Protonation reactions of the mononuclear rhenium polyhydride complexes [ReH7(PPh3)2], [ReH5(PPh3)2L](L = unidentate ligand), and [ReH4I(PPh3)3]

Abstract

Protonation of the rhenium polyhydride complexes [ReH₇(PPh₃)₂], [ReH₅(PPh₃)₂L][L = pyridine (py), NH₂(C₆H₁₁), or NH₂Bu^t], or [ReH₄I(PPh₃)₃] with HBF₄·Et₂O in acetonitrile or propionitrile leads to the seven-co-ordinate complexes [ReH (NCR)₃(PPh₃)₂L][BF₄]₂[R = Me or Et; L = RCN, PPh₃, py, NH₂(C₆H₁₁), or NH₂Bu^t]. Their ¹H and ³¹P-{¹H} n.m.r. spectral properties are consistent with pentagonal-bipyramidal or face-capped octahedral geometries in solution. These complexes show a reversible one-electron oxidation in the potential range +1.0 to +1.6 V (vs. Ag–AgCl) in 0.1 mol dm^–3 NBu₄PF₆–CH₂Cl₂, and an irreversible reduction below –1.4 V. The substitution chemistry of [ReH(NCR)₄(PPh₃)₂][BF₄]₂ has been investigated and the mixed-phosphine complexes [ReH(NCR)₃(PPh₃)(dppe)][BF₄]₂(R = Me or Et; dppe = Ph₂PCH₂CH₂PPh₂) isolated as the initial reaction products. These species have been characterized by i.r. and n.m.r. spectroscopy and by cyclic voltammetry. Further reaction with dppe leads to reductive substitution and the formation of [Re(NCR)₂(dppe)₂] BF₄.