Tetranuclear photoreactivity

In order to test the hypothesis that CO dissociation is the dominant photoreaction for tetranuclear clusters we have undertaken a study of the photochemistry of H2FeRu3(C0)i3, a cluster for which we know the efficiency of thermal CO dissociation and fragmentation as detailed above. For comparison, the clusters H2Ru4(CO)i3 and H2Fe0s3(C0)i3 have also been examined. With each of these clusters CO loss is clearly the dominant photoreaction (38). In the presence of PPI13, each cluster gives clean photosubstitution chemistry to yield primarily the mono-substituted derivatives, eq. 12. 

Although in a few tetranuclear complexes fragmentation is the primary result of photolysis, and others, e.g., (h -C5H5) Fe (CO), are inert with respect to both photo-induced M—M cleavage and carbonyl loss , substitution without fragmentation is the dominant photoreaction of tetranuclear metal carbonyls, especially of those containing second and third-row metals. Both Ir (CO),2 and H Os/CO),2 " tetranuclear... 

Although in a few tetranuclear complexes fragmentation is the primary result of photolysis , and others, e.g., (h -CjHp Fe fCO), are inert with respect to both photoinduced M—M cleavage and carbonyl loss , substitution without fragmentation is the dominant photoreaction of tetranuclear metal carbonyls, especially of those containing second and third-row metals. Both Ir (CO),2 and H Os (CO),2 " lead to tetranuclear olefin-substituted products when irradiated with alkenes, both with some rearrangement of the Ir moiety in the former case, and a hydride abstraction in the latter. Irradiation of H Ru/CO),j in the presence of P(OMe)j or PPhj leads to stepwise formation of the substituted clusters H Ru/CO), (n = 1-4) with low quantum efficiency . Carbonyl substitution also dominates the photochemistry of HjM CCO) (M = Ru, FeRuj, FeOsj) . 

---