Iridium(III) Cp* complexes for the efficient hydroamination of internal alkynes

A series of iridium(III) and rhodium(III) 1,2,3,4,5- pentamethylcyclopentadienyl (Cp*) complexes of the type [M(Cp*)(LL)Cl]BPh ₄ were synthesized, where LL is a chelating diimine or mixed pyrazolyl-phosphine or pyrazolyl-N-heterocyclic carbene donor ligand. The majority of these complexes were characterized by X-ray crystallography, allowing for a detailed comparison of their structural properties. These complexes were shown to yield active hydroamination catalysts upon in situ abstraction of the chloride coligand using AgBF ₄. The activity of these catalysts for the intramolecular hydroamination of alkyne-amines to yield indolyl and pyrolyl heterocycles was investigated. It was found that chelating ligand groups containing a strongly coordinating N-heterocyclic carbene donor led to the most effective catalysis and that an increase in the steric bulk of the ligand was detrimental to the catalyst efficiency.