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[S₂C₂B₁₀H₁₀]} (1S) with methyl acetylene monocarboxylate at ambient temperature led to {CpCo[S₂C₂B₁₀H₁₀] [CHC(CO₂Me)CHC(CO₂Me)]} (2S) and {CpCo[S₂C₂B₁₀H₈][CHCH(CO₂Me)]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 Z/Z configuration. In comparison, {CpCo[Se₂C₂B₁₀H₁₀]} (1Se) reacted with the alkyne to give rise to {CpCo[Se₂C₂B₁₀H₁₀][CHC(CO₂Me)CHC(CO₂Me)]} (2Se), {CpCo[Se₂C₂B₁₀H₉] [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.