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

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.