Nickel cyclopropenones

Another type of dimerization was observed by Japanese authors198. In the presence of Ni°, compounds like bis(l,5-cyclooctadiene) nickel(0), diphenyl and di-n-propyl cyclopropenone, and cyclohepteno cyclopropenone are transformed to tetra-substituted p-benzoquinones (261/262) by formal (2 + 2) or (3 + 3) cycloaddition of two cyclopropenone moieties effected by metal complexing. 

As mentioned in Sections 3.1.6 and 4.1.3, cyclopropenes can also be suitable starting materials for the generation of carbene complexes. Cyclopropenone di-methylacetal [678] and 3-alkyl- or 3-aryl-disubstituted cyclopropenes [679] have been shown to react, upon catalysis by Ni(COD)2, with acceptor-substituted olefins to yield the products of formal, non-concerted vinylcarbene [2-1-1] cycloaddition (Table 3.6). It has been proposed that nucleophilic nickel carbene complexes are formed as intermediates. Similarly, bicyclo[1.1.0]butane also reacts with Ni(COD)2 to yield a nucleophilic homoallylcarbene nickel complex [680]. This intermediate is capable of cyclopropanating electron-poor alkenes (Table 3.6). 

Dimerization of 2,3-disubstituted cyclopropenones catalyzed by bis(cycloocta-l,5-diene)nickel(O) gave 1,4-benzoquinones 25 via bond cleavage between Cl and C2 of the cyclopropenones. ... 

As well as formation of metallacyclobutenones, reactions of cyclopropenones with transition-metal compounds can lead to acetylene-derived products by decarbonylation, to quinones by a nickel-catalyzed cyclodimerization, and to cluster compounds involving a cleavage of the double bond of the cyclopropenone. ... 

Wilkinson s catalyst is useful for effecting intramolecular decarbonylation of aldehydes to hydrocarbons with retention of configuration (Walborsky and Allen, 1971). Decarbonylation of disubstituted cyclopropenones by iron, nickel, or cobalt carbonyls results in the formation of alkynes (Bird and Hudec, 1959). Tetraphenylethylene was obtained in 68% yield by reaction of diphenylketene with cobalt carbonyl (Hong et ai, 1968). 

---