Electrochemical reductive carbon-to-carbon coupling of σ-ethynyl complexes of transition metals

The electrochemical properties of σ-ethynyl complexes of chromium subgroup metals were studied by cyclic voltammetry and preparative-scale electrolysis. The redox cycle of C5H5(CO)3CrC=CPh was shown to give the bis-carbyne complex (η5-C5H5)(CO)2Cr≡C-C(Ph)=C(Ph)-C-Cr(CO)2(η5-C5H5) formedvia the reductive Cβ−Cβ coupling of ethynyl moieties. The influence of the nature of the metal atom and the ligand environment on the course of this reaction was considered.