New Rhodium(I) and Iridium(I) Complexes Containing Mixed Pyrazolyl–1,2,3-Triazolyl Ligands As Catalysts for Hydroamination

Two new bidentate pyrazolyl–triazolyl donor ligands,
4-((1H-pyrazol-1-yl)­methyl)-1-benzyl-1H-1,2,3-triazole,
PyT (1a), and 4-((1H-pyrazol-1-yl)­methyl)-1-phenyl-1H-1,2,3-triazole, PyS (1b), were synthesized
using the copper­(I)-catalyzed “click” reaction between
1-propargylpyrazole and benzyl azide or phenyl azide, respectively.
Cationic rhodium­(I) and iridium­(I) complexes containing the new N–N′
ligands of the general formulas [M­(N–N′)­(COD)]­X (M =
Rh or Ir, N–N′ = PyT or PyS, and X = BPh4– or BArF4– (tetrakis­[3,5-bis­(trifluoromethyl)­phenyl]­borate) 2a–c for Rh and 3a–c for Ir) and [M­(N–N′)­(CO)2]­X (M = Rh or
Ir, N–N′ = PyT or PyS, and X = BPh4– or BArF4– 4a–d for Rh and 5a–d for Ir) were successfully prepared and fully characterized. The
solid-state structures of eight of these complexes were determined
using single-crystal X-ray diffraction and show that the triazolyl
moiety coordinates to the metal center via the N3′ atom, forming
six-membered metallacycles. These metallacycles adopted a distorted
boat conformation in all of the structures determined. The M–N­(triazole)
bonds were found to be slightly shorter than the M–N­(pyrazole)
bonds, illustrating the stronger donating capacity of the triazolyl
donor in comparison to that of the pyrazolyl donor. All of the cationic
rhodium and iridium complexes reported here are catalytically active
for the intramolecular hydroamination of 4-pentyn-1-amine (6) to 2-methyl-1-pyrroline (7) at 60 °C, with TOFs
> 400 h–1 in many cases. The dicarbonyl complexes
[M­(N–N′)­(CO)2]­BArF4 (M = Rh or Ir) 4c,d and 5c,d were efficient as catalysts for the intramolecular
cyclization of nonterminal alkynamines (8a,b) to cyclic imines (9a,b) via the hydroamination
reaction and the cyclization of alkenamines (10a–c) to their corresponding cyclic amines (11a–c) also via the hydroamination reaction.