Theoretical Study on the Rhodium-Catalyzed Hydrosilylation of C=C and C=O Double Bonds with Tertiary Silane.
Theoretical Study on the Rhodium-Catalyzed Hydrosilylation of C=C and C=O Double Bonds with Tertiary Silane.
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DOI：
10.1021/acs.joc.9b00959
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发表时间：
2019-06
期刊：
影响因子：
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通讯作者：
Liming Zhao;N. Nakatani;Y. Sunada;H. Nagashima;J. Hasegawa
中科院分区：
文献类型：
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作者：
Liming Zhao;N. Nakatani;Y. Sunada;H. Nagashima;J. Hasegawa
Reaction mechanisms of hydrosilylation of ketone and alkene with tertiary silane using Wilkinson-type catalyst were theoretically investigated on the basis of density functional calculations using ωB97XD functional. Previously proposed three mechanisms, Chalk-Harrod (CH) mechanism, modified Chalk-Harrod (mCH) mechanism, as well as outer-sphere mechanism were examined. Besides, we also found two mechanisms, alternative CH (aCH) mechanism and double hydride (DH) mechanism. In the aCH mechanism, a four-coordinate rhodium hydride complex formed through elimination of R3Si-Cl is a catalytically active species. In the DH mechanism, the active species is a six-coordinate complex with two Rh-H bonds. For the C=O double bond hydrosilylation, the rate-determining steps of the aCH and DH mechanisms are both acetone insertion into the Rh-H bond, and the order of the activation barriers is that DH < aCH ≈ CH < mCH. For the C=C double bond hydrosilylation, except for the mCH pathway whose rate-determining step is the hydrosilane addition reaction, the rate-determining steps of the CH, aCH, and DH pathways are Si-C reductive elimination reaction. The order of the energy barrier is that DH ≈ mCH < aCH ≈ CH. In the outer-sphere mechanism, no stable intermediate or transition state was found. Consequently, we concluded that the DH mechanism is adopted as the mechanism for the Rh-catalyzed hydrosilylation of carbonyl group while mCH or DH is adopted as that for alkenes under a condition where their active intermediates are formed. The present result revises a hypothesis that the hydrosilylation of carbonyl group is in general accomplished by the mCH mechanism. The active species in DH mechanism has one more extra Rh-H bond than that of the other pathways, and its interaction with silyl group, trans-influence, and small steric effect are the origin of the highly efficient catalytic activity, which was not reported before.
