A new mechanism of metal-ligand cooperative catalysis in transfer hydrogenation of ketones. (15th May 2020)

• Record Type: Journal Article
• Authors: Demianets, Ivan; Cherepakhin, Valeriy; Maertens, Alexander; Lauridsen, Paul J.; Mallikarjun Sharada, Shaama; Williams, Travis J.
• Is Part Of: Polyhedron. Volume 182(2020)
• Publication Date: 2020-05-15
• Subjects: Ketone -- Alcohol -- Iridium -- Transfer hydrogenation -- Metal hydride; Chemistry, Inorganic -- Periodicals; Chimie inorganique -- Périodiques; Organometaalverbindingen; Anorganische chemie; 546.05
• DOI: 10.1016/j.poly.2020.114508
• Languages: English
• ISSNs: 0277-5387

Abstract

Graphical abstract: We report a new metal-ligand cooperative mechanism for transfer hydrogenation of ketones with alcohols enabled by iridium catalysts 1-Me and 1-F . The reaction proceeds through the nine-membered cyclic transition state, TS, which is stabilized by an extra alcohol molecule that shuttles the proton from the alcohol to the catalyst. Abstract: We report iridium catalysts IrCl(η 5 -Cp ⁎ )(κ 2 -(2-pyridyl)CH2 NSO2 C6 H4 X) (1-Me, X = CH3 and 1-F, X = F) for transfer hydrogenation of ketones with 2-propanol that operate by a previously unseen metal-ligand cooperative mechanism. Under the reaction conditions, complexes 1 (1-Me and 1-F ) derivatize to a series of catalytic intermediates: Ir(η 5 -Cp ⁎ )(κ 2 -(C5 H4 N)CHNSO2 Ar) (2 ), IrH(η 5 -Cp ⁎ )(κ 2 -(2-pyridyl)CH2 NSO2 Ar) (3 ), and Ir(η 5 -Cp ⁎ )(κ 3 -(2-pyridyl)CH2 NSO2 Ar) (4 ). The structures of 1-Me and 4-Me were established by single-crystal X-ray diffraction. A rate-determining, concerted hydrogen transfer step (2 + R2 CHOH ⇄ 3 + R2 CO) is suggested by kinetic isotope effects, Eyring parameters (Δ H ≠ = 29.1(8) kcal mol −1 and Δ S ≠ = −17(19) eu), proton-hydride fidelity, and DFT calculations. According to DFT, a nine-membered cyclic transition state is stabilized by an alcohol molecule that serves as a proton shuttle.