Activation of White Phosphorus by Low-Valent Group 5 Complexes: Formation and Reactivity of cyclo-P(4) Inverted Sandwich Compounds

[Image: see text] We report the synthesis and comprehensive study of the electronic structure of a unique series of dinuclear group 5 cyclo-tetraphosphide inverted sandwich complexes. White phosphorus (P(4)) reacts with niobium(III) and tantalum(III) β-diketiminate (BDI) tert-butylimido complexes to produce the bridging cyclo-P(4) phosphide species {[(BDI)(N(t)Bu)M](2)(μ-η(3):η(3)P(4))} (1, M = Nb; 2, M = Ta) in fair yields. 1 is alternatively synthesized upon hydrogenolysis of (BDI)Nb(N(t)Bu)Me(2) in the presence of P(4). The trinuclear side product {[(BDI)NbN(t)Bu](3)(μ-P(12))} (3) is also identified. Protonation of 1 with [HOEt(2)][B(C(6)F(5))(4)] does not occur at the phosphide ring but rather involves the BDI ligand to yield {[(BDI(#))Nb(N(t)Bu)](2)(μ-η(3):η(3)P(4))}[B(C(6)F(5))(4)](2) (4). The monocation and dication analogues {[(BDI)(N(t)Bu)Nb](2)(μ-η(3):η(3)P(4))}{B(Ar(F))(4)}(n) (5, n = 1; 6, n = 2) are both synthesized by oxidation of 1 with AgBAr(F). DFT calculations were used in combination with EPR and UV–visible spectroscopies to probe the nature of the metal–phosphorus bonding.