Redistribution at silicon by ruthenium complexes.: Bonding mode of the bridging silanes in Ru2H4(μ-η2:η2:η2:η2-SiH4)(PCy3)4 and Ru2H2(μ-η2:η2-H2Si(OMe)2)3(PCy3)2

The bis(dihydrogen) complex RuH2(eta(2)-H-2)(2)(PCy3)(2) (1) reacts with 2 equiv. of H2SiMePh to produce a mixture of Ru2H4(mu-eta(2):eta(2):eta(2):eta(2)-SiH4)(PCy3)(4) (2) and RuH2(eta(2)-H-2)(eta(2)-HSiPh3)(PCy3)(2) (4) together with HSiMePh2, HSiMe2Ph and traces of HMe2SiSiMe2H as a result of redistribution at silicon. The bridging SiH4 ligand in 2 is coordinated to the two ruthenium via four sigma-Si-H bonds in agreement with NMR, X-ray data (on 2, and 2' the analogous (PPr3)-Pr-i complex) and DFT calculations. Each interaction involves sigma-donation to a ruthenium and back-bonding from the other ruthenium. Elimination of SiH4 and formation of RuH2(CO)(2)(PCy3)(2) (5), RuH2((BuNC)-Bu-t)(2)(PCy3)(2) (6) or RuH(eta(2)-H-2)Cl(PCy3)(2) (7) were observed upon the reaction of 2 with CO, (BuNC)-Bu-t, CH2Cl2, respectively. No reaction occurred in the presence of H-2, but H/D exchange was observed under D-2 atmosphere. Another redistribution reaction at silicon can be obtained by adding 4 equiv. of HSi(OMe)(3) to 2 to produce Si(OMe)(4) and Ru(2)H2(mu-eta(2):eta(2)-H2Si(OMe)(2))(3)(PCy3)(2) (3) displaying three bridging (mu-eta(2):eta(2) alkoxysilane) ligands. Complex 3 is characterized by multinuclear NMR spectroscopies and by a crystal structure. DFT calculations show that the model complex Ru2H2(mu-eta(2):eta(2)-H2Si(OR)(2))(3)(PR3)(2) (R=H, Me) is a minimum on the potential energy surface, and support the dihydride formulation with three bridging H2Si(OMe)(2) ligands coordinated to the two ruthenium through sigma-Si-H bonds.