Metal Silylenes Generated by Double Silicon-Hydrogen Activation: Key Intermediates in the Rhodium-Catalyzed Hydrosilylation of Ketones
Metal Silylenes Generated by Double Silicon-Hydrogen Activation: Key Intermediates in the Rhodium-Catalyzed Hydrosilylation of Ketones
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DOI：
10.1002/anie.200804993
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发表时间：
2009-01-01
影响因子：
16.6
通讯作者：
Gade, Lutz H.
中科院分区：
文献类型：
--
作者：
Schneider, Nathanaelle;Finger, Markus;Gade, Lutz H.
虽然铑催化的酮类硅氢化反应已被广泛研究，但对其机理的研究相对较少该领域的大多数催化剂开发研究都参考了Ojima等人在1975年提出的一种机制（Ojima机制，OM; Scheme 1a），[2]，其中氢硅烷氧化加成到RhI配合物中得到硅金属氢化物RhIII中间体。酮与后者的内东o配位，随后将酮羰基功能插入到Rh-Si键中，最后，还原消除得到硅基醚并恢复RhI物种。然而，这一机制并不能解释几个关键的观察结果，即当使用二氢硅烷代替单氢硅烷时所观察到的速率提高，观察到的动力学同位素效应以及α， β-不饱和羰基化合物的硅氢化反应的区域选择性。基于这些数据，Zheng和Chan[3]提出了一种替代催化循环（Chan mechanism， CM; Scheme 1b），其中第一步与OM相同。随后，酮与金属键硅原子相互作用，并插入SiÀH键，在关键步骤中得到烷氧基硅铑中间体。还原消除后得到产物，活性物质得到恢复
Although the rhodium-catalyzed hydrosilylation of ketones has been extensively studied, there have been relatively few investigations into the mechanism.[1] Most catalyst development studies in this area refer to a mechanism proposed by Ojima et al. in 1975 (Ojima mechanism, OM; Scheme 1a),[2] in which an oxidative addition of the hydrosilane to a RhI complex gives a silyl metal hydride RhIII intermediate. Endon O-coordination of the ketone to the latter, followed by the insertion of the ketone carbonyl function into the Rh–Si bond and, finally, reductive elimination gives the silyl ether and recovers the RhI species.However, this mechanism does not explain several key observations, namely the rate enhancement observed when dihydrosilanes are used instead of monohydrosilanes, the observed kinetic isotope effects and the regioselectivity in the hydrosilylation of α, β-unsaturated carbonyl compounds. Based on such data, Zheng and Chan [3] proposed an alternative catalytic cycle (Chan mechanism, CM; Scheme 1b) in which the first step is the same as in the OM. Subsequently, the ketone interacts with the metal-bonded silicon atom and inserts into the SiÀH bond to give an alkoxysilylrhodium intermediate in the key step. After reductive elimination, the product is obtained and the active species is recovered.[4]