Preparation and reactivity of iodomethyl complexes of rhodium(III); crystal and molecular structure of carbonylchloroiodo(iodomethyl)bis(triethylphosphine)rhodium(III)

Abstract

Diiodomethane oxidatively added to [RhCl(CO)(PR₃)₂] formed [RhCl(I)(CH₂I)(CO)(PR₃)₂] for R₃= Me₃, Et₃ or Et₂Ph but not for R₃= EtPh₂, Ph₃, (C₆H₁₁)₃ or (OMe)₃; CH₂Br₂ gave a mixture of bromo- and chloro-methyl complexes whilst CH₂ICl gave two isomers of [RhCl(I)(CH₂Cl)(CO)(PEt₃)₂] with I or Cl trans to CH₂Cl. In polar solvents or on treatment with water or MeOH, [RhCl(I)(CH₂I)(CO)(PEt₃)₂] underwent a halide-scrambling reaction to give several compounds containing CH₂I or CH₂Cl ligands which have been identified spectroscopically. The same scrambling occurs under high pressures of CO, although IR, NMR and model studies suggest the Rh–C(O)CH₂X species are also formed by insertion of CO into the Rh–CH₂X bond. Most of the acyl products are unstable to loss of ketene, but one may be stable [ν(CO) 1665 cm^–1]. The complex [RhCl(I)(CH₂I)(CO)(PEt₃)₂] has been characterised crystallographically: triclinic, space group P, a= 12.343(3), b= 14.327(2), c= 15.426(2)Å, α= 113.78(1), β= 67.25(1), γ= 90.20(1)°, Z= 4, R= 0.0453. Each unit cell contains two pairs of molecules differing in the relative orientations of one PEt₃ ligand. In both cases, Rh–C [2.080(6), 2.063(9)Å], C–I [2.151(9), 2.121(10)Å] and Rh–C–I [119.9(5), 120.3(4)°] are similar to those reported for related compounds. Both molecules have mutually trans phosphines and CH₂I trans to I.