Tautomerism in Bis(oxazoline)s

Abstract

Abstract Bis(oxazoline)s (BOXs) are a privileged ligand class and have found widespread use in catalysis. Herein, the tautomerism of selected BOX ligands was evidenced by X‐ray diffractometry as well as by NMR and IR spectroscopy and supported by DFT calculations. In CDCl 3 solution at room temperature, the new 1,1‐bis(4,4‐dimethyl‐1,3‐oxazolin‐2‐yl)‐1‐phenylmethane ( Ph,H BOX‐Me 2 ) ligand is present as a 1:1 mixture of the diimine and iminoenamine tautomers. Thermodynamic and kinetic data for the tautomeric equilibrium were determined, which allowed comparison with related bidentate ligand classes. The other BOXs studied, H,H BOX‐Me 2 , Me,H BOX‐Me 2 , and t Bu,H BOX‐Me 2 , are largely present in the diimine form under similar conditions. IR spectroscopy was identified as a valuable tool for detecting the presence of the iminoenamine form as a minor component.