Reaction of Dialkyl-substituted Alkynes with Carbon Dioxide Catalyzed by Nickel(0) Complexes. Incorporation of Carbon Dioxide in Alkyne Dimers and Novel Cyclotrimerization of the Alkynes

Abstract

Abstract Ni(cod)2–Ph2P(CH2)4PPh2 system (cod=1,5-cyclooctadiene) catalyzed the reaction of 3-hexyne, for example, with CO2 to give a CO2 incorporated product, i.e., tetraethyl-2-pyrone, in a fairly good yield together with novel two cyclotrimers of the alkyne having cyclopentadiene structures, i.e., pentaethyl-5-(1-propenyl)-1,3-cyclopentadiene and pentaethyl-5-allyl-1,3-cyclopentadiene. The novel two cyclotrimers were formed selectively on Ni(cod)2–PPh3 system under CO2, whereas under N2 the main trimer was hexaethylbenzene. A nickelacyclopentadiene intermediate has been proposed for the pyrone formation. The novel two cyclotrimers were also formed on the oligomerization catalyzed by a cationic nickel hydride complex, [HNi(Ph2PCH2CH2PPh2)2]OCOCF3, together with a novel dimer having a methylenecyclobutene structure, i.e., 1,2,4-triethyl-3-ethylidenecyclobutene. The effect of phosphine added and that of active-hydrogen compounds on the novel oligomerization are mentioned.