Spectroscopy, molecular structure, and electrochemistry of rhenium(V) oxo and imido complexes of 1,4,8,11-tetraazacyclotetradecane (cyclam)

Abstract

trans-[ReO2(cyclam)]ReO4·1/2H2O, trans-[ReO(OEt)(cyclam)](ClO4)2, and trans-[Re(NPh)(OH)(cyclam)](ClO4)2 (cyclam = 1,4,8,11-tetraazacyclotetradecane) were prepared and structurally characterized by X-ray crystallography. The structure of trans-[ReO2(cyclam)]ReO4·1/2H2O is quite similar to that of the previously reported trans-[ReO2-(cyclam)]Cl and trans-[ReO2(cyclam)]PF6. Crystal data: trans-[ReO2(C10H24N4)]ReO 4·1/2H2O, M = 676.74, orthorhombic, space group Pnma, a = 17.717(5) Å, b = 17.073(4) Å, c = 5.466(2) Å, V = 1653.4(9) Å3, Z = 4, dcalcd = 2.719 g cm-3, μ(Mo Kα) = 14.86 mm-1; trans-[ReO(OEt)(C10H24N4)](ClO 4)2, M = 646.49, orthorhombic, space group P212121, a = 8.869(4) Å, b = 13.850(3) Å, c = 17.681(3) Å, V = 2172(1) Å3, Z = 4, dcalcd = 1.977 g cm-3, μ(Mo Kα) = 5.97 mm-1; trans-[Re(NPh)(OH)(C10H24N4)](ClO 4)2, M = 693.55, orthorhombic, space group Pnma, a = 17.651(6) Å, b = 15.702(5) Å, c = 8.695(2) Å, V = 2410(1) Å3, Z = 4, dcalcd = 1.912 g cm-3, μ(Mo Kα) = 5.50 mm-1. The rhenium-oxo bond distances in trans-[ReO2(cyclam)]+ and trans-[ReO(OEt)-(cyclam)]2+ are 1.775(9) and 1.643(9) Å, respectively. The UV-vis spectrum of trans-[ReO2(cyclam)]+ shows two ligand field transitions at 423 and 530 nm. For trans-[ReO(OEt)(cyclam)]2+, the corresponding ligand field bands red shift to 481 and 625 nm. trans-[Re(NPh)(OH)(cyclam)]2+ is stable in aqueous medium. The measured Re≡NPh distance of 1.731(9) Å and Re≡N-Ph bond angle of 176.2(8)° are consistent with the metal-imido formulation. The cyclic voltammogram of trans-[ReO2(cyclam)]+ in aqueous medium shows a quasi-reversible 2H+-2e- couple corresponding to the reduction of Re(V) to Re(III). Both trans-[ReO(OEt)(cyclam)]2+ and trans-[Re(NPh)-(OH)(cyclam)]2+ show a 1e- reduction wave in acetonitrile at potentials of -1.0 and -1.4 V vs SCE, respectively. E° of the trans-[Rev(NPh)(OH)(cyclam)]2+/trans-[Re IV(NPh)(OH)(cyclam)]2+ couple is smaller than that of trans-[ReVO(OEt)(cyclam)]2+/trans-[Re IVO(OEt)(cyclam)]+. © 1993 American Chemical Society.