Keto–enol tautomers of mixed-ligand ruthenium(II) complexes containing α-diamine and azoimine bearing alkyne group ligands

Abstract

Refluxing azoimine ligand containing terminal acetylene group (L=C6H5NNC(COCH3)NC6H4CCH) with RuCl3·3H2O in ethanol resulted hydrating the terminal acetylene group to the corresponding enol form C6H5NNC(COCH3)NC6H4C(OH)CH2 (L1), ketone form C6H5NNC(COCH3)NC6H4COCH3 (L2) and vinyl chloride: C6H5NNC(COCH3)NC6H4C(Cl)CH2 (L3) via Markovnikov selectivity. Ruthenium complexes of the later ligands and α-diamines of the formula trans-[Ru(N-N)(Y)Cl2] (Y=L1, N-N=4,4′-dimethoxy-2,2′-bipyridine; dmeb (1), 1,10-phenanthroline; phen (2), 3,4,7,8-tetramethyl-1,10-phenanthroline; tmphen (3), Y=L2, N-N=dmeb (4), phen (5), tmphen (6)) were synthesized from L, N-N ligands and RuCl3·3H2O. Complexes 1–6 were characterized by spectroscopic (IR, UV–Vis, 1H, 13C NMR, DEPT-135) and electrochemistry techniques. The crystal structures of trans-[Ru(tmphen)(L1)Cl2] (3) and trans-[Ru(bpy)(L3)Cl2] (7) were determined and found to have distorted octahedral geometry. The catalytic activity of 3 towards the hydration of cinnamaldehyde is reported.