Vibrational, P-31 NMR and crystallographic studies of diiodine adducts of some bidentate tertiary phosphine sulfides

Treatment of bis(dipbenylphosphino)methane disulfide (dppmS) or bis(diphenylphosphino)ethane disulfide (dppeS) with diiodine in dichloromethane yields the adducts dppmS .I-4 1 and dppeS .I-4 2, respectively, whose structures have been solved by X-ray crystallography. Compounds 1 and 2 consist of discrete molecular units containing bent P-S-I and linear S . . .I-I geometries that can be interpreted in terms of donation of electron density from sulfur to diiodine. Consistent with this interpretation, the P-S bonds are lengthened compared to the unco-ordinated phosphine sulfides, and the I-I bonds are lengthened compared to unco-ordinated diiodine. Both compounds can therefore be described as 'charge-transfer' complexes. The two S . . .I-I moieties in 1 are inequivalent having markedly different bond lengths and angles. In 2 both S . . .I-I moieties are identical. The structural features of 1 and 2 are in accordance with Raman and P-31 CP MAS NMR data