Intramolecular Hydroamination with Rhodium(I) and Iridium(I) Complexes Containing a Phosphine−N-Heterocyclic Carbene Ligand

Abstract

Cationic Rh(I) and Ir(I) complexes of the form [M(PC)(COD)]BPh4 (M = Rh (4), Ir (5); PC = 3-[2-(diphenylphosphino)ethyl]-1-methylimidazol-2-ylidene) were synthesized by the addition of 3-[2-(diphenylphosphino)ethyl]-1-methylimidazolium (3) to [M(μ-OEt)(COD)]2 (M = Rh, Ir; COD = 1,5-cyclooctadiene) in the presence of base. COD was successfully displaced from [Rh(PC)(COD)]BPh4 (4) by addition of carbon monoxide to a methanol/hexane suspension to form [Rh(PC)(CO)2]BPh4 (6). The analogous addition of CO to the iridium compound 5 resulted in the formation of the five-coordinate Ir(I) complex [Ir(PC)(COD)(CO)]BPh4 (7). The single-crystal X-ray structures of 4, 5, and 7 were determined. The metal centers of 4 and 5 are square planar, and the metal center of 7 is a distorted trigonal bipyramid. Complexes 4−7 are effective as catalysts for the intramolecular hydroamination of 4-pentyn-1-amine to 2-methyl-1-pyrroline. Complete conversion (>97%) of 4-pentyn-1-amine was observed using complexes 4−7 as catalysts, in both chloroform-d and tetrahydrofuran-d8. Reactions in chloroform-d in general exhibited higher turnover rates than reactions in tetrahydrofuran-d8.