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

The bis(dihydrogen) complex RuH2(9eta)^2-H2)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-H2)((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 PiPr3 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(tBuNC)2(PCy3)2(6) or RuH((eta)^2-H2)Cl(PCy3)2(7) were observed upon the reaction of 2 with CO, tBuNC, CH2Cl2, respectively. No reaction occurred in the presence of H2, but H/D exchange was observed under D2 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 Ru2H2((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.