Aryloxide ligands in metathesis of olefins and olefinic esters: catalytic behaviour of W(OAr)2Cl4 complexes associated with alkyl-tin or alkyl-lead cocatalysts; alkylation of...

Abstract

Title full: Aryloxide ligands in metathesis of olefins and olefinic esters: catalytic behaviour of W(OAr)2Cl4 complexes associated with alkyl-tin or alkyl-lead cocatalysts; alkylation of W(OAr)2Cl4 by SnMe4, Sn(n-Bu)4, Pb(n-Bu)4, MgNp2: synthesis of W(OAr)2Cl2(CHCMe3)(OR2) and W(OAr)2Cl(CHCMe3)(CH2CMe3)(O R2). Metathesis of internal and terminal olefins, as well as olefinic esters, can be achieved with the complexes W(OAr)2Cl4 (OAr = O-2,6-C6H3Me2, O-2,6-C6H3(C6H5)2 , O-2,6-C6H3Br2, O-2,6-C6H3Cl2 and O-2,6-C6H3F2) associated with MR4 (M = Sn, Pb; R = Me, n-Bu). For cis-2-pentene metathesis, many parameters play a role in the activity: the electron-withdrawing property of the aryloxide ligand, the nature of the cocatalyst and the time of interaction between the precursor and the cocatalyst. For a given cocatalyst and a given time of interaction, the activity varies with the nature of the substituent in o,o'-position on the aryloxide (X = CH3 < C6H5 < F < Cl < Sn(n-Bu)4 < Pb(n-Bu)4. For a given catalyst and cocatalyst, there is an optimum time of interaction before introducing the olefin. The decline of activity which is observed if the olefin is introduced after this optimum value can be sup-pressed if diethyl ether is added. The stereochemical results obtained with W(OAr)2Cl2 and Pb(n-Bu)4 show an increase of the stereoselectivity with the nature of the aryloxide substituents in the following order F {reversed tilde equals} Cl