Syntheses, electrochemistry, photophysics and photochemistry of nitridorhenium(v) diphosphine complexes and related nitridorhenium(v) organometallics; crystal structure of [RevN(C≡CBut)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 [(dxy)1(dπ*)1] triplet (dπ* = dxy, dyz). 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 Epc of ca. -2.0 to -2.3 V and an irreversible oxidation couple at Epa 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) nitrido complexes [ReNR2(PPh3)2] (R = C≡CBut or C6H4Me-p). The crystal structure of [ReN(C≡CBut)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) Å, Z = 4. A Re≡N distance of 1.63(2) Å has been measured.