EPA Newsletter 18 November 2012 Photocatalytic reactions with organometallic and coordination compounds applied to organic synthesis Norbert Hoffmann CNRS, Université de Reims, ICMR (UMR 7312), Equipe de Photochimie, UFR Science, B.P. 1039, 51687 Reims, France Photochemical excitation of molecules changes their electronic configuration and thus their chemical reactivity. 1 Applying photochemical reaction conditions largely broaden the reaction spectrum of a chemical compound. New product families or libraries become available or they can be more easily prepared. For these reasons, photochemical reactions are of particular interest for being applied to organic synthesis. 2,3,4 In the same way, the reactivity of coordination or organometallic compounds is modified when they are electronically excited by light absorption. 5,6 Thus their catalytic properties are influenced and new catalytic reactions can be carried out or existing reactions are improved. When applications of photochemical reactions to organic synthesis are reviewed, reactions of with organometallic or coordination compounds are generally not discussed although in the past as well in the present they play an important role in this field. Thus the Cu(I) catalysed [2+2] photocycloaddition of alkenes was frequently applied to organic synthesis. 7 In particular, when applied in catalytic reactions, electron transfer and ligand exchange play a central role. Among the reactions of organometallic and coordination compounds, these two processes are efficiently affected by electronic excitation. Therefore a lot of applications to organic synthesis have now been reported. During recent years, a lot of reactions photocatalyzed by [Ru(bpy)3] 2+ have been carried out. 8 One typical example is shown in Figure 1. The halogenated indol derivative 1 was transformed efficiently and in a stereoselctive way with 2 into the adduct 3. 9 This product is a synthesis intermediate for the production of (+)-gliocladin C. After photochemical excitation, [Ru(bpy)3] 2+ is easily reduced by the tertiary amines such as Bu3N. The resulting Ru(I) species is a potent reductant capable of transferring an electron to 1. Thus, the catalyst is regenerated. After release of bromide, the radical intermediate 4 adds