Metal carbonyls—II Carbon monoxide and chloride exchange with some cyclopentadienyl metal carbonyls

Abstract

The exchange reactions of 14CO with cyclopentadienyl metal carbonyls in solution have been studied. The nickel and cobalt cyclopentadienyl carbonyls exchange rapidly whereas the other compounds equilibrate very slowly. The exchange in (C 5H 5) 2Ni 2(CO) 2 and C 5H 5Co(CO) 2 depends on the carbon monoxide concentration and hence proceeds by a bimolecular displacement. The rates and mechanism are discussed and possible explanations are presented in terms of electronic structures, steric hindrance and MCO bond strengths. It is suggested that the results may provide some evidence in support of certain electronic differences between metals in the simple carbonyls and those in the “isoelectronic” cyclopentadienyl carbonyls. The chloride exchange with C 5H 5Fe(CO) 2Cl in 5 per cent ethanol-water is second-order in the complex and independent of the chloride ion concentration. The reaction is very slow in benzene. An attempt is made to correlate the CO and chloride exchange results.