Me6TREN-Supported Alkali Metal Hydridotriphenylborates [(L)M][HBPh3] (M = Li, Na, K): Synthesis, Structure, and Reactivity

Triphenylborane (BPh3) abstracted the β-SiH in [(L)M{N(SiHMe2)2}] (L = Me6TREN; M = Li, Na, K) in THF to give the hydridotriphenylborates [(L)M][HBPh3]. Reactions in benzene favored silazide instead of hydride abstraction to give [(L)M][Ph3B–N(SiHMe2)2]. The hydridotriphenylborates [(L)M][HBPh3] catalyzed the chemoselective hydroboration of benzophenone by pinacolborane (HBpin), with the lithium derivative being the most active. The solution structure of [(L)Li][HBPh3] was qualitatively investigated in the context of its superior catalytic activity. Fluxional coordination of L in [(L)Li(THF)]+ in tandem with a THF solvent molecule was revealed by NMR spectroscopy. para-Substituents in [HB(C6H4-p-X)3]− influenced the rate which is apparently determined by the addition of the B–H function to the isolable alkoxy borate intermediate [(L)Li][Ph2CHOBPh3].