Improving intramolecular hydroamination Rh(I) and Ir(I) catalysts through targeted ligand modification

Abstract

A series of complexes containing the phosphino-pyrazolyl ligand 1-(2-(diphenylphosphino)phenyl)pyrazole (PyPhP) and 1-(2-(diphenylphosphino) ethyl)pyrazole (PyP) were synthesized: [Ir(PyPhP)(COD)]BPh4, [Ir(PyPhP)(CO)2]BPh4, Rh(PyPhP)(CO)Cl and Ir(PyPhP)(CO)Cl. The complexes Rh(PyP)(CO)OSO2CF3 and Rh(PyPhP)(CO) OSO2CF3 were also synthesized, using the parent complexes Rh(PyP)(CO)Cl and Rh(PyPhP)(CO)Cl. The solid-state structures of the new complexes were determined by X-ray diffraction analysis. The cationic Ir(i) complex [Ir(PyPhP)(COD)]BPh4 was found to be a highly efficient catalyst for the intramolecular hydroamination of 4-pentyn-1-amine, achieving a turnover rate of 1500 h-1, with >98% conversion in 6 minutes. The efficiency of the catalyzed hydroamination of 4-pentyn-1-amine using the neutral Ir(i) and Rh(i) complexes as catalysts was significantly improved by generating active catalysts in situ through abstraction of a chloride ligand by reaction with AgOSO2CF3, TMSOSO2CF3 or NaBPh4. The catalytic efficiency of the catalysts generated from Ir(PyP)(CO)Cl and a sodium salt were found to be inversely proportional to the coordinating strength of the counter-ion of the sodium salt. Rh(PyP)(CO)OSO 2CF3 is a more efficient catalyst for the cyclization of 4-pentyn-1-amine than the complex generated in situ from AgOSO 2CF3 and chloride complex Rh(PyP)(CO)Cl indicating that the higher lability of the triflate co-ligand of Rh(PyP)(CO)OSO 2CF3, compared to the chloride co-ligand of Rh(PyP)(CO)Cl, enhances the catalytic activity of the Rh(i) complexes.