Carba-closo-dodecaborate Anions with Cluster Carbon-Phosphorous Bonds

Chiral Carborane Acids Decorated with Binol-Based Phosphonates: Synthesis, Characterization, and Application

The syntheses of hexabrominated closo-carborates decorated with different chiral Binol-derived phosphonates and their conjugate acids are described. X-ray diffraction analysis reveals a polymeric structure for the sodium salt with the anionic units connected by [B-Br-Na-O═P]+ linkages. For the acid, coordination of the proton to the phosphonate's P═O oxygen atom is assumed. The pKa value was estimated by combining experiments and computations. Application of these Brønsted acids as chiral catalysts in an imino-ene and a Mukaiyama-Mannich reaction was moderately successful.

Nonclassical Applications of closo-Carborane Anions: From Main Group Chemistry and Catalysis to Energy Storage

Classically closo-carborane anions, particularly [HCB₁₁H₁₁]^- and [HCB₉H₉]^-, and their derivatives have primarily been used as weakly coordinating anions to isolate reactive intermediates, platforms for stoichiometric and catalytic functionalization, counteranions for simple Lewis acid catalysis, and components of materials like liquid crystals. The aim of this article is to educate the reader on the contemporary nonclassical applications of these anions. Specifically, this review will cover new directions in main group catalysis utilized to achieve some of the most challenging catalytic reactions such as C-F, C-H, and C-C functionalizations that are difficult or impossible to realize with transition metals. In addition, the review will cover the utilization of the clusters as dianionic C σ-bound ligands for coordination chemistry, ligand substituents for coordination chemistry and advanced catalyst design, and covalently bound spectator substituents to stabilize radicals. Furthermore, their applications as solution-based and solid-state electrolytes for Li, Na, and Mg batteries will be discussed.

Teaching an old dog new tricks: new directions in fundamental and applied closo-carborane anion chemistry

In this feature article we cover new directions in the fundamental and applied chemistry of the closo-carborane anions [HCB₁₁H₁₁]⁻¹ and [HCB₉H₉]⁻¹, including energy storage applications, ionic liquids, anionic carborane fused heterocycles/radicals, ligand substituents, and ligands for catalysis and coordination chemistry.

Inductive effects of 10 and 12-vertex closo-carborane anions: cluster size and charge make a difference

The inductive effects of 10 and 12-vertex closo-carborane anion ligand substituents are elucidated for the first time. It is found that both of these cluster substituents are potent electron donating groups, which is in contrast to C-functionalized o-carborane. The fact that the 10-vertex cluster displays the strongest electron donating ability can be rationalized by its charge and size.

Polyfluorinated carba-closo-dodecaboranes with amino and ammonio substituents bonded to boron

The inner salts x-H3N-closo-1-CB11H11 (x = 12, 2) and 7-H3N-12-F-closo-1-CB11H11 were fluorinated with elemental fluorine in anhydrous hydrogen fluoride to give the B-perfluorinated ammonio derivatives 1-H-x-H3N-closo-1-CB11F10 (x = 12, 7, 2). Deprotonation of the ammonio group yielded the corresponding amino-functionalized anions [1-H-x-H2N-closo-1-CB11F10](-) (x = 12, 7, 2) that were isolated as [Et4N](+) salts. Hydrolysis of the highly fluorinated inner salts 1-H-x-H3N-closo-1-CB11F10 (x = 12, 7, 2) is very slow in acidic aqueous solutions. This stability of the ammonio derivatives is unprecedented because the related fluorinated anion [1-H2N-closo-1-CB11F11](-) is immediately hydrolyzed to simple boron species in the presence of aqueous acids. The ammonio derivatives 1-H-x-H3N-closo-1-CB11F10 (x = 12, 7, 2) are much more acidic compared to their non-fluorinated counterparts as assessed from potentiometric titrations and DFT calculations. The inner salts and the anions were characterized by NMR and vibrational sepectroscopy. Solid-sate structures of 1-H-12-H3N-closo-1-CB11F10·H2O, 1-H-7-H3N-closo-1-CB11F10·diglyme, 1-H-2-H3N-closo-1-CB11F10·0.5H2O, 7-H3N-12-F-closo-1-CB11H10·(CH3)2CO and [Et4N][1-H-12-H2N-closo-1-CB11F10] were determined by single-crystal X-ray diffraction.

Carba-closo-dodecaborate anions with two functional groups: [1-R-12-HC≡C-closo-1-CB₁₁H₁₀]⁻ (R = CN, NC, CO₂H, C(O)NH₂, NHC(O)H)

Disubstituted carba-closo-dodecaborate anions with one functional group bonded to the cluster carbon atom and one ethynyl group bonded to the antipodal boron atom were synthesized from easily accessible {closo-1-CB11} clusters. [Et4N][1-NC-12-HC≡C-closo-1-CB11H10] ([Et4N]4b) was prepared starting from Cs[12-Et3SiC≡C-closo-1-CB11H11] (Cs1c) via salts of the anions [1-HO(O)C-12-HC≡C-closo-1-CB11H10](-) (2b) and [1-H2N(O)C-12-HC≡C-closo-1-CB11H10](-) (3b). In a similar reaction sequence [Et4N][1-CN-12-HC≡C-closo-1-CB11H10] ([Et4N]7b) was obtained from Cs[1-H2N-12-HC≡C-closo-1-CB11H10] (Cs5b) by formamidation to yield [Et4N][1-H(O)CHN-12-HC≡C-closo-1-CB11H10] ([Et4N]6b) and successive dehydration. In addition, the synthesis of the isonitrile [Et4N][1-CN-closo-1-CB11H11] ([Et4N]7a) is presented. The {closo-1-CB11} derivatives were characterized by multinuclear NMR as well as vibrational spectroscopy, mass spectrometry, and elemental analysis. The crystal structures of [Et4N][1-HO(O)C-12-HC≡C-closo-1-CB11H10] ([Et4N]2b), [Et4N][1-H2N(O)C-12-HC≡C-closo-1-CB11H10] ([Et4N]3b), [Et4N][1-NC-12-HC≡C-closo-1-CB11H10] ([Et4N]4b), [Et4N][1-H(O)CHN-12-HC≡C-closo-1-CB11H10] ([Et4N]6b), [Et4N][1-CN-12-HC≡C-closo-1-CB11H10] ([Et4N]7b), and K[1-H(O)CHN-closo-1-CB11H11] ([Et4N]6a) were determined. The transmission of electronic effects through the carba-closo-dodecaboron cage was studied based on (13)C NMR spectroscopic data, by results derived from density functional theory calculations, and by a comparison to the data of related benzene and bicyclo[2.2.2]octane derivatives.