The Reactivity of Alkyne-Substituted Clusters

The reactivity of clusters containing coordinated alkyne or alkyne-derived ligands has not been widely investigated. This review has indicated that quite a significant number of complexes of this type have now been synthesized, but it is important to remember that quite a large proportion of these clusters are obtained in relatively low yield, and it is perhaps this aspect that has hindered further research into their reaction chemistry. However, over the last several years, an increasing number of publications reporting the reactions of alkyne-substituted 

Thermal activation of alkyne-substituted clusters frequently results in the loss of one or more carbon monoxide ligands (418, 445, 446). Concomitant with this loss is an alteration in the bonding mode of the organic ligand in order to retain the electron balance within the molecule (107). Such a reaction is shown in Fig. 41, where an osmacyclopentadiene ring is transformed into a trisubstituted-f/5-cyclopentadienyl system. Metal-metal bond formation may take place in some examples (446, 447). 

There have also been reports of cluster growth, from trinuclear to tetra- (429) or pentanuclear (448) complexes. However, in these two reactions it is important to note that the clusters involved contain functionalized alkynes. These phosphidoacetylenes show a considerable versatility in their modes of bonding. This is particularly true in the example illustrated in Fig. 42 where different reaction temperatures 

Alkyne scission also occurs when a rhodium or iridium trimetallic cluster is heated under vacuum (449). 

Photochemical activation of an allyl complex results in the loss of carbon monoxide, which leads to the formation of a coordinatively unsaturated species (450). 

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