Sulfoxygenation Catalysed by Oxidovanadium Complexes

Model complexes of vanadate‐dependent peroxidases, viz. oxidovanadium(V) complexes of the general composition [VO(H n – x L)], have been prepared and characterised. H n L is an n‐basic di‐ or trichiral aminodiethanol [HOCH(Ph)CH 2 ] 2 NR, with R = N ‐methylimidazolyl (H 2 L A ), tris(hydroxymethyl)methyl (H 5 L B , 2 isomers), 2,3‐dihydroxypropyl (H 4 L C , 2 isomers) and 2‐hydroxy‐3‐trityloxypropyl (H 3 L D ). These ligands form the complexes [VO(OH)(L A )], [VO(H 2 L B )], trigonal‐bipyramidal [VO(HL C )] tbp and octahedral Λ‐[VO(HL C )] oct . The ligands R , R , S ‐H 4 L C and R , R , R ‐H 3 L D , and the complexes Λ‐[VO( R , R , S ‐HL C )] oct and [VO( R , R , S ‐HL C )] tbp have been characterised by X‐ray structure analysis. The complexes [VO(H 2 L B )] and [VO(HL C )] were immobilised on Merrifield and Barlos resin by anchoring through a free alcoholic group in the ligand side‐chain R. {[VO(H 2 O)L E ]}, an oxidovanadium(IV) complex tethered to Merrifield resin, was prepared by treating [VO(acac) 2 ] with {HL E }, the immobilised Schiff base ligand obtained by condensation of salicylaldehyde with resin‐anchored lysine. The complexes and in situ systems ([VO(O i Pr) 3 ] + ligand) as well as the immobilised complexes were investigated for their catalytic activity in the oxygenation, by cumyl hydroperoxide, of thioanisol to its sulfoxide. All of the systems were active, with a selectivity (sulfoxide vs. sulfone) of 95–98 %. Satisfactory turnover rates and a chiral induction up to 37 % ee were observed.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)