Rhenium complexes of tetra-aza macrocycles: the synthesis and single-crystal X-ray structure of trans-[Re(O)2(cyclam)]Cl·2(BPh3·H2O)

Abstract

Reaction of [ReOCl₃(PPh₃)₂] with 1,4,8,11-tetra-azacyclotetradecane (cyclam) in CH₂Cl₂ affords an intermediate ‘ReOCl₃(cyclam)’ which hydrolyses readily to [Re(O)₂(cyclam)]⁺ in solution. trans-[Re(O)₂(cyclam)]Cl·2(BPh₃·H₂O) crystallises in the monoclinic space group P2₁/n, M= 974.26, a= 9.386 9(4), b= 13.550 4(7), c= 17.772 7(11)Å, β= 91.918(5)°, and Z= 2, implying that both the macrocyclic complex cation and the chloride counter ion lie on inversion centres. The single-crystal X-ray structure of the complex shows octahedral Re^V with the tetra-aza macrocyclic ligand bound in the equatorial plane adopting an RRSS(trans-III) configuration at the co-ordinated N donors, Re–N(1) 2.128(3), Re–N(11) 2.135(3)Å. The co-ordination shell is completed by mutually trans dioxo ligands, ReO 1.756(3)Å. The Cl^– counter ion is not co-ordinate to the Re centre. Two molecules of the adduct BPh₃·H₂O are also observed in the crystal. Extensive hydrogen bonding is observed in the crystal between the oxo ligands, water molecules, chloride counter ions, and the amine protons of the macrocyclic ligand.