Metal atoms norbornene

Well-defined nanoclusters (w 10-100 A diameter) of several metals have been prepared via the polymerization of metal-containing monomers. The synthetic approach involves the block copolymerization of a metallated norbornene with a hydrocarbon co-monomer which is used to form an inert matrix. Subsequent decomposition of the confined metal complex affords small clusters of metal atoms. For example, palladium and platinum nanoclusters may be generated from the block copolymerization of methyl tetracyclododecane (223) with monomers (224) and (225) respectively. 10,611 Clusters of PbS have also been prepared by treating the block copolymer of (223) and (226) with H2S.612 A similar approach was adopted to synthesize embedded clusters of Zn and ZnS 613,614... 

The interaction of norbornene with iron, chromium, molybdenum, and tungsten atoms affords highly unstable and uncharacterized systems of polymeric materials (102, 134). The use of other strained olefins, such as /ran.v-cyclooctene, in metal atom syntheses has yet to be explored. 

The interaction of metal atoms with carbon-halogen bonds is characterized by oxidative cleavage of that linkage and is discussed more fully in Section IV. An exception to this generalization appears to be perfluorobut-2-ene which reacts with transition metal atoms in a manner similar to C2H4 and norbornene (54, 55) ... 

The norbomene complex [Li(tmeda)]2Ni(norbornene)2 (64) (89) is analogous to 62 and 63 in having a tetrahedral arrangement of carbon atoms and donor atoms around the lithium, but the geometry of the complex necessarily brings the lithium atom into close contact with the transition metal atom. 

Slurries of finely divided Mg are prepared in TIIF at -1 IO C by v tpori/ing Mg in a rotary metal atom reactor. The resulting pyrophoric Mg clusters are "dean, alkali halide free, and extremely reactive 11311. In their Grignard reactions, there is immediate initiation. Reactions tend to be complete in short times (in the case of isopentyl bromide in THF at 2() C. a minimum time for the addition of RBr to the Mg slurry plus <1 min) and they give 100% yields of RH l rom isopenlyl bromide or f )tr/o-5-(2 -haIoeihyl)-2-norbornene]. alter quenching with 10% aqueous HCI. in reactions at temperatures from -80 to 20 C I3I. In no case have products of c (e g.. RR) been found. 

Cyclopentenes behave differently and often act through radical mechanisms this can lead to photoreduction to cyclopentanes, or photoaddition of the kind exemplified by norborneneand propan-2-ol 12.57). The photoadduct in this process is linked through the carbon atom of the alcohol, and not the oxygen atom. A related addition to acetonitrile 12.58) takes place when norbornene is irradiated in the presence of a silver(i) compound. It is likely thal a metal complex of the alkene is the real irradiation substrate, and the same may be true for copper(i)-promoted additions of haloalkanes to electron-deficient alkenes (2.59). When dichloromelhane is used in such a reaction the product can be reduced electrochemically to a cyclopropane (2.60), which is of value because the related thermal addition of CH.I, to alkenes in the presence of copper does not succeed with electron-poor compounds. 

Deprotonation of cyclobutene under similar conditions therefore may be expected to result in almost exclusive formation of the vinylic metal intermediate [198]. It is clear from these results that the vinylic hydrogen atoms in three-, four-, and five-membered cycloalkenes are more acidic than those in ethene and its homologues. Other examples of strained olefins are norbornene and norbornadiene [67]. If present in excess, these hydrocarbons can be successfully converted into the sodium or potassium compounds at low temperatures, using the systems BuLi f-BuONa (or K) in THF [77, 198] or BuLW-BuOK TMEDA in hexane [21]. Previous attempts carried out with less effective base-solvent combinations at considerably higher temperatures, gave poor results [68, 69]. 

It is accepted that this reaction involves the formation of the alkynedicobalt hexacarbonyl complex from an alkyne and Co2(CO)s by the evolving of two CO ligands, followed by the alkene coordination at one of the two enantiotopic Co atoms with concomitant CO insertion, and final reductive elimination of the metal to an a,(3-unsaturated cyclopentenone. In the traditional protocol, the reaction mixture is heated in toluene at 110°C, or tertiary amine A-oxides are added to promote the reaction at ambient temperature. For the purpose of stereochemical control, many Pauson-Khand reactions are designed as intramolecular reactions P " or using cyclic alkenes, such as norbornene. It has been found that the reactivity of cyclic alkenes is in the order of cyclohexene < cyclopentene < norbornene. For the intermolecular Pauson-Khand reaction, alkene is positioned adjacent to the less bulky acetylenic substituent during coordination because of steric hindrance, and a subsequent C-C bond forms between an alkenic... 

Chelated complexes 31 were reported by Ledoux et al. but they displayed very poor efficiencies in the ROMP of norbornene. Attempts to open up the chelate by protonating the phenolic oxygen atom did not significantly improve the catalytic activity and caused instead a rapid decomposition of the transition metal active species. 

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