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1. Effect of strain and π-acidity on the catalytic efficiency of carbones in carbodiimide hydroboration

   https://doi.org/10.1039/d5ob00062a  

   Schernikau, Max; Ogba, O Maduka (January 2025, Organic & Biomolecular Chemistry)

   Structural variations of carbone catalysts impact efficiency in carbodiimide hydroboration. Acyclic carbodiphosphoranes create strain during HBpin activation, while carbodicarbenes proceedvia1,2-addition, yielding a less reactive hydride donor. 

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2. Switchable Organocatalysis from N ‐heterocyclic Carbene‐Carbodiimide Adducts with Tunable Release Temperature

   https://doi.org/10.1002/anie.202314376  

   Pham, Le Dung; Smith‐Sweetser, Red O; Krupinsky, Briana; Dewey, Carolyn E; Lamb, Jessica R (November 2023, Angewandte Chemie International Edition)

   N‐Heterocyclic carbenes (NHCs) are powerful organocatalysts, but practical applications often require in situ generation from stable precursors that “mask” the NHC reactivity via reversible binding. Previously established “masks” are often simple small molecules, such that the NHC structure is used to control both catalytic activity and activation temperature, leading to undesirable tradeoffs. Herein, we show that NHC‐carbodiimide (CDI) adducts can be masked precursors for switchable organocatalysis and that the CDI substituents can control the reaction profile without changing the NHC structure. Large electronic variations on the CDI (e.g., alkyl versus aryl) drastically change the catalytically active temperature, whereas smaller perturbations (e.g., differentpara‐substituted phenyls) tune the catalyst release within a narrower window. This control was demonstrated for three classic NHC‐catalyzed reactions, each influencing the NHC‐CDI equilibrium in different ways. Our results introduce a new paradigm for controlling NHC organocatalysis as well as present practical considerations for designing appropriate masks for various reactions. 

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3. CAAC–IPr*: easily accessible, highly sterically-hindered cyclic (alkyl)(amino)carbenes

   https://doi.org/10.1039/D2CC05668B  

   Chu, Wenchao; Zhou, Tongliang; Bisz, Elwira; Dziuk, Błażej; Lalancette, Roger; Szostak, Roman; Szostak, Michal (December 2022, Chemical Communications)

   IPr* (IPr* = 1,3-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazol-2-ylidene) has emerged as a powerful highly hindered and sterically-flexible ligand platform for transition-metal catalysis. CAACs (CAAC = cyclic (al-kyl)(amino)carbenes) have gained major attention as strongly electron-rich carbon analogues of NHCs (NHC = N-heterocyclic carbene) with broad applications in both industry and academia. Herein, we report a merger of CAAC ligands with highly-hindered IPr*. The efficient synthesis, electronic characterization and application in model Cu-catalyzed hydroboration of alkynes is described. The ligands are strongly electron-rich, bulky and flexible around the N-Ar wingtip. The availability of various IPr* and CAAC templates offers a significant potential to expand the existing arsenal of NHC ligands to electron-rich bulky architectures with critical applications in metal stabilization and catalysis. 

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4. Systematic pore lipophilization to enhance the efficiency of an amine-based MOF catalyst in the solvent-free Knoevenagel reaction

   https://doi.org/10.3762/bjoc.21.144  

   Matseketsa, Pricilla; Pagare, Margret KR; Gadzikwa, Tendai (September 2025, Beilstein Journal of Organic Chemistry)

   Meisel, Joseph W; Flood, Amar H (Ed.)

   We systematically lipophilized an amine-based metal-organic framework (MOF) catalyst and applied the functionalized MOFs to the Knoevenagel condensation reaction. A well-defined MOF material composed of both amine- and hydroxy-bearing linkers was reacted with a series of aliphatic isocyanates (isopropyl,tert-butyl,n-hexyl, and tetradecyl) and, incongruously, was found to preferentially react at the hydroxy groups. This selective functionalization yielded MOFs in which the catalytically active amines are confined within highly lipophilic pores, reminiscent of many enzyme active sites. We determined that systematically increasing the lipophilicity of the pores results in a commensurate increase of catalyst efficiency. 

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5. Attenuating N ‐Oxyl Decomposition for Improved Hydrogen Atom Transfer Catalysts

   https://doi.org/10.1002/anie.202315917  

   Yang, Cheng; Farmer, Luke A; McFee, Elvis C; Jha, Rahul Kant; Maldonado, Stephen; Pratt, Derek A; Stephenson, Corey_R J (May 2024, Angewandte Chemie International Edition)

   Abstract The design ofN‐oxyl hydrogen atom transfer catalysts has proven challenging to date. Previous efforts have focused on the functionalization of the archetype, phthalimide‐N‐oxyl. Driven in part by the limited options for modification of this structure, this strategy has provided only modest improvements in reactivity and/or solubility. Our previous mechanistic efforts suggested that while the electron‐withdrawing carbonyls of the phthalimide are necessary to maximize the O−H bond dissociation enthalpy of the HAT product hydroxylamine and overall reaction thermodynamics, they undergo nucleophilic substitution leading to catalyst decomposition. In an attempt to minimize this vulnerability, we report the characterization ofN‐oxyl catalysts wherein the aryl ring in PINO is replaced with the combination of a substituted heteroatom and quaternary carbon. By rendering one carbonyl carbon less electrophilic and the other less sterically accessible, the correspondingN¹‐aryl‐hydantoin‐N³‐oxyl radical showed significantly higher stability than PINO as well as a modest improvement in reactivity. This proof‐of‐principle in new scaffold design may accelerate future HAT catalyst discovery and development. 

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