Synthesis and metallation of ferrocenylimines derived from ligating diaminoheteroarenes

Abstract

A regioisomeric mixture of 1,1′-didodecylferrocenedicarbaldehydes 3 was prepared from the reaction of a regioisomeric mixture of 1,1′-didodecyldilithioferrocenes and dimethylformamide. Three ligating heteroaromatics were synthesized each containing two amino substituents: 5,5′-diamino-2,2′-bipyridine and 5,5″-diamino-2,2′∶6′,2″-terpyridine were prepared from appropriate dinitro compounds by reduction with palladium on charcoal–hydrazine hydrate. The reaction of 2-cyano-5-nitropyridine and hydrazine hydrate gave an isolable amidine derivative and this was transformed with hydrazine in a separate reaction under more forcing conditions into 3,6-bis(5-amino-2-pyridyl)-1,2-dihydro-1,2,4,5-tetrazine. The latter was converted into the tetrazine by oxidation (2,3-dichloro-5,6-dicyano-1,4-benzoquinone) and then trifluoroacetylated [(CF₃CO)₂O] to give the bis(trifluoroacetylamino) derivative. Diels–Alder reaction of the latter with dodec-1-yne afforded 4-n-decyl-3,6-bis[5-(trifluoroacetylamino)-2-pyridyl]pyridazine which was deprotected (K₂CO₃) to give the corresponding diamine. Bis(ferrocenyl) Schiff bases were prepared from ferrocenecarbaldehyde and the appropriate diamine in either uncatalysed or acid-catalysed condensations. Tetracarbonylmolybdenum complexes were prepared by treating the appropriate diamines with molybdenum hexacarbonyl. Reaction of one of these complexes with ferrocenecarbaldehyde gave a heterobimetallic complex.