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)A, 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)A], C–I [2.151(9), 2.121(10)A] 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.