Reactivity of the bridged-sulfide complex Pd2Cl2(μ-S)(μ-dmpm)2 toward electrophiles

Abstract

The dipalladium(I) complex Pd₂Cl₂(dmpm)₂ (1a) [dmpm = bis(dimethylphosphino)methane] is known to react with elemental sulfur (S₈) to give the bridged-sulfide complex Pd₂Cl₂(μ-S)(dmpm)₂ (2a) but, in the presence of excess S₈, PdCl₂[P,S-dmpm(S)] (4a) and dmpm(S)₂ are generated. Treatment of 1a with elemental selenium (Se₈), however, gives only Pd₂Cl₂(μ-Se)(dmpm)₂ (3a). Complex 4a is best made by reaction of trans-PdCl₂(PhCN)₂ with dmpm(S). Complex 2a reacts with MeI to yield initially Pd₂I₂(μ-S)(dmpm)₂ and MeCl, and then Pd₂I₂(μ-I)₂(dmpm)₂ and Me₂S, whereas alkylation of 2a with MeOTf generates the cationic, bridged-methanethiolato complex [Pd₂Cl₂(μ-SMe)(dmpm)₂]OTf (5). Oxidation of 2a with m-CPBA forms a mixture of Pd₂Cl₂(μ-SO)(dmpm)₂ and Pd₂Cl₂(μ-SO₂)(dmpm)₂, whereas Pd₂Br₂(μ-S)(dmpm)₂ reacts selectively to give Pd₂Br₂(μ-SO)(dmpm)₂ (6b). Treatment of the Pd₂X₂(μ-S)(dmpm)₂ complexes with X₂ (X = halogen) removes the bridged-sulfide as S₈, with co-production of Pd^II(dmpm)-halide species. X-ray structures of 3a, 5 and 6b are presented. Reactions of dmpm with S₈ and Se₈ are clarified. Differences in the chemistry of the dmpm systems with that of the corresponding dppm systems [dppm = bis(diphenylphosphino)methane] are discussed.