Functional modeling of alcoholdehydrogenase with pyrazolylborate–zinc complexes

Unlike free isopropanol, the complex TpCum,MeZn–OCHMe2 (TpCum,Me=tris(3-cumenyl-5-methylpyrazolyl)borate) is oxidized by N-benzylnicotinamide chloride to acetone and TpCum,MeZn–Cl in small yield. The stronger oxidant 2,3-dichloro-5,6-dicyanobenzoquinone oxidizes TpCum,MeZn–phenolates with o-hydroxymethyl substituents to the corresponding zinc phenolates with o-formyl substituents. Benzaldehydes with electronegative substituents (F, NO2, CF3) are reduced by N-benzyldihydronicotinamide in the presence of TpCum,MeZn–OH to the corresponding benzyl alcohols which are isolated as TpCum,MeZn–OCH2Ar. A kinetic analysis has shown that the reduction of the aldehydes alone is roughly two times slower than that in the presence of the zinc complex.