Thiaboranes on Both Sides of the Icosahedral Barrier: Retaining and Breaking the Barrier with Carbon Functionalities

The concept of icosahedral barrier has been expanded from the chemistry of carbaboranes to the area of thiaboranes. Both representatives of this barrier, i. e., closo-1,2-C₂ B₁₀ H₁₂ and closo-1-SB₁₁ H₁₁ , are similar in their electron distribution, which is dominated by positive charge in the midpoint of the C-C vector and on the sulfur atom with experimentally determined dipole moments of 4.50 D and 3.64 D, respectively. This is a driving force for their reactivity as exemplified by their reactions with different carbon functionalities. Icosahedral closo-1-SB₁₁ H₁₁ reacts both with an electron sextet containing carbon (in the form of N-heterocyclic carbenes), reported earlier, and with methyl iodide with an electron octet on the carbon. The latter reaction provides hexamethylated thiaborane on the basis of methylation so far unknown in this area of heteroborane chemistry. The computations of the heat of formation (ΔH_f ²⁹⁸ ) make it possible to estimate the height of the barrier as well as to propose closo-thiaboranes beyond the barrier. Eleven and twelve vertex thiaboranes with nido electron count are known experimentally for breaking the barrier. These computations also suggest that the larger nido-thiaboranes are promising candidates for the corresponding experimental availability, i. e., the ΔH_f ²⁹⁸ of a 13-vertex nido-thiaborane cluster has been computed to be more negative than that of the well-known nido-SB₁₀ H₁₁ ^- cluster (-6.7 and -5.6 kcal mol^-1 per vertex, respectively).

Synthesis and Application of Monomeric Chalcogenolates of 13 Group Elements

Utilization of the N,C,N-chelating ligand L (L={2,6-(Me₂ NCH₂ )₂ C₆ H₃ }^- ) in the chemistry of 13 group elements provided either N→In coordinated monomeric chalcogenides LIn(μ-E₄ ) (E=S, Se) with unprecedented InE₄ inorganic ring or monomeric chalcogenolates LM(EPh)₂ (M=Ga, In). Complex LGa(SePh)₂ was selected as the most suitable single source precursor (SSP) for the deposition of amorphous semiconducting GaSe thin films using spin coating method.

Investigation of Thiaborane closo- nido Conversion Pathways Promoted by N-Heterocyclic Carbenes

The 12-X- closo-SB₁₁H₁₀ (X = H or I) thiaboranes react with one or two molar equivalents of various N-heterocyclic carbenes (NHCs) to give the deprotonated 12-vertex species of [12-X-SB₁₁H₉·NHC]^-[NHC-H]⁺composition as kinetic products. The use of one molar equivalent of a sterically more hindered NHC reactant leads to the formation of 12-X-SB₁₁H₁₀·NHC adducts with a heavily distorted cage and the nido electron count. Further reaction of 12-I-SB₁₁H₁₀·NHC to deboronated 12-X-SB₁₀H₉·NHC proceeds in acetone to complete the closo- nido reaction pathway under the thermodynamic control. The structures of all compounds have been investigated by NMR spectroscopy and diffraction techniques. The results are supported by theoretical methods.

Synthesis of closo-1,2-H2C2B8Me8 and 1,2-H2C2B8Me7X (X = I and OTf) Dicarbaboranes and Their Rearrangement Reactions

Methyl-camouflaged dicarbaboranes closo-1,2- and 1,10-H₂C₂B₈Me₈ have been prepared in high yields either from nido-5,6-H₂C₂B₈H₁₀ or closo-1,2-H₂C₂B₈H₈ via electrophilic methylation reactions and cluster-rearrangement methods. Prepared were also monosubstituted derivatives of general formulation closo-H₂C₂B₈Me₇-X (X = I or OTf). The permethylated compounds exhibit extreme air stability in comparison to unprotected counterparts as a consequence of rigid, egg-shaped hydrocarbon structures incorporating inner C₂B₈ carborane scaffolding. The structures of all compounds isolated were confirmed unambiguously by multinuclear (¹¹B, ¹H, ¹³C, and ¹⁹F) NMR measurements, supported by X-ray diffraction analyses and geometry optimization methods on several compounds.

Quantitative syntheses of permethylated closo-1,10-R2C2B8Me8 (R = H, Me) carboranes. Egg-shaped hydrocarbons on the Frontier between inorganic and organic chemistry

Electrophilic methylation of the closo-1,10-R2C2B8H8 (1) (R = H or Me) dicarbaboranes at higher temperatures or thermal rearrangement of the 1,6-R2C2B8Me8 (3) compounds at 400-500 °C generated the B-permethylated derivatives closo-1,10-R2C2B8Me8 (2) in quantitative (>95%) yields. The compounds exhibit extreme air stability as a consequence of a rigid, egg shaped hydrocarbon structures incorporating inner 1,10-C2B8 carborane core.

Triorganotin(iv) cation-promoted dimethyl carbonate synthesis from CO2and methanol: solution and solid-state characterization of an unexpected diorganotin(iv)-oxo cluster

NovelC,N-chelated organotin(iv) complexes bearing weakly coordinating carborane moieties were prepared and used as a catalyst precursor for the direct synthesis of dimethyl carbonate (DMC) from CO₂and methanol.

Various types of non-covalent interactions contributing towards crystal packing of halogenated diphospha-dicarbaborane with an open pentagonal belt

We have synthesized and crystalized 3-Cl-10-I-nido-7,8,9,11-P₂C₂B₇H₇. Quantum chemical calculations have demonstrated that the obtained crystal structure is stabilized by hydrogen, dihydrogen and pnictogen bonds.

A novel stibacarbaborane cluster with adjacent antimony atoms exhibiting unique pnictogen bond formation that dominates its crystal packing

We have prepared nido-7,8,9,11-Sb₂C₂B₇H₉, the first cluster with simultaneous Sb-B, Sb-C and Sb-Sb atom pairs with interatomic separations with magnitudes that approach the respective sums of covalent radii. However, the length of the Sb-Sb separation in this cluster is slightly less than the sum of the covalent radii. Quantum chemical analysis has revealed that the crystal packing of nido-7,8,9,11-Sb₂C₂B₇H₉ is predominantly dictated by pnictogen (Pn) bonding, an unconventional σ-hole interaction. Indeed, the interaction energy of a very strong Sb₂H-B Pn-bond in the nido-7,8,9,11-Sb₂C₂B₇H₉ dimer exceeds -6.0 kcal mol^-1. This is a very large value and is comparable to the strengths of known Pn-bonds in Cl₃Pnπ complexes (Pn = As, Sb).