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. 2022 Aug 19;12(16):9933-9943.
doi: 10.1021/acscatal.2c02467. Epub 2022 Aug 1.

Cobalt-Catalyzed Hydrogenation Reactions Enabled by Ligand-Based Storage of Dihydrogen

Sophie W Anferov  1 , Alexander S Filatov  1 , John S Anderson  1
Affiliations

Cobalt-Catalyzed Hydrogenation Reactions Enabled by Ligand-Based Storage of Dihydrogen

Sophie W Anferov et al. ACS Catal. .

Abstract

The use of supporting ligands that can store either protons or electrons has emerged as a powerful strategy in catalysis. While these strategies are potent individually, natural systems mediate remarkable transformations by combining the storage of both protons and electrons in the secondary coordination sphere. As such, there has been recent interest in using this strategy to enable fundamentally different transformations. Furthermore, outsourcing H-atom or hydrogen storage to ancillary ligands can also enable alternative mechanistic pathways and thereby selectivity. Here, we describe the application of this strategy to facilitate radical reactivity in Co-based hydrogenation catalysis. Metalation of previously reported dihydrazonopyrrole ligands with Co results in paramagnetic complexes, which are best described as having Co(II) oxidation states. These complexes catalytically hydrogenate olefins with low catalyst loadings under mild conditions (1 atm H2, 23 °C). Mechanistic, spectroscopic, and computational investigations indicate that this system goes through a radical hydrogen-atom transfer (HAT) type pathway that is distinct from classic organometallic mechanisms and is supported by the ability of the ligand to store H2. These results show how ancillary ligands can facilitate efficient catalysis, and furthermore how classic organometallic mechanisms for catalysis can be altered by the secondary coordination sphere.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Existing Co-based hydrogenation catalysts or active species,,,,,, and the current system highlighting ligand-based H2 storage.
Figure 2
Figure 2
SXRD Structures (from left to right) of 1 and 2. All displacement ellipsoids shown at 50%, and hydrogens omitted for clarity.
Scheme 1
Scheme 1. Synthesis of tBu,TolDHP Complexes of Co and Hydrogenation Reactivity
Figure 3
Figure 3
Perpendicular mode X-band EPR spectrum from top to bottom of 15 mM solutions of 2 and 3 at 15.9 K in toluene and 20 K in toluene, respectively. Simulation shown in black lines for each. Simulation parameters for 2: g = 2.01, 2.11, 2.61; Co-A = +56.5, +89.0, +75.6 MHz; N-A = +12.1, +5.9, +11.2 MHz. 3: g = 2.02, 2.10, 2.56; Co-A = +54.8, +61.0, +66.8 MHz, N-A = +23.1, +24.5, −14.1 MHz. Experimental conditions: microwave frequency 9.6304 GHz, microwave power 0.2 mW. The full and simulated spectra are shown in the SI (Figures S21–S27 and Table S1).
Figure 4
Figure 4
Thin-Film IR spectrum of 3 and 3-D2 with difference spectrum in the inset.
Scheme 2
Scheme 2. Mechanism for the Synthesis of 3 as well as for the Hydrogenations of Olefins (1-Hexene Used as Model Substrate)
See this image and copyright information in PMC

References

    1. Crabtree R. H.Organometallic Chemistry of the Transition Metals, 6th ed.; 2014; pp 55–56.
    2. Wen J.; Wang F.; Zhang X. Asymmetric hydrogenation catalyzed by first-row transition metal complexes. Chem. Soc. Rev. 2021, 50, 3211–3237. 10.1039/D0CS00082E. - DOI - PubMed
    1. Ito N.; Phillips S. E. V.; Stevens C.; Ogel Z. B.; McPherson M. J.; Keen J. N.; Yadav K. D. S.; Knowles P. F. Novel thioether bond revealed by a 1.7 Å crystal structure of galactose oxidase. Nature 1991, 350, 87–90. 10.1038/350087a0. - DOI - PubMed
    2. Ito N.; Phillips S. E. V.; Stevens C.; Ogel Z. B.; McPherson M. J.; Keen J. N.; Yadav K. D. S.; Knowles P. F. Three-dimensional structure of galactose oxidase: an enzyme with a built-in secondary cofactor. Faraday Discuss. 1992, 93, 75.10.1039/fd9929300075. - DOI - PubMed
    3. Branchaud B. P.; Montagne-Smith M. P.; Kosman D. J.; McLaren F. R. Mechanism-based inactivation of galactose oxidase: evidence for a radical mechanism. J. Am. Chem. Soc. 1993, 115, 798.10.1021/ja00055a067. - DOI
    4. Whittaker M. M.; Whittaker J. M. Ligand interactions with galactose oxidase: mechanistic insights. Biophys. J. 1993, 64, 762.10.1016/S0006-3495(93)81437-1. - DOI - PMC - PubMed
    5. Ito N.; Phillips S. E. V.; Yadav K. D. S.; Knowles P. F. Crystal structure of a free radical enzyme, galactose oxidase. J. Mol. Biol. 1994, 238, 794.10.1006/jmbi.1994.1335. - DOI - PubMed
    6. Knowles P. F.; Ito N.. Perspectives in Bio-inorganic Chemistry, Jai Press Ltd., 1994; Vol. 2, pp 207–244.
    7. Wachter R. M.; Branchaud B. P. Molecular modeling studies on oxidation of hexopyranoses by galactose oxidase. An active site topology apparently designed to catalyze radical reactions, either concerted or stepwise. J. Am. Chem. Soc. 1996, 118, 2782.10.1021/ja9519896. - DOI
    8. Wachter R. M.; Montagne-Smith M. P.; Branchaud B. P. β-Haloethanol substrates as probes for radical mechanisms for galactose oxidase. J.Am. Chem. Soc. 1997, 119, 7743.10.1021/ja9626695. - DOI
    9. Whittaker M. M.; Ballou D. P.; Whittaker J. W. Kinetic isotope effects as probes of the mechanism of galactose oxidase. Biochemistry 1998, 37, 8426.10.1021/bi980328t. - DOI - PubMed
    10. Whittaker J. W.; Whittaker M. M. Radical copper oxidases, one electron at a time. Pure Appl. Chem. 1998, 70, 903.10.1351/pac199870040903. - DOI
    11. Chaudhuri P.; Hess M.; Müller J.; Hildenbrand K.; Bill E.; Weyhermüller T.; Wieghardt K. Aerobic oxidation of primary alcohols (including methanol) by Copper (II)– and Zinc (II)– phenoxyl radical catalysts. J. Am. Chem. Soc. 1999, 121, 9599–9610. 10.1021/ja991481t. - DOI
    12. Cook S. A.; Hill E. A.; Borovik A. S. Lessons from nature: a bio-inspired approach to molecular design. Biochemistry 2015, 54, 4167–4180. 10.1021/acs.biochem.5b00249. - DOI - PMC - PubMed
    13. Baumgardner D. F.; Parks W. E.; Gilbertson J. D. Harnessing the active site triad: merging hemilability, proton responsivity, and ligand-based redox-activity. Dalton Trans. 2020, 49, 960–965. 10.1039/C9DT04470A. - DOI - PMC - PubMed
    1. Cook S. A.; Borovik A. S. Molecular designs for controlling the local environments around metal ions. Acc. Chem. Res. 2015, 48, 2407–2414. 10.1021/acs.accounts.5b00212. - DOI - PMC - PubMed
    1. Rakowski Dubois M.; Dubois D. L. Development of Molecular Electrocatalysts for CO2 Reduction and H2 Production/Oxidation. Acc. Chem. Res. 2009, 42, 1974–1982. 10.1021/ar900110c. - DOI - PubMed
    2. Zell T.; Milstein D. Hydrogenation and dehydrogenation iron pincer catalysts capable of metal–ligand cooperation by aromatization/dearomatization. Acc. Chem. Res. 2015, 48, 1979–1994. 10.1021/acs.accounts.5b00027. - DOI - PubMed
    3. Pegis M. L.; Wise C. F.; Martin D. J.; Mayer J. M. Oxygen reduction by homogeneous molecular catalysts and electrocatalysts. Chem. Rev. 2018, 118, 2340–2391. 10.1021/acs.chemrev.7b00542. - DOI - PubMed
    1. Luca O. R.; Crabtree R. H. Redox-active ligands in catalysis. Chem. Soc. Rev. 2013, 42, 1440–1459. 10.1039/C2CS35228A. - DOI - PubMed
    2. Arevalo R.; Chirik P. J. Enabling two-electron pathways with iron and cobalt: from ligand design to catalytic applications. J. Am. Chem. Soc. 2019, 141, 9106–9123. 10.1021/jacs.9b03337. - DOI - PMC - PubMed
    3. Ott J. C.; Bürgy D.; Guan H.; Gade L. H. 3d Metal Complexes in T-shaped Geometry as a Gateway to Metalloradical Reactivity. Acc. Chem. Res. 2022, 55, 857–868. 10.1021/acs.accounts.1c00737. - DOI - PubMed