Showing papers on "Carborane published in 2021"

A Strategy for Selective Catalytic B-H Functionalization of o-Carboranes.

Abstract: Carboranes are a class of polyhedral carbon-boron molecular clusters featuring three-dimensional aromaticity, which are often considered as 3D analogues of benzene. Their unique structural and electronic properties make them invaluable building blocks for applications ranging from functional materials to versatile ligands to pharmaceuticals. Thus, selective functionalization of carboranes has received tremendous research interest. In earlier days, the vast majority of the works in this area were focused on cage carbon functionalization via facile deprotonation of cage CH, followed by reaction with electrophiles. On the contrary, cage B-H activation is very challenging since the 10 B-H bonds on o-carborane are very similar, and how to achieve the desired transformation at specific boron vertex is a long-standing issue.As carbon is considered more electronegative than boron, this property results in different vertex charges on the o-carborane cage, which follow the order B(3,6)-H ≪ B(4,5,7,11)-H < B(8,10)-H < B(9,12)-H. We thought that this difference may trigger the favorite interaction of a proper transition metal complex with a specific B-H bond of carborane, which could be utilized to solve the selectivity issue. Accordingly, our strategy is described as follows: (1) electron-rich transition metal catalysts are good for the activation of the most electron-deficient B(3,6)-H bonds (connected to both cage C-H vertices); (2) electron-deficient transition metal catalysts are good for the activation of the relatively electron-rich B(8,9,10,12)-H bonds (with no bonding to either cage C-H vertices); and (3) directing-group-assisted transition metal catalysis is appropriate for the activation of the B(4,5,7,11)-H bonds (connected to only one cage C-H vertex), whose vertex charges lie in the middle of the range for the 10 B-H bonds. This strategy has been successfully applied by our laboratory and other groups in the development of a series of synthetic routes for catalytic selective activation of B-H bonds of the carborane cage, resulting in the synthesis of a large number of cage-boron-functionalized carborane derivatives in a regioselective and catalytic fashion. Subsequently, significant progress in this emerging area has been made.In 2013 we reported the selective tetrafluorination of o-carboranes at the B(8,9,10,12)-H bonds using an electron-deficient Pd(II) salt, [Pd(MeCN)4][BF4], as the catalyst. In 2014 we disclosed the first example of carboxy-directed alkenylation of o-carboranes at the B(4) vertex promoted by an Ir(III) catalyst. Subsequently, in 2017 we presented an electron-rich Ir(I)-catalyzed diborylation of o-carboranes at the B(3,6)-H bonds. We also uncovered the first example of Pd-catalyzed asymmetric synthesis of chiral-at-cage o-carboranes in 2018. These proof-of-principle studies have greatly stimulated research activities in selective B-H activation of carboranes and boron clusters enabled by transition metal catalysts. We have so far developed a toolbox of synthetic methods for selective catalytic cage B-olefination, -arylation, -alkenylation, -alkynylation, -oxygenation, -sulfenylation, -borylation, -halogenation, and -amination. We have recently expanded our research to base metal catalysis. As the field progresses, we expect that other methods for regioselective cage B-H activation will be invented, and the results detailed in this Account will promote these efforts.

Changing the Reactivity of Zero- and Mono-Valent Germanium with a Redox Non-Innocent Bis(silylenyl)carborane Ligand.

Abstract: Using the chelating C,C'-bis(silylenyl)-ortho-dicarborane ligand, 1,2-(RSi) 2 -1,2-C 2 B 10 H 10 [R = PhC(NtBu) 2 ], leads to the monoatomic zero-valent Ge complex ('germylone') 3 . The redox non-innocent character of the carborane scaffold has a drastic influence on the reactivity of 3 towards reductants and oxidants. Reduction of 3 with one molar equivalent of potassium naphthalenide (KC 10 H 8 ) causes facile oxidation of Ge 0 to Ge I along with a two-electron reduction of the C 2 B 10 cluster core and subsequent Ge I -Ge I coupling to form the dianionic bis(silylene)-supported Ge 2 complex 4 . In contrast, oxidation of 3 with one molar equivalent of [Cp 2 Fe][B{C 6 H 3 (CF 3 ) 2 } 4 ] as a one-electron oxidant furnishes the dicationic bis(silylene)-supported Ge 2 complex 5 . The Ge 0 atom in 3 acts as donor towards GeCl 2 to form the trinuclear mixed-valent Ge 0 -->Ge II <--Ge 0 complex 6 , from which dechlorination with KC 10 H 8 affords the neutral Ge 2 complex 7 as a diradical species.

Metal-Catalyzed B–H Acylmethylation of Pyridylcarboranes: Access to Carborane-Fused Indoliziniums and Quinoliziniums

Abstract: Metal-catalyzed mono-acylmethylation of pyridylcarboranes has been realized using α-carbonyl sulfoxonium ylides as a coupling partner. The reaction features high efficiency, excellent site-selectivity and good functional group tolerance. In the presence of pyridyl and enolizable acylmethyl, a post-coordination mode has been proposed and validated by in situ high resolution mass spectroscopy (HRMS) to rationalize the unique mono-substitution. Post-functionalization at the newly incorporated alkyl site provides additional utility of this method, including the construction of carborane-fused indoliziniums and quinoliziniums. We believe that these mono-alkylated carboranes, together with their post-functionalized derivatives, may find applications in luminescent materials and drug discovery in the near future.

Rh-Catalyzed Decarbonylative Cross-Coupling between o-Carboranes and Twisted Amides: A Regioselective, Additive-Free, and Concise Late-Stage Carboranylation.

Abstract: The convenient cross-coupling of sp2 or sp3 carbons with a specific boron vertex on carborane cage represents significant synthetic values and insurmountable challenges. In this work, we report an Rh-catalyzed reaction between o-carborane and N-acyl-glutarimides to construct various Bcage -C bonds. Under the optimized condition, the removable imine directing group (DG) leads to B(3)- or B(3,6)-C couplings, while the pyridyl DG leads to B(3,5)-Ar coupling. In particular, an unexpected rearrangement of amide reagent is observed in pyridyl directed B(4)-C(sp3 ) formation. This scalable protocol has many advantages, including easy access, the use of cheap and widely available coupling agents, no requirement of an external ligand, base or oxidant, high efficiency, and a broad substrate scope. Leveraging the RhI dimer and twisted amides, this method enables straightforward access to diversely substituted and therapeutically important carborane derivatives at boron site, and provides a highly valuable vista for carborane-based drug screening.

Highly Efficient Carborane-Based Activators for Molecular Olefin Polymerization Catalysts

Abstract: Several ammonium carborane salts ([HNR3][HCB11X11], X = H, Me, Cl) were prepared and evaluated as activators with bis-metallocene and constrained geometry precatalysts at 140 and 190 °C. Activators...

Synthesis and Structure of an o-Carboranyl-Substituted Three-Coordinate Borane Radical Anion.

Abstract: Bis(1-(4-tolyl)-carboran-2-yl)-(4-tolyl)-borane [(1-(4-MeC6 H4 )-closo-1,2-C2 B10 H10 -2-)2 (4-MeC6 H4 )B] (1), a new bis(o-carboranyl)-(R)-borane was synthesised by lithiation of the o-carboranyl precursor and subsequent salt metathesis reaction with (4-tolyl)BBr2 . Cyclic voltammetry experiments on 1 show multiple distinct reduction events with a one-electron first reduction. In a selective reduction experiment the corresponding paramagnetic radical anion 1.- was isolated and characterized. Single-crystal structure analyses allow an in-depth comparison of 1, 1.- , their calculated geometries, and the S1 excited state of 1. Photophysical studies of 1 show a charge transfer (CT) emission with low quantum yield in solution but a strong increase in the solid state. TD-DFT calculations were used to identify transition-relevant orbitals.

Direct and Regioselective Palladium(II)-Catalyzed B(4)-H Monoacyloxylation and B(4,5)-H Diacetoxylation of o-Carborane Acids with Phenyliodonium Dicarboxylates

Abstract: A direct B(4)-H monoacyloxylation via a Pd-catalyzed regioselective B(4)-H activation of o-carborane acids with phenyliodonium dicarboxylates was developed, and a series of B(4)-H monoacyloxylated o-carboranes decorated with active groups were synthesized with moderate to good yields as well as excellent selectivity. In addition, a direct B(4,5)-H diacetoxylation from o-carborane acids with phenyliodonium diacetate was demonstrated.

Recovering the Thermally Activated Delayed Fluorescence in Aggregation-Induced Emitters of Carborane.

Abstract: The aggregation-induced emission (AIE) behaviors of carborane-based hybrid emitters have been extensively reported, while their combinations with the thermally activated delayed fluorescence (TADF)...

Closo- or Nido-Carborane Diphosphane as Responsible for Strong Thermochromism or Time Activated Delayed Fluorescence (TADF) in [Cu(N^N)(P^P)]0/.

Abstract: Ortho-closo or ortho-nido-carborane-diphosphanes have been selected to prepare the heteroleptic cationic or neutral [Cu(N^N){(PPh2)2C2B10H10}]PF6 (1) and [Cu(N^N){(PPh2)2C2B9H10}] (2) [N^N = 2-(4-thiazolyl)benzimidazole], respectively. Complexes 1 and 2 display very different emissive behavior. Neutral complex 2 exhibits TADF (time activated delayed fluorescence) which has been studied both as powder and PMMA composite with similar ΔE(S1 - T1), τ(T1), and τ(S1) in both phases. Cationic complex 1 displays a much lower quantum yield than 2 and does not show TADF, but it exhibits a significant thermochromic luminescence, and its emission is very dependent on the medium. Theoretical studies show that metal-ligand (M-diphosphane) to ligand (L', diimine) transitions, MLL'CT, are responsible of the transitions which originate the emissive properties, but with very different contribution of the copper center, carborane cluster, and diphosphane phenyl rings for 1 and 2.

Borane Polyhedra Beyond Icosahedron

Abstract: Polyhedral boron cluster chemistry has been dominated over the last six decades by icosahedral borate dianions, carboranes, metallacarboranes and metallaboranes owing to their high stabilities and rich chemistry. After the first isolation of the closo-borate dianion [B10H10]2− in 1959, many other closo-[BnHn]2− anions (n = 5–9, 11 and 12) were synthesized by Hawthorne, Lipscomb, Muetterties and others. However, the first crystallographic characterization of icosahedral K2[B12H12] by Lipscomb in 1960 stimulated the chemistry and bonding investigations of these closo-[BnHn]2− (n = 6–12) anions. Interestingly, although the closo-[B7H7]2− was synthesized and partially characterized, the X-ray structure of the heptaborane dianion was not established until very recently. Bernhardt and co-worker have fully characterized closo-[B7H7]2− very recently and subsequently, we have isolated a transition metal guarded closo-heptaborane. After exploring the lower borane series, chemists have started envisaging supraicosahedral boranes. Although theoretical calculations by Lipscomb, Jemmis and Schleyer suggested that closo-borate dianions beyond icosahedron [BnHn]2− (n ˃ 12) are stable, the parent closo-borate dianions [BnHn]2− (n ˃12) have not been isolated yet. Following the first isolation of a supraicosahedral metallacarborane in 1971, carboranes, metallacarboranes and metallaboranes have been synthesized with supraicosahedral geometries. The bonding and characteristic electron counts of these supraicosahedral clusters are quite different from those of the lower nuclearity clusters. This chapter describes the synthesis, structural features and electron counts of 13–16-vertex borane, carborane, metallacarborane and metallaborane polyhedral molecules.

1,12-Diiodo-Ortho-Carborane: A Classic Textbook Example of the Dihalogen Bond

Abstract: The crystal structure of 1,12-diiodo-ortho-carborane 1,12-I2-1,2-C2B10H10 was determined by single crystal X-ray diffraction. In contrary to earlier studied 1,12-dibromo analogue 1,12-Br2-1,2- C2B10H10, its crystal packing is governed by the presence of the intermolecular I⋯I dihalogen bonds between the iodine atom attached to the carbon atom (acceptor) and the iodine atom attached to the antipodal boron atom (donor) of the carborane cage. The observed dihalogen bonds belong to the II type and are characterized by classical parameters: shortened I⋯I distance of 3.5687(9) A, C–I⋯I angle of 172.61(11)° and B–I⋯I angle of 92.98(12)°.

Excimer Formation of Perylene Bisimide Dyes within Stacking-Restrained Folda-Dimers: Insight into Anomalous Temperature Responsive Dual Fluorescence

Abstract: We have fabricated a new perylene bisimide (PBI) folda-dimer (BPBI-CB-1) by tethering two PBI moieties to the ortho-carbon positions of a carborane unit. The synthesized compound adopted distinct c...

Highly Deformed o-Carborane Functionalised Non-linear Polycyclic Aromatics with Exceptionally Long C−C Bonds

Abstract: The effect of substituting o-carborane into the most sterically hindered positions of phenanthrene and benzo(k)tetraphene is reported. Synthesised via a Bull-Hutchings-Quayle benzannulation, the crystal structures of these non-linear acenes exhibited the highest aromatic deformation parameters observed for any reported carborane compound to date, and among the largest carboranyl C-C bond length of all organo-substituted o-carboranes. Photoluminescence studies of these compounds demonstrated efficient intramolecular charge-transfer, leading to aggregation induced emission properties. Additionally, an unusual low-energy excimer was observed for the phenanthryl compound. These are two new members of the family of carborane-functionalised non-linear acenes, notable for their peculiar structures and multi-luminescent properties.

Coordination Ability of 10-EtC(NHPr)=HN-7,8-C2B9H11 in the Reactions with Nickel(II) Phosphine Complexes

Abstract: The complexation reactions of nido-carboranyl amidine 10-PrNHC(Et)=HN-7,8-C2B9H11 with different nickel(II) phosphine complexes such as [(PR2R’)2NiCl2] (R = R’ = Ph, Bu; R = Me, R’ = Ph) were investigated. As a result, a series of novel half-sandwich nickel(II) π,σ-complexes [3-R’R2P-3-(8-PrN=C(Et)NH)-closo-3,1,2-NiC2B9H10] with the coordination of the carborane and amidine components was prepared. The acidification of obtained complexes with HCl led to the breaking of the Ni-N bond with formation of nickel(II) π-complexes [3-Cl-3-R’R2P-8-PrNH=C(Et)NH-closo-3,1,2-NiC2B9H10]. The crystal molecular structure of [3-Ph3P-3-(8-PrN=C(Et)NH)-closo-3,1,2-NiC2B9H10] was determined by single crystal X-ray diffraction.

Impact of deboronation on the electronic characteristics of closo-o-carborane: intriguing photophysical changes in triazole-appended carboranyl luminophores

Abstract: 5-Phenyl-1,2,4-triazole-appended closo- (CB1 and CB2) and nido-o-carboranyl (nido-CB1 and nido-CB2) compounds were prepared and fully characterized using multinuclear NMR spectroscopy and elemental analysis. The solid-state molecular structures of both closo-compounds were analyzed by X-ray crystallography. Although the closo-compounds exhibited dual emissive patterns in the rigid state (in THF at 77 K), which were assignable to a π–π* local excitation (LE)-based emission (λem = ca. 380 nm) on the triazole moieties and to an intramolecular charge transfer (ICT)-based emission (ca. 460 nm) in which the o-carborane units acted as the acceptor (A), at 298 K in THF, the LE-based emission dominated. In contrast, the nido-compounds exhibited an intensive emission originating from ICT transitions in which the o-carborane units reversibly acted as the donor (D). In particular, the positive solvatochromic effects of both nido-compounds and the results of theoretical calculations for the o-carboranyl compounds supported the electronic role of the o-carboranyl unit in each compound. Investigation of the radiative decay mechanism of the closo- and nido-compounds using their quantum efficiency (Φem) and decay lifetime (τobs) suggested that the ICT-based radiative decay of nido-compounds occurred more efficiently than the LE-based decay of closo-compounds. These results implied that emission from the closo-compounds was drastically enhanced by the deboronation reaction upon exposure to an increasing concentration of fluoride anions, and finally became similar to the emission color (sky-blue) of the nido-compounds.

Tuning the architectures and luminescence properties of Cu(I) compounds of phenyl and carboranyl pyrazoles: the impact of 2D versus 3D aromatic moieties in the ligand backbone

Abstract: Incorporation of one or two o-carborane moieties at the backbone of the pyrazole ring was achieved by lithiation and nucleophilic addition onto the corresponding 3,5-dimethyl-1-(2-toluene-p-sulfonyloxyethyl)pyrazole. Two monosubstituted carboranyl pyrazoles (L2 and L3) and one disubstituted carboranyl pyrazole (L4) were synthesized and fully characterized. All new compounds, and the corresponding monosubstituted phenylderivative (L1) behave as N-type ligands upon coordination with CuI to afford different polynuclear Cu(I) compounds 1–4. Compounds 1–4 were fully characterized and their molecular structures were determined by X-ray diffraction. It is noteworthy that whereas the pyrazolylphenyl ligand L1, without o-carborane, provides a 1D coordination polymer (1), ligands containing carborane, L2–L3, affords 0D coordination compounds 2 and 3, and disubstituted carboranyl pyrazole ligand L4 gives rise to a 3D coordination polymer. The photoluminescence behaviour of compounds 1–4 has been investigated in the solid state and by TDDFT calculations for molecular compounds 2 and 3. Complex 2 exhibits blue emission with a maximum at 483 nm and a high fluorescence quantum yield of 66.5%. According to TDDFT calculations the emission occurs from LUMO to HOMO−1 and HOMO−2 and deexcitation could be described as cluster-centred excited state of d–s transition in origin. This result contradicts previous studies of scarce tri-coordinated rhombohedral Cu(I) clusters, where it was assumed the origin of their emissions is (X + M)LCT in nature by analogy with tetra-coordinated rhombohedral Cu(I) clusters. Complex 3 exhibits very weak emission (ΦF of 5%) in the green region with a maximum at 517 nm, which according to TDDFT is through a 3CC state. Calculations also show that, upon excitation, 3 suffers a notable distortion resulting in the total cleavage of the Cu4I4 framework. This cleavage could be the cause of the relatively large Stokes shift observed for 3. To the best of our knowledge, this is the first time that such behaviour is observed for this type of octahedral compounds. Additionally, the 1D polymer 1 exhibits weak fluorescence emission in the orange range with a maximum at 609 nm and a remarkable Stokes shift, whereas the 3D polymer 4 exhibits a similar emission to compound 2, with a moderate quantum yield (ΦF of 13.7%).

Synthesis and Catalytic Properties of Novel Ruthenacarboranes Based on nido-[5-Me-7,8-C2B9H10]2− and nido-[5,6-Me2-7,8-C2B9H9]2− Dicarbollide Ligands

Abstract: The effect of methyl substituents in the lower belt of dicarbollide ligands on the redox potential of ruthenacarboranes based thereof, as well as the ability of the metallacarboranes obtained to catalyze radical polymerization with atom transfer were studied. For this purpose, a new approach to the synthesis of closo-ruthenacarboranes based on substituted dicarbollide ligands was developed and six new complexes 3,3-(Ph2P(CH2)4PPh2)-3-H-3-Cl-9-Me-12-X-closo-3,1,2-RuC2B9H9, 3,3,8-(Ph2P(CH2)4PPh-μ-(C6H4-o))-3-Cl-9-Me-12-X-closo-3,1,2-RuC2B9H8 and 3,3,4,8-(Ph2P(CH2)4P-μ-(C6H4-o)2)-3-Cl-9-Me-9-X-closo-3,1,2-RuC2B9H7 (X = H, Me) were synthetized and characterized by single crystal X-ray diffraction, NMR and ESR spectroscopy and MALDI TOF mass-spectrometry. Comparison of the values of the redox potentials of the synthesized ruthenium complexes in 1,2-dichloroethane with the values previously found for the corresponding ruthenacarboranes based on the parent dicarbollide anion showed that the introduction of methyl substituents into the carborane cage led to a decrease in the redox potentials of the complexes, which made them more preferable catalysts for ATRP. Test experiments on the polymerization of MMA showed that the synthesized ruthenacarboranes were effective catalysts for ATRP, the most active being the complex with two methyl groups and two ortho-phenylenecycloboronated fragments.

Unsaturated Vinyl-Type Carbocation [(CH3)2C=CH]+ in Its Carborane Salts

Abstract: The isobutylene carbocation (CH3)2C=CH+ was obtained in amorphous and crystalline salts with the carborane anion CHB11Cl11-. The cation was characterized by X-ray crystallography and IR spectroscopy. Its crystal structure shows a relatively uniform ionic interaction of the cation with the surrounding anions, with a slightly shortened distance between the C atom of the =CH group and the Cl atom of the anion, pointing to a higher positive charge on this group. In the amorphous phase, the asymmetric interaction of the cation with the anion increases, approaching ion pairing. This gives rise to a strong hyperconjugation between the two CH3 groups and the 2pz orbital of the central carbon sp2 atom (the red shift of the CH stretch is 150 cm-1); this effect stabilizes the cation. Over time, as the structure of the amorphous phase becomes more ordered, the hyperconjugation weakens and disappears in the crystalline phase with the disappearance of ion pairing. The carbocation stabilization in the crystalline phase is achieved due to the transfer of a portion of the charge to the neighboring anions, whereas the charge on the C=C bond becomes the strongest: the C=C stretch frequency drops to ∼160 cm-1 relative to neutral isobutylene. The collected IR spectra for the optimized cation under vacuum (in the 6-311G ++ (d, p) basis for all HF, MP2, and DFT calculations) predict that a positive charge on the C=C bond increases its stretching frequency; this computational result contradicts the experimental data, perhaps because it does not take into account the significant impact of the environment.

Strong σ-Hole Activation on Icosahedral Carborane Derivatives for a Directional Halide Recognition.

Abstract: Crystal engineering based on σ -hole interactions is an emerging approach for realization of new materials with higher complexity. Neutral inorganic clusters derived from 1,2-dicarba- closo -dodecaborane, substituted with -SeMe, -TeMe, and -I moieties on both skeletal carbon vertices are experimentally demonstrated here as outstanding chalcogen- and halogen-bond donors. In particular, these new molecules strongly interact with halide anions in the solid-state. The halide ions are coordinated by one or two donor groups ( μ 1 - and μ 2 -coordinations), to stabilize a discrete monomer or dimer motifs to 1D supramolecular zig-zag chains. Crucially, the observed chalcogen bond and halogen bond interactions feature remarkably short distances and strong directionality. Electrostatic potential calculations further demonstrate the efficiency of the carborane derivatives, with V s,max being similar or even superior to that of reference organic halogen bond donors such as iodopentafluorobenzene.

Synthesis of a carborane-substituted bis(phosphanido) cobaltate(I), ligand substitution, and unusual P4 fragmentation

Abstract: Oxidative addition of the P–P single bond of an ortho-carborane-derived 1,2-diphosphetane (1,2-C2(PMes)2B10H10) (Mes = 2,4,6-Me3C6H2) to cobalt(−I) and nickel(0) sources affords the first heteroleptic complexes of a carborane-bridged bis(phosphanido) ligand. The complexes also incorporate labile ligands suitable for further functionalisation. Thus, the cobalt(I) complex [K([18]crown-6)][Co{1,2-(PMes)2C2B10H10}(cod)] (cod = 1,5-cyclooctadiene) bearing a labile cyclooctadiene ligand undergoes facile ligand exchange reactions with isonitriles and tert-butyl phosphaalkyne with retention of the bis(phosphanido) ligand. However, in the reaction with one equivalent of P4, the electron-rich bis(phosphanido) moiety abstracts a single phosphorus atom with formation of a new P3 chain, while the remaining three P atoms derived from P4 form an η3-coordinating cyclo-P3 ligand. In contrast, when the same reaction is performed with two equivalents of the cobalt(I) complex, a dinuclear product is formed which features an unusual P4 chain in its molecular structure.

Ring-opening and ring-expansion reactions of carborane-fused borirane

Abstract: Though the reaction chemistry of three-membered ring molecules such as cyclopropanes and their heteroatom-containing analogues has been extensively studied, the chemical properties of their boron analogues, boriranes, are little known thus far. This work describes the diverse reactivity patterns of carborane-fused borirane 2. This borirane engages in ring-opening reactions with different types of Lewis acids, such as BBr3, GeCl2, GaCl3, BH3(SMe2) and HBpin, affording a series of ring-opening products, in which M–X or B–H bonds add across the B–C(cage) bond of the three-membered ring in 2. On the other hand, borirane 2 can undergo ring-expansion reactions with unsaturated molecules such as PhCHO, CO2 and PhCN to give ring-expansion products, five-membered boracycles, via a concerted reaction mechanism as supported by DFT calculations. The results of this work not only enrich the reaction chemistry of boriranes, but also offer new routes to boron-containing compounds and heterocycles.

Trimethylammonium-containing rhodacarborane [(9-NMe3-7,8-C2B9H10)RhCl2]2 as a catalyst for the annulation of arylcarboxylic acids with alkynes

Abstract: Rhodacarborane [(9-NMe3-7,8-C2B9H10)RhCl2]2 exhibited moderate catalytic activity in the reaction of annulation of arylcarboxylic acids with alkynes, giving naphthalenes as the major products. Effects of the substituent at the carborane ligand, as well as the nature of organic substrates, on the catalytic activity and selectivity of the reaction were estimated. In particular, it was revealed that a replacement of the NMe3 group at the carborane ligand with the SMe2 one leads to a significantly decreased activity of the catalyst.