Spectroscopy, electrochemistry and catalytic properties of rutheniumII complexes containing the tetradentate Schiff base ligand N,N′-bis(7-methyl-2-pyridylmethylene)-1,3-diiminopropane

The complexes trans-[RuCl2(bpydip)] and trans-[Ru(OH2)(2)(bpydip)](PF6)(2), where bpydip is the tetradentate Schiff base ligand, N,N'-bis(7-methyl-2-pyridylmethylene)-1,3-diiminopropane, have been synthesized and characterized by elemental analysis, cyclic voltammetry, UV-Vis, FTIR and H-1 NMR spectroscopy. The electronic spectrum of the trans -[RuCl2(bpydip)] complex has been successfully simulated on the basis of the ZINDO/S method, supporting the assignment of the absorption bands at 644, 607, 458, 418 and 374 nm to Ru-11(d(pi)) --> bpydip(p(pi)*) charge-transfer transitions, and at 282 nm, to a bpydip (pi --> pi*) intraligand transition. The electrochemistry of this complex is characterized by a reversible pair of waves at +0.30 and -1.70 V, ascribed to the Ru-111/11 and bpydip(0/-1) redox couples, respectively. In contact with water, the trans-[RuCl2(bpydip)] complex spontaneously and quantitatively converts into the aqua complex, leading to pronounced changes in the electronic and electrochemical behavior. A remarkable activity in the epoxidation of cyclohexene in the presence of iodosobenzene (PhIO) has been observed for the aqua complex. (C) 2002 Elsevier Science B.V. All rights reserved.