SYNTHESIS, ELECTRONIC AND H-1-NMR PROPERTIES OF A NEW-TYPE OF POLYPYRIDYL LIGAND - LONG-RANGE RING CURRENT EFFECTS

The preparation of a series of heterocycles obtained by the condensati on of 4,5-diazafluoren-9-one with various amines is described with par ticular emphasis on bridged systems formed by the condensation of 4,5- diazafluoren-9-one with diamine compounds such as hydrazine. Due to sp (2) hybridization of the nitrogen atom in the bridge, the protons in t he two pyridine units of each bipyridine group are non-equivalent. The projection of a hydrogen atom from one of the pyridine rings into the ring current of an adjacent phenyl ring shifts the proton resonance u pfield. Proton NMR resonances have been uniquely assigned for all the compounds and electronic absorptions have been attributed to pi --> pi transitions located in the ultraviolet region of the spectrum. Reduc tion of the heterocycles occurs at the imine nitrogen bridge and is ir reversible, except for the ligand resulting from the condensation of 4 ,5- diazafluoren-9-one with hydrazine. (C) 1997 Elsevier Science Ltd.