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Abstract IMes (IMes=1,3‐bis(2,4,6‐trimethylphenyl)imidazol‐2‐ylidene) and IPr (IPr=1,3‐ bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene) represent by far the most frequently used N‐heterocyclic carbene ligands in homogeneous catalysis, however, despite numerous advantages, these ligands are limited by the lack of steric flexibility of catalytic pockets. We report a new class of unique unsymmetrical N‐heterocyclic carbene ligands that are characterized by freely‐rotatable N‐aromatic wingtips in the imidazol‐2‐ylidene architecture. The combination of rotatable N−CH₂Ar bond with conformationally‐fixed N−Ar linkage results in a highly modular ligand topology, entering the range of geometries inaccessible to IMes and IPr. These ligands are highly reactive in Cu(I)‐catalyzed β‐hydroboration, an archetypal borylcupration process that has had a transformative impact on the synthesis of boron‐containing compounds. The most reactive Cu(I)‐NHC in this class has been commercialized in collaboration with MilliporeSigma to enable broad access of the synthetic chemistry community. The ligands gradually cover %V_burgeometries ranging from 37.3 % to 52.7 %, with the latter representing the largest %V_burdescribed for an IPr analogue, while retaining full flexibility of N‐wingtip. Considering the modular access to novel geometrical space in N‐heterocyclic carbene catalysis, we anticipate that this concept will enable new opportunities in organic synthesis, drug discovery and stabilization of reactive metal centers. 

Paper No. 3989661 

We report novel sterically-hindered ligands with strong σ-donation from the C3-indazole carbene center and flexible N-substitution with a 2,6-bis(diphenylmethyl)aryl group that extends beyond the metal center in non-classical N-heterocyclic carbenes. 

The synthesis of biaryl compounds by employing carboxylic acids as double aryl group donors is reported. 

We report a new class of sterically-unsymmetrical NHC ligands. The evaluation of steric, electronic properties and coordination chemistry is described. Studies of catalytic activity in Ag, Pd and Rh-catalyzed reactions are presented. 

We report [Au(NHC)Cl] complexes featuring IPr# ligands that hinge upon modular peralkylation of aniline. Wingtip-flexible [Au(Np#)Cl] is a broadly applicable catalyst with the reactivity outperforming [Au(IPr)Cl] and [Au(IPr*)Cl] complexes.