Syntheses and characterization of ruthenium n2-dihydrogen and n2-silane complexes

Abstract

Protonation of [RCnRuH(L)(L')]+ (RCn = 1,4,7-triazacyclononane and 1,4,7-trimethyl-1,4,7-triazacyclononane, (L)(L') = (PPh3)2, dppe, and (CO)(PPh3)) and TpRuH(dppe) (Tp = hydrotris(pyrazolyl)borato) produced the corresponding dicationic dihydrogen complexes [RCnRu(H2)(L)(L')]2+ and new monocationic dihydrogen complex [TpRu(H2)(dppe)]+, respectively. pKa measurments indicate that the dicationic 庢2-H2 complexes are more acidic than their monocationic Tp and Cp counterparts. [MeCnRu(H2)(CO)(PPh3)]2+ was found to be more acidic than [HCnRu(H2)(CO)(PPh3)]2+, probably due to stronger H-H interaction in the latter complex. It is also noted that triazacyclononane and hydrotris(pyrazolyl)borato dihydrogen complexes with pseudo aqueous pKa values well above that of H3O+ can be deprotonated by H2O to form the corresponding monohydride complexes in organic/aqueous mixed solvents. It is believed that deprotonation of the dihydrogen ligands in these complexes is assisted by strong solvation of H+ by H2O. No silane complex was observed in the reaction of [TpRu(H2)(PPh3)2]+ with silane, although the 庢2-H2 ligand had undoubtedly been displaced. The silane complex had probably been formed, but it was readily attacked by nucleophilic species such as the counterion BF4- or water in the solvent. It was found that ruthenium solvent hydride complex [TpRuH(CH3CN)(PPh3)] reacted with silanes HSiR3 ( R3 = HPh2, HEt2, Ph3, Et3, H2Ph and (OEt)3) to yield the silane complexes [TpRuH(HSiR3)(PPh3)] which, instead of equilbrating between the 庢2-silane and 庢2-H2 tautomeric forms, interchanged the H atoms rapidly, and rendering them equivalent. The silane complex [TpRuH(HSiR3)(PPh3)] is analogous to the dihydrogen hydride complex TpRuH(H2)(PPh3) which we have recently reported.