Alkyl-dependent photochemistry of [Ru(i) (R) (co)2(α-diimine)] : homolysis of the Ru-R bond for R = bz and isomerisation for R = me

The complexes trans,cisand cis,cis-[Ru(I)(Me) (CO)2(α-diimine)] and trans,cis-[Ru(I)(Bz) (CO)2(α-diimine)] (α-diimine=4,4′dimethyl-2 2′-bipyridine (bpy′), N,N′-di-isopropyl-1,4-diazabutadiene (iPr-DAB)) are the subject of a photochemical study. Replacement of R = Me by R = Bz results in a dramatic change in the photochemical behaviour of the trans,cis-complexes. A photoisomerisation is observed for the complex trans,cis-[Ru(I)(Me)(CO)2(bpy′)], whereas irradiation of trans,cis-[Ru(I)(Bz)(CO)2)(α-diimine)] results in the formation of [Ru(I)2(CO)2)(α-diimine)]. According to the nanosecond transient absorption spectra, the primary photoprocess of both trans,cis and cis,cis-[Ru(I)(Me)(CO)2(bpy′)] is loss of CO, whereas the corresponding complexes trans,cis-[Ru(I)(Bz)(CO)2(αdiimine)] (α-diimine = bpy′ and iPr-DAB) undergo homolysis of the Ru-Bz bond. This dependence of the primary photoprocess on R is ascribed to a crossing to different reactive excited states after occupation of a nonreactive 1XLCT state. For R = Me mis state is proposed to have LF character, for R = Bz it is most probably the 3σπ* state.