870525-20-5Relevant academic research and scientific papers
Kinetic and spectroscopic studies of the [palladium(Ar-bian)]-catalyzed semi-hydrogenation of 4-octyne
Kluwer, Alexander M.,Koblenz, Tehila S.,Jonischkeit, Thorsten,Woelk, Klaus,Elsevier, Cornelis J.
, p. 15470 - 15480 (2005)
The kinetics of the stereoselective semi-hydrogenation of 4-octyne in THF by the highly active catalyst [Pd{(m,m′-(CF3)2C 6H3)-bian}(ma)] (2) (bian = bis(imino)acenaphthene; ma = maleic anhydride) has been investigated. The rate law under hydrogen-rich conditions is described by r = k[4-octyne]0.65[Pd]-[H2], showing first order in palladium and dihydrogen and a broken order in substrate. Parahydrogen studies have shown that a pairwise transfer of hydrogen atoms occurs in the rate-limiting step. In agreement with recent theoretical results, the proposed mechanism consists of the consecutive steps: alkyne coordination, heterolytic dihydrogen activation (hydrogenolysis of one Pd-N bond), subsequent hydro-palladation of the alkyne, followed by addition of N-H to palladium, reductive coupling of vinyl and hydride and, finally, substitution of the product alkene by the alkyne substrate. Under hydrogen-limiting conditions, side reactions occur, that is, formation of catalytically inactive palladacycles by oxidative alkyne coupling. Furthermore, it has been shown that (Z)-oct-4-ene is the primary reaction product, from which the minor product (E)-oct-4-ene is formed by an H2-assisted, palladium-catalyzed isomerization reaction.
