In this work, we study the potential catalytic role of previously identified Mn(I)-PNN complexes in the Claisen–Tishchenko reaction. An in-depth investigation of the reaction mechanism suggests that, after activation of the 16e pre-catalyst, a hydrogenated 18e active species is generated. Based on calculations, rate-limiting barriers in a range of ca. 15–20 kcal mol−1 are seen for a model process consisting in the esterification of acetaldehyde into ethyl acetate at 100 °C and 1 atm reaction conditions (in toluene solution). Our hypothesis is centred on the role of the Mn centre as the only active site involved in both elementary steps, namely hydride borrowing and C–O bond formation. During this C–O bond formation step, diastereoisomers (RN,R) and (RN,S) [or their enantiomeric pairs (SN,S) and (SN,R)] can be generated, with calculations showing a preference towards the (RN,R) pathway.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: This research has been supported by the King Abdullah University of Science and Technology (KAUST). Gratitude is also due to the KAUST Supercomputing Laboratory using the supercomputer Shaheen II for providing the computational resources. LMA is an ULPGC Postdoc Fellow, and thanks Universidad de Las Palmas de Gran Canaria (ULPGC). LMA also acknowledges the Scientific Committee of ESPA 2018 Conference for selecting him as speaker.