Synthesis of Bidentate σ-Borane–Ruthenium Complexes [Cp*Ru(PiPr3)(η2-BH3·L)]+ (L = Amines or Phosphines): Structures, Properties, and Reactivities

Abstract

Chloride abstraction from [Cp*RuCl(PiPr3)] using Na[BArf4] in the presence of BH3·L afforded bidentate σ-borane complexes [Cp*Ru(PiPr3)(η2-BH3·L)][BArf4], where L = quin (N(C2H4)3CH), NMe3, NHMe2, NHiPr2, NH2Me, PMe3, PMe2Ph; Cp* = η5-C5Me5; [BArf4] = [B{3,5-C6H3(CF3)2}4]. In these compounds, the borane ligand is coordinated to the ruthenium atom through two B–H–Ru three-center two-electron bonds. Phosphine–borane complexes exhibit fluxional behavior due to the site exchange between the bridging and terminal BH hydrogen atoms at room temperature. Secondary amine–borane derivatives release H2 on heating. BH3·NHMe2 and BH3·NHiPr2 undergo dehydrogenation even with use of a catalytic amount of [Cp*RuCl(PiPr3)] and Na[BArf4] to ultimately yield [BH2NMe2]2 and BH2=NiPr2, respectively.