Improving intramolecular hydroamination Rh(i) and Ir(i) catalysts through targeted ligand modificationCCDC reference numbers 291181 (6), 291475 (8), 291177 (9), 291474 (10), 729970 (11). For crystallographic data in CIF or other electronic format see DOI: 10.1039/b9nj00759h

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)OSO2CF3 is a more efficient catalyst for the cyclization of 4-pentyn-1-amine than the complex generated in situ from AgOSO2CF3 and chloride complex Rh(PyP)(CO)Cl indicating that the higher lability of the triflate co-ligand of Rh(PyP)(CO)OSO2CF3, compared to the chloride co-ligand of Rh(PyP)(CO)Cl, enhances the catalytic activity of the Rh(i) complexes.