Copper complexes clusters

A substantial fraction of the named enzymes are oxido-reductases, responsible for shuttling electrons along metabolic pathways that reduce carbon dioxide to sugar (in the case of plants), or reduce oxygen to water (in the case of mammals). The oxido-reductases that drive these processes involve a small set of redox active cofactors , that is, small chemical groups that gain or lose electrons. These cofactors include iron porjDhyrins, iron-sulfur clusters and copper complexes as well as organic species that are ET active. 

Scheme 27 Synthesis of rhodium, iridium, and copper polysulfido clusters from the corresponding, u-hydrogensulfido complexes...

Fig. 19.30 Molecular structure of copper complex of D-penknUamme. The ICu Cu pefl(cillajnrnate) 2CI ion (a) the central cluster of Cu and ligating atoms only, (b) the entire ion with the centra] duster oriented as In (a). From Biricer. P. J. M. W. L. Freeman. H. C. Chem. Commtm. 1976.312. Reproduced with permission.)...

Dihapto 7>ligands, in copper complexes, 2, 174 Dihydride iridium complexes, preparation, 7, 396 Dihydrido clusters, with decarutheniums, 6, 1036 Dihydrobenzofuran, carbene C-H insertions, 10, 193 Dihydrobenzopyran, carbene C-H insertions, 10, 193 ring-closing diene metathesis,... 

The structure of cluster 914 was proved by x-ray diffraction. The copper complexes with the same ratio M L [Cu(PySe)] and [Cu(6-Me3SiPySe)] were isolated according to a similar scheme, although their structure is unclear [270]. 

This is a remarkable reaction because the transition metal chemistry of N2O is sparse, especially with copper. Most N2O reductases are soluble, periplasmic homodimers however, there are examples of membrane-associated enzymes. " The best characterized N2O reductases are from Paracoccus denitrificans, Pseudomonas nautica, and Pseudomonas stutzeri, and most of the information presented here is derived from experiments on these enzymes. Where comparable data are available, N2O reductases from various organisms appear to be fairly similar, with the exception of the enzyme from Wolinella succinogenes, as noted above. The crystal stractmes of N2O reductase from P. nautica and more recently from P. denitrificans show two distinct copper clusters per subunit a bis-thiolate bridged dinuclear electron-transfer site (Cua), which is analogous to the Cua site in cytochrome c oxidase see Cyanide Complexes of the Transition Metals), and a novel four-copper cluster ligated by seven histidines, the catalytic copper site (Cuz), where N2O is thought to bind and be reduced. Cuz was proposed to be a copper-histidine cluster on the basis of the presence of nine strictly conserved histidine residues, and this was supported by a H NMR study that identified two non-CuA associated resonances that were assigned as copper-histidine N-H protons. ... 

A few years ago Smalley and coworkers were able to obtain detailed experimental information about the reactivity of specific transition metal clusters with hydrogen molecules (1). The results for copper and nickel clusters were essentially as expected from the known results for surface and metal complex activities. For copper no clusters were able to dissociate whereas for nickel all clusters were active with a slow, steady increase of activity with cluster size. For the other transition metals studied, cobalt, iron and niobium, a completely different picture emerged. For these metals a dramatic sensitivity of the reactivity to cluster size was detected. No convincing explanation for these surprising results has hitherto been suggested. It should be added that there are no dramatic differences in the activity towards Hg for the metal surfaces (or the metal complexes) of nickel on the one hand and iron, cobalt and niobium on the other. 

The reactivity of palladium and copper cluster models toward diazirine has been compared using the LCGTO-MCP-LSD method <1996SUS11> such calculations were performed to give an insight into the differential bond scission experimentally observed in the thermal decomposition of diazirine on palladium and copper surfaces. Stronger chemisorption was evident with palladium and furthermore, partial diazirine lowest-unoccupied molecular orbital (LUMO) occupation only occurred for the copper cluster model systems. The calculated N-N bond order was significantly decreased in the copper complexes of excited state diazirines, whereas palladium complexes remained unperturbed. 

Unlike the copper telluride clusters, it has not yet proven possible to generate large silver telluride cluster complexes using a combination of R3P, Ag-X and Te(SiMe3)2. This suggests that the phosphine ligands are unable to kinetically... 

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