Propene regioselective dimerization

Regioselective dimerization of propene to 2,3-dimethylbutenes (DMBs) is currently operated by Sumitomo and BP Chemicals. Both use P(cyclohexyl)3 as the bulky ligand. In the Sumitomo process [7] very high selectivities in DMBs (up to 85 %) are obtained at 20-50 °C, thanks to a sophisticated, highly efficient, Ziegler-type catalyst system (ten times more efficient than those of conventional catalysts) and by using toluene as a solvent. Isomerization of 2,3-dimethyl-1-butene (DMB-1) into 2,3-dimethyl-2-butene (DMB-2) takes place directly in... 

The cationic nickel complex [ /3-allylNi(PR3)]+, already described by Wilke etal. [21], as an efficient catalyst precursor for alkene dimerization when dissolved in chlorinated organic solvents. It proved to be very active in acidic chloroaluminate ionic liquids. In spite of the strong potential Lewis acidity of the medium, a similar phosphine effect is observed. Biphasic regioselective dimerization of propylene into 2,3-dimethylbutenes can then be achieved in chloroaluminates. However, there is a competition for the phosphine between the soft nickel complex and the hard aluminum chloride coming from the dissociation of polynuclear chloroaluminate anions. Aromatic hydrocarbons, when added to the system, can act as competitive bases thus preventing the de-coordination of phosphine ligand from the nickel complex [22 b]. Performed in a continuous way, in IFP pilot plant facilities, dimerization of propene and/or butenes with this biphasic system (Difasol process) compares... 

Many nickel-based systems catalyze the dimerization of olefins. In 1966, Wilke [5] demonstrated that the well-defined cationic ri -allylnickel complex (1) catalyzes the regioselective dimerization of propene in organic chlorinated solvent. The AICI4... 

The product of the dimerization of an unsymmetrical substituted olefin, such as propene, is dependent on the direction of coupling of the two olefinic units in general, a mixture of isomers is obtained. In order to obtain a high yield of a particular dimer, the control of the regioselectivity of the individual addition steps in the catalytic cycle or even the reversal of the direction of addition in consecutive steps is required (Section IV,E). 

The nature and distribution of the products of the dimerization or oligomerization of unsymmetrical olefins, such as propene, will depend, among others, on the direction of addition of the hydrido- and alkylnickel species to the olefin, i.e., on the regioselectivity of the catalyst (see Section 1 V,E). In order to define the direction of addition of hydrido- or alkylnickel species to terminal olefins, we shall adopt the convention nickel-to-C, addition [Eq. (12)] (Ni —> Cj) ... 

It is however clear that the use of carefully ion-exchanged amorphous supports can lead to catalysts that have superior regioselectivities in propene dimerization compared with many homogeneous systems. The approach may well be more generally applicable to, for example, other areas of transition metal mediated catalysis and this aspect is now attracting our attention. 

They confirmed the reaction mechanism and underlined the effect of tertiaiy phosphanes on the regioselectivity of the linking of propene molecules. This complex is soluble only in chlorinated hydrocarbons. Many other systems based on nickel catalyze the dimerization reaction and have been described in many publications and patents. 

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