| Abstract
| - A concerted mechanism for the title reaction has been described by DFT calculations. This mechanism is associated with low energy barriers. In the case of prochiral acetophenone and a hydride complex with a chiral diamine, two diastereoisomer transition states have been determined. The energy difference between them explains the preferential formation of the R isomer of the phenylethanol.
- Concerted mechanisms for the catalytic cycle of the carbonyl reduction by a rhodium(I)hydride complex were studied on the basis of DFT theoretical calculations. The first assumedmechanism consists of the direct transfer of a metal-bound hydride to the carbon of thecarbonyl in concert with the coordination of the oxygen to the metallic center. In the secondmechanism, the hydride of the complex and a proton of a nitrogen-containing ligand aretransferred simultaneously to the carbonyl. Several substrates such as formaldehyde, acetone,and the experimentally used acetophenone were investigated as starting materials, andseveral nitrogen-containing ligands were considered. Each postulated intermediate wasconfirmed to be a stationary point on the potential energy surface, and transition stateswere characterized, except in the case of the first mechanism, where no transition statewas found. All the activation barriers were calculated to be within the range of 3.9−18.7kcal mol-1 and are consistent with experimental reaction rates. In the case of acetophenone,the calculations for chiral diamine ligands explain the origin of the observed enantioselectivitywith a complete characterization of the diastereoisomer transition states.
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