Ferrocenylethynylnaphthalenes and acenaphthylenes; communication between ferrocenyl and cluster redox centres

Abstract

The synthesis and comparative investigation of the reactivity and communication between redox centres in peri-1,8- (3) and 1,5- (4) bis(ferrocenylethynyl)naphthalene and acenaphthylenes, and their Co₂(CO)_6–xL_x derivatives, are described. The cofacial alkyne configuration in 3 encourages acenaphthylene formation; 1-ferrocenylacenaphthylene and triferrocenylbenzo[a]acenaphthylene directly from 3 and (E,E)-diferrocenyliodobut[a]acenaphthylene-1,2-diene 9, diferrocenylcyclopent[a]acenaphthylen-8-one 10, furan[a]acenaphthylene and γ-lactone[a]acenaphthylene from reactions with ⁱPr₂NH₂⁺I^–/Co₂(CO)_6–xL_x. 9 has an (E,E) configuration (X-ray structure) and steric crowding causes significant distortion of the diene fragment. Co₂(CO)₆ and Co₂(CO)₄(dppm) complexes with 4 but not 3 have been characterised. 1,5-{PhC₂Co₂(CO)₄[P(OMe)₃]₂}₂C₁₀H₆ has the phosphite ligands in pseudo-axial sites and there is an unusually short Co–Co bond (2.437 Å). Electrochemical and spectroscopic data show that there is effective communication between two ferrocenyl or two cluster redox centres, reinforced by the transannular interaction, but the ferrocenyl and cluster electrophores act independently of one another. The primary reduction centre for the acenaphthylenes is the peri ring system. The mixed valence 10⁺ has been characterised.