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1. Synthesis, Reactivity and Aromatic Characteristics of Porphyrinoids Derived from N -Alkylcarbaporphyrin-2-Carbaldehydes: Isolation of Nickel(II) and Palladium(II) Complexes, Weakly Diatropic 21-Oxycarbaporphyrins and Strongly Aromatic Trioxycarbaporphyrins

   https://doi.org/10.1021/acs.joc.4c02145  

   Le, Kimberly; AbuSalim, Deyaa I; Lash, Timothy D (January 2025, The Journal of Organic Chemistry)

   cid catalyzed condensation of N-alkyltripyrranes with trialdehydes derived from 1,3-cyclopentadiene or methyl-1,3-cyclopentadiene, followed by oxidation with aqueous ferric chloride solutions, gave 23-alkyl-21- carbaporphyrin-2-carbaldehydes in 22−27% yield together with weakly aromatic oxycarbaporphyrins. The carbaporphyrins reacted with palladium(II) acetate or nickel(II) acetate to give organometallic complexes but in both cases alkyl group migration took place to generate 21-alkyl derivatives. Although this type of reactivity had been observed previously for palladium complexes, this is the first time the phenomenon has been seen in nickel(II) carbaporphyrins. Reactions with nickel(II) acetate in refluxing DMF for longer time periods primarily led to decomposition but unusual byproducts were identified. These could be obtained in higher yields by reacting the carbaporphyrin aldehydes with 5 equiv of (bis(trifluoroacetoxy)iodo)benzene in the presence of grade 3 alumina. Decarbonylation and oxidation generate a trioxocyclopentane moiety that is embedded in the porphyrinoid macrocycle. The new system has strongly aromatic properties that are evident from the proton NMR spectra, nucleus independent chemical shift (NICS) calculations and anisotropy of induced ring current plots. 

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2. Comparative study of CO ₂ insertion into pincer supported palladium alkyl and aryl complexes

   https://doi.org/10.1039/D3SC01459B  

   Deziel, Anthony P; Gahlawat, Sahil; Hazari, Nilay; Hopmann, Kathrin H; Mercado, Brandon Q (August 2023, Chemical Science)

   The synthesis of a range of PBP supported palladium pincer complexes with different alkyl ligands is described. The rates of CO₂insertion into the alkyl group are quantified and rationalized based on the identity of the alkyl ligand. 

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3. Visible Light Induced Brønsted Acid Assisted Pd‐Catalyzed Alkyl Heck Reaction of Diazo Compounds and N ‐Tosylhydrazones

   https://doi.org/10.1002/anie.202110924  

   Zhang, Ziyan; Kvasovs, Nikita; Dubrovina, Anastasiia; Gevorgyan, Vladimir (November 2021, Angewandte Chemie International Edition)

   Abstract A mild visible light‐induced palladium‐catalyzed alkyl Heck reaction of diazo compounds andN‐tosylhydrazones is reported. A broad range of vinyl arenes and heteroarenes with high functional group tolerance, as well as a range of different diazo compounds, can efficiently undergo this transformation. This method features Brønsted acid‐assisted generation of hybrid palladium C(sp³)‐centered radical intermediate, which allowed for new selective C−H functionalization protocol. 

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4. Base-Free Borylation of Aryl Halides Enabled by Zn-Promoted Halide Abstraction

   https://doi.org/10.1021/acs.orglett.4c03821  

   Gay, Brittany L; Prendeville, Lauren A; Wang, Ya-Nong; Hull, Kami L (December 2024, Organic Letters)

   Herein we report the palladium-catalyzed borylation of aryl halides (iodides or bromides) under base-free conditions utilizing a commercially available Lewis acidic mediator, Zn(OTf)2. Under these conditions, an array of electronically and functional group-diverse aryl iodides and bromides undergo borylation to afford the corresponding aryl boronic esters in up to 82% isolated yield. Mechanistic investigations are consistent with Zn(OTf)2 enabling transmetalation between a cationic Pd(II)-Ar intermediate and B2pin2 via halide abstraction. Furthermore, stabilization of the cationic [ArPdII]+ complex with added [BArF4]– significantly improves reaction efficiency with electron-poor arenes. 

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5. Palladium-Catalyzed Aerobic Alkene Arylboration: Coupling Aryl Boronic Acids, Alkenes, and Bis(pinacol)diboron

   https://doi.org/10.1021/acscatal.5c03926  

   Pham, Hoang_T P; Bhatt, Shreeja; Hull, Kami L (August 2025, ACS Catalysis)

   Alkyl boronic acids and esters are versatile synthetic intermediates that generally require several steps to synthesize. Three-component alkene arylboration reactions allow for the rapid synthesis of alkyl boronic esters. Herein, we report the base-free aerobic Pd-catalyzed three-component alkene arylboration, which allows direct access, in a single step, to alkyl boronic esters from readily available precursors: aryl boronic acids, alkenes, and bis(pinacol)diboron. This approach allows for the formal insertion of an alkene into an Ar–B bond, and thus, generates an alkyl boronic ester from an aryl boronic acid. The reaction proceeds with both electron-rich and electron-deficient aryl boronic acids as well as strained cyclic, internal, and terminal olefins. The reactions are regioselective: 1,2-arylboration products are formed with strained cyclic alkenes and b-alkyl-styrenes while 1,1-arylboration products are generated from terminal alkenes. Forty-five examples are presented with isolated yields of the resulting alkyl boronic esters ranging from 20-74%, along with several examples demonstrating the synthetic utility of the products. Mechanistic investigations support that the catalytic cycle occurs through direct arylboration of the alkene. Further, p-benzyl intermediates form when possible, and the rate of borylation is increased with electron-rich arenes relative to electron-poor. Finally, we demonstrate that aryl boroxines, generated in situ, are essential for the transformation as they rapidly undergo base-free transmetalation with the proposed palladium peroxo intermediate. 

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