Study of the Efficiency of Amino-Functionalized Ruthenium and Ruthenacycle Complexes as Racemization Catalysts in the Dynamic Kinetic Resolution of 1-Phenylethanol

The ruthenium‐amino structural motif in ruthenacycles and aminomethylpyridine ruthenium complexes turned out to be a useful basis for the design of readily accessible and active catalysts for the racemization of alcohols. Inspired by the proven ligand acceleration of 2‐aminomethylpyridine (ampy) ligands in ruthenium‐catalyzed hydrogen transfer, the readily accessible ampy‐based oxazolines 8a and 8b were tested and led to novel and active ruthenium racemization catalysts. The highly active ortho‐metalated‐ampy Ru complex 7 was demonstrated to be a fast racemization catalyst (100 % racemization of 1‐phenylethanol at 70 °C within 10 min). When used in the dynamic kinetic resolution of 1‐phenylethanol towards 1‐phenylethyl acetate, the cycloruthenated amine 5 was most active, leading to 86 % of the (R)‐1‐phenylethylacetate with>99 % ee.