Ethylene oligomerisation chromium catalysts with unsymmetrical PCNP ligands.

Chromium(iii) complexes of chelating diphosphines, with PNP or PCNCP backbones, are excellent catalysts for ethylene tetra- and/or trimerisations. A missing link within this ligand series are unsymmetric chelating diphosphines based on a PCNP scaffold. New bidentate PCNP ligands of the type Ph2PCH2N(R)PPh2 (R = 1-naphthyl or 5-quinoline groups, 2a-d) have been synthesised and shown to be extremely effective ligands for ethylene tri-/tetramerisations. Three representative tetracarbonyl Cr0 complexes bearing a single PN(R)P (5), PCN(R)P (6), or PCN(R)CP (7) diphosphine (R = 1-naphthyl) have been prepared from Cr(CO)4(η4-nbd) (nbd = norbornadiene). Furthermore we report a single crystal X-ray diffraction study of these compounds and discuss their structural parameters.

N,N-Bis(diphenyl-phosphino)-1,2-dimethyl-propyl-amine.

The diphenyl-phosphine groups in the title compound, C(29)H(31)NP(2), are staggered relative to the PNP backbone. The N atom adopts an almost planar geometry with the two P atoms and the C atom attached to it, in order to accommodate the steric bulk of the phenyl groups and the alkyl group. Three C atoms of the 1,2-dimethylpropylamine group are disordered over two positions in a 9:1 ratio. The mol-ecules pack diagonally in the unit cell across the ac plane in a head-to-tail fashion.

Mechanistic investigations of the ethylene tetramerisation reaction.

The unprecedented selective tetramerisation of ethylene to 1-octene was recently reported. In the present study various mechanistic aspects of this novel transformation were investigated. The unusually high 1-octene selectivity in chromium-catalyzed ethylene tetramerisation reactions is caused by the unique extended metallacyclic mechanism in operation. Both 1-octene and higher 1-alkenes are formed by further ethylene insertion into a metallacycloheptane intermediate, whereas 1-hexene is formed by elimination from this species as in other reported trimerisation reactions. This is supported by deuterium labeling studies, analysis of the molar distribution of 1-alkene products, and identification of secondary co-oligomerization reaction products. In addition, the formation of two C6 cyclic products, methylenecyclopentane and methylcyclopentane, is discussed, and a bimetallic disproportionation mechanism to account for the available data is proposed.

Highly functionalised cyclobutanols via samarium(II) iodide-induced pinacol cyclisations of carbohydrate-derived 1,4-diketones.

D-Ribofuranose and D-arabinofuranose derivatives were converted in a few steps into their 1,4-diketone derivatives, which were pinacol cyclised under the action of SmI2 to form the corresponding chiral cyclobutanediol products. These products can potentially be applied to the synthesis of anti-viral agents, some of whose structures incorporate chiral cyclobutanediol moieties.

Highly selective chromium-based ethylene trimerisation catalysts with bulky diphosphinoamine ligands.

In situ prepared chromium catalysts containing bulky diphosphinoamine (PNP) ligands, upon activation with MAO, are extremely efficient catalysts for the trimerisation of ethylene to 1-hexene.

Ethylene trimerisation and tetramerisation catalysts with polar-substituted diphosphinoamine ligands.

Chromium-based catalyst systems with polar-substituted diphosphinoamine ligands are selective for either trimerisation or tetramerisation of ethylene, depending on the position of the polar groups on the aryl rings.

Ethylene tetramerization: a new route to produce 1-octene in exceptionally high selectivities.

Linear alpha-olefins, such as 1-hexene and 1-octene, are important comonomers in the production of linear low-density polyethylene (LLDPE). The conventional method of producing 1-hexene and 1-octene is by oligomerization of ethylene, which yields a wide spectrum of linear alpha-olefins (LAOs). While there exists several processes for producing 1-hexene via ethylene trimerization, a similar route for the selective production of 1-octene has so far been elusive. We now, for the first time, report an unprecedented ethylene tetramerization reaction that produces 1-octene in selectivities exceeding 70%, using an aluminoxane-activated chromium/((R2)2P)2NR1 catalyst system.