2505-03-5Relevant articles and documents
Selective ethylene oligomerization with chromium complexes bearing pyridine-phosphine ligands: Influence of ligand structure on catalytic behavior
Yang, Yun,Gurnham, Joanna,Liu, Boping,Duchateau, Robbert,Gambarotta, Sandro,Korobkov, Ilia
, p. 5749 - 5757 (2015/02/19)
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)PiPr2, 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.
Six- vs seven-membered ring formation from the 1- bicyclo[4.1.0]heptanylmethyl radical: Synthetic and ab initio studies
Kantorowski, Eric J.,Eisenberg, Shawn W. E.,Fink, William H.,Kurth, Mark J.
, p. 570 - 580 (2007/10/03)
The viability of utilizing 1-bicyclo[4.1.0]heptanylmethyl radical (3) to serve as a progenitor of seven-membered carbocycles was examined. Rate constants for the rearrangement of this radical to 3-methylenecycloheptyl radical (4) and 2-methylenecyclohexyl-1-methyl radical (6) were measured using the competition method of 3 with thiophenol over the temperature range of -75 to 59 °C. Arrhenius functions were calculated for the conversions of 3 to 4 and 3 to 6 and found to be log(k/s-1) = (12.38 ± 0.20) - (5.63 ± 0.23)/θ and log(k/s-1) = (11.54 ± 0.32) - (5.26 ± 0.37)/θ, respectively. The rate constants for these conversions at 25 °C are 1.86 x 108 s-1 and 5.11 x 107 s-1, respectively. Hence, the seven-membered ring-expanded carbocycle is formed 3.6 times faster at 25 °C than the nonexpanded species. This suggests that the 1-bicyclo[4.1.0]heptanylmethyl radical system may be synthetically useful in seven-membered ring-forming methodology. Preliminary theoretical examination of this radical system qualitatively predicted the experimentally determined energies of activation: PMP4/6-31G*//HF/6-31G*ΔE(a) (3 → 6 - 3 → 4) = 3.0 kcal/mol with zero point energy correction. The HF/6-31G* optimized reaction coordinate stationary points suggest cyclopropyl substituent eclipsing interactions play an important role in determining the kinetic outcome of these rearrangements.
CLEAVAGE OF (3-CHLORO-2-METHYLENECYCLOALKYL)PALLADIUM CHLORIDE DIMERS: FORMATION OF OLEFINS AND α-METHOXYOLEFINS
Donaldson, William A.
, p. 2901 - 2908 (2007/10/02)
The cleavage of the title compounds (7) in methanolic potassium hydroxide gives mixtures of olefins and α-methoxyolefins in good yields.The ratio of the products is dependent on the size of the carbocyclic ring.The mechanism proposed involves cleavage of 7 to the corresponding allylic chloride (8).Solvolysis of the chloride gives the α-methoxyolefin.Alternatively, oxidative addition of 8 to Pd(O) generates a new ?-allyl complex which affords the olefin product upon subsequent cleavage.
