• Início
  • Resultados da busca
  • The "catalytic nitrosyl effect": NO bending boosting the efficiency of rhenium based alkene hydrogenations.

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

Journal of the American Chemical Society (2013-02-07)
Yanfeng Jiang, Birgitta Schirmer, Olivier Blacque, Thomas Fox, Stefan Grimme, Heinz Berke
RESUMO

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 (29)Si- and (15)N 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.

MATERIAIS
Número do produto
Marca
Descrição do produto

Sigma-Aldrich
Rhenium, powder, 99.995% trace metals basis
Sigma-Aldrich
Rhenium, foil, thickness 0.25 mm, 99.98% trace metals basis
Sigma-Aldrich
Rhenium, powder, −100 mesh, ≥99.9% trace metals basis
Sigma-Aldrich
Rhenium, foil, thickness 1.0 mm, 99.98% trace metals basis