Application of UV-Vis spectroscopy to high throughput screening of hydroamination catalysts

Potential catalysts for the hydroamination of 2-(2-phenylethynyl)aniline 2 which have been identified through high throughput screening methods were investigated. Two complexes were shown to be highly active hydroamination catalysts in acetone: the in situ combinations of [Rh(CO)2Cl]2–mesBIAN–NaBF4 (mesBIAN = bis(2,4,6-trimethylphenylimino)acenapthene) and [Ir(COD)Cl]2–NaBF4 (COD = 1,5-cyclooctadiene). The isolated complexes [M(N–N)XCl]BF4 (M = Rh, Ir; N–N = bidentate nitrogen donor ligand; X = CO or Cp*) were found to be inactive as catalysts for the conversion of 2 to 3. However, chloride abstraction from these complexes through the addition of AgBF4 was found to generate extremely active catalysts. Particularly active was the complex [Rh(CO)ClmesBIAN]–AgBF4 (5 mol%) which achieved complete conversion of 2 to 3 in 12 minutes at 50 °C. Also identified was the formation of the unusual product, N-(2-methylvinyl)-2-phenylindole 5, catalysed by [IrCp*Cl2]2–NaBF4 from starting material 2via the incorporation of one molecule of acetone.