Oligomerization and isomerization of olefins by catalysts derived from nickel complexes of dithio-β-diketonates

Abstract

The complexes [Ni{R1C(S)CRzC(S)R3},] 1 and [Ni{R1C(S)CR2C(S)R3}(PL1LZL3)X] 2 (R, L = alkyl, aryl or CF, ; X = CI, Br or I) have been prepared. The complexes 2 can be chemically anchored t o polystyrene or silica-alumina supports via pendant phosphine ligands to form the derivatives 3. The species 2 and 3 in combination with a suitable co-catalyst form extremely active catalysts for the oligomerization of ethylene, propylene or butenes. The immobilised systems show no significant signs of leaching after 24 h operation. In general the oligomerization is highly selective to dimers, however, selectivity and catalyst activity are markedly affected by changes in L. Changes in R affect catalyst activity only.Catalytic dimerization/oligomerization is a useful method for the conversion of moderately cheap lower molecular weight (i.e., C2-C4) feed olefins into industrially important olefins of higher molecular weight. The use of organometallic complexes in catalysts for this purpose has been widely studied'-' and several processes have been commercialised.*-' O Branched products from the dimerization and co-dimerization of propylene and butylene are suitable as gasoline blending components. Linear products from the dimerization and oligomerization of C3-C, olefins are desirable for the production of c&', plasticiser and detergent range olefins.We have been seeking new olefin oligomerization catalysts which give improved turnover numbers (i,e., number of converted substrate molecules per active site on the catalyst per unit time) and/or improved selectivity or specificity as to the type or variety of the dimer(s) or oligomer(s) produced from a particular olefin feedstock. Nickel( 11) complexes of the formula [Ni( R ' C(S)CR 2C( S)R 3, -(PL'L2L3)X] 2 (R, L = alkyl, aryl or CF,; X = C1, Br or I) containing dithioacetylacetonate (sacsac) or substituted derivatives form extremely active and highly selective catalysts for the oligomerization of lower olefins when activated by an appropriate co-catalyst. R3' 2The compounds [Ni(sacsac)( PEt,)Cl], [Ni( MeC(S)C(CH 2-CH=CH,)C(S)Me)(PEt,)Cl] and [Ni(sacsac)(PBu,)Cl] have been reported previously and their crystal structures determined. ' '-' ,

Novel polymer-supported β-dithioketonate nickel catalysts for selective propylene dimerization

“…2 Cl (I;R = Cy, X = Cl) was preliminarily checked in propylene oligomerization (Table 1, entry H1). Et 2 AlCl and chlorobenzene were used as co-catalyst and reaction medium, respectively, because they were known to convert propylene to branched olefins with the highest activity and selectivity [7]. Moreover, a molar ratio Al/I = 50, about double that previously described [7], was adopted in order to work under the same conditions as those of the experiments based on the heterogenized catalysts, where an analogous molar ratio Al/anchored nickel was in general used.…”

“…Et 2 AlCl and chlorobenzene were used as co-catalyst and reaction medium, respectively, because they were known to convert propylene to branched olefins with the highest activity and selectivity [7]. Moreover, a molar ratio Al/I = 50, about double that previously described [7], was adopted in order to work under the same conditions as those of the experiments based on the heterogenized catalysts, where an analogous molar ratio Al/anchored nickel was in general used. The catalytic activity was extremely high, a turnover frequency (TF) of 28,000 being obtained much higher (about three times) than that reported in the literature for the same catalyst [7].…”

“…Attempts to heterogenize nickel complexes I by anchoring them to phosphinated crosslinked polystyrenes and silica-alumina were unsatisfactory, because of the drop of catalytic activity [7]. Although the above supported nickel catalysts were claimed [7] to work as heterogeneous systems, this statement was based only on a quite short single recycling experiment.…”

“…Although the above supported nickel catalysts were claimed [7] to work as heterogeneous systems, this statement was based only on a quite short single recycling experiment. Accordingly, the above polymer-bound nickel catalyst showed an extensive metal release when applied to 1-hexene oligomerization at 40°C [12].…”

“…Moreover, catalytic activity and selectivity strictly depend on the nature of X and R groups, the selectivity being mainly affected by the type of the ancillary phosphine ligand [7]. In particular, basic phosphines with bulky substituents lead to a significant enhancement of the selectivity towards DMB.…”