Reactivity of CpCo 16e half-sandwich complexes containing a chelating 1,2-dicarba-closo-dodecaborane-1,2-dichalcogenolate ligand toward phenylacetylene

The reaction of the 16e half-sandwich complex CpCo[S₂C ₂B₁₀H₁₀] (1S) with phenylacetylene at ambient temperature led to 2S, 3S, and 4S. In 3S the alkyne is twofold inserted into one of the Co-S bonds. In 4S B-substitution occurs at the ortho-carborane cage in the position B(3)/B(6) with the formation of a C-B bond. Upon heating, 3S catalyzed the cyclotrimerization of alkyne to give rise to 1,3,5- and 1,2,4-triphenylbenzenes. In comparison, CpCo[Se₂C₂B ₁₀H₁₀] (1Se) did not react with the alkyne at ambient temperature. However, if heated to 80°C, 2Se and 4Se (an analogue to 4S) were generated. Mechanistic implications on metal-induced B-H bond activation and catalytic cyclotrimerization of alkynes were elucidated. The solid-state structures of 2Se, 3S, and 4S have been determined by X-ray crystallography.