Syntheses, electrochemistry, photophysics and photochemistry of nitridorhenium(V) diphosphine complexes and related nitridorhenium(V) organometallics; crystal structure of [ReVN(CCBut)2(PPh3)2]

Abstract

A series of nitrido complexes [ReNL₂X]ⁿ[L = dppe(Ph₂PCH₂CH₂PPh₂), X = F, Cl, Br, NCS, NCO or N₃(n= 1) or MeCN (n= 2); L = dppbz(Ph₂PC₆H₄PPh₂-o), X = Cl (n= 1) or MeCN (n= 2)] have been synthesized and shown to exhibit long-lived photoluminescence in both the solid state and fluid solution, derived from the [(d_xy)¹(d_π*)¹] triplet (d_π*= d_xz, d_yz). The positions of the d–d absorption and emission bands have been found to be dependent on the identity of X. The luminescence quantum yields of [ReNL₂(MeCN)]²⁺ are greatly enhanced with respect to their chloro analogues. Cyclic voltammetric studies show that the [ReNL₂X]⁺ complexes display an irreversible reduction couple at E_pc of ca.–2.0 to –2.3 V and an irreversible oxidation couple at E_pa of ca.+1.3 to +1.9 V vs. the ferrocenium–ferrocene couple in MeCN (0.1 mol dm^–3 NBu₄PF₆). An additional irreversible reduction couple is observed at ca.–1.67 and –1.63 V for [ReN(dppe)₂(MeCN)]²⁺ and [ReN(dppbz)₂(MeCN)]²⁺, respectively. The reactivities of the nitrido complexes toward trifluoroacetic acid and electron donors such as alkoxybenzenes and organic amines have been investigated by Stern–Volmer quenching experiments and transient absorption difference spectroscopy. The electrochemical and spectroscopic properties of [ReNL₂X]ⁿ⁺ have been compared with those of organorhenium(V) nitro complexes [ReNR₂(PPh₃)₂](R = CCBu^t or C₆H₄Me-p). The crystal structure of [ReN(CCBu^t)₂(PPh₃)₂] has been determined: monoclinic, space group P2₁/n, a= 13.708(8), b= 19.161(6), c= 17.246(3)Å, β= 109.49(4)°, U= 4270(3)ų, Z= 4. A ReN distance of 1.63(2)Å has been measured.