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

Abstract

This Award Article targets the evolving, yet surprisingly fruitful, chemistry of N-heterocyclic carbenes with low-oxidation-state main-group elements. Specifically, the chemistry of carbene-stabilized diatomic allotropes, diborenes, gallium octahedra, beryllium borohydride, and a host of related compounds will be presented. Providing a valuable historical perspective, the foundational work concerning the organometallic chemistry of gallium with sterically demanding m-terphenyl ligands from this laboratory will also be discussed.

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

“…The isolation of the first stable N ‐heterocyclic carbenes (NHCs) greatly expanded the number of unusual low‐valent main‐group element compounds, providing, for instance, the carbene‐stabilized diphosphorus and diarsenic species (IDipp) 2 P 2 ( II , IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene), (IMes) 2 P 2 ( III , IMes=1,3‐bis(2,4,6‐trimethylphenyl)imidazolin‐2‐ylidene) and (IDipp) 2 As 2 ( IV ) by reduction of the adducts (NHC)ECl 3 with potassium graphite (KC 8 ) . These pnictogen(0) compounds feature P−P and As−As single bonds, and their oxidation to the corresponding radical cations [(IDipp) 2 E 2 ] .…”

“…To provide an insight into the factorsc ontributingt ot he structural stabilityo ft he pnictogen dihalide andd ipnictene compounds, quantum chemicalc alculations were performed at the domain-based local pair natural orbitalc oupled-cluster (DLPNO-CCSD(T)) level. Al ocal energy decomposition (LED) analysiso ft he interaction between thec arbene and the pnictogen dihalide or dipnictene moiety demonstrates that London dispersion is an essentialf actor for the stabilization of these compounds.The isolation of the first stable N-heterocyclic carbenes (NHCs) [10][11][12][13][14] greatlye xpanded the number of unusuall owvalentm ain-group elementc ompounds, [15][16][17] providing, for instance,t he carbene-stabilized diphosphorus and diarsenic species (IDipp) 2 P 2 (II,I Dipp = 1,3-bis(2,6-diisopropylphenyl)imidazo-Figure 1. Selected dipnictogen and dipnictenecompounds (Dipp = 2,6-diisopropylphenyl, Mes = 2,4,6-trimethylphenyl).…”

N‐Heterocyclic Carbenes as Promotors for the Rearrangement of Phosphaketenes to Phosphaheteroallenes: A Case Study for OCP to OPC Constitutional Isomerism

“…[6] Sodium phosphaethynolate Na(OCP) (1)i sr emarkably stable [7,8] but so far HO À C Ph as neither been prepared nor observed. [10] Ac alculation of the stabilizing energy given by the hypothetical reaction H À O À P = C + NHC ! [9] This compound contains al ong PÀPb ond (2.441 ) and is best described as av ery intimate ion pair between ac yclic 1,2,3diazaphospholenium cation [(HC) 2 (NR) 2 P] + (NHP + )w ith adelocalized 6p-electron ring skeleton and the OCP À anion.…”

Synthesis and Characterization of N-Heterocyclic Carbene-Coordinated Silicon Compounds Bearing a Fused-Ring Bulky Eind Group

“…Over many years, a number of unsaturated silicon compounds have been successfully obtained by virtue of the complexation of metal ions and/or coordination of ligands (mainly Lewis bases) in addition to steric protection with bulky substituents [1][2][3][4][5][6][7][8][9][10][11]. Among them, the coordination chemistry of highly-reactive halosilylenes, i.e., halogen-substituted divalent Si(II) species, have attracted a lot of attention as potentially useful precursors for the construction of a wide range of silicon-containing compounds [12][13][14][15][16][17].…”