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.