The 鈥淐atalytic Nitrosyl Effect鈥? NO Bending Boosting the Efficiency of Rhenium Based Alkene Hydrogenations
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- 作者：Yanfeng Jiang ; Birgitta Schirmer ; Olivier Blacque ; Thomas Fox ; Stefan Grimme ; Heinz Berke
- 刊名：The Journal of the American Chemical Society
- 出版年：2013
- 出版时间：March 13, 2013
- 年：2013
- 卷：135
- 期：10
- 页码：4088-4102
- 全文大小：632K
- 年卷期：v.135,no.10(March 13, 2013)
- ISSN：1520-5126
文摘
Diiodo Re(I) complexes [ReI2(NO)(PR3)2(L)] (3, L = H2O; 4 , L = H2; R = iPr a, Cy b) were prepared and found to exhibit in the presence of 鈥渉ydrosilane/B(C6F5)3鈥?co-catalytic systems excellent activities and longevities in the hydrogenation of terminal and internal alkenes. Comprehensive mechanistic studies showed an inverse kinetic isotope effect, fast H2/D2 scrambling and slow alkene isomerizations pointing to an Osborn type hydrogenation cycle with rate determining reductive elimination of the alkane. In the catalysts鈥?activation stage phosphonium borates [R3PH][HB(C6F5)3] (6, R = iPr a, Cy b) are formed. VT 29Si- and 15N NMR experiments, and dispersion corrected DFT calculations verified the following facts: (1) Coordination of the silylium cation to the ONO atom facilitates nitrosyl bending; (2) The bent nitrosyl promotes the heterolytic cleavage of the H鈥揌 bond and protonation of a phosphine ligand; (3) H2 adds in a bifunctional manner across the Re鈥揘 bond. Nitrosyl bending and phosphine loss help to create two vacant sites, thus triggering the high hydrogenation activities of the formed 鈥渟uperelectrophilic鈥?rhenium centers.