Stability of thetrans-Bis(H···Si) Structure in the Complex RuH2(PCy3)2(κ-η2-H···SiMe2-o-C6H4-SiMe2···H), Studied by Density Functional Theory

The complex RuH 2 (PCy 3 ) 2 ( trans -κ-η 2 -H···SiMe 2 - o -C 6 H 4 -SiMe 2 ···H) exhibits a number of intriguing structural features, in particular the apparent trans configuration of the two H···Si units, the nearly collinear axial trans -H−Ru−H bonds, and the adoption of a near- C 2 v symmetry. Theoretical studies indicate that, in the experimental structure, the drastic distortion of the two H···Si units avoids the competition for σ*-back-donation while strengthening both the axial Ru−H and the Ru−Si bonds through a favorable orbital interaction with the metal d-orbitals. Such distortion is enhanced by the presence of chelation which forces a small Si−Ru−Si angle. The H···Si interaction distance is 1.842 Å, and the density Laplacian plot (−∇ 2 ρ) reveals that the extent of H···Si interaction is quite weak, with little sign of competition for the metal-to-ligand back-donation. Comparisons with the unchelated model complex RuH 2 (PH 3 ) 2 (H···SiH 3 ) 2 show that the chelation causes a weaker H···Si interaction, with an H···Si distance of the unchelated complex of ∼1.750 Å.