Activationof White Phosphorus by Low-Valent Group5 Complexes: Formation and Reactivity of cyclo-P4 Inverted Sandwich Compounds

摘要

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 (P4) reacts with niobium(III) and tantalum(III) β-diketiminate (BDI) tert-butylimido complexes to produce the bridging cyclo-P4 phosphide species {[(BDI)(N^tBu)M]2(μ-η³:η³P4)} (>1, M = Nb; >2, M = Ta) in fair yields. >1 is alternatively synthesized upon hydrogenolysis of (BDI)Nb(N^tBu)Me2 in the presence of P4. The trinuclear side product {[(BDI)NbN^tBu]3(μ-P12)} (>3) is also identified. Protonation of >1 with [HOEt2][B(C6F5)4] does not occur at the phosphide ring but rather involves the BDI ligand to yield {[(BDI^#)Nb(N^tBu)]2(μ-η³:η³P4)}[B(C6F5)₄]₂ (>4). The monocation and dication analogues {[(BDI)(N^tBu)Nb]₂(μ-η³:η³P₄)}{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.