Aromatization of a Dihydro-3-ruthenaindolizine Complex

The complex RuHCl(η2-H2)(PiPr3)2 (1) reacts with KTp (Tp = hydridotris(pyrazolyl)borate) to give the hydride−dihydrogen derivative RuHTp(η2-H2)(PiPr3) (2), which has been characterized by X-ray diffraction analysis (dH−H = 1.00(3) Å). Treatment of a toluene solution of 2 with 2-vinylpyridine leads to the 1,2-dihydro-3-ruthenaindolizine derivative Ru(CH2CH2−C5H4N)Tp(PiPr3) (3). Complex 3 aromatizes in toluene at 80 °C to afford the 3-ruthenaindolizine complex Ru(CHCH−C5H4N)Tp(PiPr3) (4) by loss of a hydrogen molecule in the absence of any hydrogen acceptor. The aromatic character of 4 is supported by X-ray diffraction analysis, NMR spectroscopy, and DFT calculations.