H2 Activation and Direct Access to Terminal Nitride and cyclo-P3 Complexes by an Acceptor-Free Rhenium(II) β-Diketiminate

Abstract

The rhenium(II) complex Re(η5-Cp)(BDI) (B; BDI = N,N'-bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate; Cp = cyclopentadienyl) was subjected to a number of reactivity studies that highlight its unique combination of oxidation state and acceptor-free coordination environment. In the reactions under study we found that this low-valent paramagnetic species yields diamagnetic rhenium(III) or rhenium(V) products, indicating a combination of reducing power and radical character are the primary variables that control its reactivity. Namely, B has been found to promote the cleavage of dihydrogen to yield the rhenium(III) hydride Re(H)(η5-Cp)(BDI) (C), as well as the three-electron reduction of organic azides to yield a rhenium(V) terminal nitride complex NRe(η3-Cp)(BDI) (3), which features a low-hapticity Cp ligand. Additionally, we found that B readily activates white phosphorus (P4) to form the rhenium(V) cyclo-P3 complex (cyclo-P3)Re(η5-Cp)(BDI) (4). One-electron oxidation of 4 gave the paramagnetic rhenium(VI) salt [(cyclo-P3)Re(η5-Cp)(BDI)][OTf] (5-OTf), which was characterized by electron paramagnetic resonance and electron-nuclear double resonance spectroscopy spectroscopies. Density functional theory calculations and X-ray crystallography also provided a useful basis for understanding the reactivity and electronic structure of B and its derivatives.