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Triangular Triplatinum Complex with Four Bridging Si Ligands: Dynamic Behavior of the Molecule and Catalysis

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journal contribution
posted on 03.05.2017, 12:49 authored by Makoto Tanabe, Megumi Kamono, Kimiya Tanaka, Kohtaro Osakada
A triangular triplatinum(0) complex with bridging diphenylsilylene ligands, [{(Pt­(PMe3)}3(μ-SiPh2)3] (1a), reacts with H2SiPh2 to produce the 1:1 adduct, [{Pt­(PMe3)}3(H)2(μ-SiPh2)4] (2a), which was isolated and characterized by X-ray crystallography. Two Pt–Pt bonds of the triangular Pt3 core are bridged by a diphenylsilylene ligand, while the remaining Pt–Pt bond has two unsymmetrical bridging Si ligands. Dissolution of 1a and H2SiPh2 at a 1:3 molar ratio forms a mixture of complex 2a and unreacted 1a. NMR measurement of the solution at −90 °C revealed the structure of 2a as having two hydride ligands and four bridging silylene ligands. Two 31P­{1H} NMR signals of 2a at −90 °C coalesce on warming to −50 °C owing to facile exchange of the four Si ligands. Reversible addition of H2SiPh2 to 1a yielded 2a with ΔG° = −8.0 kJ mol–1, ΔH° = −51.7 kJ mol–1, and ΔS° = −146 J mol–1 K–1. Addition of bis­(4-fluorophenyl)­silane and bis­(4-methylphenyl)­silane to the complexes, which have three bis­(4-fluorophenyl)­silylene and bis­(4-methylphenyl)­silylene ligands, respectively, also occurs reversibly in the solution, and the diarylsilane with an electron-withdrawing substituent is favored for the formation of Pt3Si4 complexes. Complex 1a catalyzes hydrosilyation of benzaldehyde with H2SiPh2 to produce diphenyl­(benzyloxy)­silane along with concurrent hydrosilyation and dehydrosilyation of phenyl­(methyl)­ketone. Dehydrogenative coupling of H2SiPh2 and phenol is also catalyzed to yield diphenyl­(phenoxy)­silane. The 31P­{1H} NMR spectra of the mixtures during the catalytic reaction show 2a as the major Pt-containing species.