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Stabilization of Vinylidene-type and Acetylene-type Si2H2 Species by Coordination with Rhodium(I) and Platinum(0) Complexes. Theoretical Proposals

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posted on 2005-07-18, 00:00 authored by Yuki Kuramoto, Noriyuki Sawai, Yusuke Fujiwara, Michinori Sumimoto, Yoshihide Nakao, Hirofumi Sato, Shigeyoshi Sakaki
Rh(I) and Pt(0) complexes of Si2H2 species were theoretically investigated. RhCl(PMe3)2(Si2H2) (2-Rha) containing vinylidene-type Si2H2 species is the most stable among various Rh(I) complexes of Si2H2, while the vinylidene-type Si2H2 species (2) is much less stable than the most stable 2H-bridged Si2H2 species (3) by 11.5 kcal/mol, where the energy calculated by the DFT method is given hereafter. RhCl(PMe3)2(Si2H2) (1-Rh) containing acetylene-type Si2H2 species easily isomerizes to the Rh complex (4-Rh) of the 1H-bridged Si2H2 species with a small activation barrier (2.6 kcal/mol). Complex 4-Rh further isomerizes to 2-Rha with a very small activation barrier (1.9 kcal/mol), while RhCl(PMe3)2(Si2H2) (3-Rh) containing the 2H-bridged Si2H2 species isomerizes to 2-Rha with a considerable activation barrier (11.8 kcal/mol). Pt(PR3)2(Si2H2) (3-Pt or 3-Pt‘ for R = H or Me, respectively) containing the 2H-bridged Si2H2 species has almost the same energy as the Pt complex (2-Pta or 2-Pta‘) of the vinylidene-type Si2H2 species; the energy difference is only 0.2−0.3 kcal/mol. Pt(PR3)2(Si2H2) (1-Pt and 1-Pt‘) containing the acetylene-type Si2H2 species is moderately less stable than 3-Pt and 3-Pt‘ by 6.6 (4.9) kcal/mol, while the acetylene-type Si2H2 species (1) is much less stable than 3 by 20.0 kcal/mol, where the energy values for R = H and Me are given without parentheses and in parentheses, respectively. Complex 1-Pt isomerizes to 4-Pt with a moderate activation barrier (5.4 kcal/mol), which further isomerizes either to 2-Pt with a very small activation barrier (1.9 kcal/mol) or to 3-Pt with a moderately small activation barrier (4.1 kcal/mol). From these results, several theoretical predictions are proposed, as follows:  (1) The vinylidene-type Si2H2 species is stabilized by Rh(I) and Pt(0) complexes. (2) The acetylene-type Si2H2 species is stabilized by the Pt(0) complex. And, (3) the vinylidene-type Si2H2 species can be isolated as the Rh(I) complex.

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