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The "catalytic nitrosyl effect": NO bending boosting the efficiency of rhenium based alkene hydrogenations


Jiang, Y; Schirmer, B; Blacque, O; Fox, T; Grimme, S; Berke, H (2013). The "catalytic nitrosyl effect": NO bending boosting the efficiency of rhenium based alkene hydrogenations. Journal of the American Chemical Society, 135(10):4088-4102.

Abstract

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 “hydrosilane/B(C6F5)3” 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’ 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–H bond and protonation of a phosphine ligand; (3) H2 adds in a bifunctional manner across the Re–N bond. Nitrosyl bending and phosphine loss help to create two vacant sites, thus triggering the high hydrogenation activities of the formed “superelectrophilic” rhenium centers.

Abstract

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 “hydrosilane/B(C6F5)3” 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’ 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–H bond and protonation of a phosphine ligand; (3) H2 adds in a bifunctional manner across the Re–N bond. Nitrosyl bending and phosphine loss help to create two vacant sites, thus triggering the high hydrogenation activities of the formed “superelectrophilic” rhenium centers.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:2013
Deposited On:07 Feb 2014 15:23
Last Modified:07 Dec 2017 08:43
Publisher:American Chemical Society
ISSN:0002-7863
Publisher DOI:https://doi.org/10.1021/ja400135d
PubMed ID:23384075

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