Modified catalytic pathways in supported ionic liquids

The interaction of the immobilized complex [Pd(DPPF)(CF₃CO₂)₂] with a thin film of the ionic liquid 1-ethyl-3-methyl-imidazolium chloride supported on SiO₂ was studied by ¹H MAS NMR spectroscopy. Dissolution of the complex in the ionic liquid phase led to the formation of structured solvent cages. The effect of the solvent cages on the catalytic properties of the material was tested for the hydroamination of styrene with aniline, which yielded N-(1-phenylethyl)aniline as Markownikoff product and N-(2-phenylethyl)aniline as anti-Markownikoff product. The chemoselectivity of this system could be tuned over a wide range. The Markownikoff product was obtained under kinetic control, while the anti-Markownikoff product was formed preferentially under thermodynamic control. In another series of experiments, acetophenone was selectively hydrogenated to (S)-1-phenylethanol using [Rh((S)-BINAP)(COD)]ClO₄·thf/K₂CO₃ immobilized in a thin film of a phosphonium based ionic liquid on silica as catalyst. An enantiomeric excess (ee) of up to 74 % was achieved, while only 4 % ee were reported for the same catalyst-substrate pair in methanol. The improved enantioselectivity was attributed to enhancement of the substrate-catalyst interactions, which was caused by the solvent cages. This is an abstract of a paper presented at the 2007 AIChE Annual Meeting (Salt Lake City, UT 11/4-9/2007).