Fused polycyclic nucleophilic carbenes – synthesis, structure, and function

Abstract

Interest in stable nucleophilic carbenes has grown rapidly since the isolation of the first "bottle-able" example in 1991. Not only has the structural variation of this class of compounds seen an incredible expansion from laboratories around the world, but the chemical reactivity of these compounds has opened many new opportunities for improvements in chemical transformations and invention of new processes. This article reflects our particular interest in fused polycyclic carbenes and focuses on this broad chemical class from both a structural and reactivity perspective.

London Dispersion Interactions in Pnictogen Cations [ECl2]+ and [E=E]2+ (E=P, As, Sb) Supported by Anionic N‐Heterocyclic Carbenes

“…In recent years, anionic N ‐heterocyclic carbenes have emerged as an important class of novel NHC ligands . Contributions of our group have been based on the consideration that frustrated Lewis pairs, composed of bulky imidazolin‐2‐ylidenes and boranes such as B(C 6 F 5 ) 3 , would form abnormal carbene adducts, in which the weakly coordinating anionic (WCA) borate unit is attached to the 4‐position of the N ‐heterocycle . The corresponding anionic carbenes were termed WCA‐NHCs and introduced as ancillary ligands in transition metal complexes and homogeneous catalysts .…”

“…[36] Contributions of our group have been based on the consideration that frustrated Lewis pairs, composed of bulky imidazolin-2-ylidenes and boranes such as B(C 6 F 5 ) 3 ,w ould form abnormalc arbene adducts,i nw hich the weakly coordinating anionic (WCA) borate unit is attached to the 4-position of the N-heterocycle. [37][38][39][40][41] The corresponding anionic carbenes were termed WCA-NHCsa nd introduced as ancillary ligandsi nt ransition metal complexes and homogeneous catalysts. [42][43][44][45] Thereby, the additional negative chargep rovided neutral analogues of cationicm etal NHC complexes, for example, well-established Au I and Ir I pre-catalysts.…”

Carbenes and Nitrenes

“…59 Such deactivation has been explained by a transfer of the alkylidene on a proximal aromatic ring borne by the NHC moiety giving the intermediate (20), which then undergoes a Buchner ring enlargement to the cycloheptatriene-containing complex (21). These experimental results have been supported by DFT calculations.…”

Organocatalytic Green Approach Towards the Fabrication of Fused Benzo N,N‐containing Heterocycles Facilitated by Ultrasonic Irradiation

“…Benzimidazoles, apart from containing a significant moiety in the nucleotides, have also been found to exhibit promising pharmaceutical property by displaying a broad spectrum of biological activity ranging from anti‐ulcer to anti‐protozoal activity . It also finds importance as ligands in various material applications . Quinoxaline derivatives find its applications not only in the pharmaceuticals but also as an important component in dyes and photochemical materials.…”