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 Re≡N distance of 1.839(8) and Re=O distances of 1.785(8) and 1.766(8) Å have been measured. The [ReNL2Cl]+ and trans-[ReO2L2]+ complexes exhibit intense ν(Re≡N) and νasym(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 Epc of ca. -2.1 to -2.4 and an irreversible oxidation couple at Epa 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.