Synthesis, crystal structures and spectroscopic properties of cis- and trans-[RhCl2L2]+[L = 1,3-bis(dimethylphosphino)propane or 1,2-bis(dimethylphosphino)ethane (dmpe)]: reinvestigation of the dmpe complexes

Abstract

Two pairs of geometrical isomers, cis- and trans-[RhCl₂L₂]⁺[L = 1,3-bis(dimethylphosphino)propane or 1,2-bis(dimethylphosphino)ethane], have been synthesized and their structures and spectroscopic properties investigated. The previous characterization of the dmpe complexes made by other workers was found to be erroneous. A convenient method of preparation and separation of the complexes into isomers has been found. The geometrical structures of the isomers have been confirmed by ¹H, ¹³C and ³¹P NMR spectroscopy and by single-crystal X-ray structure determinations. The Rh–Cl bond lengths in the cis complexes are considerably longer than those in the corresponding trans isomers, and the Rh–P bonds trans to Cl in the cis isomers are relatively shorter than those of mutually trans phosphine ligands in both the cis- and trans-isomers, exhibiting a strong trans influence of the dimethylphosphino group. The ¹H, ¹³C and ³¹P NMR spectra of the complexes were found to be consistent with the structures found by single-crystal X-ray analyses, and the chemical shifts (δ_p) and coupling constants [¹J(RhP) and ²J(PP)] correspond well with the structural parameters (Rh–P bond length and P–Rh–P angle). The electronic spectra and isomerization reactions of the complexes were also determined.