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

A triangular triplatinum(0) complex with bridging diphenylsilylene ligands, [{(Pt­(PMe<sub>3</sub>)}<sub>3</sub>(μ-SiPh<sub>2</sub>)<sub>3</sub>] (<b>1a</b>), reacts with H<sub>2</sub>SiPh<sub>2</sub> to produce the 1:1 adduct, [{Pt­(PMe<sub>3</sub>)}<sub>3</sub>(H)<sub>2</sub>(μ-SiPh<sub>2</sub>)<sub>4</sub>] (<b>2a</b>), which was isolated and characterized by X-ray crystallography. Two Pt–Pt bonds of the triangular Pt<sub>3</sub> core are bridged by a diphenylsilylene ligand, while the remaining Pt–Pt bond has two unsymmetrical bridging Si ligands. Dissolution of <b>1a</b> and H<sub>2</sub>SiPh<sub>2</sub> at a 1:3 molar ratio forms a mixture of complex <b>2a</b> and unreacted <b>1a</b>. NMR measurement of the solution at −90 °C revealed the structure of <b>2a</b> as having two hydride ligands and four bridging silylene ligands. Two <sup>31</sup>P­{<sup>1</sup>H} NMR signals of <b>2a</b> at −90 °C coalesce on warming to −50 °C owing to facile exchange of the four Si ligands. Reversible addition of H<sub>2</sub>SiPh<sub>2</sub> to <b>1a</b> yielded <b>2a</b> with Δ<i>G</i>° = −8.0 kJ mol<sup>–1</sup>, Δ<i>H</i>° = −51.7 kJ mol<sup>–1</sup>, and Δ<i>S</i>° = −146 J mol<sup>–1</sup> K<sup>–1</sup>. 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 Pt<sub>3</sub>Si<sub>4</sub> complexes. Complex <b>1a</b> catalyzes hydrosilyation of benzaldehyde with H<sub>2</sub>SiPh<sub>2</sub> to produce diphenyl­(benzyloxy)­silane along with concurrent hydrosilyation and dehydrosilyation of phenyl­(methyl)­ketone. Dehydrogenative coupling of H<sub>2</sub>SiPh<sub>2</sub> and phenol is also catalyzed to yield diphenyl­(phenoxy)­silane. The <sup>31</sup>P­{<sup>1</sup>H} NMR spectra of the mixtures during the catalytic reaction show <b>2a</b> as the major Pt-containing species.