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

The N-alkyphosphine-substituted benzimidazoles 5 (R = methylenedicyclohexylphosphine), 7 (R = ethylene-di(tBu)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)PR3] [6]–[9]. Depending on the steric demand of the PR3, 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.