title: The "catalytic nitrosyl effect": NO bending boosting the efficiency of rhenium based alkene hydrogenations.
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 (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.
authors: Anorganisch-Chemisches Institut, Universität Zürich, Winterthurerstrasse 190, CH-8037, Zürich, Switzerland.
authors: Yanfeng
authors: Y
authors: Jiang
authors: Birgitta
authors: B
authors: Schirmer
authors: Olivier
authors: O
authors: Blacque
authors: Thomas
authors: T
authors: Fox
authors: Stefan
authors: S
authors: Grimme
authors: Heinz
authors: H
authors: Berke
mesh_terms: D000473:Alkanes / Q000138:chemical synthesis* / Q000737:chemistry; D000475:Alkenes / Q000737:chemistry*; D002384:Catalysis; D006865:Hydrogenation; D008958:Models, Molecular; D015394:Molecular Structure; D009569:Nitric Oxide / Q000737:chemistry*; D009603:Nitroso Compounds / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011789:Quantum Theory; D012211:Rhenium / Q000737:chemistry*
chemical_list: D000473:Alkanes; D000475:Alkenes; D009603:Nitroso Compounds; D009942:Organometallic Compounds; D009569:Nitric Oxide; D012211:Rhenium