ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Catalytic systems of nickel chelates and organometallic compounds in cyclohexene hydrogenation

J. Reguli and A. Staško

Department of Physical Chemistry, Slovak Technical University, CS-812 37 Bratislava

Abstract: Catalytic systems NiL₂ (L: 3,5-diisopropylsalicylate /, acetylacetonate //, stearate / / / , and benzohydroxamate IV) with organometals (Et₃Al, i-Bu₃Al, BuLi) were studied. The cyclohexene hydrogenation rate for the most active catalysts, prepared under very mild conditions (30 °C,p₀(H₂) = 120 kPa, c(Ni) ≈ 2 mmol dm^-3) was about 0.76 mol min^-1' related to 1 g Ni. Catalytic activity a(i) decreased in order of Ni chelates a (I) > a (II) ≻ a (III) > > a(IV). The optimal ratio was п(Аl) / п(Ni) = 3, n(Li) /n(Ni) = 4 for I, and n(Аl) / n(Ni) = n(Li) / n(Ni) = 2 for //, ///, IV The presence of aromat­ ic compounds slowed down the hydrogenation rate and was accompanied by reduction and sedimentation of nickel in colloid form. The activation en­ ergy of cyclohexene hydrogenation using Ni(dips)₂ — Et₃Al was E = 28.4 kJ mol^-1 The reaction order with respect to catalyst is equal to one and to substrate zero. The structure of active centre and mechanism of reaction of Ni(dips)2 with organoaluminium compounds was suggested by means of EPR.

Full paper in Portable Document Format: 413a299.pdf

Chemical Papers 41 (3) 299–310 (1987)