Molybdenum and tungsten eta2-alkyne-1-thio complexes acting as sulfur donors in homoleptic Werner type complexes with nickel(II) and palladium(II)

Facile access to the eta2-alkyne-1-thio complexes Tp'M(CO)2{eta2-(BnS)CC(S)}] (Tp' = hydrotris(3,5-dimethylpyrazolyl)borate; Bn = benzyl; M = Mo, W) by reductive removal of one benzyl group in the corresponding bis(benzylthio)acetylene complexes, Tp'M(CO)2{eta2-(BnS)CC(SBn)}](PF6), has been thoroughly investigated. Experimental evidence of the intermediates, Tp'M(CO)2{eta2-(BnS)CC(SBn)}] (M = Mo, W), and the fate of the cleaved benzyl group by isolation of the byproduct, Tp'W(CO){C(O)Bn}{eta2-(BnS)CC(SBn)}], is provided. Neutral eta2-alkyne-1-thio complexes Tp'M(CO)2{eta2-(BnS)CC(S)}] bearing a free terminal sulfur atom have been established as monodentate ligands L in homoleptic pentanuclear M'L4]2+ complexes with nickel(II) and palladium(II). Comparison of the NMR and IR spectroscopic as well as cyclovoltammetric data of the heterobimetallic complexes with the free thio-alkyne complexes reveals a strong electronic coupling of the redox-active eta2-CC-bound metal centers and the sulfur-coordinated metal ion.