Group 5 hydride and borohydride complexes supported by cyclopentadienyl-imido ligand sets.

Reactions of Cp*Ta(NAr)Cl2 and CpM(NAr)Cl2 (M = Nb, Ta; Ar = 2,6-C6H3(i)Pr2) with NaBH4 in the presence of an excess of PMe3 provided facile access to the corresponding dihydride derivatives Cp(R)M(NAr)H2(PMe3) (Cp(R) = 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(η(2)-BH4). When the corresponding reactions for CpM(NAr)Cl2 (M = Nb, Ta) were carried out in the absence of an excess of phosphine, dimeric M(IV) products [CpM(μ-NAr)(η(2)-BH4)]2 containing M-M single bonds were formed.