Spectroscopic and structural studies of thermally unstable intermediates generated in the reaction of [Pt(PPh3)2(η2-C2H4)] with dihydrodisilanes

The reaction of [Pt(PPh3)(2)(eta(2)-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 degrees 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 center dot)(2 center dot)] (3a) by 1,2-migration of the silyl group with a first-order rate constant of 5.5 (2) x 10(-4) s(-1) at -40 degrees C. The silylplatinurn 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 degrees C for 2 days. Then, the dimerization and reductive elimination of dihydrogen of 4a at room temperature afforded the symmetrical dinuclear complex [Pt(PPh3)(mu-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 degrees C; this formation reaction was considerably faster than that of 3a, and no disilanylplatinum hydride was detected. While 3b was stable below 0 degrees C, it underwent dimerization at room temperature to afford the unsymmetrical dinuclear complex [(PPh3)(2)Pt(H)(mu-SiMe2)(mu-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)(mu-SiHMe2)](2) (6b), which was similar to 6a; the H-1 and (31)p {H-1} 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.