Metal−Silane Interaction in the Novel Pseudooctahedral Silane Complexcis-Mo(CO)(PH3)4(H···SiH3) and Some Related Isomers: Anab InitioStudy

Abstract

Ab initio calculations at the second-order Mφller-Plesset perturbation theory (MP2) level have been performed on the cis and trans isomers of the title model complex. For the cis isomer, the optimized structure shows a H···Si interaction distance of 1.813 A, in close agreement with the experimental value of 1.769 A for cis-Mo(CO)(depe)2(H···SiHPh2). Analysis of the density Laplacian (∇2ρ) around the Mo−(H···Si) triangle reveals a predominantly covalent Mo−Si bond and a likely dative H-→Mo bond, with a heavily curved H···Si bond path, suggesting that the H···Si covalent interaction is severely weakened. The trans structure is 9.9 kcal/mol less stable than the cis isomer, caused by the competition of metal d-electrons between CO and H···Si, and is manifested by the shorter H···Si distance of 1.715 A. The inability to locate a stable 7-coordinate structure with a H···Si distance greater than 2.5 A suggests that a classical−nonclassical tautomerism analogous to that in some dihydrogen complexes seems not very...