Clusters, photosubstitution

Explain the photochemistry of organometallic compounds from the point of view of photodissociation of simple organometallics, metal-to-metal bond cleavage and the photosubstitution of cluster species. 

On irradiation, the cluster molecule Os3(CO)12 is resistant to Os-Os bond cleavage and instead undergoes photosubstitution with a low quantum yield ... 

Generally, clusters of nuclearity >3 undergo photosubstitution with low quantum yield ... 

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. 

Cp 2 2(00) 5, which may be considered to contain a V=V bond, was prepared by photolysis of CpV(CO)4 in t.h.f. Photocleavage of this bond is not observed photosubstitution of carbon monoxide e.g. by phosphines) occurs instead. The photochemical formation of CpV(NO)2CO by irradiation of CpV(CO)4 and [Co(NO)2Br]2 has been described. Photolysis of CpNb(CO)4 in hexane solution gives the unusual cluster Cp3Nb3(CO)7, whereas in t.h.f. the useful reagent... 

DiBenedetto JA, Ryba DW, Eord PC (1989) Reaction dynamics of photosubstitution intermediates of the tri-ruthenium cluster Ru3(CO)i2 as studied by flash photolysis with infrared detection. Inorg Chem 28 3503-3507... 

---