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

Article abstract of DOI:10.1016/S0022-328X(98)00992-9

The complexes RuCl₂(L¹)(arene) (3-4) (L1=HC=NCH₂CH₂NR, R=Et, arene=p-MeC₆H₄CHMe₂ or C₆Me₆) and RuCl₂(L²)(arene) (5-6) (L²=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 (Z)-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.