(OC-6-35)-(2,2′-Bipyridine-κ2 N,N′)dimethyl(3-sulfidopropionato-κ2 S,O)platinum(IV)

The title complex, [Pt(CH3)2(SCH2CH2CO2)(C10H8N2)], is formed by the unusual oxidative addition of the disulfide, R 2S2 (R = CH2CH2CO2H), to (2,2′-bipyridine)dimethylplatinum(II) with elimination of RSH. The product contains an unusual six-membered thiolate–carboxylate chelate ring. This slightly distorted octahedral complex exhibits cis angles ranging from 77.55 (11) to 97.30 (8)° due to the presence of the thiolate–carboxylate chelate ring and the constrained bipyridine group. The crystal packing appears to be controlled by a combination of π-stacking [centroid–centroid distance = 3.611 (2) Å] and C—H⋯O interactions.

We would like to thank the NSERC (Canada) for financial support.
complexes (Aye et al., 1993;Bonnington et al., 2008). Unexpectedly, the oxidative addition of 3,3'-dithiodipropionic acid led to the formation of a thiolate-carboxylate chelate ring. This type of chelate ring is not without precedent (Henderson et al., 2000;Phillips & Burford, 2008) but the title complex, (I), is the first example of a thiolate-carboxylate chelate with platinum(IV) (McCready & Puddephatt, 2011). In this context, the crystal structure of (I) is presented.
The stereochemistry at the platinum(IV) center is octahedral with two mutually cis methyl groups and chelating 2,2'bipyridine and 3-thiolatopropionato groups ( Fig. 1 and Table 1). The distance Pt-N2 = 2.149 (3) Å is significantly longer than Pt-N1 = 2.107 (3) Å, because the methyl group has a higher trans influence than the thiolato group. The angles at platinum(IV) between cis ligands range from 77.55 (11) to 97.30 (8) °, Table 1, as a result of constraints of the chelate ligands and lie in the expected ranges (Aye et al., 1988;Achar et al., 1993).
The chief intermolecular interactions arise through π-stacking between the bipyridine rings of centrosymmetrically related molecules of (I) (Fig. 2). The mean interplanar spacing between the bipyridine rings comprising the dimer unit is 3.36 Å, which is consistent with observed values of about 3.3 Å for platinum(IV) complexes of 2,2'-bipyridine (Au et al., 2009).

Experimental
Dimethyl(2,2'-bipyridine)platinum(II) was prepared according to a previously published procedure by Monaghan and Puddephatt (1984 2H, 3 J(H 6 H 5 ) = 6 Hz, H 5 ]. A solution of PtMe 2 (bipy) (0.010 g, 0.026 mmol) in minimum acetone was added to a solution of dithiopropionic acid (0.0056 g, 0.026 mmol) in minimum acetone. Mixing of the two solutions led to the formation of a red-brown colour which persists while precipitation of the product is observed. After 30 h the red-orange precipitate can be isolated by decantation of the solvent and was washed with diethyl ether. PtMe 2 (bipy) (0.0010 g) was then dissolved in minimal chlorobenzene and added to an NMR analysis tube. To this solution, a buffer layer of chlorobenzene followed by acetone was added in order to slow the rate of diffusion of the subsequently added acetone solution of (0.0006 g) of dithiopropionic acid. The sample was placed in a cool dark place and allowed to crystallize over the course of two weeks producing crystals of (I

Refinement
The C-bound H atoms were placed in calculated positions (C-H 0.95-0.99 Å) and were included in the refinement in the riding model approximation with U iso (H) values equal to 1.2U eq (C) The maximum and minimum residual electron density peaks of 0.92 and -1.42 e Å -3 , respectively, were located 0.64 Å and 0.74 Å from the Pt1 atom respectively. Fig. 1. A view of the molecular structure of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and hydrogen atoms have been omitted.  Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.