Metal-acetylene reactions

Acetylenic molecules are versatile ligands in organometallic chemistry [152— 154]. Examples of acetylene-metal reactions include facile complexations of one triple bond with Co2(CO)s [155-157] and two triple bonds with CpCo(CO)2 (Scheme 31) [158,159]. The hb-PYs contain numerous triple bonds and should be readily metallized through their complexations with the cobalt carbonyls. Upon admixing hb-P20 and the cobalt carbonyls in THF at room temperature, the solution color changed from yellow to brown, accompanied by CO gas evolution. The mixtures remained homogenous towards... 

Since the utility of these materials is improved by the incorporation of these reactive functionalities without severely decreasing other favorable properties such as thermooxidative stability and solvent resistance the chemistry of the isoimide isomerization and acetylene crosslinking reactions is of considerable interest. Previous work in our laboratory has shown that these materials, when loaded with metal powders, provide a convenient and effective method of optimizing the electrical conductance and thermal stability of aluminum conductor joints. 

Philipsborn and coworkers [83] have successfully used the Co signals in the substituted Co(i)Cp complexes 72, in connection with understanding the mechanism of pyridine/acetylene trimerization reactions. The metal resonance was found to vary strongly with the catalyst structure and a correlation of d Co with reactivity was observed. 

The polymerization of acetylene by Ziegler catalysts very likely involves metal alkyl-acetylene insertion reactions also 26). 

Another unusual three-component coupling reaction involving an imine as intermediate has been developed by Ishii who has shown that a C-H bond adjacent to the nitrogen atom of an imine can be activated by an iridium complex. Carbo-metallation reactions of acetylenic compounds may then be achieved, which lead to unsaturated imines 155 (Scheme 8.67) [122]. 

Generally, insertion of the alkyne into a metal-P bond is observed (Scheme 10).188,190 When aminoalkynes are used, the formation of a C=N double bond inhibits the interaction of that carbon with the metal centers of the cluster.186 187 When two PR groups are present, the alkyne has been observed to bridge between them as seen in Scheme 10.195,285 A second equivalent of diphenylacetylene can substitute for two carbonyl groups on the iron triangle.195 The hetero-main group element species Fe3(CO)9(NPh) (P Bu) and Fe3(CO)9(NPh)2 have been reacted with diphenylacetylene.273 Some of the products involved in the acetylene addition reaction are shown here (241-243). 

Some Ziegler-type catalysts have been used to polymerize terminal acetylenes (56, 57). Highly dispersed or soluble catalysts based on TiCl, Ti(OR), metal chelates (Co, Ni, V, Fe) plus AlEt have been most successful. Acetylenes, unlike a-olefins, polymerize with Group VIII transition metal compounds. With some acetylenes, trimerization reactions leading to the corresponding substituted benzene derivatives take place. 

Studies on the preparation and reactions of olefin complexes have been the subject of several recent reviews. In particular olefin and acetylene complexes of platinum and palladium have been reviewed by Hartley 0, characterised ole-fin-metal complexes by Quinn and Tsai ) and some acetylene-metal complexes by Greaves, Lock and Maitlis 3>. 

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