OLIGOMERISATION CATALYSTS

1,240,992. Oligomerisation catalysts. INTERNATIONAL SYNTHETIC RUBBER CO. Ltd. 19 Sept., 1968 [20 Sept., 1967; 7 March, 1968], Nos. 42862/67 and 11270/68. Heading B1E. [Also in Division C5] A catalyst system comprises (a) a zero valent nickel phosphorus complex having the general formula wherein each A is a hydrogen atom or an alkyl, cydoalkyl, aryl, aralkyl, alkoxy or aryloxy radical, which radical may be unsubstituted or substituted, for example with a halogen atom or an alkyl radical, or may contain ether or thioether linkages or imines, secondary or tertiary nitrogen atoms, each B is a halogen atom and x is 0, 1, 2 or 3 with the proviso that x is not 3 in at least one of the (PA x B 3-x ) ligands, (b) an aluminium trihalide or aluminium dihalohydride, and (c) an organometallic compound of a metal selected from Groups I, II and III. Component (a) may be a nickel tetrakisphosphorus trihalide, for example nickel tetrakisphosphorus trichloride. Component (b) may be an aluminium trichloride or aluminium tribromide, the aluminium trichloride may be in the form of a hydrocarbon-soluble aluminium trichloride complex, for example a complex with an ether, for example anisole, a thioether or a cyanide. Component (c) may be triethyl aluminium or an alkyl lithium, for example n-butyl lithium, an aryl lithium or an aralkyl lithium. The components (a), (b) and (c) are present in amounts preferably such that the molar ratio of component (a) to component (b) is 1 to at least 7.5, for example between 1 to 15 and 1 to 25, and the molar ratio of component (a) to component (c) is 1 to at least 15, for example between 1 to 25 and 1 to 35; in a preferred catalyst system, the molar ratio of the components (a):(b):(c) is 1:20:30. The components (a), (b) and (c) preferably are dissolved or dispersed in dry air-free organic solvent; suitable solvents are saturated aliphatic straight-chain hydrocarbons, for example hexane, saturated cyclic hydrocarbons, for example cyclohexane, and aromatic hydrocarbons, for example benzene and toluene; chlorinated solvents may be used but are not preferred. Component (a) advantageously is used in an amount such as to provide a concentration thereof of 0.5 millimeters or less, for example 0.25 milimoles, per litre of solvent; the components (a), (b) and (c) are added in the order preferably (a), (b), (c) and less preferably (b), (a), (c). The catalyst system may be used in the oligomerisation of ethylene or in the cooligomerisation of ethylene and