Mixture Of 1-hexene Research Articles

Isolation and Characterization of a Class II Mixed-Valence Chromium(I)/(II) Self-Activating Ethylene Trimerization Catalyst

Reduction of the tetranuclear {((t-Bu)NPPh2)- Cr(μ-(t-Bu)NPPh2)2Cr}2(μ-Cl)2 (1) with either KC8 or vinyl Grignard afforded the dinuclear, mixed-valence (Me3P)Cr(μ- (t-Bu)NPPh2)3Cr (2) with the two metals possessing distinctively different coordination environments. According to the formulation of 2 as Cr(I)/Cr(II) mixed-valence species, 2 acts as a self-activating catalyst, producing under pressure of ethylene a mixture of 1-butene and 1-hexene. Activation with three different activators selectively produced three different products, namely, 1-butene with TEAL, 1-hexene with DMAO/TEAL, and LAO-free highly linear HMWPE with DMAO. Mixtures of 1-hexene and 1-butene were also obtained upon activation with vinyl Grignard. In this case it was possible to isolate, albeit in very low yield, an intriguing butadiene/butadiene-diyl cluster, {((η 4 -butadiene)Cr (μ,η 4 -butadienediyl)(μ- NP)Mg)2(μ-Cl)4Mg(THF)2}{((THF)3Mg)2(μ-Cl)3}2 (3), which is also a highly selective self-activating trimerization catalyst.

N-substituted diphosphinoamines: Toward rational ligand design for the efficient tetramerization of ethylene

Bis(diphenylphosphino)amine (PNP) ligands with different alkyl and cycloalkyl substituents attached to the N atom of the ligand backbone were synthesised and tested together with chromium as ethylene tetramerization catalysts. On activation with a methylaluminoxane-based activator, the catalysts displayed good activity and selectivity toward 1-octene and 1-hexene, with the best ligand systems containing cyclopentyl or cyclohexyl moieties. In addition, it was established that substitution at the 2 position of the cyclohexyl skeleton and, more importantly, an increase in steric bulk at that point, led to a drastic reduction of side product formation (i.e., methyl- and methylenecyclopentane). Interestingly, additional methyl substitution in the 6 position of the cyclohexyl ring changed the selectivity of the catalyst from predominantly tetramerization to a 1:1 mixture of 1-hexene and 1-octene. Structurally similar ligands, such as cyclohexylmethyl and cyclohexylethyl PNP, were also tested and were also found to yield efficient tetramerization catalysts. It was concluded that structural fine tuning of the N-alkyl moiety of the PNP ligand is essential for obtaining efficient tetramerization catalysts, with the best systems achieving combined selectivities as high as 88% (1-octene and 1-hexene) with exceptionally high activities exceeding 2,000,000 g/(g-Cr h).