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

Four novel N-aryl-2-thienyl substituted 1,4-diazabutadiene (alpha-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 H-1 and C-13 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 H-1, C-13 and P-31 NMR, and MS-CI spectroscopy. The phosphenium triiodide salt 15, and ligands 5-7 and 12 were also structurally authenticated.