Synthesis of Rhodium(I) Complexes Bearing Bidentate NH,NR-NHC/Phosphine Ligands

The N -alkyphosphine-substituted benzimidazoles 5 (R = methylenedicyclohexylphosphine), 7 (R = ethylene-di( t Bu)phosphine), and 8 (R = ethylenedicyclohexylphosphine) have been prepared. The benzimidazoles react with [RhCl(COE) 2 ] 2 in the presence of tertiary phosphines under formal tautomerization of the benzimidazole and chelating coordination of the resulting bidentate NH,NR-NHC/phosphine ligand (P ∧ C) to give complexes [RhCl(P ∧ C)PR 3 ] [ 6 ]–[ 9 ]. Depending on the steric demand of the PR 3, the phosphines of the P ∧ C ligands, and on the spacer linking the benzimidazole ring nitrogen atom to the alkylphosphine, complexes with cis -P,P and trans -P,P geometry have been obtained and crystallographically characterized.