Rhodium zerovalent

An alternative approach to stabilize nanoparticles is to use polyoxoanions (see Scheme 9.5). Finke and coworkers described polyoxoanion- and ammonium-stabilized rhodium zerovalent nanoclusters for the hydrogenation of classical benzene compounds [95, 108]. This organometallic approach allows reproducible preparation of stable nanoparticles starting from a well-defined complex in terms of composition and structure (see Section 9.3.5). 

The transition-metal catalyzed decomposition of thiirene dioxides has been also investigated primarily via kinetic studies103. Zerovalent platinum and palladium complexes and monovalent iridium and rhodium complexes were found to affect this process, whereas divalent platinum and palladium had no effect. The kinetic data suggested the mechanism in equation 7. 

Transition metal ions, within the zeolite framework, may undergo a reductive carbonylation to give mononuclear monovalent carbonyl coumpounds M(I)(CO) and ultimatly to give zerovalent polynuclear carbonyl clusters. The rhodium(I)and iridium(i)carbonyIs were identified using spectroscopic and volumetric methods, the zerovalent rhodium and Iridium clusters M (CO)j were also synthetized in the zeolite matrix and their structure investigated using IR, NMR and spin labelling methods. 

As the VCO absorption bands due to the dicarbonyl decreased an IR band at 2340 cm due to CO. developed gradually together with a set of absorptions around 2100-2000 cm- due to new linear carbonyls and absorptions around 1800 cm- presumably due to bridged carbonyls (14). CO- appearance was interpreted as an indication of the further reduction of the monovalent rhodium either by CO or via the water gas shift reaction producing H- which is reported to occur on monoculear monovalent carbonyls (19, 20). As rhodium I was reduced to the zerovalent state, the observed VCO bands were ascribed to Rh (C0)j2 compound, in view of the excellent agreement between the observed frequencies and those reported for Rh (C0)j- in CI C or nujol or when adsorbed on fully dehydrated zeolite. 

The diruthenium(O) complexes [Ru2(CO) J,-(RO)2PN(Et)P(OR)2 2] (3, R = Me, Pr) (Scheme 2) have been reported to react with dihydrogen affording l,2-dihydrides.[13] Despite the formal similarity between these compounds and the previously described iridium and rhodium dppm derivatives, they display different coordination environments around the metal atoms. This could be related to the fact that, unlike the typical planar structure of most mononuclear d species, the unsaturated zerovalent ruthenium fragments adopt a structure which resembles a trigonal bipyramid with an empty equatorial site. [14]... 

---