Reactions of the Bis(dialkylphosphino)methane Complexes Pd2X2(μ-R2PCH2PR2)2 (X = halogen, R = Me or Et) with H2S, S8, COS, and CS2; Detection of Reaction Intermediates

The Pd2X2(dmpm)2 complexes [X = Cl (1a), Br (1b), I (1c); dmpm = bis(dimethylphosphino)methane. In all the dipalladium complexes mentioned in this paper, the dmpm, depm, and dppm ligands (unless stated otherwise) are bridging, but for convenience the μ-symbol is omitted.] react with H2S to yield H2 and the bridged-sulfido complexes Pd2X2(μ-S)(dmpm)2 (2a–c), of which 2a and 2b are structurally characterized. With 1a, two rapid reversible equilibria are observed by NMR spectroscopy below −30 °C, and two reaction intermediates are detected; both are likely hydrido(mercapto) species. Reaction of 1a with 1 equiv of elemental sulfur also yields 2a. The reaction of 1a with COS results in the initial formation of Pd2Cl2(μ-COS)(dmpm)2 (3) that undergoes decarbonylation to yield 2a and Pd2Cl2(μ-CO)(dmpm)2 (4), which is also formed via reversible insertion of the CO into the Pd–Pd bond of 1a. The solid-state molecular structure of the previously reported complex Pd2Cl2(μ-CS2)(dmpm)2 (5), together with solution NMR data for 3 and 5, reveal that the bridging heterocumulene ligands coordinate in an η2-C,S fashion. Analogous findings were made for the corresponding Pd2X2(depm)2 complexes [X = Cl (1a′), Br (1b′), I (1c′); depm = bis(diethylphosphino)methane], although no μ-COS species was detected. The Pd2X2(μ-S)(depm)2 complex was structurally characterized. Differences in the chemistry of the previously studied, corresponding dppm systems (dppm = bis(diphenylphosphino)methane) are discussed.