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Abstract The synthesis and characterization of (tBuPBP)Ni(OAc) (5) by insertion of carbon dioxide into the Ni−C bond of (tBuPBP)NiMe (1) is presented. An unexpected CO2cleavage process involving the formation of new B−O and Ni−CO bonds leads to the generation of a butterfly‐structured tetra‐nickel cluster (tBuPBOP)2Ni4(μ‐CO)2(6). Mechanistic investigation of this reaction indicates a reductive scission of CO2by O‐atom transfer to the boron atom via a cooperative nickel‐boron mechanism. The CO2activation reaction produces a three‐coordinate (tBuP2BO)Ni‐acyl intermediate (A) that leads to a (tBuP2BO)−NiIcomplex (B) via a likely radical pathway. The NiIspecies is trapped by treatment with the radical trap (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO) to give (tBuP2BO)NiII(η2‐TEMPO) (7). Additionally,13C and1H NMR spectroscopy analysis using13C‐enriched CO2provides information about the species involved in the CO2activation process.
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Ambient Electroreductive Carboxylation of Unactivated Alkyl Chlorides and Polyvinyl Chloride (PVC) Upgrading
Abstract Electrosynthesis of alkyl carboxylic acids upon activating stronger alkyl chlorides at low‐energy cost is desired in producing carbon‐rich feedstock. Carbon dioxide (CO2), a greenhouse gas, has been recognized as an ideal primary carbon source for those syntheses, and such events also mitigate the atmospheric CO2level, which is already alarming. On the other hand, the promising upcycling of polyvinyl chloride to polyacrylate is a high energy‐demanding carbon‐chloride (C−Cl) bond activation process. Molecular catalysts that can efficiently perform such transformation under ambient reaction conditions are rarely known. Herein, we reveal a nickel (Ni)‐pincer complex that catalyzes the electrochemical upgrading of polyvinyl chloride to polyacrylate in 95 % yield. The activities of such a Ni electrocatalyst bearing a redox‐active ligand were also tested to convert diverse examples of unactivated alkyl chlorides to their corresponding carboxylic acid derivatives. Furthermore, electronic structure calculations revealed that CO2binding occurs in a resting state to yield an η2‐CO2adduct and that the C−Cl bond activation step is the rate‐determining transition state, which has an activation energy of 19.3 kcal/mol. A combination of electroanalytical methods, control experiments, and computational studies were also carried out to propose the mechanism of the electrochemical C−Cl activation process with the subsequent carboxylation step.
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- PAR ID:
- 10532163
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- ChemSusChem
- Volume:
- 17
- Issue:
- 23
- ISSN:
- 1864-5631
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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