Intramolecular Hydroamination Catalyzed by Cationic Rhodium and Iridium Complexes with Bidentate Nitrogen-Donor Ligands

Cationic rhodium(I) and iridium(I) complexes of the general formula [M(N−N)(CO)2]+[X]-, incorporating the bidentate heterocyclic nitrogen donor ligands (N−N) bis(1-methylimidazol-2-yl)methane (bim) and bis(1-pyrazolyl)methane (bpm), are efficient catalysts for
hydroamination. The cyclization of an aliphatic aminoalkyne to the corresponding five-membered imine heterocycle was achieved in good yield with excellent regioselectivity using
both rhodium and iridium catalysts. The nature of the counterion to the cationic catalysts
has a significant effect on the rate of the hydroamination reaction and interionic contacts
between the metal complexes and their counterions in solution were clearly visible by NMR
spectroscopy using the nuclear Overhauser effect, indicating a strong anion/cation interaction
in solution. The nature of the coligands also had a significant effect on the efficiency of the
metal complexes as catalysts, and complexes containing phosphine coligands were less
effective catalysts compared to those complexes containing CO coligands. The X-ray crystal
structure of the new iridium(I) complex [Ir(bim)(CO)2]+[BPh4]- (2) is reported, as well as
the synthesis and characterization of the Rh complex [Rh(bpm)(CO)2]+[BPh4]- (3).