PtII‐Catalyzed Hydroxylation of Terminal Aliphatic C(sp3)−H Bonds with Molecular Oxygen. Issue 45 (9th July 2019)

• Record Type: Journal Article
• Authors: Janssen, Michiel; De Vos, Dirk E.
• Is Part Of: Chemistry. Volume 25:Issue 45(2019)
• Page Start: 10724
• Page End: 10734
• Publication Date: 2019-07-09
• Subjects: C−H activation -- hydroxylation -- molecular oxygen -- platinum -- primary C−H bonds; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201901803
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: The practical application of Shilov‐type Pt catalysis to the selective hydroxylation of terminal aliphatic C−H bonds remains a formidable challenge, due to difficulties in replacing Pt IV with a more economically viable oxidant, particularly O2 . We report the potential of employing FeCl2 as a suitable redox mediator to overcome the kinetic hurdles related to the direct use of O2 in the Pt reoxidation. For the selective conversion of butyric acid to γ‐hydroxybutyric acid (GHB), a significantly enhanced catalyst activity and stability (turnover numbers (TON)>30) were achieved under 20 bar O2 in comparison to current state‐of‐the‐art systems (TON<10). In this regard, essential reaction parameters affecting the overall activity were identified, along with specific additives to attain catalyst stability at longer reaction times. Notably, deactivation by reduction to Pt 0 was prevented by the addition of monodentate pyridine derivatives, such as 2‐fluoropyridine, but also by introducing varying partial pressures of N2 in the gaseous atmosphere. Finally, stability tests revealed the involvement of Pt II and FeCl2 in catalyzing the non‐selective overoxidation of GHB. Accordingly, in situ esterification with boric acid proved to be a suitable strategy to maintain enhanced selectivities at much higher conversions (TON>60). Altogether, a useful catalytic system for the selective hydroxylation of primary aliphatic C−H bonds with O2 is presented. Abstract : Shilov chemistry, a means to an end : Through the implementation of FeCl2 as suitable redox mediator, a highly active and durable Pt‐based system (TON>60, TOF>10 h −1 ) has been developed that uses O2 as an economically viable and readily available oxidant for the site‐selective hydroxylation of terminal aliphatic C−H bonds.