Rhodium‐Catalyzed ON‐OFF Switchable Hydrogenation Using a Molecular Shuttle Based on a [2]Rotaxane with a Phosphine Ligand. Issue 15 (19th February 2022)

• Record Type: Journal Article
• Authors: Tang, Yu‐Ping; Luo, Yi‐Er; Xiang, Jun‐Feng; He, Yan‐Mei; Fan, Qing‐Hua
• Is Part Of: Angewandte Chemie international edition. Volume 61:Issue 15(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-02-19
• Subjects: Hydrogenation -- Molecular Shuttles -- P Ligands -- Rotaxanes -- Switchable Catalysis; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.202200638
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: A novel pH‐responsive molecular shuttle based on a [2]rotaxane with a phosphine ligand has been designed and synthesized. In the rhodium‐catalyzed hydrogenation of α, β‐dehydroamino acid esters and aryl enamides, ON/OFF‐switchable catalysis was accomplished with high ON/OFF ratios by adjusting the movements of the rotaxane wheels located at the catalyst terminals with acid/base. Mechanistic studies using NMR spectroscopy and quasi in situ X‐ray photoelectron spectroscopy revealed that Rh III ‐hydride species are possibly formed in a H2 atmosphere when the catalyst is in the OFF state. During the reaction, a heterolytic activation of dihydrogen occurs by the interlocked rotaxane dibenzylamine and Rh I catalytic center acting as a frustrated Lewis pair. Subsequent homolytic splitting of dihydrogen with the newly formed Rh I ‐hydride species generates Rh III ‐hydride species. These findings show that a substrate‐selective hydrogenation can be achieved by using the OFF‐state catalyst. Abstract : A molecular shuttle based on a [2]rotaxane with a phosphine ligand has been applied to the rhodium‐catalyzed hydrogenation of α, β‐dehydroamino acid esters and aryl enamides. The hydrogenation can be switched ON/OFF efficiently by adjusting the movement of the rotaxane wheels with acid/base. Mechanistic studies have revealed that the formation of inactive Rh III ‐hydride species might be the reason for shutdown of the reaction.