Reaction of ferrocenecarboxylic acid with N, N′-disubstituted carbodiimides: synthesis, spectroscopic and X-ray crystallographic analysis of N, N′-disubstituted N-ferrocenoylureas and identification of a one-pot coupling reagent for the formation of ferrocenecarboxamides in a non-aqueous solvent

Abstract

N, N ′-dicyclohexyl- N-ferrocenoylurea 2, N, N ′-diisopropyl- N-ferrocenoylurea 3, N, N ′-di- p-tolyl- N-ferrocenoylurea 4 and N, N ′-di- tert-butyl- N-ferrocenoylurea 5 were obtained by reaction of ferrocenecarboxylic acid 1 with N, N ′-dicyclohexylcarbodiimide (DCC), N, N ′-diisopropylcarbodiimide (DIC), N, N ′-di- p-tolylcarbodiimide 10 and N, N ′-di- tert-butylcarbodiimide 11, respectively. Both N- tert-butyl- N ′-ethyl- N-ferrocenoylurea 6 and N ′- tert-butyl- N-ethyl- N-ferrocenoylurea 7 were obtained by reaction of 1 with N- tert-butyl- N ′-ethylcarbodiimide 12. In all cases a small amount of ferrocenecarboxylic anhydride 8 was formed as a by-product. All compounds were characterized by 1H NMR, 13C NMR, IR and MS. Single crystal X-ray structural analyses were made of 2, 3 and 4. From the consistent results, the reaction products of 1 with carbodiimides appear different from those proposed by some earlier workers. With N-(3-dimethylaminopropyl)- N ′-ethylcarbodiimidehydrochloride 9 ferrocenoylurea was not isolated, but the main product was rather 8. The suitability of 8 as acylation reagent was applied by using 9 to obtain N-(3-triethoxysilyl)-propylferrocenecarboxamide in a one-pot reaction from 1 and 3-(triethoxysilyl)-propylamine.