Iridium monovalent

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. 

However, whereas in solution, rhodium catalysts were shown to be the most active, in zeolites, iridium appeared to be an order of magnetitude more active than rhodium. Moreover, CH3CI could be used as the promoter while it could not be in solution. This is due, probably, to the fact that this molecule is strongly polarized by the electrostatic field and, possibly, to the modification of the redox properties of the monovalent precursor complex. This hypothesis was confirmed by the observation that the Si/Al ratio has a large influence on the activity of the rhodium complex (66). 

The structure and dynamics of Rh(77 -C3H5)3 were studied by DFT analysis. The chemistry of Ir(77 -allyl)3 and Rh( j -allyl)3 was compared. While addition of phosphorus ligands such as P(OPh)3 to Rh( 7 -allyl)3 gave monovalent Rh( j -allyl)L, the iridium analog provided stable mixed sigma/pi-tris(allyl) complexes, as evidenced by the structural characterization of mono-, bi-, and tridentate ligand complexes. The addition of CO also provided substantial differences, as shown in Scheme 56. ... 

Iridium clusters were also prepared from polynuclear iridium carbonyl clusters prepared by a so-called ship-in-a-bottle synthesis. Lefebvre et al. [196] were the first to study the in situ synthesis of iridium carbonyls using IR and NMR spectroscopy. Monovalent dicarbonyls were formed by contacting an Ir(NH3)5CF -exchanged zeoHte calcined at 300 K with CO. Tetranuclear iridium carbonyls, Ir4(CO)i2, were formed by contacting the zeolite with a CO/H2O atmosphere, and Ir6(CO)i6 was synthesized merely by heating the Ir4(CO)i2-... 

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