NUCLEOPHILIC ACTIVATION OF COORDINATED CARBON MONOXIDE. 2. REACTIONS OF THE MONONUCLEAR COMPLEXES M(CO)5 WITH HYDROXIDE AND WITH METHOXIDE

Article abstract of DOI:10.1021/ja00294a027

Quantitative studies of the rections of the nucleophiles CH3O(10) and OH(1-) with the pentacarbonyl complexes M(CO)5 are described.For methoxide the product in each case is the methoxycarbonyl adduct M(CO)4(CO2CH3)(1-).Infrared spectra in THF solution show this species to undergo specific ion pairing interaction with Na(1+) at the CO2CH3 group.The rates of NaOCH3 reaction with the metal carbonyl complexes follow the order Os(CO)5 > Ru(CO)5 > Fe(CO)5 and are markedly solvent dependent with second-order rate constants for Fe(CO)5 ranging from 1.1x1E3 M^-1 s^-1 in methanol to 9.7x1E4 M^-1 s^-1 in 90/10 (v/v) THF/CH3OH solution (25 deg C).Reaction with NaOH to give the hydroxycarbonyl adduct M(CO)4(CO2H)(1-) is somewhat slower and is followed by decarboxylation to give the metal hydride complex HM(CO)4(1-).Detailed investigation of the decarboxylation of Fe(CO)4(CO)2H)(1-) has led to the conclusion that in relatively nonpolar aqueous THF solutions this step occurs via a base-independent β-elimination , i.e. hydrogen transfer to the metal concerted with cleavage of the metal-carbon bond.The relevance of these data to the mechanism of the water gas shift reaction as catalyzed by iron carbonyls is discussed.