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

The reaction of [Pt(PPh 3 ) 2 (η 2 -C 2 H 4 )] ( 1 ) with 1,2-dihydrodisilane HSiR 2 SiR 2 H (R = Ph, Me) was investigated by NMR spectroscopy and X-ray diffraction analysis. In the case of R = Ph, the treatment of 1 with HSiPh 2 SiPh 2 H at −60 °C afforded the disilanylplatinum hydride [Pt(PPh 3 ) 2 (H)(SiPh 2 SiPh 2 H)] ( 2a ) by an oxidative addition of Si−H to the Pt center. Complex 2a was converted to the bis(silyl)platinum complex [Pt(PPh 3 ) 2 (SiHPh 2 ) 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(PPh 3 ) 2 (H)(SiHPh 2 )] ( 4a ) was formed by the elimination of a SiPh 2 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(PPh 3 )(μ-SiHPh 2 )] 2 ( 6a ). Complex 6a also was obtained by an alternative method wherein 1 reacted with HSiPh 2 SiPh 2 H at room temperature. In the case of R = Me, the bis(silyl)platinum complex [Pt(PPh 3 ) 2 (SiHMe 2 ) 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 [(PPh 3 ) 2 Pt(H)(μ-SiMe 2 )(μ-SiHMe 2 )Pt(PPh 3 )] ( 5b ), in which one hydride of the Pt(PPh 3 ) 2 site binds to the Pt center in a terminal binding mode and the other hydride of the Pt(PPh 3 ) site bridges between the Pt and the Si atoms in a nonclassical 3c−2e interaction. The liberation of one PPh 3 from the Pt(PPh 3 ) 2 site in 5b afforded [Pt(PPh 3 )(μ-SiHMe 2 )] 2 ( 6b ), which was similar to 6a; the 1 H and 31 P{ 1 H} NMR data after the addition of excess PPh 3 to 6b indicated the equilibrium between 5b and 6b . These results suggest that the reaction in the 1 /HSiR 2 SiR 2 H system proceeds in the following order: an oxidative addition of Si−H, 1,2-migration, elimination of SiR 2, dimerization accompanying the reductive elimination of dihydrogen, and liberation of PPh 3 .