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

Cationic Rh(I) and Ir(I) complexes of the form [M(PC)(COD)]BPh 4 (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)]BPh 4 ( 4 ) by addition of carbon monoxide to a methanol/hexane suspension to form [Rh(PC)(CO) 2 ]BPh 4 ( 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)]BPh 4 ( 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- d 8 . Reactions in chloroform- d in general exhibited higher turnover rates than reactions in tetrahydrofuran- d 8 .