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. 2022 Aug 24;144(33):15038-15046.
doi: 10.1021/jacs.2c02937. Epub 2022 Aug 12.

Distinct Reactivity Modes of a Copper Hydride Enabled by an Intramolecular Lewis Acid

Emily E Norwine  1 , John J Kiernicki  1 , Matthias Zeller  2 , Nathaniel K Szymczak  1
Affiliations

Distinct Reactivity Modes of a Copper Hydride Enabled by an Intramolecular Lewis Acid

Emily E Norwine et al. J Am Chem Soc. .

Abstract

We disclose a 1,4,7-triazacyclononane (TACN) ligand featuring an appended boron Lewis acid. Metalation with Cu(I) affords a series of tetrahedral complexes including a boron-capped cuprous hydride. We demonstrate distinct reactivity modes as a function of chemical oxidation: hydride transfer to CO2 in the copper(I) state and oxidant-induced H2 evolution as well as alkyne reduction.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1.
Figure 1.
Top: Representative copper hydride complexes in the Cu(I) state (top left) and oxidized states (top right). Bottom: TACN ligand with bulky tert-butyl groups provide access to stable pseudo-tetrahedral complexes (bottom left) and extension to include an appended boron Lewis acid (this work, bottom right).
Figure 2.
Figure 2.
Synthetic approaches to generate complexes 2-X. Molecular structures of 1-X and 2-X displayed with 50% probability ellipsoids. H-atoms not attached to allylic moieties and any minor disordered moieties are omitted and the 9-BBN substituents are displayed in wireframe for clarity.
Figure 3.
Figure 3.
A) Synthesis and reversibility of 3. B) Molecular structure and Wiberg bond indices of 3 as well as of limiting bonding descriptions of Cu-H and B-H. The structure of 3 is displayed with 50% probability ellipsoids. H-atoms not attached to copper are omitted and the 9-BBN is displayed in wireframe for clarity. C) Voltammetry comparison between 3 (top, red) and 2-I (bottom, blue).
Figure 4.
Figure 4.
A: CO2 reduction by 3 and formation of 4. The molecular structure of 4 is displayed with 50% probability ellipsoids. H-atoms not connected to the formate moieties are omitted and 9-BBN substituents are displayed in wireframe for clarity. Cutout: free energy landscape for monomer/dimer formation of the Cu-OCHO-BR3. B: 1) chemical oxidation of 3 and formation of H2, 2) formation of H2 via delivery of an H-atom to Cu(I) via acid/reductant combination, and 3) control reaction. C: 1) Cu(I) no reaction with phenylacetylene, 2) redirection of reactivity via oxidation to facilitate substrate reduction and 3) control reactions.
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