Tetrairidium clusters

Kawi, S., Chang, J.-R., and Gates, B. C., Tetrairidium clusters supported on y-AI2O3 Formation from [Ir4(CO)i2] and CO-induced morphology changes. J. Phys. Chem. 97, 5375 (1993). 

The mono- and bis-diphosphine tetrairidium clusters 65 and 66 have been reported 66 readily loses CO to give the orthometalated 67.49... 

Triantafillou, N. D., and Gates, B. C., Magnesia-supported tetrairidium clusters derived from [It4(CO)i2]./. Phys Chem. 98, 8431 (1994). 

Fig. 7. Reactions of tetrairidium clusters with alkynes and alkenes.

This distinct switch in the intimate mechanism in response to the steric reqnirements of the incoming ligand represents a more extreme example of the earlier studies with the tetrairidium clusters and is thonght to arise from the ability of this clnster to open to a bridged bntterfly structure on adduct formation with the stericaUy less-demanding ligands. 

Alexeev O, Panjabi G, Gates BC (1998) Partially decarbonylated tetrairidium clusters on y-Alj03 Structural characterization and catalysis of toluene hydrogenation. J Catal 173 196... 

Goellner JF, Guzman J, Gates BC (2002) Synthesis and structure of tetrairidium clusters on TiOj powder Characterization by infrared and extended X-ray absorption fine structure spectroscopies. J Phys Chem B 106 1229... 

Kawi S, Chang J-R, Gates BC (1993) Tetrairidium clusters supported on y-alumina Formation from [Ir lCOljJ and carbon monoxide-induced morphology changes. J Phys Chem 97 5375... 

These ligand exchange and association reactions require complexes (catalysts) that are stable during the synthesis. An alternative is the In situ formation of the supported species, illustrated by the formation of a supported tetrairidium cluster, as follows ... 

Metal clusters have also been considered as heavy metal labels for determining the phasing in crystallography of large biological molecules.Heavy atom labeling by a tetrairidium cluster was used to determine the X-ray crystal structure of the small subunit from Thermus thermophilus. Attachment of the cluster was made to the surface-exposed SH groups prior to crystallization. The positions of these sulfhydryls were localized in difference Fourier maps that were constructed with the multiple isomorphous replacement (MIR). ... 

The chemistry of the successive formation of these anionic clusters on basic MgO surfaces is analogous to that in solution, [37] and each of these cluster anions could be extracted from MgO. Since the octairidium cluster (which is a dimer of the tetrairidium clusters) was evidently not formed in the NaX zeolite, it was inferred that the confinement of the iridium in the cages prevented its formation. This example illustrates the subtle control of the reactivity exerted by the cages. 

The confinement affects what can be formed in the cages. For example, when iridium carbonyl clusters are synthesized either on the surface of MgO or in solution, [HIr4(CO)n] is formed first, followed by [Ir8(CO)22p (which is a dimer of the tetrairidium cluster), and finally [Ir (CO)isp. In contrast, within the super-cages of NaX zeolite, [HIt4(CO),i] and then [Ir6(CO)is] are formed, but [Irg(CO)22] is not observed, presumably because it is too large to fit in the cage and therefore cannot exist there. 

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