Stabilization of the Pd–NHC framework with 1,2,4-triazol-5-ylidene ligands toward decomposition in alkaline media

Abstract

New NHC ligands containing a base-ionizable RNH substituent at the C3 atom of the 1,2,4-triazole ring provide superior stability of the Pd–NHC bond against cleavage in strong alkaline media.

Discovery of the N–NHC Coupling Process under the Conditions of Pd/NHC- and Ni/NHC-Catalyzed Buchwald–Hartwig Amination

“…Understanding M/NHC catalyst transformations involving the M–NHC bond cleavage during catalysis may be of great importance for developing more robust and efficient catalytic systems. ,− Among intermediates of the Buchwald–Hartwig, typical for cross-coupling complexes I and II are involved (Scheme A). Coordination of amine ligands is also a well-known process (Scheme A, intermediates III ), for example, for C–C cross-coupling reactions in the presence of amines as bases.…”

Probing the mechanism of adaptive aromaticity in metallapyridiniums

“…All calculations involved in this study were performed by DFT calculations with the Gaussian 16 package. 42 DFT calculations have been widely used in mechanism [43][44][45][46][47][48] and aromaticity 39,49,50 studies. The geometries of all complexes in their lowest singlet and triplet states were optimized using the (U)B3LYP 51,52 method in the gas phase.…”

Selective Buchwald–Hartwig arylation ofC-amino-1,2,4-triazoles and other coordinating aminoheterocycles enabled by bulky NHC ligands and TPEDO activator

“…In addition, fast formation of Pd-black was observed in the reaction mixtures containing precatalysts 1a-c. Apparently, complexes 1a-c suffer facile decomposition via O-NHC, 52,67 N-NHC, 68 H-NHC and C-NHC coupling reactions. [69][70][71][72] More stable complexes 1d and 1e with bulkier NHC ligands provided 6% and 19% yields of 4a, respectively (Table 1, entries 1 and 2).…”

“…Moreover, 3-arylamino-1,2,4-triazoles were recently studied as promising photoactive compounds possessing aggregation-induced emission (AIE) 49 and precursors for N-heterocyclic carbene ligands. [50][51][52] Although various methods based on the cyclization of acyclic precursors 42,[53][54][55][56][57] or amination of 3(5)-bromo-1,2,4-triazoles [58][59][60] have been reported in the literature, arylation of easily available C-amino-1,2,4-triazoles 19,61 may be considered one of most efficient pathways to diverse 3(5)-arylamino-1,2,4-triazoles. However, noncatalytic arylation of C-amino-1,2,4-triazoles is limited to activated arylating agents such as nitrochloroarenes, 62 whereas metal-catalyzed arylation is encumbered by the strongly coordinating character of these substrates and the low nucleophilicity of the amino group.…”

“…Moreover, 3-arylamino-1,2,4-triazoles were recently studied as promising photoactive compounds possessing aggregation-induced emission (AIE) 49 and precursors for N-heterocyclic carbene ligands. 50–52…”