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

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posted on 03.04.2020, 13:58 authored by Leslie D. Field, Barbara A. Messerle, Khuong Q. Vuong, Peter Turner, Tim Failes
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, 3b3d and M = Rh, 4b4d), [Ir(R2PyP)(CO)2]BPh4 (R = Me, iPr, 5b,5c), and [M(R2PyP)(CO)Cl] (R = Me, iPr, Ph, M = Ir, 6b6d and M = Rh, 7b7d) 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(R2PyP)(COD)]BPh4 (R = H, Me, iPr, and Ph, 3a3d), 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 (Nt) 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, 5a5c), 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.