Improved synthesis of Bn<sub>5</sub>CpRu(CO)<sub>2</sub>Cl and its application as racemization catalyst in preparative-scale metalloenzymatic dynamic kinetic resolution of 1-phenylethanol

Mavrynsky, Denys; Kanerva, Liisa T.; Sillanpää, Reijo; Leino, Reko

doi:10.1351/PAC-CON-10-09-05

Pure Appl. Chem., 2011, Vol. 83, No. 3, pp. 479-487

http://dx.doi.org/10.1351/PAC-CON-10-09-05

Published online 2010-12-15

Improved synthesis of Bn₅CpRu(CO)₂Cl and its application as racemization catalyst in preparative-scale metalloenzymatic dynamic kinetic resolution of 1-phenylethanol

Denys Mavrynsky¹, Liisa T. Kanerva²*, Reijo Sillanpää³ and Reko Leino¹*

¹ Laboratory of Organic Chemistry, Åbo Akademi University, 20500 Åbo, Finland
² Laboratory of Synthetic Drug Chemistry and Department of Chemistry, University of Turku, 20014 Turku, Finland
³ Department of Chemistry, University of Jyväskylä, 40351 Jyväskylä, Finland

Abstract: An improved gram-scale synthesis of Bn₅CpRu(CO)₂Cl is reported based on heating of pentabenzylcyclopentadiene with Ru₃(CO)₁₂ at 160 °C under argon atmosphere in mesitylene followed by addition of chloroform, continued heating, and evaporation of the solvents. Subsequent washing of unreacted ligand precursor with hexane provided pure title compound in 77 % yield. In combination with Candida antarctica lipase B (CAL-B) (Novozym 435), this complex forms a highly active racemization catalyst for metallo-enzymatic dynamic kinetic resolution (DKR) of secondary alcohols as demonstrated in the present work by converting 100 g of racemic 1-phenylethanol to (R)-1-phenylethanol in >99 % ee and 93 % overall yield over two steps using 0.05 mol % loading of the metal catalyst and 1 mass % loading of immobilized enzyme. In addition, the synthesis and crystallographic characterization of the palladium congener Bn₅CpPd(PPh₃)Cl are briefly discussed.