Aminophosphine-Based Chromium Catalysts for Selective Ethylene Tetramerization

Chromium complexes of three new ligands, Ph₂PN­(Me)­(CH₂)₂-X [X = NMe₂ <b>(PNN</b>); PPh₂ (<b>PNP</b>); Py <b>(PNPy</b>)], have been examined vis-à-vis their ability to promote ethylene tetramerization, (PNN)­CrCl₃(L) [L = THF (<b>1</b>); CH₃CN (<b>2</b>)], (PNPy)­CrCl₃(L) [L = THF (<b>3</b>); CH₃CN (<b>4</b>)], and (PNP)­CrCl₃(THF) (<b>5</b>). In the case of <b>2</b> and <b>4</b>, it was possible to grow crystals suitable for X-ray diffraction. The reaction of <b>3</b> with Et₃Al afforded the dinuclear [(HN­(Me)­(CH₂)₂Py)­CrCl₂Et]₂ (<b>6</b>) containing a trivalent chromium connected to an Et group. During the alkylation though, the ligand has been fragmented with removal of the side arm and protonation of the N atom of the remaining NP residue. All the complexes have been tested for ethylene oligomerization activity. Complex <b>1</b> displayed the highest selectivity for 1-octene, upon activation with DMAO in MeCy. Contrary to expectations, complex <b>6</b> is not a self-activating catalyst

Aminophosphine-Based Chromium Catalysts for Selective Ethylene Tetramerization

Chromium complexes of three new ligands, Ph₂PN­(Me)­(CH₂)₂-X [X = NMe₂ <b>(PNN</b>); PPh₂ (<b>PNP</b>); Py <b>(PNPy</b>)], have been examined vis-à-vis their ability to promote ethylene tetramerization, (PNN)­CrCl₃(L) [L = THF (<b>1</b>); CH₃CN (<b>2</b>)], (PNPy)­CrCl₃(L) [L = THF (<b>3</b>); CH₃CN (<b>4</b>)], and (PNP)­CrCl₃(THF) (<b>5</b>). In the case of <b>2</b> and <b>4</b>, it was possible to grow crystals suitable for X-ray diffraction. The reaction of <b>3</b> with Et₃Al afforded the dinuclear [(HN­(Me)­(CH₂)₂Py)­CrCl₂Et]₂ (<b>6</b>) containing a trivalent chromium connected to an Et group. During the alkylation though, the ligand has been fragmented with removal of the side arm and protonation of the N atom of the remaining NP residue. All the complexes have been tested for ethylene oligomerization activity. Complex <b>1</b> displayed the highest selectivity for 1-octene, upon activation with DMAO in MeCy. Contrary to expectations, complex <b>6</b> is not a self-activating catalyst

Chromium-Catalyzed CO₂–Epoxide Copolymerization

Iminopyrrole, aminopyrrole, and aminophosphine ligands were complexed with various chromium sources, producing eight complexes that were tested for their catalytic behavior toward epoxide–CO₂ copolymerization. As elucidated by MALDI-TOF-MS, copolymerizations afforded polycarbonates and poly­(ether-carbonates) exhibiting linear or cyclic topologies

Chromium-Catalyzed CO₂–Epoxide Copolymerization

Iminopyrrole, aminopyrrole, and aminophosphine ligands were complexed with various chromium sources, producing eight complexes that were tested for their catalytic behavior toward epoxide–CO₂ copolymerization. As elucidated by MALDI-TOF-MS, copolymerizations afforded polycarbonates and poly­(ether-carbonates) exhibiting linear or cyclic topologies

Selective Ethylene Oligomerization with Chromium Complexes Bearing Pyridine–Phosphine Ligands: Influence of Ligand Structure on Catalytic Behavior

Chromium complexes bearing a series of pyridine–phosphine ligands have been synthesized and examined for their catalytic behavior in ethylene oligomerization. The choice of solvent, toluene versus methylcyclohexane, shows a pronounced influence on the catalytic activity for all these complexes. Variations of the ligand system have been introduced by modifying the phosphine substituents affecting ligand bite angles and flexibility. It has been demonstrated that minor differences in the ligand structure can result in remarkable changes not only in catalytic activity but also in selectivity toward α-olefins versus polyethylene and distribution of oligomeric products. Ligand PyCH₂N­(Me)­P^<i>i</i>Pr₂, in combination with CrCl₃(THF)₃ afforded selective ethylene tri- and tetramerization, giving 1-hexene and 1-octene with good overall selectivity and high purity, albeit with the presence of small amounts of PE