Reactions of Cp*Ta(NAr)Cl2 and CpM(NAr)Cl2 (M = Nb, Ta; Ar = 2,6-C6H3iPr2) with NaBH4 in the presence of an excess of PMe3 provided facile access to the corresponding dihydride derivatives CpRM(NAr)H 2(PMe3) (CpR = Cp, Cp*). Reaction of Cp*Nb(NAr)Cl2 with NaBH4 in the absence of phosphine gave the Nb(+5) borohydride-hydride complex Cp*Nb(NAr) H(η2-BH4). When the corresponding reactions for CpM(NAr)Cl2 (M = Nb, Ta) were carried out in the absence of an excess of phosphine, dimeric MIV products [CpM(μ-NAr)(η2- BH4)]2 containing M-M single bonds were formed. © 2014 The Royal Society of Chemistry.
