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((LL)-L-boolean AND)(C-2)]BAr24F (where M = Rh or Ir, (LL)-L-boolean AND = bis(pyrazol-1-yl) methane (bpm), bis(N-methylimidazol-2-yl)methane (bim) or 1-(2-(diphenylphosphino)ethyl)-3,5-diphenylpyrazole (Ph2PyP), C-2 = 1,5-cyclooctadiene (COD) or (CO)(2) and BAr24F = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) were synthesised in good yields. The solid-state structure of a number of complexes, including [Ir(Ph2PyP)(COD)]BAr24F, [Ir(bpm)(COD)]BAr24F and [Ir(bim)(COD)]BAr24F 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 BAr24-F 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)]BAr24F as a catalyst. The use of a microwave reactor for enhancing the catalysed reactions was also investigated.