Donor/acceptor organotriiron(II) hydrazone chromophores: structural, spectroscopic and electrochemical properties

Abstract

Two new trinuclear organoiron(II) complexes, in which a trans-1,2-ferrocenyl-ferrocenylene ethene unit (electron-donors) is attached to an electron-deficient cationic mixed sandwich via a conjugated hydrazone bridge, giving complexes of the type ( E ) - [ CpFe ( η 5 - C 5 H 4 ) – CH CH – ( η 5 - C 5 H 4 ) Fe ( η 5 - C 5 H 4 ) – CH NNH – ( η 6 - p - RC 6 H 4 ) FeCp ] + PF 6 - ( Cp = η 5 - C 5 H 5 ; R = Me , 4 + PF 6 - ; MeO , 5 + PF 6 - ) , have been prepared. The complexes were fully characterised by 1H NMR, IR, UV–Vis spectroscopy. Their electrochemical properties have been studied by means of cyclic voltammetry, showing an effective electronic coupling between the two ferrocenyl fragments. The X-ray crystal structure of compound 4 + PF 6 - shows that it adopts the sterically more hindered syn-conformation about the 1,1′-ferrocenediyl core, with a parallel disposition of the conjugated dinucleating ligands, therefore, favouring an efficient electron delocalization through the entire π-framework. At the same time, the (C 5-ring)Fe moieties adopt an anti, anti-conformation with the iron atoms on the opposite faces of their respective bridging ligand.