Alexander Himmelspach

Tetrahedral Gold(I) Clusters with Carba‐closo‐dodecaboranylethynido Ligands: [{12‐(R3PAu)2CC‐closo‐1‐CB11H11}2]

The increasing interest in the supramolecular chemistry of gold(I) compounds is a result of the unusual, for example optical properties, of these substances that are a result of interand intramolecular aurophilic interactions. In turn, the self-assembly is often based on the intermolecular gold– gold interactions. 5] Salts of the tetranuclear bis(triphenylphosphane gold(I))halonium dications A that contain four gold atoms in a distorted tetrahedral arrangement with four relatively short intermolecular Au···Au distances and two longer intramolecular Au···Au distances are unusual compounds of this type, which are only stable in the solid state. The bis(trigoldoxonium) dication B and the bis(tetraauriomethane) complex C are the only other examples with a similar arrangement. Similar to A, complexes B and C were only observed in the solid state and they dissociate in solution because of electrostatic repulsion. A series of other tetranuclear gold(I) clusters that consist of two dinuclear gold(I) complexes in which the four gold atoms lie at the corners of a distorted square is known, for example {[(Ph3PAu)2SCH2Ph]2} 2+ (D). An important class of building blocks for supramolecular gold(I) compounds are Au alkynyl complexes. Coinage-metal clusters can be prepared through the p-coordination of the alkynes to coinage-metal ions in combination with metallophilic interactions. Only a limited number of such coinage-metal clusters that solely consist of gold(I) cations with ethynido/alkyne ligands have been described. Herein we report distorted tetrahedral Au4 clusters with carboranylethynido ligands. These clusters are formed by selfassembly of two dinuclear gold(I) complexes and they are present in the solid sate and for the first time in solution, as well. Cesium ethynylcarba-closo-dodecaborate reacts with [R3PAuCl] and potassium bis(trimethylsilyl)amide in THF to give the neutral dinuclear gold(I) complexes [12-(R3PAu)2C C-closo-1-CB11H11] (R = Me (1), Et (2), iPr (3), tBu (4)) in 63–95% yield and which are thermally stable up to 220 8C (1; Scheme 1).

Microwave-assisted Kumada-type cross-coupling reactions of iodinated carba-closo-dodecaborate anions.

The microwave-assisted Pd-catalyzed Kumada-type cross-coupling reaction of iodinated carba-closo-dodecaborate anions requires smaller amounts of Grignard reagent and catalyst and results in higher yields in much shorter reaction times in comparison to a reaction with conventional heat transfer. 12-Ph(3)P-closo-1-CB(11)H(11) was identified as the side product of the cross-coupling reactions that use [PdCl(2)(PPh(3))(2)]. The inner salt, which is the first example for a {closo-1-CB(11)} cluster with a B-P bond, was selectively synthesized via a related microwave-assisted cross-coupling protocol and characterized by NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction. In addition, the crystal structures of the tetraethyl ammonium salts of [12-Ph-closo-1-CB(11)H(11)](-), [12-(4-MeOC(6)H(4))-closo-1-CB(11)H(11)](-), and [12-(H(2)C═(Me)CC≡C)-closo-1-CB(11)H(11)](-) are described.

Quantum‐Chemical and Electrochemical Investigation of the Electrochemical Windows of Halogenated Carborate Anions

The range of electrochemical stability of a series of weakly coordinating halogenated (Hal=F, Cl, Br, I) 1-carba-closo-dodecaborate anions, [1-R-CB(11)X(5)Y(6)](-) (R=H, Me; X=H, Hal, Me; Y=Hal), has been established by using quantum chemical calculations and electrochemical methods. The structures of the neutral and dianionic radicals, as well as the anions, have been optimized by using DFT calculations at the PBE0/def2-TZVPP level. The calculated structures are in good agreement with existing experimental data and with previous calculations. Their gas-phase ionization energies and electron affinities were calculated based on their optimized structures and were compared with experimental (cyclic and square-wave) voltammetry data. Electrochemical oxidation was performed in MeCN at room temperature and in liquid sulfur dioxide at lower temperatures. All of the anions show a very high resistance to the onset of oxidation (2.15-2.85 V versus Fc(0/+)), with only a minor dependence of the oxidation potential on the different halogen substituents. In contrast, the reduction potentials in MeCN are strongly substituent dependent (-1.93 to -3.32 V versus Fc(0/+)). The calculated ionization energies and electron affinities correlate well with the experimental redox potentials, which provide important verification of the thermodynamic validity of the mostly irreversible redox processes that are observed for this series. The large electrochemical windows that are afforded by these anions indicate their suitability for electrochemical applications, for example, as supporting electrolytes.

Salts of the Lewis-Acidic Dianion [Hg(closo-1-CB11F11)2]2−: Coordination of Acetonitrile and Water

The coordination of acetonitrile and water to the Hg atom in [Hg(closo-1-CB(11)F(11))(2)](2-) (1) reveals the Lewis acidity of the Hg(II) center, which is unprecedented, since 1 is a dianion. Both coordination compounds were characterized by single-crystal X-ray diffraction, vibrational spectroscopy, and differential scanning calorimetry (DSC). In contrast, the Hg atom in [PhHg(closo-1-CB(11)F(11))](-) (2) does not coordinate to CH(3)CN and H(2)O, although it has only a single negative charge.

Difunctionalized {closo‐1‐CB11} Clusters: 1‐ and 2‐Amino‐12‐ethynylcarba‐closo‐dodecaborates

Carba-closo-dodecaborate anions with two functional groups have been synthesized via a simple two-step procedure starting from monoamino-functionalized {closo-1-CB11 } clusters. Iodination at the antipodal boron atom provided access to [1-H2 N-12-I-closo-1-CB11 H10 ](-) (1 a) and [2-H2 N-12-I-closo-1-CB11 H10 ](-) (2 a), which have been transformed into the anions [1-H2 N-12-RCC-closo-1-CB11 H10 ](-) (R=H (1 b), Ph (1 c), Et3 Si (1 d)) and [2-H2 N-12-RCC-closo-1-CB11 H10 ](-) (R=H (2 b), Ph (2 c), Et3 Si (2 d)) by microwave-assisted Kumada-type cross-coupling reactions. The syntheses of the inner salts 1-Me3 N-12-RCC-closo-1-CB11 H10 (R=H (1 e), Et3 Si (1 f)) and 2-Me3 N-12-RCC-closo-1-CB11 H10 (R=H (2 e), Et3 Si (2 f)) are the first examples for a further derivatization of the new anions. All {closo-1-CB11 } clusters have been characterized by multinuclear NMR and vibrational spectroscopy as well as by mass spectrometry. The crystal structures of Cs1 a, [Et4 N]2 a, K1 b, [Et4 N]1 c, [Et4 N]2 c, 1 e, and [Et4 N][1-H2 N-2-F-12-I-closo-1-CB11 H9 ]⋅0.5 H2 O ([Et4 N]4 a⋅0.5 H2 O) have been determined. Experimental spectroscopic data and especially spectroscopic data and bond properties derived from DFT calculations provide some information on the importance of inductive and resonance-type effects for the transfer of electronic effects through the {closo-1-CB11 } cage.

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.

2-Aza-niumylcarba-closo-dodeca-borate ethanol monosolvate.

Two formula units of the title compound, 2-H3N-closo-1-CB11H11·CH3CH2OH or CH14B11N·C2H5OH, form a ring motif of R 4 2(8) type in the solid state that surrounds a crystallographic center of symmetry. The ring motif is a result of N—H⋯O hydrogen bonds. In contrast to many structures of {closo-1-CB11} clusters, the assignment of the position of the cluster C atom in the structure of the title compound is unambigious. The relatively long B—N bond length [1.5396 (10) Å] documents the absence of any B—N π-interaction in the title compound although this was observed for a related 2-aminocarba-closo-dodecaborate.