Low temperature activation of molecular hydrogen in Co/H₂ mixtures in the presence of CoRh(CO)₇

Molecular hydrogen (0.8-8 bar) reacts with CoRh(CO)₇ at 0°C in the presence of 2 bar carbon monoxide in n-hexane to yield HCo(CO)₄ and Rh₄(CO)₁₂. When a solution of CoRh(CO)₇ (10^-3 mmol/1) and 3,3-dimethyl-1-butene (0.2 mol/1) in n-hexane is treated with 2 bar carbon monoxide and 8 bar hydrogen at 0°C, the catalytic formation of 4,4-dimethylpentanal is observed (25% conversion after 24 h). Although the reaction path of the molecular hydrogen activation is not known, the formation of an unobserved intermediate such as H₂CoRh(CO)₇, and its subsequent fragmentation to give HCo(CO)₄ and a very unstable hydridorhodium species such as HRh(CO)₃ rapidly yielding Rh₄(CO)₁₂ seems likely. The results show that low temperature activation of molecular hydrogen can be achieved at 0°C even in the presence of substantial concentrations of carbon monoxide using CoRh(CO)₇. © 1988.