Kinetic and spectroscopic studies of the [palladium(Ar-bian)]-catalyzed semi-hydrogenation of 4-octyne.
The kinetics of the stereoselective semi-hydrogenation of 4-octyne in THF by the highly active catalyst [Pd{(m,m'-(CF(3))(2)C(6)H(3))-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][H(2)], 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 H(2)-assisted, palladium-catalyzed isomerization reaction.
Kluwer
Alexander M
AM
Van't Hoff Institute for Molecular Sciences, Universiteit van Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands.
Koblenz
Tehila S
TS
Jonischkeit
Thorsten
T
Woelk
Klaus
K
Elsevier
Cornelis J
CJ
D000480:Alkynes / Q000737:chemistry*; D002384:Catalysis; D006865:Hydrogenation; D007700:Kinetics; D009795:Octanes / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D013057:Spectrum Analysis
D000480:Alkynes; D009795:Octanes; D010165:Palladium