Universiw of Toronto, Department of Chemistry, Toronto, Ontario M5S 1Al Received March 21,1975

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Preparation and Properties of some Trimethylgermyl and Trimethylplumbyl

Esters of Dimethylcarbamic and Dimethylthiocarbamic Acids

Universiw of Toronto, Department of Chemistry, Toronto, Ontario M5S 1 A l Received March 21,1975

A. E. LEMIRE and J. C. THOMPSON. Can. J. Chem. 53,3727 (1975).

The preparation of the trimethylgermyl esters of N,N-dimethylcarbamic, N,N-dimethylmonothiocarbamic, and N,N-dimethyldithiocarbamic acids and the trimethylplumbyl ester of N,N-dimethylmonothiocarbamic acid is reported. Some of these esters exhibit temperature dependent n.m.r. spectra. Infrared and U.V. spectra for these and related compounds are also described.

A. E. LEMIRE et J. C. THOMPSON. Can. J. Chem. 53,3727 (1975).

On rapporte la prtparation des esters trimethylgermylts des acides N,N dimethylcarba- mique, N,N-dimethylmonothiocarbamique et N,N-dimtthyldithiocarbamique et la preparation de l'ester trimtthylplumbyle de l'acide N,N-dim~thylmonothiocarbamique. Dans quelques uns de ces esters, le spectre r.m.n. varie en fonction de la temptrature. On dkrit aussi les spectres i.r. et U.V. de ces composes et d'autres qui leur sont relits.

[Traduit par le journal] While many reports of the stannyl esters of

dialkyldithiocarbamic acid may be found in the literature (1, 2), there is comparatively little in- formation on germyl and plumbyl esters. Satgt

I

_{et al.}_{(3) have reported the preparation of a few} esters of diethyldithiocarbamic acid and diethyl- carbamic acid. The trimethylplumbyl ester of dimethyldithiocarbamic has also been pre-

'

pared (4).

As part of a systematic n.m.r. study (5-7) of hindered rotation in such esters we had occasion to synthesize the trimethylgermyl and trimethylplumbyl esters of dimethylcarbamic and dimethylthiocarbamic acids and in this paper report upon their synthesis and properties.

Generally the synthesis of such compounds has been carried out by reacting aminosilanes, germanes, or stannanes with CO,, CS,, or COS (1,3), although the dithiocarbamates have some- times been prepared by reacting the trialkyl group IV halide with sodium dialkyldithiocar- bamate. We have found that the monothiocarbamates and carbamates may also be con- veniently prepared by the reaction between the group IV halide and an acid salt; this procedure obviates the necessity of working directly with the aminosilanes etc., which are often quite moisture sensitive.

Experimental Svnthesis

stoichiometric amount of Me,NC(X)YH.HNMe, (8, 9) (X = 0 , S ; Y = 0 , S) in hexane under a nitrogen at- mosphere. The reaction mixture was stirred for 2 h, then filtered under nitrogen and the solvent was evaporated under vacuum to yield an oil. The oil was distilled under vacuum with warming and condensed in a Dry Ice trap. Results of analyses are listed in Table 1.

The compound Me2NC(0)SGeMe3 appears to be somewhat air sensitive; it also decomposes after standing several months in a sealed tube (under vacuum). It may also be prepared by the direct reaction of Me3GeNMe, and COS.

An attempt to prepare Me2NC(S)OGeMe3 by the reaction of Me,NC(S)CI and Me3GeOLi was made but only starting materials were recovered.

Solutions of Me,NC(S)SPbMe, are unstable; a white precipitate forms if the solution is allowed to stand for a few hours.

Me,NC(O)SPbMe, decomposes (turns grey) on standing several weeks in a sealed tube.

Spectra

Nuclear magnetic resonance spectra were obtained on a Varian A56-60D n.m.r. spectrometer. Details of sample preparation have been described previously (5-7).

Infrared spectra were run on a Perkin-Elmer 180 i.r. spectrometer. Demountable cells with NaCl windows and a 1 mm path length were used. Solutions of

-

10 molpl, concentration in CC14 and CHCl, were used. The spectrometer was calibrated using the standard polystyrene film.

Ultraviolet spectra were run on a Unicam SP 800 spectrometer over the range 21&450 nm. Solutions were made up to cover the concentration range 0.05-0.00005 mol 1-'.

Results and Discussion The following general procedure was followed for all

of the compounds except Me,NC(S)SPbMe, (4). Nuclear Magnetic Resonance A solution of the trimethylgermyl halide or trimethyl- The 'H chemical shifts for the

plumbyl acetate in hexane was added to a slurry of the described herein are listed in Table 2. AS would

Can. J. Chem. Downloaded from cdnsciencepub.com by 134.122.89.123 on 06/15/21

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TABLE 1. Analytical data

0

Analysis

5

C H N S 0 C

Compound Melting point 0 _z

("c) Calcd. Found Calcd. Found Calcd. Found Calcd. Found Calcd. Found

-

P

Me2NC(0)OGeMe3 Colorless 35.02 34.94 7.35 7.43 6.81 6.93 - 15.55 15.79 < 0 liquid !- Me2NC(0)SGeMe3 28-30 32.48 32.49 6.82 6.78 6.31 6.35 14.45 14.81 7.21 7.25 La

-

W Me2NC(S)SGeMe3 25-26 30.29 30.34 6.36 6.83 5.89 5.93 26.95 26.52 Me2NC(S)SPbMe3 19.35 19.53 4.07 4.19 3.77 3.72

5

Me2NC(S)OPbMe3 58-60 20.25 20.51 4.24 4.79 3.93 3.91 8.99 8.72 4.49 4.59 VI

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LEMIRE AND THOMPSON: PREPARATION OF CARBAMATE ESTERS

TABLE 2. 'H chemical shifts Chemical shifts 6*

J(207PLC-'H) Compound NMe2 Ester grouping (Hz) Me3GeOC(0)NMe2 2.84 0.53 Me3GeSC(0)NMe2 3.01 0.61 Me3GeSC(S)NMe2 3.26 0.66 Me3PbSC(0)NMe2 2.96 1.35 66.4 3.08 Me3PbSC(S)NMe2 3.45 1.40 64.7

*In 10 molX solution in CCI4 at the ambient temperature of the probe.

be expected, the chemical shifts of the protons of the ester group -Y-MMe, follow the same pattern as that observed in the tetramethyl compounds Me,M (10).

The carbamate and dithiocarbamate esters exhibit a single resonance for the N-methyl protons at room temperature.

When the temperature is lowered the N- methyl resonance of trimethylgermyl N,N-di- methyldithiocarbamate (in CHCl, solution) splits into a doublet of separation

-

1.3 Hz below 250 K. However, no splitting of the resonance was observed in hexane solutions at temperatures as low as 214 K. The trimethylplumbyl ester of

N,N-dimethyldithiocarbamic acid showed no splitting of the N-methyl resonance at 21 1 K in either chloroform or n-hexane solutions.

Similarly trimethylgermyl dimethylcarbamate showed no splitting of the N-methyl peak at 214 K in n-hexane and chloroform solution. In chloroform solution, however, the N-methyl peak was broad at room temperatures and shar- pened at lower temperatures.

The N-methyl resonance of the trimethylgermyl monothiocarbamate splits into a doublet just below room temperature in both chloroform

and n-hexane solution.

In chloroform solution the two N-methyl peaks were asymmetric at low temperatures with the low field peak being broader than the high field one. At temperatures just below the coales- cence temperature, however, they appeared to have the same widths. In n-hexane solution the two peaks had the same widths at low temperatures.

The trimethylplumbyl monothiocarbamate showed a splitting of the N-methyl resonance in both n-hexane and chloroform solutions at room temperature. In both solutions at low temperatures the low field N-methyl peak was slightly broader.

The splitting of the N-methyl resonance in these compounds is due to hindered rotation about the C-N bond which causes the two N- methyl groups to reside in slightly different magnetic environments; the situation is exactly analogous to that in amides. Activation parameters for the hindered rotation in these and similar compounds have been determined (27).

The unequal line widths of the two N-methyl resonances in the monothiocarbamates are somewhat unusual. We have also observed unequal N-methyl line widths in solutions of trimethyl- stannyl dimethylmonothiocarbamate (7). A similar broadening was reported in the compound (CH3)2CClSn(SSeCNC(CH3),), and attributed to unequal coupling with the 77Se isotope (1 1). In light of the results of our work, it appears that the effect is more general and is not due to selenium coupling.' We have previously suggested that the broadening may be due to the formation of dimeric or higher polymeric species at low temperatures (7).

Infrared Spectra

Normal coordinate analysis of the dimethyl- dithiocarbamate anion (12) and dimethylamides and thioamides (13) suggest that a high degree of coupling of i.r. modes takes place and hence few of the bands can be described as 'pure'. Thus a detailed analysis of the i.r. spectra would prove quite difficult.

However, a few major bands may be identified.

The dithiocarbamates have a strong band at -1489 cm-' which may be identified as the 'thioureide' band which Chatt et al. (14) have

'A referee has suggested that the unequal broadening may be due to unequal quadrupole broadening as part of unresolved J('H-14N) coupling. If this were indeed the case, however, it is rather strange that analogous broaden- ing is not observed in the spectra of all the compounds studied.

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3730 CAN. J. CHEM. VOL. 53, 1975

suggested arises from a polar

~-c-S

vibra- tion.

Trimethylgermyl dimethylcarbamate has a strong band at 1662 cm-' in (10% CCl, solutions) which may be identified as the carbonyl stretch. The band position shifts 20 cm-' to lower wave numbers in chloroform solution. This is consistent with an H-bonding interaction between the carbamate and the chloroform which tends to weaken the carbon-oxygen bond.

The monothiocarbamates also have a strong band in the carbonyl stretching region (1630 cm-', Me2NC(0)SGeMe3; 1609 cm-' Me2- NC(O)SPbMe,) and the monothiocarbamates may thus be established as being the S-esters rather than the 0-esters.

Ultraviolet Spectra

The U.V. spectra of these and related com-

pounds are listed in Table 3.

The U.V. spectra of dithiocarbamates have been fairly extensively studied (15-23) and four types of bands may be distinguished which have been assigned as follows: (a) Type I, n + n* (280-360 nm);

(b)

Type 11, n + n (280 nm); (c) Type 111, n + n* (24C250 nm);

(d)

Type IV, unassigned (220 nm).

In the trimethylsilyl and trimethylgermyl dithiocarbamates, bands I and I1 shift to longer wavelengths relative to the analogous tert-butyl ester while band I11 shifts to shorter wavelengths. The shift of the n + n* (band I) transition in these esters suggests that the extent of conjugation at the ester sulfur with the thiocarbonyl group is being reduced (15, 16, 24). This might arise if the trimethylsilyl and trimethylgermyl groups were acting as n acceptors (Si > Ge). The trimethylplumbyl dithiocarbamate has a U.V. spectrum very similar to the methyl and tert-butyl esters and thus shows little evidence of conjugation. The U.V. spectra of the trimethyl- stannyl dithiocarbamate is considerably different from the silyl and germyl derivatives. This may reflect some internal coordination in the tin structure in solution; some internal coordination in the solid state has been demonstrated in its crystal structure (25).

The trimethylgermyl and plumbyl monothiocarbamates have only an n + n* transition in the region above 220 nm; the n + n* transitions are presumably shifted to lower wavelengths. Once again the shift of the n + n* transition in the germyl ester suggests that the -GeMe3 group is acting as a n acceptor. The position of the

TABLE 3. Ultraviolet spectral data

Compound (nm) log E Dithiocarbamates Me2NC(S)SMe 226.4 248.0 278.5 344.0 Me2NC(S)SCMe3 226.5 249.0 282.0 Monothiocarbamates 0-Esters Me2NC(S)OMe 282.0 359.0 232.0 (shoulder) 3.88 246.0 4.02 283.5 3.93 356.5 1.62 248.5 4.03 286.5 3.82 348.0 1.70 248.5 279.5 (shoulder) 345.0 (shoulder) 277 0.82 End absorption End absorption 28 3 0.98 283.5 0.71 End absorption Carbamates

No U.V. absorption was found in sol~tions of any of

the carbamate esters.

*Extinction coefficients could not be determined accurately because of the instability o f the solutions.

n + n* transition in the trimethylplumbyl monothiocarbamate is obscured by strong end absorption which has a broad tail and presumably arises from the expected n + n* transition below 220 nm.

The carbamates showed no U.V. absorption

above 220 nm.

It must be noted that for all the compounds studied the shifts of the U.V. bands were slight

and hence interpretation of the reason for these shifts is somewhat speculative. Nonetheless the trend of the shifts appear to be real in that in a recent paper (26) quite similar shifts were reported for group IV esters of several dithioacids.

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LEMIRE AND THOMPSON: PREPARATION OF CARBAMATE ESTERS 373 1

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