Dimeric copper acetylide complexes

In the polycoupling reactions, the formation of the diyne units proceeded via a Glaser-Hay oxidative coupling route [35-38]. Despite its wide applications in the preparation of small molecules and linear polymers containing diyne moieties, its mechanism remains unclear [38-40]. It has been proposed that a dimeric copper acetylide complex is involved, whose collapse leads to the formation of the diyne product (Scheme 9). 

This activation process can be assumed to be the initial step in the formation of dinuclear copper(II) acetylide complexes, as first proposed by Bohlmann and coworkers 40 years ago (Scheme 6) [10f]. Deprotonated alkyne units 11 (or the corresponding JT-complexes 10) generated therein, stepwise displace the negatively charged counter ions of copper(II) salt dimers (12). The dinuclear copper(II) acet-ylide complex which finally results (14) collapses to the coupled product under reductive elimination of copper(I). The existence of higher-order copper acetylide... 

In contrast to the lithium acetylide reaction, addition of copper(I) phenylacetylide to (i75-C5H5)(PPh3)2RuCl (1) affords the monomeric ruthenium acetylide-copper chloride adduct (62) as the major product. An X-ray crystal structure of this complex reveals an tj1, -bridging acetylide between the ruthenium and copper centers, respectively (62). A small amount of the dimeric chloride bridged complex 61 was also isolated. The copper chloride can be removed from the monomeric complex by the... 

The mechanism of the Glaser coupling and related methods is very complex and is not fully understood. Studies revealed that the mechanism is highly dependent on the experimental conditions. The early proposal involving a radical mechanism has been rejected. The currently accepted mechanism involves dimeric copper(ll)acetylide complexes. 

The acetylide anion 3 is likely to form an alkynyl-copper complex by reaction with the cupric salt. By electron transfer the copper-II ion is reduced, while the acetylenic ligands dimerize to yield the -acetylene 2 ... 

Copper(I) acetylides provide a useful route to the synthesis of a variety of organic acetylenic compounds and heterocycles, by reaction with aryl and other halides. A particularly important indirect use, where acetylides are probable intermediates, is the oxidative dimerization of acetylenes. A common procedure is to use the N, N,N, TV -tetramethylethylenediamine complex of CuCl in a solvent, or CuCl in pyridine-methanol, and oxygen as a reoxidant for Cu+ ... 

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