Improved synthesis of [closo-1-CB9H10]– anion and new C-substituted derivatives

Transformation of various multicenter bondings within bicapped-square antiprismatic motifs: Z-rearrangement

Reported herein are mutual rearrangements in the whole series of seven bicapped-square antiprismatic closo-C₂B₈H₁₀ by means of high-quality computations that disprove the earlier postulated dsd (diamond-square-diamond) scheme for these isomerizations. The experimentally existing closo-1,2-C₂B₈H₁₀ was able to be converted to 1,6-, and 1,10-isomers by pyrolysis, and the dsd (diamond-square-diamond) mechanism was offered as an explanation of these processes. However, these computations disprove the postulated dsd scheme for these isomerizations that take place in the ten-vertex closo series. Experimentally observed thermal rearrangements, both in the parent and substituted closo-1,2-C₂B₈H₁₀, closo-1-CB₉H₁₀^-, and closo-B₁₀H₁₀^2-, indirectly support these refined computations. All these processes are based on the new concept of the so-called Z-mechanism, being consistent with a transition state of a boat shape with an open hexagonal belt that results from the initial breakage of three bonds. Such bond breakings and the consequent bond formations bring to mind the shape of the letter Z. In effect, the pattern of multicenter bonding shifts from reactant through a transition state to product. The molecular rearrangements that are available experimentally favour either the axial or equatorial isomers, and this ratio depends on temperature and the type of cluster and its substitution.

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.

Regioselective Functionalization of the [ closo-1-CB9H10]- Anion through Iodonium Zwitterions

Reactions of [ closo-1-CB₉H₉-1-R]^- (2, R = H, COOH, C₅H₁₁) with PhI(OAc)₂ lead to mixtures of regioisomers [ closo-1-CB₉H₈-1-R-6-IPh] (5[6]) and [ closo-1-CB₉H₈-1-R-10-IPh] (5[10]) in ratios of ∼3:1 to 1:1, of which the former isomer undergoes selective reactions with nucleophiles (MeCN, pyridine, MeC(═NH)NH₂, CN^-). The products and the unreacted 10-isomers 5[10] are separated achieving kinetic resolution of the isomeric iodonium zwitterions. Pure 5[10] is reacted with nucleophiles (pyridine, 4-C₇H₁₅OPyridine, Me₂NCHS, PhCO₂^-, CN^-, N₃^-, I^-, MeC(═NH)NH₂, and MeCN), giving substitution products. The mechanism of the substitution is investigated with density functional theory (DFT) methods. Some of the nucleophilic substitution products are transformed further, expanding the scope of available functional groups for the [ closo-1-CB₉H₁₀]^- anion. Four derivatives are characterized with single-crystal XRD methods: [ closo-1-CB₉H₉-10-N₂] (4[10]a), [ closo-1-CB₉H₉-6-NC₅H₅] (9[6]a), [ closo-1-CB₉H₉-10-NC₅H₅] (9[10]a), and [ closo-1-CB₉H₉-10-NHC(NH₂)Me] (10[10]a). Spectroscopic data for selected derivatives are interpreted in terms of transmission of electronic effects through the { closo-1-CB₉} cluster (NMR) and interaction with substituents (IR, UV). The latter results are compared to those of TD-DFT computational methods.

A systematic examination of classical and multi-center bonding in heteroborane clusters

A systematic revision of bonding types on a broad series of heteroboranes covering closo, nido, arachno and hypho architectures with incorporated tetrel, pnictogen or chalcogen heterovertices.

Rhodium(iii)-catalyzed dehydrogenative dialkenylation of the monocarba-closo-decaborate cluster by regioselective B–H activation

The regioselective double B–H activation of the {CB₉} carborane by rhodium catalysis is reported, affording novel inorganic–organic hybrid clusters.

Quantitative Assessment of Substitution NMR Effects in the Model Series of o-Carborane Derivatives: α-Shift Correlation Method

The principles of a new α-shift correlation (ASC) NMR method are demonstrated on a model series of substituted derivatives of o-carborane for which reliable NMR data are available. This graphical method revealed an acceptable linear correlation between α(¹¹B) or α(¹³C) shifts and those induced by substituents in unsubstituted (u) positions of the carborane cluster. The linearity holds for all nuclei involved in skeletal bonding: Δδ(N)_u = g × α (where N = ¹¹B, ¹³C, and ¹H). The factor g (slope of the correlation line × 10²) becomes an important measure of sensitivity of a given cage position to substituent changes. The β, γ, and δ = A (= antipodal) shifts can be therefore derived from the α-shift, are linearly proportional, and reflect additive character in double substitution. The ASC method appears to be an important tool for quantitative assessment of substituent NMR effects in all exo-substituted boron-cluster systems.

Below the 12-vertex: 10-vertex carborane anions as non-corrosive, halide free, electrolytes for rechargeable Mg batteries

The synthesis and application of the first high voltage, non-corrosive, Mg battery electrolyte based on small carborane anions are reported. This electrolyte displays equal oxidative stability compared to its larger 12-vertex cousin, but is more cost effective to prepare.

11B-NMR shielding effects in theclosoborane series: sensitivity of shifts and their additivity

NMR shielding effects for [X_m-closo-B_nH_n−m]²⁻anions exhibit a simple linear behaviour in all positions of the borane cluster.

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.