Synthesis of Ruthenium Complexes with a Nonspectator Si,O,P-Chelate Ligand: Interconversion between a Hydrido(η²-silane) Complex and a Silyl Complex Leading to Catalytic Alkene Hydrogenation

Abstract

A ruthenium complex bearing a new phosphine­(η2-silane) chelate ligand connected by a xanthene backbone, Ru­{κ4(Si,H,O,P)- t Bu2xantSiP­(H)}­(H)­Cl­(PPh3) (2), was synthesized by a ligand substitution reaction of Ru­(H)­Cl­(PPh3)3 with 2,7-di-tert-butyl-4-dimethylsilyl-5-diphenylphosphino-9,9-dimethylxanthene (1, t Bu2xantSiP­(H)). Dehydrogenation reaction of 2 with styrene, a hydrogen acceptor, gave a 16-electron phosphine­(silyl) complex Ru­{κ3(Si,O,P)- t Bu2xantSiP}­Cl­(PPh3) (3) together with ethylbenzene. Complex 2 was reproduced quantitatively by exposure of 3 to H2 (1 atm) at room temperature. Thus, hydrido­(η2-silane) complex 2 and silyl complex 3 are interconvertible through alkene hydrogenation (from 2 to 3) and dihydrogen addition to the Ru–Si bond (from 3 to 2) in which t Bu2xantSiP functions as a nonspectator ligand by reversibly releasing and accommodating a hydrogen atom. Complex 2 was also found to catalyze hydrogenation of alkenes via this interconversion.

Catalysts for Regio- and Stereoselective C(sp3)–H Deuteration of Tricyclohexylphosphine with Benzene-d6 Generated via Dehydrochlorination of Chlorido(dihydrido)iridium Complexes Containing a Xanthene-Based Bis(silyl) Chelate Ligand

“…Because the p -tolyl group is bulkier than the methyl group, xantSi Me Si p ‑Tol is expected to stabilize the active species by steric protection. The precursor of the xantSi Me Si p ‑Tol ligand, 2,7-di- tert -butyl-4-dimethylsilyl-5-di- p -tolylsilyl-9,9-dimethylxanthene (xantSi Me Si p ‑Tol H 2 ), was synthesized in 54% yield by lithiation of a 4-bromo-5-silylxanthene derivative using t -BuLi in toluene, followed by salt elimination with ClSiH­( p -Tol) 2 in the presence of TMEDA (Scheme ). The reaction of xantSi Me Si p ‑Tol H 2 with 0.5 equiv of [IrCl­(coe) 2 ] 2 in toluene at room temperature for 10 min followed by treatment of the reaction mixture with a 2e-donor ligand L (pyridine and PCy 3 ) gave the bis­(silyl) chelate complexes Ir­(κ 2 Si,Si -xantSi Me Si p ‑Tol )­(H) 2 (L)Cl (L = pyridine ( 2-py ), PCy 3 ( 2-PCy )) in 82% and 85% isolated yields, respectively, via Si–H oxidative addition and ligand substitution (Scheme ).…”

“…PCy 3 (Strem Chemicals), (Me 3 Al) 2 ·DABCO (Sigma-Aldrich), and BH 3 ·THF (1 M solution in THF, Sigma-Aldrich) were stored under argon in a glovebox. 4-Bromo-2,7-di- tert -butyl-5-dimethylsilyl-9,9-dimethylxanthene, ClSiH­( p -Tol) 2 , [IrCl­(coe) 2 ] 2 , and Ir­(κ 2 Si,Si -xantsil)­(H) 2 (PCy 3 )Cl ( 1 ) were prepared according to previously reported methods.…”

Insights into the Interfacial Effects in Heterogeneous Metal Nanocatalysts toward Selective Hydrogenation

“…In homogeneous hydrogenation, ligands can serve as binding sites for protons during the hydrogenation process. − In these cases, the ligand often bears a strong binding site for the coordinating metal center together with a proton-accepting moiety such as an amine group . Similarly, such a concept has been successfully applied in the design of heterogeneous metal nanocatalysts with their surface modified by organic ligands. − For instance, Kunz and co-workers nicely demonstrated that the modification of Pt nanoparticles by l -proline (PRO) can enhance the catalytic performance in the hydrogenation of acetophenone (Figure a) .…”

Exploiting the Versatility of Phosphinobenzylsilanes for the Stabilization of 14‐Electron Rhodium(III) and Iridium(III) Complexes

“…Steric properties can be regulated by the choice of substituents at both P and Si and the linkage between the two . Thus one can achieve efficient catalyzed transformations including carbon dioxide reduction, alkene hydrogenation or hydrosilylation and even dinitrogen conversion to ammonia . On the other hand, unsaturated late transition metal complexes are key intermediates in important stoichiometric and catalytic processes, and a better access to species featuring less than 16 valence shell electrons would be advantageous for crucial processes including C–H bond activation, functionalization and many other catalytic processes , .…”