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

Dalton Transactions Pub Date: 2008-11-18 DOI: 10.1039/B814168A

Abstract

A series of cationic rhodium(I) and iridium(I) complexes of the type [M(L∩L)(C2)]BArF24 (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 BArF24 = 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)]BArF24, [Ir(bpm)(COD)]BArF24 and [Ir(bim)(COD)]BArF24 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 BArF24? 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]BArF24 as a catalyst. The use of a microwave reactor for enhancing the catalysed reactions was also investigated.

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