Cluster unsaturated

This kind of reaction implies that there is a transfer of electrons to the clusters. Therefore, if there is no cluster unsaturation before the reaction, these oxidative additions will involve ligand substitution or metal-metal cleavage. 

Another example of orthometallation is the series of reactions shown in Fig. 2.65. The thermal treatment of the compound Os3(CO)n(PPh2R)(R = Ph or Me) induces loss of carbon monoxide providing cluster unsaturation which promotes in turn the activation of a C-H bond in the phosphine giving finally Os3(CO)9( 3-C6H4)(/i3-PR). The metallation of two carbon atoms observed in... 

The main synthetic route to high nuclearity metal carbonyl clusters involves a condensation process (/) a reaction induced by coordinatively unsaturated species or (2) a reaction between coordinatively saturated species in different oxidation states. As an example of (/), Os2(CO)22 can be condensed to form a series of higher coordinated species (89). 

Regioselective coniugale reduction and reductive silylation of a,p-unsaturated ketones, esters, and aldehydes using a stable copper (I) hydride cluster (Ph3P)CuH 6... 

One of the m jor attractions in the metal-atom synthesis of dimer and cluster species is the ability to isolate highly unsaturated species, M Lm, that may then be considered to be models for chemisorption of the ligand, L, on either a bare, or a supported, metal surface (,100). It is quite informative to compare the spectral properties of these finite cluster-complexes to those of the corresponding, adsorbed surface-layers (100), in an effort to test localized-bonding aspects of chemisorption, and for deciphering UPS data and vibrational-energy-loss data for the chemisorbed state. At times, the similarities are quite striking. 

Class 111-type behavior is the consequence of this impossibihty to create step-edge-type sites on smaller particles. Larger particles wiU also support the step-edge sites. Details may vary. Surface step directions can have a different orientation and so does the coordinative unsaturation of the atoms that participate in the ensemble of atoms that form the reactive center. This wiU enhance the activation barrier compared to that on the smaller clusters. Recombination as well as dissociation reactions of tt molecular bonds will show Class 111-type behavior. 

Apparently, the cohesive energy of these clusters shows a very slow convergence with the size of the molecule. This should not be surprising, since the number of unsaturated valences "dangling bonds" per carbon atom is one in 1,1/2 in 2 and 1/3 in 3. 

Preliminary indications are quite clear that coordin-atively unsaturated transition metal clusters are reactive, and, importantly, reactive in a controlled way. This chemistry is likely to include RC-H insertion, arom-atization etc., with the chemistry tending to produce... 

The (100) face is modelled by neutral clusters of general formula (Mo03)n (model 3), both containing coordinatively unsaturated Mo and Om with respective coordination of 5 and2. 

A review22 with 100 references, is given on the chemistry of coordinatively unsaturated tripalladium and triplatinum clusters and on the relation between this chemistry and that which occurs on a Pt surface during chemisorption and catalysis. 

The reaction with [Mn(CO)5]2 or [Co(CO)4]2 also led to mixed-metal clusters.962,963 Osmium-palladium mixed-metal carbonyl clusters were made using the unsaturated cluster [Os3(CO)io(/r-H)2] and the carbido cluster [Os5(/U5-C)(CO)15].964 970 Treatment of [Os3(CO)10Gu-H)2] with [Pd2(/u-dppm)2Cl2] afforded the novel high-nuclearity osmium-palladium mixed-metal carbonyl clusters [Os5Pd6(CO)13( -CO)5(/u-H)2(/u-dppm)2], [Os5Pd6(CO)13(//-CO)6(/u-dppm)2], and... 

Oxidative addition reactions have been observed also for the binuclear clusters of other d-transition elements with multiple M-M bonds [1,116,117]. The multiplicity of the M-M bonds must decrease in these reactions. It is known from organic chemistry that similar reactions are extremely characteristic of unsaturated organic compounds. We believe that the capacity for oxidative... 

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