Synthesis and single-crystal X-ray structure determination of trans-[RhCl2(tmc)]PF6(tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetradecane)

Abstract

Reaction of RhCl₃·3H₂O with one molar equivalent of tmc (1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetradecane) in refluxing MeOH affords the complex cation [RhCl₂(tmc)]⁺. The complex [RhCl₂(tmc)]PF₆ crystallises in the orthorhombic space group Pnma, with each anion and each cation lying on a crystallographic mirror plane. The single-crystal X-ray structure of the octahedral complex shows the chloride ions mutually trans to one another, Rh–Cl 2.355(3) and 2.362(3)Å, with the tetra-aza macrocycle adopting an RRSS conformation with two methyl groups lying above, and two methyl groups lying below the RhN₄ plane [Rh–N 2.110(8) and 2.114(8)Å]. trans-[RhCl₂(tmc)]⁺ shows a quasi-reversible Rh^III–Rh^II redox couple at E_½=–0.99 V vs.[Fe(η-C₅H₅)₂]–[Fe(η-C₅H₅)₂]⁺ in MeCN; slow loss of chloride occurs on electrochemical reduction of the complex.