Main Group Carbenes

Abstract

This article describes the chemistry of main group carbene complexes. Although not limited to, the article particularly summarizes the coordination of N‐heterocyclic carbenes to main group species. Usually, carbene ligands cannot be stabilized by electron‐poor coordination fragments because traditional carbenes show a pronounced tendency toward metal‐to‐ligand π back‐donation. However, N‐heterocyclic carbenes do not rely on back‐donation for stabilization because of the delocalization of the nitrogen lone pair in these carbenes. Thus, they are able to form stable complexes with metals that normally show no tendency for π back‐donation. In general, the carbene acts as a two‐electron donor ligand in a similar fashion to phosphines. Carbene complexes of the alkali and alkaline earth metals, which show a preference for σ‐bonding, are described. The high nucleophilicity of the N‐heterocyclic carbenes is shown by alane, gallane, and indane complexes that have much greater stability than normally observed for Lewis base adducts of group 13. Nucleophilic carbenes also react with Lewis acidic group 14 complexes with the formation of neutral or ionic compounds via simple adduct formation or displacement of a halide ion. Furthermore, N‐heterocyclic carbenes are sufficiently nucleophilic to enable depolymerization of cyclopolyphosphines and cyclopolyarsines to occur with the isolation of carbene–pnictinidene adducts. These carbenes can also form stable adducts with strong electron acceptors, such as pnictogen pentafluorides, if the reactivity is moderated. In addition, stable chalcogen–carbene and halide–carbene complexes are also discussed.

N-Heterocyclic Carbene—Main-Group Chemistry: A Rapidly Evolving Field

“…The main-group chemistry of carbenes has experienced impressive growth over the past two decades. − ,− The carbene ligands employed in our projects are sterically demanding NHCs [L: = :C{N(2,6-Pr i 2 C 6 H 3 )CH} 2 ; L′: = :C{N(2,4,6-Me 3 C 6 H 2 )CH} 2 ; L″: = :C{(Pr i )NC(Me)} 2 ]. These NHCs not only are relatively robust themselves but also may provide sufficient kinetic stability to target highly reactive main-group cores.…”

Carbene Stabilization of Highly Reactive Main-Group Molecules

“…To this end, N-heterocyclic carbenes (NHCs), discovered by Arduengo et al and extensively utilized in organic and transition-metal catalysis, are attractive in this regard. Indeed, we have witnessed remarkable progress in carbene-based main-group chemistry. − In this article, we highlight the syntheses, structures, and computational studies of NHC-stabilized, low-oxidation-state, main-group molecules that were recently discovered in our laboratory. These carbene-stabilized main-group molecules with unusually low oxidation states not only exhibit structural novelty but also provide a unique platform from which novel main-group molecules may be further accessed.…”

Molecular versus Ionic Structures in Adducts of GaX3 with Monodentate Carbon-Based Ligands

“…Therefore, we focused our study on the former category, which has already found applications in catalysis . Well-defined N -heterocyclic carbene adducts of Group 13 trihalides have been described . With aluminum and gallium, , molecular 1:1 complexes have been crystallographically characterized.…”