A flat carborane with multiple aromaticity beyond Wade–Mingos’ rules

Abstract

It is widely known that the skeletal structure of clusters reflects the number of skeletal bonding electron pairs involved, which is called the polyhedral skeletal electron pair theory (PSEPT) or Wade and Mingos rules. While recent computational studies propose that the increase of skeletal electrons of polyhedral clusters leads to the flat structure beyond the PSEPT, little experimental evidence has been demonstrated. Herein, we report the synthesis of a C2B4R4 carborane 2 featuring a flat ribbon-like structure. The C2B4 core of 2 bearing 16 skeletal electrons in the singlet-ground state defies both the [4n + 2] Hückel’s rule and Baird’s rule. Nevertheless, the delocalization of those electrons simultaneously induces two independent π- and two independent σ-aromatic ring currents, rendering quadruple aromaticity.

From a Möbius-aromatic interlocked Mn2B10H10 wheel to the metal-doped boranaphthalenes M2@B10H8 and M2B5 2D-sheets (M = Mn and Fe): a molecules to materials continuum using DFT studies

“…85 The removal of 2H from the B3 and B8 centers of The realization of III (Scheme 1a) with two bare B-centers suggests the possibility of obtaining boranaphthalene (10 and 11) in solution. 21 It should be noted that icosahedral arrangements of M 2 B 10 H 10 (M ¼ Mn and Fe), similar to icosahedral M 2 B 10 (M ¼ Rh and Ir), 86 are more stable than 7 and 8 (Fig. S9 and Table S1 ‡).…”

“…The last two decades has witnessed explosive growth in three apparently parallel elds in the area of boron chemistry. [1][2][3][4][5][6][7] The rst part of this growth involved several successful attempts to stabilize boron complexes with an increasing number of boron atoms in the solution phase, [8][9][10][11][12][13][14][15][16][17][18] e.g., B 4 (I, II), 19,20 carboranes (C 2 B 4 R 4 ; III), 21 and metallaborocycles ((CO) 2 FeB 4 R 4 ; IV). 22 Here, the electron deciency of boron was fullled using Lewis donor ligands and transition-metal templates, and this led to many unusual structural and bonding variations.…”

“…However, the synthesis of the tetra-atomic boron(0) complex II, starting from a B 2 complex stabilized by Lewis donor ligands, paved the way to achieving the rule-breaking planar C 2 B 4 R 4 complex III, as reported by Kinjo and co-workers recently. 20,21 The presence of labile PMe 3 ligands in II gives space to increase the ring size. Due to the lack of labile ligands in complex III, increasing the ring size further is not easy and necessitates an alternative path.…”

Regioselectivity of Pd-catalyzedo-carborane arylation: a theoretical view

“…Carboranes are a class of boron clusters in which one or more B-H vertices are replaced by C-H units. [1][2][3] Since the 1960s, the precursor works and the definition for this kind of compound have been reported. 4 Meanwhile, the icosahedral carboranes as the most important carboranes have attracted widespread attention due to their many attractive properties, such as unique thermal and chemical stability, 5,6 enriched boron content, [7][8][9] three-dimensional aromaticity 10,11 and so on.…”

Access to cationic polyhedral carboranes via dynamic cage surgery with N-heterocyclic carbenes

“…Examples in synthetic organic chemistry and catalysis include the early use of diborane in organic chemistry as a reducing agent 4 ; ionic closo-carboranes as weakly-coordinating anions, transfer agents 5 or recently as a supporting scaffold for the stabilisation of low-valent main-group elements by silylenes [4][5][6][7][8][9][10] ; and lowcoordinate boron species for the one-pot reduction of dinitrogen to ammonium chloride [11][12][13] . Especially the last case, based on Robinson's idea, further developed by Braunschweig, of the use of supporting N-heterocyclic carbene (NHC) ligands [14][15][16][17][18][19] , could open avenues for synthetic applications. There are also a number of applications in multidisciplinary areas such as energy storage and conversion 20 , materials science 21 , nuclear-waste treatment and medicine 22,23 , which confirms the broad scope of this area of chemistry.…”