Boron Clusters with a Ferrocenylalkynyl Group Bonded to Boron: Synthesis, Characterization, and Electrochemical Trends

Sonogashira Coupling of the Ethynyl Monocarborane [CB11H11-12-CCH]–

The Sonogashira cross coupling between the monocarborane cluster 12-ethynylmonocarba-closo-dodecaborate [CB11H11-12-CCH]– and bromoarenes under Pd catalysis has been developed, providing access to aryl carboranyl alkynes in yields of 42–95%. The transformations...

C(1)-Phenethyl Derivatives of [closo-1-CB11 H12 ]- and [closo-1-CB9 H10 ]- Anions: Difunctional Building Blocks for Molecular Materials

C(1)-vinylation of [closo-1-CB₉ H₁₀ ]^- (A) and [closo-1-CB₁₁ H₁₂ ]^- (B) with 4-benzyloxystyryl iodide followed by hydrogenation of the double bond and reductive deprotection of the phenol functionality led to C(1)-(4-hydroxyphenethyl) derivatives. The phenol functionality was protected as the acetate. The esters were then treated with PhI(OAc)₂ and the resulting isomers were separated kinetically (for derivatives of anion A) or by chromatography (for derivatives of anion B) giving the difunctionalized building blocks in overall yields of 9 % and 50 %, respectively. A similar series of reactions was performed starting with anions A and B and 4-methoxystyryl bromide and iodide. Significant differences in the reactivity of derivatives of the two carborane anions were rationalized with DFT computational results. Application of the difunctionalized carboranes as building blocks was demonstrated through preparation of two ionic liquid crystals. The extensive synthetic work is accompanied by single crystal XRD analysis of six derivatives.

Thermal and Photophysical Properties of Highly Quadrupolar Liquid-Crystalline Derivatives of the [closo-B12 H12 ]2- Anion

Two series of 1,12-bis-zwitterionic derivatives of the [closo-B₁₂ H₁₂ ]^2- anion (B), containing either two 4-alkoxypyridinium groups (1B[n]-p) or one 4-alkoxypyridinium and one 4-pentylthianium groups (2B[n]-p), were prepared and their structural (XRD, DFT), thermal, and photophysical properties were compared with those of the analogous derivatives of the [closo-B₁₀ H₁₀ ]^2- anion (1A[n]-p and 2A[n]-p). Some 1,7-derivatives of B were isolated and investigated. Both series 1[n] and 2[n] exhibit nematic and crystalline polymorphism; the 12-vertex derivatives (B) have higher transition temperatures than those of the 10-vertex analogues (A). All compounds fluoresce with quantum yields higher for 1B (Φ_F =0.37 for 1B[7]-p and Φ_F =0.27 for 2B[7]-p) than those for the 10-vertex analogues (Φ_F =0.04 for 2A[5]-p). DFT calculations demonstrate an order of magnitude lower first hyperpolarizability, β_(-ω,ω,0) , for 2B[7]-p than that for the 10-vertex analogue 2A[7]-p (1.7×10^-30 vs. 18.9×10^-30  esu at ω=0).

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.

Catalyst-Free Polyhydroboration of Dodecaborate Yields Highly Photoluminescent Ionic Polyarylated Clusters

The incorporation of polyhedral boranes into novel photoluminescent materials is an area with increasing interest. While the neutral carboranes have been widely investigated for this purpose, the dodecaborate ion has received much less attention. Herein we report a significant expansion to the scope of substitution reactions for the dodecaborate ion, whereby this cluster was observed to react directly with a wide range of arenes in a step-wise and controlled manner. In the products of these reactions, the dodecaborate ion serves as a core upon which up to nine mono- or polycyclic aromatic hydrocarbon ligands are exohedrally bonded. Spectroscopic evidence suggests the presence of conjugation between the π systems of the aryl ligands and the dodecaborate core, resulting in materials which exhibit high solution-phase photoluminescence, as well as molar absorptivities and Stokes shifts that are significantly larger than those of the free arenes from which they were derived. We propose that this broad reactivity is a valuable synthetic tool for the incorporation of polyhedral boron into novel organic structures.