Cyclic (Alkyl)(amino)carbenes (CAACs) in Ruthenium Olefin Metathesis

Abstract

Discovered in 2005, cyclic (alkyl)(amino)carbenes (CAACs) have led to numerous

Ruthenium Complexes Featuring Unsymmetrical N‐Heterocyclic Carbene Ligands–Useful Olefin Metathesis Catalysts for Special Tasks

“…It shall be however noted that catalysts such as Ru35, bearing so-called cyclic alkylamino carbene (CAAC) ligands-specially designed for ethenolysis-usually provide even better results in this reaction. [40] Matching the pieces of information resulted from our research to date, we designed a catalyst with an extended planar aryl moiety, namely 9-phenyl-anthracene, in the uNHC to modulate the steric congestion of this neutral ligand. Satisfyingly, this structural modification led to the formation of complex Ru36 whose high stability and activity were similar to those of Hov-SIMes (Scheme 6).…”

Bonding and stability of dinitrogen-bonded donor base-stabilized Si(0)/Ge(0) species [(cAACMe–Si/Ge)2(N2)]: EDA-NOCV analysis

“…58 The adduct (bulky group-cAAC bulky group )SiCl 4 can be utilized as a precursor under reduced (KC 8 ) condition to prevent the dimerization of (bulky group-cAAC bulky group )Si unit under dinitrogen atmosphere. In recent time, several bulky cAAC ligands 59,60 have been synthesized, isolated and utilized for catalytic organic transformation. 60 The bulky substituents around C cAAC -atom is suggested here to prevent the dimerization of 2cAAC-E to (cAAC-E) 2 creating the possibility of N 2 binding by two cAAC-E fragments under suitable reaction condition via the prevention of self dimerization of 2 cAAC-E units.…”

“…In recent time, several bulky cAAC ligands 59,60 have been synthesized, isolated and utilized for catalytic organic transformation. 60 The bulky substituents around C cAAC -atom is suggested here to prevent the dimerization of 2cAAC-E to (cAAC-E) 2 creating the possibility of N 2 binding by two cAAC-E fragments under suitable reaction condition via the prevention of self dimerization of 2 cAAC-E units. The later process is thermodynamically more favourable over binding of N 2 by 2 cAAC-E units.…”

Carbene B−H Insertion Reactions for C−B Bond Formation

“…[24] Discovered in 2005, the CAACs are among the most nucleophilic and also electrophilic (σ-donating and πaccepting) stable singlet carbenes known to date, which differ significantly from traditional N-heterocyclic carbenes (NHCs) because of the presence of a σ-donating alkyl group adjacent to the carbene carbon instead of a σ-attracting and π-donating amino group. [25,26] As a result, the chemical behavior of CAACs and NHCs are very different. The reaction of CAACs with boranes initially delivered Lewis base-acid adducts 22-A.…”