Metal-induced B-H bond activation: Addition of methyl acetylene monocarboxylate to CpCo half-sandwich complexes containing a chelating 1,2-dicarba-closo-dodecaborane-1,2-dichalcogenolate ligand

The reaction of the 16e half-sandwich complex {CpCo[S₂C ₂B₁₀H₁₀]} (IS) with methyl acetylene monocarboxylate at ambient temperature led to {CpCo[S₂C₂B ₁₀H₁₀] [CHC(CO₂Me)CHC(CO₂Me)]) (2S) and {CpCo[S₂C₂B₁₀H₈][CHCH(CO ₂Me)]₂} (3S). In2S the alkyne is 2-fold inserted into one of the Co-S bonds. 3S is a 16e B-disubstituted complex with the olefinic units in a ZIZ configuration. In comparison, {CpCo[Se₂C₂B ₁₀H₁₀]} (ISe) reacted with the alkyne to give rise to {CpCo[Se₂C₂B₁₀H₁₀]-[CHC(CO ₂Me)CHC(CO₂Me)]} (2Se), {CpCo[Se₂C ₂B₁₀H₉] [CH₂C(CO₂Me)]} (4Se), and {CpCo[Se₂C₂B₁₀H₈]- [CH₂C(CO₂Me)][CHCH(CO₂Me)]] (5Se). 2Se is the analogue of 2S. Upon heating, 2S and 2Se catalyze cyclotrimerization of the alkyne to generate 1,3,5- and 1,2,4-tricarboxylatebenzenes. 4Se is an 18e B-substituted species with a B-CH₂ unit. 5Se is analogous to 4Se, but contains an olefinic substituent at the B(3)/B(6) site of the carborane in a Z configuration. Mechanistic implications on metal-induced B-H bond activation and catalytic cyclotrimerization of alkyne were elucidated. All new complexes were characterized by NMR spectroscopy (¹H, ₁₁B, ₁₃C), and X-ray structural analyses were reported for 2S, 2Se, 3S, 4Se, and 5Se.