Ruthenium(II) complexes of new chelating indolizino[2,3-b]pyrazine- and indolizino[2,3-b]quinoxaline-derived ligands: Syntheses, electrochemistry and absorption spectroscopy

Abstract

The highly conjugated chelating ligands 5-(2-pyridyl)indolizino[2,3-b] pyrazine 1, 5-(2-pyridyl)indolizino[2,3-b]quinoxaline 2, and 8,9-dimethyl-5-(2-pyridyl)indolizino[2,3-b]quinoxaline 3 were prepared in one step, with good yields, from di-2-pyridylmethane and 2,3-dichloropyrazine, 2,3-dichloroquinoxaline, and 8,9-dimethyl-2,3-dichloroquinoxaline, respectively. Compounds 13 display long-wavelength absorption maxima in the green (1) and yellow (2 and 3) to give intensely coloured red and purple solutions, respectively. Bis(2,2′-bipyridyl)ruthenium(ii) and bis(4,4′- dimethyl-2,2′-bipyridyl)ruthenium(ii) complexes were prepared in moderate to good yields, characterized by NMR spectroscopy and mass spectrometry, and studied by cyclic voltammetry and absorption spectroscopy. Copper(ii) and silver(i) nitrate complexes of the ligands were prepared and complexes [Cu(NO3)2(1)], [Cu(NO3)2(2)] 2, and [Ag(NO3)(3)2] were characterized by X-ray crystallography. These structures revealed the planar nature of the ligands and confirmed the proposed chelating mode.