Intramolecularly alkylated salen complexes: new models for coenzyme B12 with a cobalt-to-ligand carbon bridge

Abstract

The synthesis of H₂salen {2,2′-[ethane-1,2-diylbis(nitrilomethylidyne)]diphenol} derived models 1 for coenzyme B₁₂ with a carbon bridge between the ligand and cobalt has been accomplished by condensation of salicylaldehyde and ω-substituted 1,2-diamines 8 followed by complexation with Co^II, reduction to Co^I complexes, and intramolecular alkylation. The structures of intramolecularly alkylated Co(salen) complexes with a bridge of three, 1b, and of four methylene groups, 1c, have been investigated by NMR spectroscopy and determined by X-ray crystallography.