5.1. Introduction
The nature of the organic backbone in diselenide compounds can influence the Se-Se bond. A comparison of the Se-Se bonds in the organodiselenide compounds Se2naph, dibenzo[ce]-1,2-diselenide, diphenyl diselenide, and 2,-di- tert-butylnaphtho[1,8-cd][1,2]diselenide suggested that the more rigid the organic
backbone, the longer the Se-Se bond (Figure 5-1). By chelating these ligands to a metal center, we hope to better understand the effects that the organic backbone has upon complexation and the distortions that can occur in the various backbones.
There are very few metal complexes that have either Se2naph (or any
naphthalene derivative) or dibenzSe as a ligand. These are limited to the platinum(II) bisphosphine complexes, [Pt(Se2naph)(PPh3)2],
75
Se Se
d
Se Se Se Se Se Se
a b c
Figure 5-1. Line drawings of a) naphtha[1,8-c,d]-1,2-diselenide, b)
dibenzo[ce]-1,2-diselenide, c) diphenyl diselenide, and d) 2,-di-tert-
[Pt(Se2naph)(PMe3)2], and [Pt(dibenzSe2)(PPh3)2].1,2 In addition, there are only a
few reported mononuclear square planar complexes having two -SePh ligands. These include cis- and trans-[Pt(SePh)2(PPh3)2], trans-[Pt(SePh)2(P(n-Bu)3)2], and trans-[Pt(SePh)2(PEt3)2], and some mononuclear germanium complexes,
including: [Ge(SePh)2(R)2], where R = Me, Et, n-Pr, n-Bu, and Ph) and
[Ge(SePh)2(R)], where R = -(CH2)4- or -(CH2)5-.3-6 The only reported crystal
structure of the germanium complexes is that of [Ge(SePh)2((-CH2-)4)], while the
crystal structures of several platinum complexes are known.7
In contrast to the above mononuclear platinum and germanium examples, the vast majority of complexes synthesized with -SePh ligands are dinuclear. These complexes have the -SePh moieties bridging two metal centers forming a diamond core structure as in Figure 5-2, which shows a few examples of known complexes with bridging -SePh ligands.8-11
To date, there is only one reported series. This series contains platinum bis-triphenylphosphine complexes containing like selenium ligands with the general formula LPt(PPh3)2, where L is Se2naph, dibenzo[ce]-1,2-diselenide, or
diphenyl diselenide (Figure 5-3). These complexes were not synthesized as a series in a single laboratory, but have been reported independently by several groups. In those reports, the syntheses of [Pt(PPh3)2(Se2naph)],
[Pt(PPh3)2(dibenzSe2)], and cis-[Pt(PPh3)2(SePh)2] were obtained via an oxidative
addition reaction with [Pt(PPh3)4] and the respective neutral diselenide.1,3,12 It has
further been reported that [Pt(PPh3)2(Se2naph)] and cis-[Pt(PPh3)2(SePh)2] have M Se Se M Ph Ph PhSe PR3 R3P SePh M = Hg; R = C6H11or Ph M = Pd; R = Ph Pt Se Se Pt Ph Ph R PRR'2 R'2RP R R = Ph R' = Me
Figure 5-2. Known complexes with a diamond core structure.
been synthesized by first reducing the Se-Se bond followed by addition of the reduced diselenide to a solution of cis-[PtCl2(PPh3)2].
Pt PPh3 PPh3 Se Se Pt PPh3 PPh3 Se Se Pt PPh3 PPh3 Se Se a b c
Figure 5-3. a) [Pt(PPh3)2(Se2naph)], b) [Pt(PPh3)2(dibenzSe2)], and c) cis-
[Pt(PPh3)2(SePh)2].
In order to expand the number of diselenide complexes and to obtain a series of diselenide platinum complexes from which to draw structural insights, we have synthesized and characterized a new series of complexes produced by reactions using cis-[PtCl2(P(OPh)3)2] as a starting material. The ligands
naphtha[1,8-c,d]-1,2-diselenide (Se2naph), 2-mono-tert-butylnaphtho[1,8- c,d][1,2]diselenole (mt-Se2naph) dibenzo[ce]-1,2-diselenide (dibenzSe2), and
diphenyl diselenide have been used as ligands for the resulting four-coordinate mono- and di-nuclear platinum(II) bisphosphine complexes are [Pt(Se2naph)(P(OPh)3)2] (5.1), [Pt(mt-Se2naph)(P(OPh)3)2] (5.2),
[Pt2(dibenzSe2)2(P(OPh)3)2] (5.3), cis-[Pt(SePh)2(P(OPh)3)2] (5.4), and trans-
[Pt2(SePh)4(P(OPh)3)2] (5.5) (Figure 5-4). The X-ray structures of these
compounds are reported along with a detailed comparison of their structures focussing on the geometry about the selenide ligands.
5.2. Results and Discussion Pt P(OPh)3 P(OPh)3 Se Se Pt P(OPh)3 P(OPh)3 Se Se (5.1) Pt P(OPh)3 P(OPh)3 Se Se (5.2) (5.4) Pt Se Se Pt Ph Ph PhSe P(OPh)3 (PhO)3P SePh Pt Se Se Pt Se P(OPh)3 (PhO)3P Se (5.3) (5.5)
Figure 5-4. [Pt(Se2naph)(P(OPh)3)2] (5.1), [Pt(mt-Se2naph)(P(OPh)3)2] (5.2),
[Pt2(dibenzSe2)2(P(OPh)3)2] (5.3), cis-[Pt(SePh)2(P(OPh)3)2] (5.4), and trans-
[Pt2(SePh)4(P(OPh)3)2] (5.5).
5.2.1. Synthesis and Characterization
Complexes 5.1-5.5 were synthesized under nitrogen by first creating a lithium selenide salt by addition of LiBEt3H to a dry THF solution of the
appropriate ligand. Then, cis-[PtCl2(P(OPh)3)2] was added to the mixture. After
stirring overnight, silica gel was added to the reaction mixture and the solvent was removed under vacuum. Purification was performed by column chromatography via the addition of the silica/product solid to a silica gel column followed by elution of impurities with hexane. The product was then eluted from the column using dichloromethane. X-ray quality crystals were obtained for complexes 5.1- 5.5 by pentane diffusion into a dichloromethane solution. The synthetic scheme is shown in Scheme 5-1.
Of this series of complexes, not all have been fully characterized, but all have yielded molecular structures through X-ray crystallography. Complexes 5.1
and 5.2 have been fully characterized by EA, MS, IR, Raman, and 1H, 13C, 31P,
77Se, and 195Pt NMR. Complex 5.1 was synthesized in a 53% yield. The calculated
elemental analysis (EA) data for 5.1 best fits the experimental data for the complex plus one molecule of dichloromethane. Mass spectrometry data show a molecular ion peak at 1100 corresponding to the desired M+ value. Complex 5.2 was crystallized in a 50% yield. Calculated EA data fit the experimental data with a trace amount of dichloromethane. Mass spectrometry showed a molecular ion peak at 1156 corresponding to the desired M+. We were unable to isolate bulk samples of complexes 5.3, 5.4, and 5.5, so their degree of characterization is less. Only their X-ray structures have accurately been determined, along with some multi-nuclear NMR data. The mass spectrometry for the samples containing 5.3 and 5.4/5.5 showed a desired peak at 1631 and 1635.6, respectively that matches the theoretical isotope profile for M+; however, there are higher molecular ion peaks in both spectra.
THF