2-imidazoline and 1,4,5,6-tetrahydropyrimidine-ruthenium(II) complexes and catalytic synthesis of furan

The complexes RuCl2(L-1)(arene) (3-4) (L1 = HC=NCH2CH2NR, R = Et, arene = p-MeC6H4CHMe2 or C6Me6) and RuCl2(L-2)(arene) (5-6) (L-2 = HC=NCH2CH2CH2NR, R = Me; Ph, CH2Ph, p-MeC6H4) have been synthesized by reaction of [RuCl2(arene)](2), with 1-alkyl-2-imidazoline (1) or 1-alkyl-1,4,5,6-tetrahydropyrimidine (2). In each of these complexes (3-6) the ligand is bound via the imine (N=C) nitrogen atom. The new complexes are capable of catalyzing the activation of (2)-3-methylpent-2-en-4-yn-1-ol into 2,3-dimethylfuran in very good yield, via intramolecular cyclization, and the 1,4,5,6-tetrahydropyrimidine complexes 5 and 6 appeared to be the best catalyst precursors. Cyclic voltammetry shows that the nature of the arene ligand, rather than that of the nitrogen containing ligand, controls the electron-richness of the complexes. (C) 1999 Elsevier Science Ss.A. All rights reserved.