3 + CH3I. EtOH. H3C. As. ONa ONa. + NaI. (2.10). The alkaline solution is neutralised and acidied with conc. HCl to convert the arsonate to arsonic acid. Meyer's general route was further rened in later reports. The reaction times, the amount of alcohol added and the acidity of the mixture were described. 89,90 Meyer's discovery is of huge signicance. The oxidation of arsenite to arsonic acid with alkyl halide is frequently and deservedly referred to as Meyer's reaction in the literature. Unfortunately, the use of Meyer's reaction is limited for alkylarsonic acids only. 91 Arylarsonic acids need to be prepared by dierent routes which will be introduced in the next section.. 40.

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