Carbonyl clusters with higher nuclearity

Although anionic species with nickel in the oxidation state -I have been postulated, such as [Ni2(CO)6]2, these have not been confirmed. Nickel does, however, form a number of anionic carbonyl clusters with higher nuclearity, e.g., [Ni5(CO)l2]2-, in which the metal carries a partial negative charge. 

Addition of either nucleophilic or electrophilic metallic species can result in the capping of triangular- or square-metal faces in carbonyl clusters. These redox reactions provide high yield syntheses of higher nuclearity clusters and somewhat resemble surface reconstruction on metals. With a few examples,... 

Metal carbonyl anions react with main group halides and oxides to yield a number of main-group transition-metal carbonyl complexes in good yields. These complexes serve as starting materials for a number of higher nuclearity cluster complexes. 

Although polynuclear alkyne completes are often prepared by reaction of the alkyne with a suitable metal cluster fragment, heteropolynuclear complexes 69 (Scheme 4-38) have been obtained also by isolobal metal fragment substitution, as noted previously [26]. Higher-nuclearity alkyne complexes also can be produced by the addition of various metal carbonyl fragments to a lower-nuclearity alkyne complex [119], A novel entry to heterobi- (and tri-)metallic neutral p-propargyl complexes (e.g., Fe/Mo) via protonation of trinuclear p-Ti, T1 -o-propargyl derivatives 70 was recently described by Wojcicki and coworkers [120,121]. 

The variety and size of homo- and heterometallic transition metal carbonyl clusters have increased enormously over the last 30 years. Of all the transition metals, is unique in being 100% abundant with 7=1/2 and it is timely to review the NMR developments and studies on hexa- and higher-nuclearity Rh-containing clusters. These have enabled ... 

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