- The metathesis of polyunsaturated fatty esters using the homogeneousW(O-2,6-C6H3X2)2Cl 4/Me4Sn catalytic systems
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Promoted with a small amount of Me4Sn, W(O-2,6-C 6H3X2)2Cl4 (X=Ph, Cl) complexes are highly active metathesis catalysts for polyunsaturated fatty esters. Upon metathesis of methyl linoleate, substrate conversions of ca. 95 and 78% were obtained in 2h with the W(O-2,6-C6H3Ph 2)2Cl4/Me4Sn and W(O-2,6-C 6H3Cl2)2Cl4/Me 4Sn catalytic systems respectively. The lower activity of the W(O-2,6-C6H3Cl2)2Cl 4/Me4Sn catalytic system was attributed to the highly deactivating nature of the Cl substituents on the o,o′-position of the aryloxide ligand. Highly electron-withdrawing Cl substituents cause the tungsten atom to be electron-deficient and thus more susceptible to attack by the electron-rich ester groups. However, the W(O-2,6-C6H 3Cl2)2Cl4/Me4Sn system was more selective towards dicarboxylic esters. The latter are interesting starting materials for the synthesis of polyesters and polyamides. The W(O-2,6-C6H3X2)2Cl 4/Me4Sn catalytic systems were rapidly deactivated by bromine-containing olefinic esters. Deactivation was attributed to a side reaction between the Br-group and the electron-deficient W-centre.
- Marvey,Du Plessis,Vosloo
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p. 151 - 157
(2008/10/09)
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- W(O-2,6-C6H3X2)2Cl4/Bu4Sn as metathesis catalyst of 1-alkenes
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Tungsten compounds with aryloxo ligands, i.e., W(O-2,6-C6H3X2)2Cl4 (X = Cl, Ph) and Bu4Sn, were investigated as catalytic systems for the metathesis of 1-alkenes of varying carbon lenghts. The catalytic system was activated at 85°C for 20 min prior to use. Optimum metathesis activity with 1-alkenes was observed at 85°C and a Sn/W molar ratio = 3. The W(O-2,6-C6H3X2)2Cl4/Bu4Sn catalytic system is very active for the metathesis of 1-alkenes with a carbon chain length of about six to eight and it favours a more polar solvent such as chlorobenzene.
- Van Schalkwyk,Vosloo,Du Plessis
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p. 167 - 173
(2008/10/09)
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- Aryloxide ligands in the metathesis of olefins: Syntheses of W(OAr)xCl6-x complexes with x = 2, 3, and 4. Crystal structures of W(O-2,6-C6H3-i-Pr2)3Cl3 and W(O-2,6-C6H3Ph2)2Cl4
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Syntheses and characterization of three families of aryloxide complexes of W(VI), which are useful precursors for metathesis of olefins, are reported: W(OAr)x(Cl)6-x (x = 2, 3, 4). The structures of Cl3W(O-2,6-C6H3-i-Pr2)3 and Cl4W(O-2,6-C6H3Ph2)2 are described. Both complexes have slightly distorted octahedral coordination spheres. For the structure of Cl3W(O-2,6-C6H3-i-Pr2)3, the chlorines occupy the meridional sites, while in the case of Cl4W(O-2,6-C6H3Ph2)2, the OC6H3Ph2 groups are cis to each other. Crystal data for Cl3W(O-2,6-C6H3-i-Pr2)3: space group P21/n, monoclinic, a = 13.446 (2) ?, b = 17.824 (4) ?, c = 16.289 (3) ?, β = 99.55 (1)°, V = 3851 ?3, mol wt 882.02, ρcalcd = 1.418 g cm-3 for Z = 4. For Mo Kα 7164 unique reflections were collected at 298 K over the range 4° ≤ 20 ≤ 50° with 5582 reflections > 3σ(I) used in the final refinement. RF = 0.023 and RwF = 0.031. Crystal data for Cl4W(O-2,6-C6H3Ph2) 2·1/2C7H8: space group P1, triclinic, a = 10.547 (3) ?, b = 13.669 (1) ?, c = 14.632 (1) ?, α = 84.89 (2)°, β = 78.34 (1)°, γ = 83.48 (2)°, V = 2062 ?3, mol wt 816.26, ρcalcd = 1.317 g cm-3 for Z = 2. For Mo Kα 2915 reflections were collected at 298 K over the range 4° ≤ 2θ ≤ 40° with 2588 reflections ≥3σ(I) used in the final refinement. RF = 0.058 and RwF = 0.094.
- Quignard, Francoise,Leconte, Michel,Basset, Jean-Marie,Hsu, Leh-Yeh,Alexander, John J.,Shore, Sheldon G.
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p. 4272 - 4277
(2008/10/08)
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