Rhodium(I) and Iridium(I) Complexes with Bidentate Phosphine−Pyrazolyl Ligands:  Highly Efficient Catalysts for the Hydroamination Reaction

A range of rhodium(I) and iridium(I) complexes containing bidentate phosphine−pyrazolyl ligands of general formulas [M(R 2 PyP)(COD)]BPh 4 (R = Me, i Pr, Ph, M = Ir, 3b − 3d and M = Rh, 4b − 4d ), [Ir(R 2 PyP)(CO) 2 ]BPh 4 (R = Me, i Pr, 5b, 5c ), and [M(R 2 PyP)(CO)Cl] (R = Me, i Pr, Ph, M = Ir, 6b − 6d and M = Rh, 7b − 7d ) were successfully synthesized. A number of these complexes and their analogues with unsubstituted ligands are extremely active as catalysts for the intramolecular hydroamination of alkynes. The air-stable cationic iridium complexes containing 1,5-cyclooctadiene, COD, as co-ligands, [Ir(R 2 PyP)(COD)]BPh 4 (R = H, Me, i Pr, and Ph, 3a − 3d ), are efficient as catalysts for the cyclization of 4-pentyn-1-amine ( 8 ) to 2-methyl-1-pyrroline ( 9 ) with the turnover rate at 50% conversion ( N t ) of up to 3100 h -1, at 60 °C. The cationic iridium complexes containing carbonyl co-ligands, [Ir(R 2 PyP)(CO) 2 ]BPh 4 (R = H, Me, i Pr, 5a − 5c ), are moderately effective in catalyzing this reaction, and the neutral complexes [M(R 2 PyP)(CO)Cl] (M = Ir, 6a Ir, 7a ) are ineffective. Generally, an increase in steric bulk of the substituent R near the nitrogen donor leads to an improvement in catalytic performance of the resulting metal complexes.