Stability of the trans-bis(H center dot center dot center dot Si) structure in the complex RuH2(PCy3)(2)(kappa-eta(2)-H center dot center dot center dot SiMe2-o-C6H4-SiMe2 center dot center dot center dot H), studied by density functional theory

The complex RuH2(PCy3)(2)(trans-kappa-eta(2)-H ... SiMe2-o-C6H4-SiMe2... H) exhibits a number of intriguing structural features, in particular the app arent trans configuration of the two H ... Si units, the nearly collinear a xial trans-H-Ru-H bonds, and the adoption of a near-C-2v symmetry. Theoreti cal studies indicate that, in the experimental structure, the drastic disto rtion of the two H ... Si units avoids the competition, for sigma*back-dona tion. while strengthening both the axial Ru-H and the Ru-Si bonds through a favorable orbital interaction with the metal d-orbitals. Such distortion i s enhanced by the presence of chelation. which forces a small Si-Ru-Si angl e. The H ... Si interaction distance is 1.842 Angstrom, and the density Lap lacian plot (-del(2)rho) reveals that the extent of H ... Si interaction is quite weak, with little sign of competition for the metal-to-ligand back-d onation. Comparisons with the unchelated model complex RuH2(PH3)(2)(H ... S iH3)(2) show that the chelation causes a weaker H ... Si interaction, with an H ... Si distance of the unchelated complex of similar to 1.750 Angstrom .