Issue 46, 2022

Room temperature chemoselective hydrogenation of C[double bond, length as m-dash]C, C[double bond, length as m-dash]O and C[double bond, length as m-dash]N bonds by using a well-defined mixed donor Mn(i) pincer catalyst

Abstract

Chemoselective hydrogenation of C[double bond, length as m-dash]C, C[double bond, length as m-dash]O and C[double bond, length as m-dash]N bonds in α,β-unsaturated ketones, aldehydes and imines is accomplished at room temperature (27 °C) using a well-defined Mn(I) catalyst and 5.0 bar H2. Amongst the three mixed-donor Mn(I) complexes developed, κ3-(R2PN3NPyz)Mn(CO)2Br (R = Ph, iPr, tBu); the tBu-substituted complex (tBu2PN3NPyz)Mn(CO)2Br shows exceptional chemoselective catalytic reduction of unsaturated bonds. This hydrogenation protocol tolerates a range of highly susceptible functionalities, such as halides (–F, –Cl, –Br, and –I), alkoxy and hydroxy, including hydrogen-sensitive moieties like acetyl, nitrile, nitro, epoxide, and unconjugated alkenyl and alkynyl groups. Additionally, the disclosed method applies to indole, pyrrole, furan, thiophene, and pyridine-containing unsaturated ketones leading to the corresponding saturated ketones. The C[double bond, length as m-dash]C bond is chemoselectively hydrogenated in α,β-unsaturated ketones, while the aldehyde's C[double bond, length as m-dash]O bond and imine's C[double bond, length as m-dash]N bond are preferentially reduced over the C[double bond, length as m-dash]C bond. A detailed mechanistic study highlighted the non-innocent behavior of the ligand in the (tBu2PN3NPyz)Mn(I) complex and indicated a metal–ligand cooperative catalytic pathway. The molecular hydrogen (H2) acts as a hydride source, whereas MeOH provides a proton for hydrogenation. DFT energy calculations supported the facile progress of most catalytic steps, involving a crucial turnover-limiting H2 activation.

Graphical abstract: Room temperature chemoselective hydrogenation of C [[double bond, length as m-dash]] C, C [[double bond, length as m-dash]] O and C [[double bond, length as m-dash]] N bonds by using a well-defined mixed donor Mn(i) pincer catalyst

Supplementary files

Article information

Article type
Edge Article
Submitted
21 Sept. 2022
Accepted
02 Nov. 2022
First published
03 Nov. 2022
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2022,13, 13764-13773

Room temperature chemoselective hydrogenation of C[double bond, length as m-dash]C, C[double bond, length as m-dash]O and C[double bond, length as m-dash]N bonds by using a well-defined mixed donor Mn(I) pincer catalyst

A. B. Shabade, D. M. Sharma, P. Bajpai, R. G. Gonnade, K. Vanka and B. Punji, Chem. Sci., 2022, 13, 13764 DOI: 10.1039/D2SC05274A

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