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Carboranes are an interesting class of aromatic molecules with icosahedral geometry, high stability, and unique electronic effects. We herein report a Pd-catalysed coupling reaction of carborane thiols with aryl halides. This protocol was applicable to the controlled synthesis of di(carboranyl) sulfides, and their catalytic performance for aromatic halogenation was examined. [ABSTRACT FROM AUTHOR]

A highly efficient Pd-catalyzed B(9)–H/B(9)–H oxidative dehydrogenation coupling of carboranes to synthesize 9,9′-bis-o-carboranes has been developed. The properties and derivatization of 9,9′-bis-o-carborane were also examined, which provided diverse bis-o-carborane derivatives and bis-nido-carborane. [ABSTRACT FROM AUTHOR]

We report the heterogenization of molecular, electrochemically switchable ortho-substituted carboranes (POCb, POCb-Pyr) for selective metal capture. Films of POCb and POCb-Pyr on glassy carbon and carbon fiber (CF) electrodes demonstrated heterogeneous electrochemical behaviour that was enhanced by the inclusion of single-walled carbon nanotubes (CNTs). Galvanostatically charged CF‖CNT‖POCb and CF‖CNT‖POCb-Pyr electrodes selectively captured and released actinides (Th4+, UO22+) from mixed solutions containing alkali (Cs+), lanthanide (Nd3+, Sm3+) and actinide (Th4+, UO22+) metal ions. [ABSTRACT FROM AUTHOR]

A high yielding method was accomplished for the synthesis of polyfunctionally-substituted carboranes by the Michael addition reaction of various carbon- and boron carborane nucleophiles with α,β-unsaturated compounds containing an electron withdrawing group using Triton-B (benzyltrimethylammonium hydroxide) as a catalyst. This method of synthesizing carborane derivatives involves mild conditions, simple procedures and high yields of the products. As a result, a series of functionalized carborane compounds were obtained and fully characterized. [ABSTRACT FROM AUTHOR]

The visible-light water splitting enhancement of B in ZnO/CdS was systematically studied and the B-doped ZnO/CdS rods (B-ZnO/CdS) showed an excellent H2 generation rate of 13 100 μmol h−1 g−1, mostly 2 times higher than that of ZnO/CdS (ca. 5249 μmol h−1 g−1, λ > 420 nm), indicating that due to the introduction of the B element, the electron separation efficiency in ZnO/CdS was improved significantly. Through various characterization methods (e.g., PL spectroscopy, UV-Diffuse reflection spectroscopy and photoelectric response), the enhanced electron separation efficiency in the B-ZnO/CdS system was directly demonstrated. In addition, according to the density functional theory (DFT) calculation results, B-ZnO/CdS exhibited a negative adsorption energy of water (EH2O* = −1.22 eV), and the d-band center of the Cd atom had a positive shift from −8.46 to −8.45 eV, which was favorable for water absorption and dissociation. From the charge density difference and density of states, it could be found that electrons tend to transfer from ZnO to H2O at the Cd active sites. The accumulated electrons in H2O could extend the H–OH bond length from 0.975 Å to 0.983 Å, thereby facilitating the dissociation of H2O. [ABSTRACT FROM AUTHOR]

A series of mono- and polyfunctional carborane organosilicon derivatives were prepared with good yields based on the hydrosilylation reactions of allylcarboranes with hydride-containing organosilicon compounds such as tetramethyldisiloxane, decamethylpentasiloxane and triethoxysilane in the presence of Karstedt's catalyst. The functionalization of the double bonds in the allylcarboranes proceeded regioselectively in accordance with the Farmer's rule, providing efficient access to carborane silicon compounds. It was found for 9-o- and 9-m-allylcarboranes that an excess of Karstedt's catalyst could promote the migration of a double bond in allylcarboranes to form boron-substituted propenyl derivatives; the structure of the ortho-isomer was supported by X-ray diffraction analysis. [ABSTRACT FROM AUTHOR]

We report herein the first example of the controlled isomerisation of a C,C′-bound (to metal) bis(ortho-carborane) ligand to C,B′-bound with no other change in the molecule. Since the C and B vertices of carboranes have different electron-donating properties this transformation allows the reactivity of the metal centre to be fine-tuned. [ABSTRACT FROM AUTHOR]

Carborane maleimides were prepared in good yields through the thermal cyclization of maleamic acids prepared by the reaction of 3-amino-o-carborane with maleic or 3-bromomaleic anhydrides, respectively. The selective reactivity of synthesized maleimides towards S-nucleophiles was demonstrated. As a result a series of boronated thiosuccinimide- or thiomaleimide-substituted compounds including boron rich ones was obtained and fully characterized. Furthermore the opportunity of variation with substitution patterns may lead to the development of potential candidates for biological applications or the development of new materials. [ABSTRACT FROM AUTHOR]

The reactive borane reagent FpXylBH2•SMe2 was prepared from 1,4-bis(trifluoromethyl)benzene by treatment with n-BuLi, followed by H3B·SMe2 and subsequent removal of hydride. It undergoes a regioselective hydroboration reaction with 1,2-bis(trimethylsilylethynyl)benzene to give the "dimeric" product 13a featuring a conjugated 14-membered core heterocyclic structure that contains a pair of FpXylB units. [ABSTRACT FROM AUTHOR]

The reaction between alkynyl bridged bisferrocenyl derivatives and decaborane results in new symmetrical ferrocenyl substituted carboranes 8–11. All the new compounds have been identified and fully characterized by means of NMR and HRMS. The molecular structures of target compounds 8–11 were determined by single-crystal X-ray analysis. The electrochemistry studies of the ferrocenyl substituted carboranes are reported, and the results suggest that there is a considerable amount of electronic communication between the two ferrocenyls in these symmetrical conjugated oligomers. The thermodynamic stability of the mixed-valent species increases in the order 11 < 8 < 10 < 9. [ABSTRACT FROM AUTHOR]

A multimeric MRI contrast agent based on the closo-borane motif is reported. Twelve copies of a modified AAZTA chelate with an alkyne end group are appended on an azide-functionalized closo-borane motif using Cu(I) catalyzed click chemistry. The presence of two water molecules on the Gd-bound AAZTA chelate results in high relaxivity for the closomer in vitro/in vivo. [ABSTRACT FROM AUTHOR]

The reaction of (diphenylmethylene)hydrazone or 1,4-bis-hydrazone-ylidene(phenylmethyl)benzene with Lewis acidic boranes B(2,4,6-F3C6H2)3 or B(3,4,5-F3C6H2)3 generates the Lewis acid–base adducts. Alternatively, when (9H-fluoren-9-ylidene)hydrazone is employed several products were isolated including 1,2-di(9H-fluoren-9-ylidene)hydrazone, the 2 : 1 borane adduct of NH2–NH2 and the 1-(diarylboraneyl)-2-(9H-fluoren-9-ylidene)hydrazone in which one ArH group has been eliminated. The benzhydrazide starting material also initially gives an adduct when reacted with Lewis acidic boranes which upon heating eliminates ArH generating a CON2B heterocycle. [ABSTRACT FROM AUTHOR]

Icosahedral carboranes in medicine are still an emerging class of compounds with potential beneficial applications in drug design. These highly hydrophobic clusters are potential “new keys for old locks” which open up an exciting field of research for well-known, but challenging important therapeutic substrates, as demonstrated by the numerous examples discussed in this review. [ABSTRACT FROM AUTHOR]

Carboranes, a class of carbon–boron molecular clusters, are often viewed as three-dimensional analogues of benzene. They are finding increasing applications as useful functional building blocks in materials science, medicine, organometallic/coordination chemistry and more. Thus, functionalization of carboranes has received considerable attention. In comparison with the weakly acidic cage C–H bonds that can be readily functionalized, selective cage B–H functionalization among ten chemically similar BH vertices in o-carboranes is very challenging. Only in the recent few years, considerable progress has been made in transition metal catalyzed vertex-specific BH functionalization. This review summarizes recent advances in this research area. [ABSTRACT FROM AUTHOR]

Vertex-specific functionalization of carboranes has received considerable research interest, due to the valuable application of carborane derivatives in medicine, coordination/organometallic chemistry and materials. In comparison with a protic cage C–H bond, cage B–H is hydridic and generally less polar, with a bond dissociation energy of ca. 108 kcal mol−1. These features make B–H activation quite different from that of the C–H bond. In addition, selectivity among ten very similar BH vertices in o-carborane is challenging yet crucial to the effective construction of carborane-based functional molecules. To address these issues, a brand new strategy of cage B–H nucleophilic substitution has recently been presented and developed for straightforward and regioselective cage B–H functionalization. The regioselectivity can be controlled by the electronic/steric properties of the cage carbon substituents. This Frontier article highlights the recent advancement in the nucleophilic cage B–H substitution of carboranes. [ABSTRACT FROM AUTHOR]

Insertion of a P− anion into a P–P bond yielding the first carborane-substituted 1,2,3-triphospholanide 1 was achieved by treating a carborane-substitued 1,2-diphosphetane with sodium phosphaethynolate. The triphospholanide 1 can serve as a versatile nucleophilic building block for unprecedent functionalised triphospholanes and carborane-substituted polyphosphanes. [ABSTRACT FROM AUTHOR]

The synthesis of [1,1′-bis(o-carboranyl)]boranes was achieved through the deprotonation of 1,1′-bis(o-carborane) reagents followed by salt metathesis with (iPr)2NBCl2. X-ray crystallography confirms planar central BC4 rings and Gutmann–Beckett studies reveal an increase in Lewis acidity at the boron center in comparison to their biphenyl congener, 9-borafluorene. [ABSTRACT FROM AUTHOR]

A one pot deboronation/cyclization of 9-amide-o-carboranes for the synthesis of nido-7,8-carborane fused oxazole by cooperation of Pd(OAc)2, AgOAc and K2CO3 has been developed. A plausible mechanism involving an amide directed electrophilic palladation of the B–H bond and deboronation/cyclization process was proposed based on the successful isolation and structural characterization of the key deboronated intermediate. [ABSTRACT FROM AUTHOR]

Iridium(iii)-induced selective B(2,3)–H and C–H bond activations at mono- and bi-p-methoxybenzeneazo-substituted m-carboranes have been investigated. A powerful methodology is introduced for the preparation of unique polynuclear complexes featuring m-carboranyl ligands in a single step. The experimental results highlight that the base employed in the reaction plays a key role in the formation and the structures of the complexes. [ABSTRACT FROM AUTHOR]

By changing the charge distribution of boron vertices via introducing an amide on cage B(9), the selective B(4) arylation of o-carboranes via Suzuki–Miyaura coupling has been developed. A series of o-carborane derivatives decorated with diverse active groups have been synthesized with moderate to good yields, which have been proved to be further transformed to a novel kind of tri-substituted nido-carborane fused oxazole with potential application in boron neutron capture therapy, organometallic as well as coordination chemistry. [ABSTRACT FROM AUTHOR]

Alkylnitrilium derivatives of nido-carborane 10-RC≡N-7,8-C2B9H11 (R = Me, Et) have been prepared by the reaction of the parent anion [7,8-C2B9H12]− with mercury(ii) chloride in mixtures of the corresponding nitriles and benzene. Hydrolysis of 10-EtC≡N-7,8-C2B9H11 resulted in iminol 10-EtC(OH)=HN-7,8-C2B9H11 which on treatment with a base gave the corresponding amide 10-EtC(=O)HN-7,8-C2B9H11. The reactions of 10-EtC≡N-7,8-C2B9H11 with alcohols and thiols were found to give stable imidates and thioimidates 10-EtC(XR)=HN-7,8-C2B9H11 (X = O, R = Me, Et, iPr, Bu; X = S, R = Et, Bu, Hx) as mixtures of E- and Z-isomers that were successfully separated by column chromatography. The crystal molecular structures of E-10-EtC(OR)=HN-7,8-C2B9H11 (R = Et, i-Pr, Bu) and Z-10-EtC(SEt)=HN-7,8-C2B9H11 were determined by single crystal X-ray diffraction. [ABSTRACT FROM AUTHOR]

Alkylnitrilium derivatives of nido-carborane 10-RC≡N-7,8-C2B9H11 (R = Me, Et) have been prepared by the reaction of the parent anion [7,8-C2B9H12]− with mercury(ii) chloride in mixtures of the corresponding nitriles and benzene. Hydrolysis of 10-EtC≡N-7,8-C2B9H11 resulted in iminol 10-EtC(OH)=HN-7,8-C2B9H11 which on treatment with a base gave the corresponding amide 10-EtC(=O)HN-7,8-C2B9H11. The reactions of 10-EtC≡N-7,8-C2B9H11 with alcohols and thiols were found to give stable imidates and thioimidates 10-EtC(XR)=HN-7,8-C2B9H11 (X = O, R = Me, Et, iPr, Bu; X = S, R = Et, Bu, Hx) as mixtures of E- and Z-isomers that were successfully separated by column chromatography. The crystal molecular structures of E-10-EtC(OR)=HN-7,8-C2B9H11 (R = Et, i-Pr, Bu) and Z-10-EtC(SEt)=HN-7,8-C2B9H11 were determined by single crystal X-ray diffraction. [ABSTRACT FROM AUTHOR]

In this study, density functional theory calculations have been used to investigate the decisive role that the carborane (Cab) ligand plays in ethylene polymerization catalyzed by Cab-containing metal complexes. In the catalytic process, a large amount of charge transfer (CT) from Cab to the metal centre was found to facilitate ethylene insertion. Besides this, the (Cab)B–H…H–C(alkyl) dihydrogen bond interaction was demonstrated to be the main factor in stabilizing the intermediates. [ABSTRACT FROM AUTHOR]

A binuclear iridium complex, (Cp2*Ir2(CH2O)C2B10H8) (6), with a unique metal-metal bond has been synthesized and fully characterized. Importantly, this complex is constructed via selective C-H and B(3)-H bond activation on the carborane precursor. Additionally, when the proligand (2-pyridine)(o-carboranyl) methanol ligand was combined with a half-sandwich iridium complex, selective B(6)-H bond activation or metal-carbon bond formation can be induced by the use of different bases. And the rhodium complex constructed from (2-pyridine)(o-carboranyl)methanol ligand containing a metal-carbon bond has been obtained and fully characterized. [ABSTRACT FROM AUTHOR]

Reported are procedures leading to the first types of methyl camouflaged dicarbadecaboranes with fewer than eleven vertices. The compounds contain the closo-1,6-C2B8 scaffolding inside the egg-shaped hepta – decamethyl sheath, which imparts unusually high air and solvolytic stability to all of these compounds. [ABSTRACT FROM AUTHOR]

Ir(iii) and Rh(iii)-mediated site-selective cage B–H and C–H bond activation in o-carboranylmethyl derivatives has been achieved. The selectivity of the reaction is related to the electron donating properties of the ligand. 1,2,3-Triazole-derivatives use the N2 position of the triazole ring to direct the selective o-carborane B–H bond activation, whereas the corresponding triazolylidene derivatives lead to the cage C–H bond activation with complete site-selectivity. [ABSTRACT FROM AUTHOR]

Two novel C,N-chelated organotin(iv) complexes bearing weakly coordinating carborane moieties were prepared by the reaction of the corresponding C,N-chelated organotin(iv) chloride (i.e. LCNR2SnCl, R = n-Bu (1) and Ph (2); LCN = 2-(N,N-dimethylaminomethyl)phenyl)) with monocarba-closo-dodecaborate silver salt (AgCB11H12; Ag·3). Both products of the metathesis, [LCN(n-Bu)2Sn]+[CB11H12]− (4) and [LCNPh2Sn]+ [CB11H12]− (5), respectively, were characterized by both multinuclear NMR spectroscopy and elemental analysis. The instability of 4 and 5 towards water is discussed. The solid-state structure of LCN(n-Bu)2SnOH·B(C6F5)3 (4a) as a model compound with a Sn–O(H)…B linkage is also reported. The evaluation of the catalytic activity of 4 and 5 was carried out within the direct synthesis of dimethyl carbonate (DMC) from methanol and CO2. While 5 was shown to be definitively inactive, presumably due to cleavage of the Sn–Ph bond, compound 4 exhibits a beneficial action, since it leads to an amount of DMC higher than the stoichiometry (nDMC/nSn(cat) = 1.5). In addition, the solid state structures of [BnNMe3]+[CB11H12]− (6) and [(n-Bu)20Sn10O2(OMe)6(CO3)2]2+·2[CB11H12]− (7), isolated as single-crystals and resulting from the recombination of 4 under the reaction conditions (methanol/CO2), were established by sc-XRD analyses within the term of this work as well. 6 and 7 were also fully characterized by IR spectroscopy, multinuclear NMR in solution and elemental analysis. [ABSTRACT FROM AUTHOR]

Dual-emissive properties and their environment responsiveness are reported based on the tolane-o-carborane dyad having various substituents at the tolane moiety. A series of o-carborane dyads were synthesized and characterized. It was shown that their luminescent colors were tuned by the substituents at the tolane moiety. Some derivatives with strong electron-donating substituents such as –OMe, –(OMe)3 and –NMe2 simultaneously showed dual emission bands from the locally-excited (LE) state in the parallel conformation and an intramolecular charge transfer (ICT) state in the twisted one in the octane solution. Furthermore, intensity ratios between two emission bands were varied by heating. These results mean that the electronic properties of the o-carborane dyad system can be modulated by the degree of electron donating properties at the substituents via electronic conjugation. [ABSTRACT FROM AUTHOR]

The crystal structure of the deprotonated monocarba-closo-dodecaborate [12-CN-CB11H11]− is reported. This dianion, featuring a delocalized endohedral negative charge and an exo-cluster C–[Li] moiety, was used for the synthesis of ditopic ligands with the potential to form novel supramolecular frameworks. [ABSTRACT FROM AUTHOR]

The luminescence properties of nido-carborane (7,8-dicarba-nido-carborate anion)-substituted tolane derivatives were investigated. It was shown that the nido-carborane unit acted as an electron-donating group in all derivatives, and their emission colors can be tuned by the substituents at the tolane moiety. According to theoretical investigation, it was proposed that frontier orbitals were distinctly separated by the twisted structure of the methyl substituents at the nido-carborane unit. Thus, in the absorption spectra, drastic changes were obtained because the HOMO–LUMO transition was forbidden. These structural and electrical substituent effects should serve as good guidelines for designing optoelectronic materials based on nido-carboranes. [ABSTRACT FROM AUTHOR]

Ir-Catalyzed –COOH directed site-selective B–H/C–H dehydrogenative cross-coupling of o-carborane with thiophenes has been achieved for the first time. Without any pre-functionalization, carboranyl carboxylic acids and thiophenes can serve as suitable coupling partners, resulting in the preparation of 4-thienyl-o-carboranes in a simple one-pot process for potential applications in materials. [ABSTRACT FROM AUTHOR]

The C-carboranyl iminophosphorane compounds derived from triphenylphosphine (I1) and o-(methylthiophenyl)-diphenylphosphine (I2) were obtained and structurally characterized. Functionalization with sulfur on the other cage carbon atom gave the corresponding disulfides (L1L1 and L2L2). In the case of I1 it was also possible to isolate the trisulfide (L1SL1) and the thiol (L1H), which is not in the expected zwitterionic form, showing that the carborane group reduces the basicity of the nitrogen atom. The disulfides were made to react with the zero-valent metal precursors [M(PPh3)4], where M = Pd, Pt. The structural analysis of the final complexes revealed the non-coordinating nature of the nitrogen atom. The isolated platinum complexes (PtL1 and PtL2) show metalation on an adjacent boron atom of the carborane cage while the palladium complexes (PdL1 and PtL2) do not complete the BH activation and are isolated as pseudo-agostic complexes. The weak pseudo-agostic interaction can be displaced by incoming ligands. Thus, reaction of PdL1 with dppm and dppe diphosphines leads to the isolation of the cis-bis(thiolates) [Pd(L1)2(dppm)] (PdL1dppm) and [Pd(L1)2(dppe)] (PdL1dppe). The non-carboranyl disulfide analogue (L3L3) was prepared and made to react with the zero-valent palladium precursor. The structure of the non-carboranyl palladium analogue (PdL3) shows the coordinating ability of the nitrogen donor atom, proving the deactivating effect of the C-carboranyl group. [ABSTRACT FROM AUTHOR]

Double deboronation of 1,1′-bis(ortho-carborane) results in a mixture of racemic and meso diastereoisomers which are sources of the [7-(7′-7′,8′-nido-C2B9H10)-7,8-nido-C2B9H10]4− tetraanion. Consistent with this, metalation of the mixture with {Ru(p-cymene)} affords the diastereoisomers α-[1-(8′-2′-(p-cymene)-2′,1′,8′-closo-RuC2B9H10)-3-(p-cymene)-3,1,2-closo-RuC2B9H10] (3α) and β-[1-(8′-2′-(p-cymene)-2′,1′,8′-closo-RuC2B9H10)-3-(p-cymene)-3,1,2-closo-RuC2B9H10] (3β) in which the primed cage has undergone a spontaneous 3′,1′,2′ to 2′,1′,8′-RuC2B9 isomerisation. Analogous cobaltacarboranes α-[1-(8′-2′-Cp-2′,1′,8′-closo-CoC2B9H10)-3-Cp-3,1,2-closo-CoC2B9H10] (4α) and β-[1-(8′-2′-Cp-2′,1′,8′-closo-CoC2B9H10)-3-Cp-3,1,2-closo-CoC2B9H10] (4β) are formed by metalation with CoCl2/NaCp followed by oxidation, along with a small amount of the unique species [8-(8′-2′-Cp-2′,1′,8′-closo-CoC2B9H10)-2-Cp-2,1,8-closo-CoC2B9H10] (5) if the source of the tetraanion is [HNMe3]2[7-(7′-7′,8′-nido-C2B9H11)-7,8-nido-C2B9H11]. Two-electron reduction and subsequent reoxidation of 4α and 4β afford species indistinguishable from 5. The reaction between [Tl]2[1-(1′-3′,1′,2′-closo-TlC2B9H10)-3,1,2-closo-TlC2B9H10] and [CoCpI2(CO)] leads to the isolation of a further isomer of (CpCoC2B9H11)2, rac-[1-(1′-3′-Cp-3′,1′,2′-closo-CoC2B9H10)-3-Cp-3,1,2-closo-CoC2B9H10] (6), which displays intramolecular dihydrogen bonding. Thermolysis of 6 yields 4α, allowing a link to be established between the α and β forms of 3 and 4 and racemic and meso forms of the [7-(7′-7′,8′-nido-C2B9H10)-7,8-nido-C2B9H10]4− tetraanion, whilst reduction–oxidation of 6 again results in a product indistinguishable from 5. [ABSTRACT FROM AUTHOR]

An iridium(iii)-catalyzed C–N-bond-forming direct synthesis of carborane azo derivatives was developed. The reaction of o-carborane monocarboxylate with aryldiazonium salt in the presence of a catalytic amount of [Cp*IrCl2]2 and NaOAc in CH3CN at 80 °C gave the corresponding carborane azo derivative in good yield. A series of cyclometalated iridium/rhodium complexes that contain Cp*M–B (M = Ir, Rh) bonds, and are stabilised by the intramolecular coordination of nitrogen donors, were successfully isolated and structurally characterised. [ABSTRACT FROM AUTHOR]

An air-stable mononuclear Co(ii) complex bearing an o-carborane dithiolate ligand has been synthesized which shows slow relaxation of magnetization in the absence of an applied field and a hysteresis loop at 1.8 K. This is the first example of a carborane-incorporated complex that displays SMM properties. [ABSTRACT FROM AUTHOR]

The activation of O–H bonds of water at room temperature driven by the cage-opening rearrangement of a biscarborane-based cluster is reported. The reaction of the 12-vertex-closo-12-vertex-nido biscarborane cluster with water led to the quantitative and selective two-vertex decapitation of a carborane cluster and formation of the pendent boronic acid hydride B(H)(OH) group. Remarkably, this transformation can be quantitatively reversed with the release of water and re-formation of the starting biscarborane cage. The flexibility of cage decapitation/expansion and its influence on the reactivity of an exohedral substituent represent a new approach to cluster-induced organic transformations. [ABSTRACT FROM AUTHOR]

Imidazolium salts linked by an ethyl tether to closo-dicarbadodecaboranes were reacted with [IrCp*Cl2]2, [RhCp*Cl2]2 or [Ru(p-cymene)Cl2]2 in the presence of Ag2O to prepare complexes of the type [MCp*(NHC)Cl2] (M = Ir, Rh; NHC = N-heterocyclic carbene) or [Ru(p-cymene)(NHC)Cl2]. When the NHC contained an N-tBu substituent, C–H activation of the tBu and subsequent alkyl coordination was observed at Ir. Coordination of the closo-dicarbadodecaborane moiety to Ir was possible to give 7-membered metallacycles, coordinated through the carbenic carbon of the NHC and either a carbon atom or a boron atom of the carborane. Examination of the Ir complexes in the transfer hydrogenation of acetophenone to 1-phenylethanol reveals that cyclometallation of the carborane moiety is important for catalytic efficacy, indicating a bifunctional mechanism and involvement of the dicarbadodecaborane anion. [ABSTRACT FROM AUTHOR]

Metalation of the [7-(1′-1′,2′-closo-C2B10H11)-7,8-nido-C2B9H10]2− dianion with various {NiPP2+} or {NiP22+} fragments (PP = chelating diphosphine; P = monodentate phosphine or phosphite) leads either to unisomerised 3,1,2-NiC2B9 species or to isomerised 4,1,2-NiC2B9 or 2,1,8-NiC2B9 species, all with a pendant C2B10 substituent. The products [1-(1′-1′,2′-closo-C2B10H11)-3-dppe-3,1,2-closo-NiC2B9H10] (1), [2-(1′-1′,2′-closo-C2B10H11)-4-dppe-4,1,2-closo-NiC2B9H10] (2), [8-(1′-1′,2′-closo-C2B10H11)-2-dmpe-2,1,8-closo-NiC2B9H10] (3), [1-(1′-1′,2′-closo-C2B10H11)-3,3-(PMe3)2-3,1,2-closo-NiC2B9H10] (4), [1-(1′-1′,2′-closo-C2B10H11)-3,3-(PMe2Ph)2-3,1,2-closo-NiC2B9H10] (6), [1-(1′-1′,2′-closo-C2B10H11)-3,3-{P(OMe)3}2-3,1,2-closo-NiC2B9H10] (9) and [1-(1′-1′,2′-closo-C2B10H11)-2,2-{P(OMe)3}2-2,1,8-closo-NiC2B9H10] (10) were fully characterised spectroscopically and crystallographically, whilst [2-(1′-1′,2′-closo-C2B10H11)-4,4-(PMePh2)2-4,1,2-closo-NiC2B9H10] (8) was characterised spectroscopically. Overall the results suggest that an important factor in a 3,1,2 to 4,1,2 isomerisation is the relief gained from steric crowding, whereas a 3,1,2 to 2,1,8 isomerisation appears to be favoured by strongly electron-donating ligands on the metal. [ABSTRACT FROM AUTHOR]

Boron clusters and organic molecules display manifestly different electronic, physical, chemical and geometrical characteristics. These differences highlight the complementarity of organic synthons and boron clusters, and therefore the feasibility of producing hybrid polymers incorporating both types of fragments. This review focuses on the development of hybrid organic–inorganic π conjugated, silane, siloxane and coordination polymers containing icosahedral boron clusters in the last few decades, which have received considerable academic and technological interest due to the combination of the electronic, optical and thermal properties of traditional inorganic materials with many of the desirable properties of organic plastics, including mechanical flexibility and low production costs. [ABSTRACT FROM AUTHOR]

A palladium catalyzed/silver tuned selective mono- and tetra-acetoxylation of o-carboranes has been developed, and a series of mono- and tetra-acetoxylated o-carboranes decorated with active groups have been synthesized with moderate to good yields as well as excellent selectivity. A mechanism involving electrophilic palladation and cyclopalladation of the B–H bond was proposed. [ABSTRACT FROM AUTHOR]

Four reaction pathways have been found in the reaction of a C,C′-linked nido-biscarborane tetraanionic salt with [Ru(p-cymene)Cl2]2, leading to the isolation and structural characterization of redox, triple cage B–H oxidative addition, cage expansion and cage carbon extrusion products. Among these, the unprecedented cage carbon extrusion results in the formation of a new 6π-electron carboranyl ligand [C2B10H10]2−. The bonding interactions between this ligand and the Ru(ii) center have also been discussed on the basis of DFT calculations. [ABSTRACT FROM AUTHOR]

The syntheses of the first carboranyl N-heterocyclic carbene complexes with transition metals are reported. Both unsymmetrical mono-anionic and symmetrical dianionic NHCs readily react with ClAuSMe2 to afford unusual zwitterionic and anionic Au(i) dimethyl sulfide adducts. The compounds are characterized by NMR, mass spectrometry, and single crystal X-ray diffraction studies. Percent buried volume (%Vbur) calculations indicate that replacement of an adamantyl group by a hydride substituted icosahedral carborane anion results in a 3.7% increase in %Vbur. [ABSTRACT FROM AUTHOR]

Four brand new hybrid ligands combining an N-heterocyclic carbene tethered with two isomeric nido-dicarbaundecaborane dianions, a neutral closo-dicarbadodecaborane or a closo-dicarbadodecaborane anion are described. Versatile coordination of the ligands to RhI is demonstrated, in which both NHC and carborane moieties covalently coordinate a metal centre. [ABSTRACT FROM AUTHOR]

A family of heteroleptic iridium(iii) cyclometalates, [4-(2-RCB)ppy]2Ir(acac) (3c–3g; CB = o-carboran-1-yl; ppy = 2-phenylpyridinato-C2,N; acac = acetylacetonate; R = iPr (3c), iBu (3d), Ph (3e), CF3C6H4 (3f), C6F5 (3g)) with various 2-R substituted o-carboranes at the 4-position in the phenyl ring of the ppy ligand, were prepared. The X-ray crystal structure of all complexes, including 3a (R = H) and 3b (R = Me), showed that while the carboranyl C–C bond distance increases with the increasing steric effect of the 2-R substituent (3a–3d), the bond distance is more likely to be influenced by the electronic effect of the substituent for the 2-aryl substituted complexes (3e–3g). The absorption and emission bands of all complexes were red-shifted with respect to those of the parent (ppy)2Ir(acac) (4). While 3a–3d exhibited intense green phosphorescence with good quantum efficiency in toluene (ΦPL = 0.17–0.47), the complexes were poorly emissive in THF (ΦPL ＜ 0.004). In a PMMA film, however, 3a–3d became substantially emissive (ΦPL = 0.11–0.14, 8 wt% Ir), albeit less emissive than 4 (ΦPL = 0.15). In contrast, the 2-aryl substituted 3e–3g were almost non-emissive in both the solution and solid states. All complexes underwent facile carborane-centered, electrochemical reduction (Eonset = −2.01 to −1.22 V). The potential values of these reductions increased with increases in the electron accepting ability of the 2-R group (H ＜ alkyl ＜ aryl) and were largely shifted anodically with respect to those of 4 and 5-carborane substituted complexes. This reduction behavior of 3a–3g implies that the LUMO contribution of 2-R-o-carborane units increases through the substitution at the 4-position of the ppy ligand and is influenced by the nature of the 2-R group, which may be responsible for facile carboranyl C–C bond variation leading to efficient quenching of the emissive excited states. [ABSTRACT FROM AUTHOR]

1,10-Dicarboxy-1,10-dicarba-closo-decaborane, a classical dicarboxylate spacer ligand type similar to the prototypical terephthalic acid, proved to be different not only from the latter, but also from its closest relative compound, 1,12-dicarboxy-closo-1,12-dicarbadecaborane, with regard to the topology of its derived PCPs. Highly porous and robust compounds of zinc (rob net) and cobalt (‘quasi’pcu) as well as a topologically unexpected copper compound (lvt) define the individuality of the 10-vertex carborane cage as a new fundamental spacer type in PCP chemistry. A combination of a lower steric demand compared to the 12-vertex analogue, a preferred orientation angle of 45° between the carboxylate planes and a moderately low rotation barrier are held responsible for the uniqueness of the 10-vertex analogue. [ABSTRACT FROM AUTHOR]

The new nitrosocarboranes [1-NO-2-R-1,2-closo-C2B10H10] [R = CH2Cl (1), CH3OCH2 (2) p-MeC6H4 (3), SiMe3 (4) and SiMe2tBu (5)] and [1-NO-7-Ph-1,7-closo-C2B10H10] (6) were synthesised by reaction of the appropriate lithiocarborane in diethyl ether with NOCl in petroleum ether followed by quenching the reaction with aqueous NaHCO3. These bright-blue compounds were characterised spectroscopically and, in several cases, crystallographically including structural determinations of 2 and 6 using crystals grown in situ on the diffractometer from liquid samples. In all cases the nitroso group bonds to the carborane as a 1e substituent (bent C–N–O sequence) and has little or no influence on ＜δ11B＞, the weighted average 11B chemical shift, relative to that in the parent (monosubstituted) carborane. Mono- and dinitroso derivatives of 1,1′-bis(m-carborane), compounds 7 and 8 respectively, were similarly synthesised but attempts to prepare the mononitroso 1,1′-bis(o-carborane) by the same protocol led only to the hydroxylamine species [1-(1′-1′,2′-closo-C2B10H11)-2-N(H)OH-1,2-closo-C2B10H10] (9); the desired compound [1-(1′-1′,2′-closo-C2B10H11)-2-NO-1,2-closo-C2B10H10] (10) was only realised by switching to a non-aqueous work-up. The involvement of water in effecting the net reduction of the NO function in 10 to N(H)OH in 9 was confirmed by a series of experiments involving [1-N(H)OH-2-Ph-1,2-closo-C2B10H10] (11), [1-(1′-2′-D-1′,2′-closo-C2B10H10)-2-D-1,2-closo-C2B10H10] (12) and [1-(1′-2′-D-1′,2′-closo-C2B10H10)-2-N(H)OH-1,2-closo-C2B10H10] (13). It is suggested that during aqueous work-up a water molecule, H-bonded to the acidic C2′H of 10, is “delivered” to the adjacent C2NO unit. The ability of the NO group in nitrosocarboranes to undergo Diels–Alder cycloaddition reactions with cyclic 1,3-dienes was established via the syntheses of [1-(NOC10H14)-1,2-closo-C2B10H11] (14) and [1-(NOC6H8)-2-Ph-1,2-closo-C2B10H10] (15). This strategy was then utilised to prepare derivatives of the elusive dinitroso compounds of [1,2-closo-C2B10H12] and 1,1′-bis(o-carborane) leading to the sterically-crowded products [1,2-(NOC6H8)2-1,2-closo-C2B10H10] (16, prepared as meso and racemic diastereoisomers), [1-{1′-2′-(NOC6H8)-1′,2′-closo-C2B10H10}-2-(NOC6H8)-1,2-closo-C2B10H10] (17) and [1-(1′-1′,2′-closo-C2B10H11)-2-(NOC6H8)-1,2-closo-C2B10H10] (18). [ABSTRACT FROM AUTHOR]

Doubly-deprotonated 1,1′-bis(o-carborane) reacts with [RuCl2(p-cymene)]2 to afford [Ru(κ3-2,2′,3′-{1-(1′-1′,2′-closo-C2B10H10)-1,2-closo-C2B10H10})(p-cymene)] (1) in which 1,1′-bis(o-carborane) acts as an X2(C,C′)L ligand where “L” is a B3′–H3′⇀Ru B-agostic interaction, fluctional over four BH units (3′, 6′, 3 and 6) at 298 K but partially arrested at 203 K (B3′ and B6′). This interaction is readily cleaved by CO affording [Ru(κ2-2,2′-{1-(1′-1′,2′-closo-C2B10H10)-1,2-closo-C2B10H10})(p-cymene)(CO)] (2) with the 1,1′-bis(o-carborane) simply an X2(C,C′) ligand. With PPh3 or dppe 1 yields [Ru(κ3-2,3′,3-{1-(1′-1′,2′-closo-C2B10H10)-1,2-closo-C2B10H10})(PPh3)2] (3) or [Ru(κ3-2,3′,3-{1-(1′-1′,2′-closo-C2B10H10)-1,2-closo-C2B10H10})(dppe)] (4) via unusually facile loss of the η-(p-cymene) ligand. In 3 and 4 the 1,1′-bis(o-carborane) has unexpectedly transformed into an X2(C,B′)L ligand with “L” now a B3–H3⇀Ru B-agostic bond. Unlike in 1 the B-agostic bonding in 3 and 4 appears non-fluctional at 298 K. With CO the B-agostic interaction of 3 is cleaved and a PPh3 ligand is lost to afford [Ru(κ2-2,3′-{1-(1′-1′,2′-closo-C2B10H10)-1,2-closo-C2B10H10})(CO)3(PPh3)] (5), which exists as a 1 : 1 mixture of isomers, one having PPh3trans to C2, the other trans to B3′. With MeCN the analogous product [Ru(κ2-2,3′-{1-(1′-1′,2′-closo-C2B10H10)-1,2-closo-C2B10H10})(MeCN)3(PPh3)] (6) is formed as only the former isomer. With CO 4 affords [Ru(κ2-2,3′-{1-(1′-1′,2′-closo-C2B10H10)-1,2-closo-C2B10H10})(CO)2(dppe)] (7), whilst with MeCN 4 yields [Ru(κ2-2,3′-{1-(1′-1′,2′-closo-C2B10H10)-1,2-closo-C2B10H10})(MeCN)2(dppe)] (8). In 5 and 6 the three common ligands (CO or MeCN) are meridional, whilst in 7 and 8 the two monodentate ligands are mutually trans. Compound 1 is an 18-e, 6-co-ordinate, species but with a labile B-agostic interaction and 3 and 4 are 16-e, formally 5-co-ordinate, species also including a B-agostic interaction, and thus all three have the potential to act as Lewis acid catalysts. A 1% loading of 1 catalyses the Diels–Alder cycloaddition of cyclopentadiene and methacrolein in CH2Cl2 with full conversion after 6 h at 298 K, affording the product with exo diastereoselectivity (de ＞77%). Compounds 1–8 are fully characterised spectroscopically and crystallographically. [ABSTRACT FROM AUTHOR]

In recent times, luminescent materials with tunable emission properties have found applications in almost all aspects of modern material sciences. Any discussion on the recent developments in luminescent materials would be incomplete if one does not account for the versatile photophysical features of boron containing compounds. Apart from triarylboranes and tetra-coordinate borate dyes, luminescent materials consisting of boron clusters have also found immense interest in recent times. Recent studies have unveiled the opportunities hidden within boranes, carboranes and metalloboranes, etc. as active constituents of luminescent materials. From simple illustrations of luminescence, to advanced applications in LASERs, OLEDs and bioimaging, etc., the unique features of such compounds and their promising versatility have already been established. In this review, recent revelations about the excellent photophysical properties of such materials are discussed. [ABSTRACT FROM AUTHOR]

Carboranes have attracted increasing interest in the scientific community due to their remarkable structures and strong electron-withdrawing abilities. In this article, four platinum complexes [(C^N^N)PtC≡CPh](1), [(C^N^N)PtC≡C-TPA](2), [(C^N^N)PtC≡C-TAB](3), [(C^N^N)PtC≡C-CB](4) (where TPA = triphenylamine, TAB = triarylboryl, CB = o-carborane) have been calculated via density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods to mainly explore the influence of carborane substituents on electronic structures, photophysical properties and radiative decay processes. The calculated results reveal that 2 with electron-donating triphenylamine has a low radiative decay rate constant and a red-shifted emission band, but 3 and 4 containing electron-withdrawing triarylboryl and o-carborane exhibit the opposite properties, especially 4 is supposed to have the highest phosphorescence quantum yield with the smallest nonradiative decay rate constant. These findings successfully illustrated the structure–property relationship and the designed complex 4 with carborane can serve as a highly efficient phosphorescent material in the future. [ABSTRACT FROM AUTHOR]

New carborane anions carrying one or three triflyloxy substituents are described. The mono-triflyloxy substituted carborane can be halogenated to give pentabromo and decachloro derivatives with preservation of the B–OTf linkage. The use of [HCB11Cl10OTf]− as a weakly coordinating anion is demonstrated. [ABSTRACT FROM AUTHOR]