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(R₂PyP)(COD)] BPh₄ (R = Me, iPr, Ph, M = Ir, 3b-3d and M = Rh, 4b-4d), [Ir(R ₂PyP)(CO)₂]BPh₄ (R = Me, iPr, 5b,5c), and [M(R₂PyP)(CO)Cl] (R = Me, iPr, 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 ₂PyP)(COD)]BPh₄ (R = H, Me, iPr, 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(R₂PyP)(CO) ₂]-BPh₄ (R = H, Me, iPr, 5a-5c), are moderately effective in catalyzing this reaction, and the neutral complexes [M(R₂PyP)(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.