Tetraphenyl-1,4-dilithio-1,3-butadiene

In the stannole series, the reactions could be explained by the extraordinary reactivity of the exocyclic tin-carbon bonds with regard to lithium reagents. Thus, the reaction of 1,4-dilithio-1,2,3,4-tetraphenyl-1,3-butadiene with 1,1 -dialkyl-2,3,4,5-tetraphenylstannole leads to alkyl-tin bond cleavage-cyclization by the dilithium reagent33 (equation 61). 

Recent studies on the allylation of alkynes with bis (7r-allyl) nickel have revealed that the Ni(0) generated in this process causes the trimeri-zation and, more importantly, the reductive dimerization of a portion of the alkyne (8). A deuterolytic work-up led to the terminally di-deuter-ated diene (5), supporting the presence of a nickelole precursor (4) (Scheme 1). The further interaction of 4 with 1, either in a Diels-Alder fashion (6) or by alkyne insertion in a C-Ni bond (7), could lead to the cyclic trimer 8 after extrusion of Ni(0), thereby accounting for the trimerizing action of Ni(0) on alkynes. This detection of dimer 5 then provided impetus for the synthesis of the unknown nickelole system to learn if its properties would accord with this proposed reaction scheme. Therefore, E,E-l,4-dilithio-l,2,3,4-tetraphenyl-l,3-butadiene (9) was treated with bis (triphenylphosphine) nickel (II) chloride or l,2-bis(di-phenylphosphino ethane)nickel(II) chloride to form the nickelole 10 (9) (Scheme 2). The nickelole reacted with dimethyl acetylenedicarboxylate to yield 11 and with CO to produce 12. Finally, in keeping with the hypothesis offered in Scheme 1, 10a did act as a trimerizing catalyst toward diphenylacetylene (13) to yield 14. 

Pentamethylcyclopentadienyl derivatives are obtained by reaction of alkyllithiums with (77 -Gp )Ni(acac). In the presence of PMes, LiMe leads to the complex (r7 -Gp )Ni(Me)(PMe3), and with 2,4-dilithio-l,2,3,4-tetraphenyl-butadiene the internally stabilized alkenyl complex 247 is formed. The latter rearranges at 60°G to give a mixture of isomeric allyl complexes (Scheme 78). The binuclear decacyclene complex 248 readily undergoes the... 

Pauer F, Power PP (1994) l,4-Dilithio-l,2,3,4-tetraphenyl-butadiene - oystal stmcture of the 1,2-dimethoxyethane adduct. J Organomet Chem 474 27-30... 

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