Weakly coordinating counter-ions for highly efficient catalysis of intramolecular hydroamination

A series of cationic rhodium(i) and iridium(i) complexes of the type [M(L^∩L)(C₂)]BAr^F₂₄ (where M = Rh or Ir, L^∩L = bis(pyrazol-1-yl)methane (bpm), bis(N-methylimidazol-2-yl)methane (bim) or 1-(2-(diphenylphosphino)ethyl)-3,5- diphenylpyrazole (Ph₂PyP), C₂ = 1,5-cyclooctadiene (COD) or (CO)₂ and BAr^F₂₄ = tetrakis[3,5- bis(trifluoromethyl)phenyl]borate) were synthesised in good yields. The solid-state structure of a number of complexes, including [Ir(Ph ₂PyP)(COD)]BAr^F₂₄, [Ir(bpm)(COD)]BAr ^F₂₄ and [Ir(bim)(COD)]BAr^F₂₄ was determined using X-ray crystallography. The efficiency of the complexes as catalysts for the intramolecular hydroamination of 4-phenyl-3-butyn-1-amine, 4-pentyn-1-amine and 2-(2-phenylethynyl)aniline was established. The incorporation of the BAr^F₂₄^- counter-ion in the Rh(i) and Ir(i) complexes was found to significantly improve the catalytic activity of the complexes, compared to the analogous Rh(i) and Ir(i) complexes containing BPh₄^- as the counter-ion. Excellent conversions were achieved for the cyclisation of 2-(2-phenylethynyl)aniline to 2-phenylindole using [Rh(bpm)(CO)₂]BAr^F₂₄ as a catalyst. The use of a microwave reactor for enhancing the catalysed reactions was also investigated.