Part I. Coenzyme B12 as a hydroformylation-type catalyst. Part II. Mechanisms of hydrogen transfer in the methylmalonyl coenzyme a mutase reaction

Part I

The mechanism of the hydroformylation reaction was studied. Using cobalt deuterotetracarbonyl and 1-pentene as substrates, the first step in the reaction, addition of cobalt tetracarbonyl to an olefin, was shown to be reversible.

Part II

The role of coenzyme B₁₂ in the isomerization of methylmalonyl coenzyme A to succinyl coenzyme A by methylmalonyl coenzyme A mutase was studied. The reaction was allowed to proceed to partial completion using a mixture of methylmalonyl coenzyme A and 4, 4, 4-tri-²H-methylmalonyl coenzyme A as substrate. The deuterium distribution in the product, succinyl coenzyme A, was shown to best fit a model in which hydrogen is transferred from C-4 of methylmalonyl coenzyme A to C-5’ of the adenosyl moiety of coenzyme B₁₂ in the rate determining step. The three hydrogens at the 5’-adenosyl position of the coenzyme B₁₂ intermediate are then able to become enzymatically equivalent before hydrogen is transferred from the coenzyme B₁₂ intermediate to form succinyl coenzyme A.

The PPh3 ligand modified Rh/SiO2 catalyst for hydroformylation of olefins

A novel family of hybrid catalyst with high turnover frequency (TOF) and high selectivity towards aldehydes for hydroformylation of olefins could be successfully approached through direct coordination with the PPh3 ligand to the highly dispersed Rh metal particle precursors. A further advantage is that the catalyst is easily prepared and recyclable. The results revealed that hydroformylation of olefins to aldehydes dominantly took place on the surface of PPh3 ligand modified Rh metal particles of the hybrid catalyst. It was found that the formation of chemical coordination bond between the Rh metal particles and the lone-pair electron of PPh3 was evident through the TG and P-31 NMR measurement. Moreover, the addition of PPh3 onto the Rh/SiO2 exert a significant influence on the adsorption state of reactant CO, H-2 and C2H4 on the PPh3-Rh/SiO2 sample, which probably lead to good catalytic performances for hydroformylation of olefins. (C) 2004 Elsevier B.V. All rights reserved.