Minimizing side reactions in chemoenzymatic dynamic kinetic resolution: organometallic and material strategiesThis paper is dedicated to Prof. David J. Cole-Hamilton on occasion of his retirement in celebration of his distinguished (and ongoing) contribution to transition metal catalysis, and his role in introducing ACM to organometallic chemistry for homogeneous catalysis, his enthusiasm was truly infectious

Chemoenzymatic dynamic kinetic resolution (DKR) of rac -1-phenyl ethanol into R -1-phenylethanol acetate was investigated with emphasis on the minimization of side reactions. The organometallic hydrogen transfer (racemization) catalyst was varied, and this was observed to alter the rate and extent of oxidation of the alcohol to form ketone side products. The performance of highly active catalyst [(pentamethylcyclopentadienyl)IrCl 2 (1-benzyl,3-methyl-imidazol-2-ylidene)] was found to depend on the batch of lipase B used. The interaction between the bio- and chemo-catalysts was reduced by employing physical entrapment of the enzyme in silica using a solgel process. The nature of the gelation method was found to be important, with an alkaline method preferred, as an acidic method was found to initiate a further side reaction, the acid catalyzed dehydration of the secondary alcohol. The acidic gel was found to be a heterogeneous solid acid. Strategies for reducing the side-reactions of chemoenzymatic DKR: tuning the organometallic catalyst and entrapping the biocatalyst.