The metathesis of polyunsaturated fatty esters using the homogeneousW(O-2,6-C<inf>6</inf>H<inf>3</inf>X<inf>2</inf>)<inf>2</inf>Cl <inf>4</inf>/Me<inf>4</inf>Sn catalytic systems

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. © 2003 Elsevier B.V. All rights reserved.