Reductive dimerization diphenylacetylene

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. 

The oxomolybdenuni(IV) porphyrin treated with trimethylsilylchloride produces the trans dichloro derivative Mo(OEP)Cl2 which gives Mo(OEP)(PhC=CPh) by reduction with LiAlH4 in the presence of diphenylacetylene. The dimer is then obtained by vacuum pyrolysis of this five coordinate complex. Molybdenum(II) dimers are also obtained by heating a mixture of MoCl2(CO)4 and H2(Por) in oxygen-free toluene (Eq. 26) where Por is OEP, its 5-formyl-, 5-amino-, and 5-isocyanato derivative, or 5,15-dimethyletiopor-phyrin II. 

Thermolysis of thione 362 contrasts with its oxygen analogue 14 in giving only small quantities of diphenylacetylene the mass spectrum of 362, unlike that of 14, shows a molecular ion peak. The photochemistry of 362 is complex depending upon the conditions employed diphenylacetylene, tetraphenylthiophenothiophene, diphenylcyc-lopropenethione dimers, thioacrylates and thietes or mixtures thereof are formed Oxidation of 362 with lead tetraacetate delivers 14 and the electrochemical reduction has... 

Eisch et al. have attempted to synthesize borirenes on reductive ring closure of the haloboration products of diphenylacetylene (35) <67JOM(8)53, 79JOM(l71)141>. The authors failed to isolate borirenes, and their occurrence was inferred from the dimerization products (36 n = 2), or from the products of deuterolysis (cf. Section 1.10.9.2.2). 

---