Rhodium complexes nitrido clusters

The two isostructural clusters [Co6N(CO)i5] and [Rh6N(CO)i5] were synthesized by reaction of the octahedral clusters [M6(CO)i5] (M = Co, Rh) with nitrosonium tetrafluoborate. Better yields of the rhodium species were obtained by treatment, in a strongly reducing medium, of [RhyjCOjie] " with NO (diluted 1 1 with CO). The reactions are complex and no intermediate step could be identified. However, a nitrosyl derivative is very likely to be involved, and subsequent reduction, by the reaction medium or the starting reduced carbonyl itself, would yield the nitrido cluster. 

We have already alluded to the diversity of oxidation states, the dominance of oxo chemistry and the cluster carbonyls. Brief mention should be made too of the tendency of osmium (shared also by ruthenium and, to some extent, rhodium and iridium) to form polymeric species, often with oxo, nitrido or carboxylato bridges. Although it does have some activity in homogeneous catalysis (e.g. of m-hydroxylation, hydroxyamination or animation of alkenes, see p. 558, and occasionally for isomerization or hydrogenation of alkenes, see p. 571), osmium complexes are perhaps too substitution-inert for homogeneous catalysis to become a major feature of the chemistry of the element. The spectroscopic properties of some of the substituted heterocyclic nitrogen-donor complexes may yet make osmium an important element for photodissociation energy research. 

---