Important role of CH–π interaction in linkage isomers of bis(2,2′-bipyridine)ruthenium(II) complexes with pyrimidine-2-thione and related ligands

Abstract

Nine ruthenium(II) complexes containing pyrimidine-2-thione and related ligands were prepared and characterized by elemental analysis, UV/VIS and ¹H and ¹³C NMR spectra: [Ru(L-N,S)(bipy)₂]ClO₄[H_nL = Hpymt (pyrimidine-2-thione), Hmpymt (4-methylpyrimidine-2-thione), Hdmpymt (4,6-dimethylpyrimidine-2-thione), Hapymt (4-aminopyrimidine-2-thione), Hdapymt (4,6-diaminopyrimidine-2-thione), H₂tuc(2,3-dihydro-2-thioxo-1H-pyrimidin-4-one, 2-thiouracil), 5-H₂mtuc (5-methyl-2-thiouracil), 6-H₂mtuc (6-methyl-2-thiouracil) or 6-H₂ptuc (6-propyl-2-thiouracil); bipy = 2,2′-bipyridine]. Two linkage isomers, adjacent and remote, exist for all the complexes with unsymmetrical ligands except for apymt. The crystal structure of [Ru(mpymt)(bipy)₂]ClO₄ was determined. The mpymt ligand co-ordinates through the S²/N³ donors and the complex adopts an adjacent linkage form where the 4-methyl group lies just over one of the bipy chelate rings irrespective of steric hindrance. The CH–π attractive interaction between the 4- or 6-alkyl group of the thione ligand and the π system of bipy affects the isomer ratios in a striking manner.