3274-07-5Relevant academic research and scientific papers
Oxidative Addition of Nickel(0) Complexes to Carbon-Carbon Bonds in Cyclobutadiene. The Question of the Interconvertibility of Cyclobutadiene-nickel(0) Complexes and the Nickelaring Systems
Eisch, John J.,Piotrowski, Andrzej M.,Aradi, Allen A.,Krueger, Carl,Romao, Maria J.
, p. 624 - 635 (2007/10/02)
Bis(triethylphosphine)(η4-tetraphenylcyclobutadiene)nickel (4) was synthesized by the reduction of (η4-tetraphenylcyclobutadiene)nickel(II)bromide (3) with t-butyllithium in the presence of Et3P, and its structure was determined by X-ray crystallography.Furthermore, its reactivity towards CO, CH3CO2H, PhCCPh, LiAlH4 and O2 were investigated. 1,1-Bis(triethylphosphine)-2,3,4,5-tetraphenylnickelole (14) was synthesized from (E,E)-1,4-dilithio-1,2,3,4-tetraphenyl-1,3-butadiene (15) and bis(triethylphosphine)nickel(II)bromide.Since the resulting crystals of the nickelole were not suitable for X-ray structure determination, the compound was characterized by elemental analyses, spectral data and carbonylation to yield tetraphenylcyclopentadienone (6).Analogous reductions of (η4-tetraphenylcyclobutadiene)nickel(II)bromide (3) in the presence of Ph3P or Ph2PCH2CH2PPh2, followed by carbonylation, led to 6 in 40percent yield, demonstrating that about half of the cyclobutadiene rings in 3 undergo cleavage upon reduction to give the nickelole.Reactions of the dilithium reagent 15 with NiBr2 complexed with Me2PCH2CH2PMe2, Ph3P or Et2PCH2CH2PEt2, led to the formation of thermolabile nickeloles, as demonstrated by carbonylation which yielded 6.Warming of the nickeloles and subsequent treatment with CH3CO2H led to the formation of 1,2,3,4,5,6,7,8-octaphenyl-1,3,5,7-octatetraene (8) and, in one case, octahenylcyclooctatetraene (5).The relevance of these findings to the mechanism of the Reppe nickel-catalyzed oligomerization of alkynes is discussed. - Key words: Insertion Reaction, Oxidative Addition, Cyclobutadiene-Nickel(0) Complexes, Nickelacyclopentadiene, Nickelole
