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. 2023 Mar 17;88(6):3822-3829.
doi: 10.1021/acs.joc.3c00023. Epub 2023 Feb 27.

Dual Nickel Photocatalysis for O-Aryl Carbamate Synthesis from Carbon Dioxide

Aleksi Sahari  1 , Jukka Puumi  1 , Jere K Mannisto  1 , Timo Repo  1
Affiliations

Dual Nickel Photocatalysis for O-Aryl Carbamate Synthesis from Carbon Dioxide

Aleksi Sahari et al. J Org Chem. .

Abstract

We report the use of dual nickel photocatalysis in the synthesis of O-aryl carbamates from aryl iodides or bromides, amines, and carbon dioxide. The reaction proceeded in visible light, at ambient carbon dioxide pressure, and without stoichiometric activating reagents. Mechanistic analysis is consistent with a Ni(I-III) cycle, where the active species is generated by the photocatalyst. The rate-limiting steps were the photocatalyst-mediated reduction of Ni(II) to Ni(I) and subsequent oxidative addition of the aryl halide. The physical properties of the photocatalyst were critical for promoting formation of O-aryl carbamates over various byproducts. Nine new phthalonitrile photocatalysts were synthesized, which exhibited properties that were vital to achieve high selectivity and activity.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Scheme 1
Scheme 1. (A) Examples of High Value Compounds Containing an O-Aryl Carbamate Group; (B) Conventional O-Arylcarbamate Syntheses Use Phosgene Derivatives as a Carbonyl Sources;, (C) Previous Work on the O-Aryl Carbamate Synthesis Using Carbon Dioxide; (D) The Method Described in This Article
Scheme 2
Scheme 2. Reaction Scope with Different Amines
Reaction conditions: 1.0 mmol of 4-iodo/bromobenzotrifluoride, 2.0 mmol of TMG, 2.0 mmol of amine, 0.05 mmol of Ni(dtbbpy)Br2, 1.0 μmol of 4DPAPN-tBu 7c, diluted to 4 mL with DMF. Flushed with CO2. 2 × 30W CFL, 22 h, 43 °C. Isolated yield for iodides, NMR-yield in parentheses, NMR-yield for bromides. Blue LEDs instead of CFL in breackets. (a) Isolated yield, NMR-yield was 86%. (b) Only phenol is formed. (c) 1.0 mmol of piperazine, 2.0 mmol of iodobenzotrifluoride. (d) Diluted to 0.05 M for solubility.
Scheme 3
Scheme 3. Reaction Scope with Different Aryl Iodides
Reaction conditions: 1.0 mmol of aryl iodide, 2.0 mmol of tetramethylguanidine, 2.0 mmol of amine, 0.05 mmol of Ni(dtbbpy)Br2, 1.0 μmol of 4DPAPN-tBu 7c, diluted to 4 mL with DMF. Flushed with CO2. 2 × 30W CFL, 22 h, 43 °C. (a) 44 h reaction time. (b) 66 h reaction time. (c) 1.1 mmol of morpholine.
Scheme 4
Scheme 4. Investigation on to Primary Amine Reactivity: (A) Study of Primary Amine Derived Carbamate Decomposition under Reaction Conditions; (B) Effect of Base to the Reaction Selectivity; (C) Reaction with Cyclic Carbamate 40 Shows That N-Reactivity of Carbamates Is Possible
3% N-arylated product. 13% N-arylated product. Lithium carbamate of 36 was premade in THF. Added 0.2 equiv of Et3N.
Figure 1
Figure 1
Carbamate formation over time (min). 0.2 mmol of 4-iodobenzotrifluoride, 0.4 mmol TMG and morpholine, 0.01 mmol Ni(dtbbpy)Br2, 0.2 umol 4DPAPN-tbu in 8 ml of DMF. Yield was measured with 19F{1H}-NMR with hexafluorobezene as internal standard.
Scheme 5
Scheme 5. Study of Catalytic Activity and Stoichiometric Reactivity of Ni(dtbbpy)(o-tolyl)Br
Measured with 19F{1H}-NMR, with hexafluorobenzene as internal standard. Measured with GC-MS yields with mesitylene as internal standard calibrated with a genuine sample.
Scheme 6
Scheme 6. (A) Measured Rate Order Coefficients for Each Reagents (Root Mean Square Error in Brackets); (B) Plausible Mechanisms for Catalyst Deactivation and Reactivation Which Lead to Fractional Rate Orders; (C) Possible Catalytic Cycle
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