Models of Vanadate-dependent Peroxidases and Their Properties in Catalytic Sulfoxidation

Abstract

The present work addresses the synthesis and characterization of oxidovanadium(V) complexes which are structural and functional models, for the sulfoxigenation reaction, of the active centers of the VHPOs. Suitable model complexes have been obtained with ligands derived from chiral aminodiethanols.

Reaction of the ligands with VO(OiPr)3 yields complexes. The coordination geometries attained by the complexes are distorted trigonal-bipyramidal, ideally trigonal-bipyramidal or octahedral.

Additional complex systems have been prepared by aggregation of carbasilatranes, followed by reaction with the vanadium precursor, and by immobilization on silica gel, Merrifield and Barlos resins.

Catalytically conducted reactions have been carried out in homogenous systems, using the complexes or mixtures of the ligand and VO(OiPr)3 (“in situ“), or – with the aggregated and immobilized complexes – under heterogeneous conditions. All of the systems investigated are catalytically active in the sulfoxigenation of methylphenylsulfide by cumylhydroperoxide in chlorinated hydrocarbons. As evidenced by 51V NMR, the active catalyst is a peroxido intermediate. The turn-over rate, selectivity and enantiomeric excess vary with the systems under investigation and the reaction conditions such as temperature. While the chirality (R) of the catalyst system is commonly induced upon the product under homogeneous reaction conditions (R-sulfoxide), chiral conversion occurs in the heterogeneous systems (S-sulfoxide).