Spectroscopic and Structural Studies of Thermally Unstable Intermediates Generated in the Reaction of [Pt(PPh3)2(η2-C2H4)] with Dihydrodisilanes

Abstract

The reaction of [Pt(PPh3)2(η2-C2H4)] (1) with 1,2-dihydrodisilane HSiR2SiR2H (R = Ph, Me) was investigated by NMR spectroscopy and X-ray diffraction analysis. In the case of R = Ph, the treatment of 1 with HSiPh2SiPh2H at −60 °C afforded the disilanylplatinum hydride [Pt(PPh3)2(H)(SiPh2SiPh2H)] (2a) by an oxidative addition of Si−H to the Pt center. Complex 2a was converted to the bis(silyl)platinum complex [Pt(PPh3)2(SiHPh2)2] (3a) by 1,2-migration of the silyl group with a first-order rate constant of 5.5(2) × 10−4 s−1 at –40 °C. The silylplatinum hydride [Pt(PPh3)2(H)(SiHPh2)] (4a) was formed by the elimination of a SiPh2 unit from the toluene solution of 3a maintained at –20 °C for 2 days. Then, the dimerization and reductive elimination of dihydrogen of 4a at room temperature afforded the symmetrical dinuclear complex [Pt(PPh3)(μ-SiHPh2)]2 (6a). Complex 6a also was obtained by an alternative method wherein 1 reacted with HSiPh2SiPh2H at room temperature. In the case of R = Me, the bis(silyl)platinum complex [Pt(PPh3)2(SiHMe2)2] (3b) was formed even at a temperature as low as −70 °C; this formation reaction was considerably faster than that of 3a, and no disilanylplatinum hydride was detected. While 3b was stable below 0 °C, it underwent dimerization at room temperature to afford the unsymmetrical dinuclear complex [(PPh3)2Pt(H)(μ-SiMe2)(μ-SiHMe2)Pt(PPh3)] (5b), in which one hydride of the Pt(PPh3)2 site binds to the Pt center in a terminal binding mode and the other hydride of the Pt(PPh3) site bridges between the Pt and the Si atoms in a nonclassical 3c−2e interaction. The liberation of one PPh3 from the Pt(PPh3)2 site in 5b afforded [Pt(PPh3)(μ-SiHMe2)]2 (6b), which was similar to 6a; the 1H and 31P{1H} NMR data after the addition of excess PPh3 to 6b indicated the equilibrium between 5b and 6b. These results suggest that the reaction in the 1/HSiR2SiR2H system proceeds in the following order: an oxidative addition of Si−H, 1,2-migration, elimination of SiR2, dimerization accompanying the reductive elimination of dihydrogen, and liberation of PPh3.