Facile syntheses of thiophene-substituted 1,4-diazabutadiene (α-diimine) ligands and their conversion to phosphenium triiodide salts

Abstract

Four novel N-aryl-2-thienyl substituted 1,4-diazabutadiene (α-diimine) ligands 5–8 have been prepared by cyanide ion-catalyzed intermolecular coupling of the appropriate aromatic aldimines. A ligand featuring a phenyl spacer moiety between a thiophene carbon atom and each imino nitrogen atom (12) has been prepared by a similar synthetic route. Ligands 5–8 and 12 were characterized on the basis of ¹H and ¹³C NMR, IR and MS-CI spectroscopy. Upon treatment with PI₃ in CH₂Cl₂ solution, ligands 5–8 undergo redox reactions to furnish the triiodide salts of the corresponding phosphenium cations 13–16 which were characterized by ¹H, ¹³C and ³¹P NMR, and MS-CI spectroscopy. The phosphenium triiodide salt 15, and ligands 5–7 and 12 were also structurally authenticated.