Syntheses, spectroscopy and X-ray crystal structures of luminescent nitrido- and trans-dioxo-rhenium(V) complexes of phosphines and arsines

Abstract

Reaction of [ReNCl₂(PPh₃)₂] and [ReO₂(PPh₃)₂I] with a variety of phosphines and arsines, L, yielded the respective complex cations [ReNL₂Cl]⁺ and trans-[ReO₂L₂]⁺. The X-ray crystal structures of [ReN(dpae)₂Cl]⁺ and trans-[ReO₂(dadpe)₂]⁺[dpae = 1,2-bis(diphenylarsino)ethane, dadpe = 1-diphenylarsino-2-diphenylphosphinoethane] have been determined: [ReN(dpae)₂Cl]⁺, monoclinic, space group Cc, a= 10.362(2), b= 22.823(5), c= 21.363(6)Å, β= 92.74(2)°, Z= 4; trans-[ReO₂(dadpe)₂]⁺, monoclinic, space group Cc, a= 9.868(3), b= 22.608(5), c= 21.887(8)Å, β= 91.87(3)°, Z= 4. A ReN distance of 1.839(8) and ReO distances of 1.785(8) and 1.766(8)Å have been measured. The [ReNL₂Cl]⁺ and trans-[ReO₂L₂]⁺ complexes exhibit intense ν(ReN) and ν_asym(ReO₂) stretches at 1043–1049 and 785–790 cm^–1, respectively. Excitation of solid samples of [ReNL₂Cl]ClO₄ and trans-[ReO₂L₂]ClO₄ at 350–380 nm at room temperature results in yellow-green and orange emission, respectively. Both [ReN(dppbz)₂Cl]⁺ and [ReN(R-1,2-dppp)₂Cl]⁺[dppbz = 1,2-bis(diphenylphosphine)benzene, R-1,2-dppp =R-1,2-bis(diphenylphosphino)propane] exhibit intense long-lived room-temperature luminescence in fluid solutions. Concentration quenching has been observed for both [ReN(dppbz)₂Cl]⁺ and [ReN(R-1,2-dppp)₂Cl]⁺ in MeCN (0.1 mol dm^–3 NBu₄PF₆) with self-quenching rate constants of ca. 5.7 × 10⁷ and 3.2 × 10⁸ dm³ mol^–1 s^–1, respectively, and inherent lifetimes of ca. 15 and 0.9 µs at infinite dilution. All the trans-[ReO₂L₂]⁺ complexes exhibit room-temperature luminescence in MeCN. Cyclic voltammetric studies show that the [ReNL₂Cl]⁺ complexes display an irreversible reduction couple at E_pc of ca.–2.1 to –2.4 and an irreversible oxidation couple at E_pa of ca.+1.4 to +1.7 V vs. ferrocene–ferrocenium in MeCN (0.1 mol dm^–3 NBu₄PF₆). Irreversible reduction and oxidation couples are also observed for the trans-[ReO₂L₂]⁺ species. A direct comparison of the photophysical and spectroscopic properties of [ReNL₂Cl]⁺ and trans-[ReO₂L₂]⁺ has been made.