Yx. Wang et Dp. Rillema, SYNTHESIS, ELECTRONIC AND H-1-NMR PROPERTIES OF A NEW-TYPE OF POLYPYRIDYL LIGAND - LONG-RANGE RING CURRENT EFFECTS, Tetrahedron, 53(37), 1997, pp. 12377-12390
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.