Hydroformylation hydrogen abstraction

Abstract The applications of hybrid DFT/molecular mechanics (DFT/MM) methods to the study of reactions catalyzed by transition metal complexes are reviewed. Special attention is given to the processes that have been studied in more detail, such as olefin polymerization, rhodium hydrogenation of alkenes, osmium dihydroxylation of alkenes and hydroformylation by rhodium catalysts. DFT/MM methods are shown, by comparison with experiment and with full quantum mechanics calculations, to allow a reasonably accurate computational study of experimentally relevant problems which otherwise would be out of reach for theoretical chemistry. 

With added CO, but not in its absence, ethylene reacts rapidly with HRh(CO)L3 solutions to give the acyl complex EtCORh(CO)2iL2- With 1 atm of H2 and CO (in a 2 1 ratio) propionaldehyde forms with a half-life of 5 minutes. Using a 1 2 mixture of H2 and CO instead of 2 1 increases the half-life to an hour, suggesting that CO dissociation from the 18-electron acyl complex is necessary before oxidative addition of H2. Isomerization and hydrogenation are much slower under hydroformylation conditions (with H2 and CO) than under H2 alone. These reactions are typically only 1-2% of the hydroformylation rate. The reason must be high rates of capture of 16-electron alkyl rhodium complexes by CO compared to rates of H2 capture or jS -hydride abstraction to form isomerized hydrido-olefin complexes. 

Abstract The application of QM/MM methods to the study of the reaction mechanisms involved in chemo-, regio-, and enantio- selective processes has been a very productive area of research in the last two decades. This review summarizes basic general ideas in both QM/MM methods and the computational study of selectivity and presents selected results on the study of three of the most representative examples of these applications rhodium-catalyzed hydrogenation, rhodium-catalyzed hydroformylation, and copper-catalyzed cyclopropanation. 

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