“Abnormal” Addition of NHC to a Conjugate Acid of CAAC: Formation of N‐Alkyl‐Substituted CAAC

Abstract

The addition reactions of N-heterocyclic carbenes (NHCs) are mostly known to occur through the carbenic centre (C2), which leads to a "normal" adduct. Herein, we report the "abnormal" addition of NHC 1 (1,3-(2,6-iPr C H )-imidazole-2-ylidene) to a conjugate acid of cyclic (alkyl)(amino)carbene 2 (CAAC =1-iPr-3,3,5,5-Me -pyrrolinium triflate). Mechanistic study revealed that this reaction proceeded through the in situ formation of 1,3-(2,6-iPr C H )-imidazolium cation 4 and N-iPr-substituted CAAC 5 followed by the oxidative addition of compound 5 across the C4-H bond (alias backbone C-H) of compound 4. The in situ formation of compound 5 was also proven by the oxidative addition of it to the N-H group of iPrNH . DFT calculations also supported the mechanistic findings. A different methodology for the in situ generation of compound 5 by using TMPLi is also described.

Trisubstituted geminal diazaalkene derived transient 1,2-carbodications

“…12 Please do not adjust margins Please do not adjust margins During the course of the reaction between 1 and 2 R we observed the formation of a small amount of pentamethylimidazolium triflate salt along with the desired monocations, 3 R . 13 Subsequent treatment of 3 R with KHMDS afforded the target alkenes 4 R (Scheme 2). 12 The 1 H NMR spectrum of 4 iPr displays two equal intensity doublets at  = 2.86 ppm and 4.03 ppm with a coupling constant of 3 J ( 1 H, 1 H) = 10.7 Hz for allylic-and vinylic-H, respectively.…”

Disclosing Cyclic(Alkyl)(Amino)Carbenes as One‐Electron Reductants: Synthesis of Acyclic(Amino)(Aryl)Carbene‐Based Kekulé Diradicaloids

“…This is most likely due to the steric hindrance at the N ‐center. Also, we did not observe any reaction between 1 and 3 [SbF 6 ] which is in contrast with that of the N ‐ i Pr analogue [20] …”

N,N′‐Ethylene‐Bridged Bis‐2‐Aryl‐Pyrrolinium Cations to E‐Diaminoalkenes: Non‐Identical Stepwise Reversible Double‐Redox Coupled Bond Activation Reactions

“…The molecular structures of 7 H and 7 Me exhibit central C−C bond distances of 1.358(6) and 1.380(3) Å, which are lengthened compared to the parent E ‐diaminoalkenes 6 H (1.332(2) Å) and 6 Me (1.338(3) Å) (Figure and Figure S5 in Supporting Information). Exocyclic N−C bond distances are 1.370(9) and 1.364(5) Å for 7 H and 7 Me , respectively, indicating partial double bond character there as well . These unique, structurally characterized radical cations underscore the propensity of the electron‐rich diazaolefinic compounds 6 H and 6 Me to undergo clean and facile one‐electron oxidations with the appropriate oxidizing agent.…”

“…Exocyclic NÀC bond distances are 1.370(9) and 1.364(5) for 7 H and 7 Me , respectively, indicating partial double bond character there as well. [19] These unique, structurally characterized radical cations underscore the propensity of the electron-rich diazaolefinic [20] compounds 6 H and 6 Me to undergo clean and facile one-electron oxidations with the appropriate oxidizing agent.…”