A new series of iron catalysts bearing tridentate pyridine−bis(imine) ligands are reported for the isospecific polymerization of propylene (PP). The catalytic activities are moderate, with maximum ...activities exceeding 1600 kg PP/mol Fe h under 1 atm of propylene pressure at −20 °C . End-group analyses of the resultant materials are performed and indicate that the polymerization proceeds via a 2,1 mechanism of propagation leading to the exclusive formation of 1-propenyl end groups following β-H elimination/abstraction and chain transfer. The polymers are highly regioregular, but the regioregularity decreases with decreasing steric bulk of the tridentate ligands. Isotacticities are determined for a number of catalysts bearing ligands with variable ortho substituent patterns and symmetries. In all cases, isotactic material is obtained; the m4 methyl pentad content is always in the range of 55−67%. 13C NMR spectroscopy is used to demonstrate that the isotacticity arises from a chain-end control mechanism. These catalysts represent the first isospecific systems known to operate by a 2,1 mechanism of propagation.
Kinetics for the reaction between 1-tetradecene and heptanoic acid to make tetradecyl heptanoates on dry Amberlyst
®
15 catalyst at 90 °C are extremely complex. Observed kinetics of simultaneous ...double bond isomerization and esterification cannot be reconciled with a single type of catalytic site. Esterification and
most
of the double bond isomerization must occur on separate sites. Relative rates of esterification for tetradecene isomers suggest that adsorption coefficients on the esterification sites follow 1-tetradecene > 2-tetradecene > 3+-tetradecenes. These relative adsorption coefficients imply that, on this esterification site, 2-tetradecene isomerizes to 3-tetradecene faster than 3-tetradecene isomerizes to 2-tetradecene or 4-tetradecene, a truly novel finding not previously reported for any other acidic site. The site where most of the double bond isomerization occurs does not display this behavior, and isomerization of linear tetradecenes proceeds to thermodynamic equilibrium. Kinetic data indicate that esters form when carboxylic acid traps rapidly isomerizing carbenium ions on the catalyst’s surface. Competition is fierce for esterification sites among olefins, carboxylic acid, and esters, and olefins occupy few esterification sites. Contrastingly, olefins triumph in competition for isomerization sites, and olefin isomerization is much faster than esterification. Heptanoic acid exists primarily in dimer form, but the monomer form reacts to make esters. A complex kinetic model fit experimental data for double bond isomerization, conversion of olefin to esters, and the distribution of secondary esters that formed over 22 h.
Graphic abstract
A family of chromium complexes bearing tridentate pyridine-based ligands are disclosed as highly active precatalysts for the oligomerization of ethylene. The ligands are comprised of two distinct ...types: Type 1, in which both ketone groups of 2,6-diacetylpyridine are converted to imines to produce pyridine bisimine NNN ligands; and Type 2, in which only one ketone group of 2,6-diacetylpyridine is condensed with an aniline derivative to give monoimine NNO coordination sets. Ligands of either type are coordinated to chromium(II) or chromium(III) chlorides, and activation of the resultant complexes with methylaluminoxane (MAO) produces highly active ethylene oligomerization and polymerization catalysts. Catalysts of Type 1 (NNN set) generally produce 1-butene when only two ortho alkyl substituents are present but switch to making waxes or polyethylene when the size and/or number of ortho substituents are increased. Catalysts of Type 2 (NNO set) produce waxes and polyethylene under all of the substitution patterns studied. The butene-producing catalysts can make 1-butene with 99.5+% purity, and the wax-producing catalysts make highly linear to moderately branched waxes, depending on the presence of an α-olefin comonomer.
Upon activation with modified methylalumoxane (MMAO), tridentate pyridine bisimine cobalt catalysts dimerize α-olefins with lower productivity than analagous iron systems, as indicated by comparing ...the batch dimerization of 1-butene (TON ∼42 000 for Co, ∼147 000 for Fe). The cobalt-produced dimers are extremely linear (>97%) and contain only traces of trimeric species. The cobalt catalysts also have a tendency to isomerize α-olefins, as evidenced by the approximately equal levels of dimerization and isomerization achieved when 1-butene is dimerized. When the cocatalyst is changed to diethylaluminum chloride, isomerization occurs exclusively to give cis- and trans-2-olefins selectively. To mitigate the effects of feed isomerization, dimerization of propylene was also studied. GC analysis of the products reveals a stepwise oligomerization process that makes linear hexenes, nonenes, and dodecenes, with the hexenes comprising up to 70% of the product mix. The hexenes are over 99% linear and may contain over 50% 1-hexene. Catalyst productivity is high, with turnover numbers exceeding 200 000 mol propylene/mol Co (17 000 g oligomers/g Co complex).
Stoichiometric Schiff base condensations of sterically bulky primary amines with acenaphthenequinone yield isolable monoimines. In the presence of iron(II) chloride, the remaining ketone reacts with ...a second primary amine bearing a pendant donor atom to give asymmetric, tridentate, α-diimine complexes that possess remarkable structural variability. A series of NNP and NNS tridentate iron(II) complexes are prepared; these coordination compounds become active catalysts for ethylene oligomerization when activated with methylalumoxanes. X-ray crystallographic studies of the precatalyst complexes confirm that the ligand binds in a tridentate fashion. Correlations between the precatalyst solid-state structures and catalyst activity and α-olefin product distribution are explored.
Stoichiometric Schiff base condensations of sterically bulky primary amines with acenaphthenequinone yield isolable monoimines. In the presence of Fe or other transition metals, the remaining ketone ...reacts with a second primary amine bearing a pendent donor atom to give asymmetric, tridentate, α-diimine complexes. Upon activation with alumoxanes, these complexes are highly active for the oligomerization of ethylene to linear α-olefins, with turnover numbers (TONs) exceeding 2.5 × 106 mol ethylene/mol Fe. Product purities are high, with 1-hexene and 1-octene exceeding 99% purity in most examples.
Selective tetramerization of ethylene to produce 1-octene may be viewed as an extension of the well-studied process for ethylene trimerization to form 1-hexene, which is commercially practiced by ...Chevron Phillips Chemical (CPChem) and others. The tetramerization reaction was first reported by researchers at SASOL in 2004, but CPChem and others have also reported proprietary systems. Tetramerization reactions are always coupled with some degree of 1-hexene formation, with 1-octene:1-hexene ratios typically varying from 1:2 to 4:1. These mixtures imply the intertwining of the tetramerization and trimerization catalytic cycles, and the primary products are always formed with two types of coproducts. These coproducts include cotrimer and cotetramer C10–C14 species resulting from product reincorporation, as well as other byproducts ranging from C2 species to waxes, and various cyclic hydrocarbons. Gas chromatography (GC) is used to deconvolute these overlapping catalytic cycles, and a model for using GC data to explain the ethylene efficiency in each cycle is presented.
A series of pyridine bis-imine iron catalysts previously reported for the oligomerization of ethylene and propylene are now reported as active catalysts for the dimerization of α-olefins to make ...linear internal olefins. The dimers possess up to 80% linearity, depending on the catalyst structure and the reaction conditions. The dimer byproducts consist almost exclusively of methyl-branched species and only traces of vinylidene (2-alkylalkene), trisubstituted, or α-olefin products. The linear dimers are formed by a unique mechanism that precludes the formation of multiple dimer products. The dimer content is verified by hydrogenation, which produces only a linear paraffin and a methyl-branched paraffin upon GC analysis. The dimer composition is also verified by 1H NMR, which shows >95% disubstituted internal olefin and less than 5% total vinylidene and trisubstituted olefin. Observations regarding the dimer structures are used to elucidate the structures of the branched α-olefin (BAO) byproducts that are made when ethylene is oligomerized by the same catalysts.
PDF
