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Catalytic Reduction of Carbonyl Functional Groups in 2-Propanol by Molybdocene Hydrides

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journal contribution
posted on 06.05.2003, 00:00 by Louis Y. Kuo, David M. Finigan, Nicholas N. Tadros
The catalytic reduction of acetophenone in 2-propanol by the organometallic complex [Cp2Mo(μ-OH)2 MoCp2](OTs)2 (I) proceeds through a molybdocene hydride intermediate. Activation parameters for the reduction of acetophenone to 1-phenylethyl alcohol in 2-propanol-d8 are 19 kcal mol-1 and −26 cal mol-1 K-1 for ΔH and ΔS, respectively. These parameters suggest 2-propanol and I are involved in a C−H activation step to form a molybdocene monohydride that may be the active species in the hydrogenation catalysis. When the catalysis reaction was performed with (CH3)2CHOD as the solvent, 1-deuterio-1-phenylethyl alcohol was almost quantitatively formed. This is consistent with a mechanism where a Cp2Mo hydride, formed in the C−H activation of (CH3)2CHOD, is converted to the deuteride by the solvent's alcoholic deuteron. The labeling experiment further supports the a molybdocene hydride as the catalytic species.