ORGANOMETALLIC COMPLEXES FORMED FROM ACETYLENES

In Table 27 are shown the skeletal frameworks oftheclasses of complexes most commonly found in the dimerization and trimerization reactions of acetylenes. The table also exemplifies the classification used in this chapter. 

Monoacetylene, mononuclear complexes acetylenes as 2-electron ligands 

In the earlier discussion of the ethylene-metal bond (Chapter 1), the ethylene was compared, in ex eme examples, to the carbon monoxide ligand or to two alkyl groups. In the former situation the ethylene is behaving as an essentially monodentate ligand whilst in the latter it behaves as a bidentate ligand. Acetylenes are similar in their behaviour. 

Treatment of 7r-C5H5Mn(CO)3 with acetylenes and irradiation with ultraviolet light gives monoacetylene complexes, 8.1 

Ethylenic complexes analogous to these acetylene complexes, 8.1, are known and it seems a reasonable assumption that the acetylene-metal bond should resemble the ethylene-metal bond in these complexes. Thus the acetylene, which has two orthogonal / 3i-bonds, would use one filled / jr-bond to donate to the manganese and back-donation from the metal would take place mainly into the corresponding anti-bonding / jr -bond of the acetylene. A number of acetylene-platinum complexes are known in which again it may be assumed that the acetylene-metal bond is similar 

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Table XIII contains data for organometallic complexes that do not fall into one of the preceding categories. The nonlinearities of the chloro complexes were used in conjunction with those of terminal acetylenes to demonstrate the importance of electronic communication between ligated metal and acetylide ligand in derivative metal acetylide complexes formed from combining these precursors.49133 134 Evaluation of vinylidene, as with sesqui-fulvalene and carbene, is only experimentally straightforward following metal complexation. The vinylidene cation [Ru(C=CHC6H4-4-N02)...

Mo and W catalysts used by other researchers for the polymerization of acetylenes are shown in Table 7. They are all organometallics, and are usually less active than those in Table 3. It is reported that ladder polymers form from acetylenes in the presence of the toluene Mo(CO)3 complex 8). Katz and Lee have succeeded in polymerizing acetylenes with Fischer s carbene (3 a) and Casey s carbene (3b)9) ... 

Transition metal compounds of diverse types undergo reactions with alkynes to yield a large variety of organometallic and organic products. In some cases, simple acetylene complexes are obtained. Often, however, more complex ligands result from insertion or oligomerization reactions. Undoubtedly, the formation of the latter products in most cases proceeds by way of initially formed acetylene complexes, but these are often undetectable. 

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