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 = C 6 H 5 N NC(COCH 3 ) NC 6 H 4 C CH) with RuCl 3 ·3H 2 O in ethanol resulted hydrating the terminal acetylene group to the corresponding enol form C 6 H 5 N N C(COCH 3 ) NC 6 H 4 C(OH) CH 2 (L1), ketone form C 6 H 5 N NC(COCH 3 ) NC 6 H 4 COCH 3 (L2) and vinyl chloride: C 6 H 5 N N C(COCH 3 ) N C 6 H 4 C(Cl) CH 2 (L3) via Markovnikov selectivity. Ruthenium complexes of the later ligands and α-diamines of the formula trans -[Ru(N-N)(Y)Cl 2 ] (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 RuCl 3 ·3H 2 O. Complexes 1 – 6 were characterized by spectroscopic (IR, UV–Vis, 1 H, 13 C NMR, DEPT-135) and electrochemistry techniques. The crystal structures of trans -[Ru(tmphen)(L1)Cl 2 ] ( 3 ) and trans -[Ru(bpy)(L3)Cl 2 ] ( 7 ) were determined and found to have distorted octahedral geometry. The catalytic activity of 3 towards the hydration of cinnamaldehyde is reported.