Electrostatically immobilised BOX and PYBOX metal catalysts: application to ene reactions

Copper(I), copper(II) and scandium(III) triflate complexes of BOX and PYBOX ligands have been electrostatically immobilised on silica. The performance of the immobilised catalysts, in the two carbonyl-ene reactions studied, compares very well with that of their homogeneous equivalents. The immobilised catalysts were successfully reused a number of times. In the case of a scandium complex, a variation in enantioselectivity of up to 73% was observed on immobilisation compared to its use homogeneously. The reason for this variation in enantioselectivity is explored with the aid of molecular modelling.