Photochemical and photocatalytic behaviour of ‘flyover-bridge’ complexes

Abstract

The photochemical behaviour of a number of flyover-bridge complexes [Fe₂(CO)₆{(RC₂R)₂CO}] is discussed with regard to their electronic structure. In the case of [Fe₂(CO)₆{(PhC₂Ph)₂CO}] the overall photochemical event is the formation of an unsaturated species upon CO loss, which evolves, in the absence of any Lewis bases, to the fragments [Fe(CO)₃{(PhC₂Ph)₂CO}], C₄Ph₄CO, and [Fe(CO)₅]. Photosubstitution of CO by phosphine occurs very rapidly and proceeds stereospecifically in a pseudo-axial position as assessed by ¹³C n.m.r. studies. The title complexes exhibit photocatalytic activity toward olefin isomerization and, interestingly, this reaction can be activated simply by sunlight exposure. The dienone chain clasps the metal–metal bond, preventing complex decomposition and acts as a good sensitizer for the sunlight.