Synthesis, structure, and theoretical calculations of 1h-3,7- difurylcyclopenta[3,4-d]pyridazine

Treating [M{η⁵-1,2-C₅H₃(COC ₄H₃O)₂}(CO)₃] (3) (M = Mn, 3A, M = Re, 3B) with excess hydrazine hydrate in methanol afforded the desired 5,6-fused ring pyridazine complexes, [M(CO)3{η⁵-1,2-C₅H ₃(CC₄H₃ON)(CC₄H₃ON)}] (4) (M = Mn, 4A, M = Re, 4B), in high yield (76%). However, when X-ray crystallographic analysis of the pyridazyl complexes 4A and 4B was attempted, all recrystallization trials led to ligand loss to the 1,2-difurylpyridazine, 1,2-C₅H₃(CC₄H₃ONH)(CC ₄H₃ON) (5). Compound 5 was observed to have a coplanar stacking arrangement in the solid state along the crystallographic b axis. Theoretical calculations performed on compound 5 indicate a high degree of intramolecular electronic delocalization as well intermolecular orbital interaction.