Syntheses and Reactivity of Cationic Borane−Ruthenium Complexes (η5-C5R5) Ru (PMe3) 2 (η1-BH3·EMe3) BArf4 (R = H, Me; E = N, P; BArf4 = B3, 5-C6H3 (CF3) 24)

Chloride displacement from (η5-C5R5) Ru (PMe3) 2Cl by NaBArf4 in the presence of BH3·EMe3 afforded cationic borane σ complexes containing an unsupported B−H−Ru bridge, (η5-C5R5) Ru (PMe3) 2 (η1-BH3·EMe3) BArf4 (4a: R = H, EMe3 = PMe3; 4b: R = Me, EMe3 = PMe3; 4c: R = H, EMe3 = NMe3; BArf4 = B3, 5-C6H3 (CF3) 24). Compounds 4a−c were fully characterized, and their structures were determined by X-ray crystallographic analysis. In these complexes, the borane ligand is coordinated to the ruthenium atom through a B−H−Ru three-center two-electron bond. They exhibit fluxional behavior due to site exchange between the BH hydrogen atoms. Complexes 4a and 4c are remarkably stable. However, they are hydrolyzed by a trace amount of water to produce a cationic dihydride, trans-CpRuH2 (PMe3) 2+ (6, Cp = η5-C5H5). The reactivity of 4a toward various substrates was investigated.