Bromination Improves the Electron Mobility of Tetraazapentacene.

A cyclocondensation of TIPS-ethynyl-substituted diaminoarenes with in situ obtained 4,5-dibromocyclohexa-3,5-diene-1,2-dione has led to the synthesis of tetrabromotetraazapentacene (BrTAP). BrTAP is easily reduced to its air-stable radical anion and electron mobilities >0.56 cm  V  s can be achieved in thin-film transistors.

Isolation and Characterization of Crystalline, Neutral Diborane(4) Radicals.

Diaryldihalodiboranes(4) were reacted with bis(amidinato)- and bis(guanidinato)silylenes to generate the first neutral diborane-centered radicals. These formally non-aromatic 5π electron systems are stable in the solid state as well as in solution and were characterized by solid-state structure determination, high-resolution mass spectrometry, and EPR spectroscopy. The reactivity of one of these radicals with the oxidant 1,4-benzoquinone led to ring-opening and B-O bond formation.

Closely related yet different: a borylene and its dimer are non-interconvertible but connected through reactivity.

The self-stabilizing, tetrameric cyanoborylene [(cAAC)B(CN)] (, cAAC = 1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene) and its diborene relative, [(cAAC)(CN)B[double bond, length as m-dash]B(CN)(cAAC)] (), both react with disulfides and diselenides to yield the corresponding cAAC-supported cyanoboron bis(chalcogenides). Furthermore, reactions of or with elemental sulfur and selenium in various stoichiometries provided access to a variety of cAAC-stabilized cyanoboron-chalcogen heterocycles, including a unique dithiaborirane, a diboraselenirane, 1,3-dichalcogena-2,4-diboretanes, 1,3,4-trichalcogena-2,5-diborolanes and a rare six-membered 1,2,4,5-tetrathia-3,6-diborinane. Stepwise addition reactions and solution stability studies provided insights into the mechanism of these reactions and the subtle differences in reactivity observed between and .

DFT Studies on the Reactions of Boroles with Alkynes.

DFT calculations were performed to investigate the reactions of boroles with alkynes, in which boranorbornadiene, borepin and/or boracyclohexadiene can be formed depending on the substituents on the borole and alkyne. Our computational results indicated that formation of boranorbornadiene and borepin is generally kinetically favoured and that the products can interconvert. Formation of boracyclohexadiene is kinetically unfavourable in most reactions.

Direct access to a cAAC-supported dihydrodiborene and its dianion.

The two-fold reduction of (cAAC)BHX (cAAC = 1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene; X = Cl, Br) provides a facile, high-yielding route to the dihydrodiborene (cAAC)BH. The (chloro)hydroboryl anion reduction intermediate was successfully isolated using a crown ether. Overreduction of the diborene to its dianion [(cAAC)BH] causes a decrease in the B-B bond order whereas the B-C bond orders increase.

Reactions of Digallanes with p- and d-Block Lewis Bases: Adducts, Bis(gallyl) Complexes, and Naked Ga as Ligand.

A range of double carbene adducts of digallanes(4) are prepared from an existing double digallane adduct, and their halides are subsequently exchanged, establishing the feasibility of both base and halide-exchange reactions from digallane adducts. Furthermore, a range of digallium species are treated with transition-metal Lewis bases, leading alternatively to oxidative addition products, species with monocoordinate Ga ligands, and an unusual ditopic metal-only Lewis pair (MOLP). These results underline the manifold and unpredictable chemistry of halogallane species with Lewis bases.

Isolation of diborenes and their 90°-twisted diradical congeners.

Molecules containing multiple bonds between atoms-most often in the form of olefins-are ubiquitous in nature, commerce, and science, and as such have a huge impact on everyday life. Given their prominence, over the last few decades, frequent attempts have been made to perturb the structure and reactivity of multiply-bound species through bending and twisting. However, only modest success has been achieved in the quest to completely twist double bonds in order to homolytically cleave the associated π bond.

Bottleable Neutral Analogues of [B H ] as Versatile and Strongly Binding η Donor Ligands.

Herein we report the discovery that two bottleable, neutral, base-stabilized diborane(5) compounds are able to bind strongly to a number of copper(I) complexes exclusively through their B-B bond. The resulting complexes represent the first known complexes containing unsupported, neutral σ diborane ligands. Single-crystal X-ray analyses of these complexes show that the X-Cu moiety (X=Cl, OTf, C F ) lies opposite the bridging hydrogen atom of the diborane and is near perpendicular to the B-B bond, interacting almost equally with both boron atoms and causing a B-B bond elongation.

Release of Isonitrile- and NHC-Stabilized Borylenes from Group VI Terminal Borylene Complexes.

A family of doubly isonitrile-stabilized terphenyl borylenes could be obtained by addition of three equivalents of isonitrile to the corresponding Cr and W terminal terphenyl-borylene complexes. The mechanism of isonitrile- and carbon-monoxide-induced borylene liberation was investigated computationally and found to be significantly exergonic in both cases. Furthermore, addition of a small N-heterocyclic carbene (NHC) to a terminal Cr borylene complex results in release of an NHC-stabilized borylene carbonyl species, whereas the analogous reaction with bulkier phosphines results in metal-centered substitution.

CO Binding and Splitting by Boron-Boron Multiple Bonds.

The room-temperature, ambient-pressure reactions of CO with two species containing boron-boron multiple bonds led to the incorporation of either one or two CO molecules. The structural characterization of a thermally unstable intermediate in one case indicates that an initial [2+2] cycloaddition is the key step in the reaction mechanism.

Synthesis, Photophysical, and Electrochemical Properties of Pyrenes Substituted with Donors or Acceptors at the 4- or 4,9-Positions.

We report herein an efficient and direct functionalization of the 4,9-positions of pyrene by Ir-catalyzed borylation. Three pinacol boronates (-Bpin), including 4-(Bpin)-2,7-di( tert-butyl)pyrene (5), 4,9- bis(Bpin)-2,7-di( tert-butyl)pyrene (6), and 4,10- bis(Bpin)-2,7-di( tert-butyl)pyrene (7), were synthesized. The structures of 6 and 7 have been confirmed by single-crystal X-ray diffraction.

Nitrogen fixation and reduction at boron.

Currently, the only compounds known to support fixation and functionalization of dinitrogen (N) under nonmatrix conditions are based on metals. Here we present the observation of N binding and reduction by a nonmetal, specifically a dicoordinate borylene. Depending on the reaction conditions under which potassium graphite is introduced as a reductant, N binding to two borylene units results in either neutral (BN) or dianionic ([BN]) products that can be interconverted by respective exposure to further reductant or to air.

Unsymmetrical, Cyclic Diborenes and Thermal Rearrangement to a Borylborylene.

Cyclic diboranes(4) based on a chelating monoanionic benzylphosphine linker were prepared through boron-silicon exchange between arylsilanes and B Br . Coordination of Lewis bases to the remaining sp boron atom yielded unsymmetrical sp -sp diboranes, which were reduced with KC to their corresponding trans-diborenes. These compounds were studied with a combination of spectroscopic methods, X-ray diffraction, and DFT calculations.

Stable Organic (Bi)Radicals by Delocalization of Spin Density into the Electron-Poor Chromophore Core of Isoindigo.

The first isoindigo (bi)radicals were obtained by proton coupled oxidation of their 4-hydroxyaryl substituted precursors. Optical and magnetic spectroscopic studies revealed a singlet open-shell biradicaloid electronic ground state for the bisphenoxyl-isoindigo (=1.20) with a small singlet-triplet energy gap of 0.

Dialumination of unsaturated species with a reactive bis(cyclopentadienyl) dialane.

A new bis(cyclopentadienyl) dialane is prepared, which shows controlled, selective dialumination reactions with a conventional alkyne, an electron-rich alkyne, and an azide. The reactions provide structurally diverse products, featuring a range of aluminium coordination numbers, cyclopentadienyl binding modes, and cyclic motifs. The variable nature of the bonding in the Cp*Al units allows a range of binding modes depending on the electronic requirements of the Al atom and provides new possibilities to the chemistry of dialanes, as demonstrated by the isolation of a double internal Lewis adduct with "ring-slipped" Cp* rings in this work.

Boryl- and Silyl-Substituted Mixed Sandwich Compounds of Scandium.

An improved, one-pot synthesis of the linear sandwich compound [Sc(η -C H )(η -C H )] is presented. The synthetic procedure is amenable to boryl- and silyl-substituted cyclopentadienyl and cyclooctatetraenyl ligands, thereby yielding the first functionalized derivatives. We found that the synthesis of the silyl-substituted mixed sandwich complexes produces higher yields when the ligand exchange is carried out stepwise, by isolating the intermediate trimethylsilylated half-sandwich complex [Sc(η -C H SiMe )Cl(THF)] (THF=tetrahydrofuran).

Half-Sandwich Complexes of an Extremely Electron-Donating, Redox-Active η-Diborabenzene Ligand.

The heteroarene 1,4-bis(CAAC)-1,4-diborabenzene (1; CAAC = cyclic (alkyl)(amino)carbene) reacts with [(MeCN)M(CO)] (M = Cr, Mo, W) to yield half-sandwich complexes of the form [(η-diborabenzene)M(CO)] (M = Cr (2), Mo (3), W (4)). Investigation of the new complexes with a combination of X-ray diffraction, spectroscopic methods and DFT calculations shows that ligand 1 is a remarkably strong electron donor. In particular, [(η-arene)M(CO)] complexes of this ligand display the lowest CO stretching frequencies yet observed for this class of complex.

Nucleophilic addition and substitution at coordinatively saturated boron by facile 1,2-hydrogen shuttling onto a carbene donor.

The reaction of [(cAAC)BH] (cAAC = 1-(2,6-PrCH)-3,3,5,5-tetramethylpyrrolidin-2-ylidene) with a range of organolithium compounds led to the exclusive formation of the corresponding (dihydro)organoborates, Li[(cAACH)BHR] (R = sp-, sp-, or sp-hybridised organic substituent), by migration of one boron-bound hydrogen atom to the adjacent carbene carbon of the cAAC ligand. A subsequent deprotonation/salt metathesis reaction with MeSiCl or spontaneous LiH elimination yielded the neutral cAAC-supported mono(organo)boranes, [(cAAC)BHR]. Similarly the reaction of [(cAAC)BH] with a neutral donor base L resulted in adduct formation by shuttling one boron-bound hydrogen to the cAAC ligand, to generate [(cAACH)BHL], either irreversibly (L = cAAC) or reversibly (L = pyridine).

Transition-Metal π-Ligation of a Tetrahalodiborane.

The reaction of tetraiododiborane (B I ) with trans-[Pt(BI )I(PCy ) ] gives rise to the diplatinum(II) complex [{(Cy P)(I B)Pt} (μ :η :η -B I )], which is supported by a bridging diboranyl dianion ligand [B I ] . This complex is the first transition-metal complex of a diboranyl dianion, as well as the first example of intact coordination of a B X (X=halide) unit of any type to a metal center.

Alkylideneborate zwitterions and C-C coupling by atypical diboration of electron-rich alkynes.

The combination of electron-rich diaminoalkynes and ditopic Lewis acids diboranes(4) leads to unusual uncatalysed diboration reactions involving internal Lewis adduct, zwitterion, and C-C bond formation. The products are novel multicyclic, charge-separated compounds with intramolecular dative bonds.

Increasing the Reactivity of Diborenes: Derivatization of NHC-Supported Dithienyldiborenes with Electron-Donor Groups.

A series of NHC-supported 1,2-dithienyldiborenes was synthesized from the corresponding (dihalo)thienylborane NHC precursors. NMR and UV/Vis spectroscopic data, as well as X-ray crystallographic analyses, were used to assess the electronic and steric influences on the B=B double bond of various NHCs and electron-donating substituents on the thienyl ligands. Crystallographic data showed that the degree of coplanarity of the diborene core and thienyl groups is highly dependent on the sterics of the substituents.

CuOTf-mediated intramolecular diborene hydroarylation.

Upon complexation to CuOTf, a PMe-stabilized bis(9-anthryl) diborene slowly undergoes an intramolecular hydroarylation reaction at room temperature. Subsequent triflation of the B-H bond with CuOTf, followed by a PMe transfer, finally yields a cyclic sp-sp boryl-substituted boronium triflate salt.

The First Boron-Tellurium Double Bond: Direct Insertion of Heavy Chalcogens into a Mn=B Double Bond.

The base-stabilized borylene [Cp(OC) Mn=BtBu(IMe)] readily reacts with elemental chalcogens in an insertion reaction that yields borachalcone complexes [Cp(OC) Mn-E=BtBu(IMe)] (E=S, Se, Te). The tellurium example features the first double bond between boron and tellurium, making Te the heaviest main-group element to make multiple bonds with boron. This unprecedented interaction has been fully investigated both experimentally and computationally.

Preparation, Properties, and Structures of the Radical Anions and Dianions of Azapentacenes.

A series of diazapentacenes (5,14-diethynyldibenzo[b,i]phenazine, 6,13-diethynylnaphtho[2,3-b]phenazine) and tetraazapentacenes (7,12-diethynylbenzo[g]quinoxalino[2,3-b]quinoxaline, 6,13-diethynylquinoxalino[2,3-b]phenazine) were reduced to their radical anions and dianions, employing either potassium anthracenide or lithium naphthalenide in THF. The anionic species formed were investigated by UV-vis-NIR, fluorescence and EPR spectroscopy, spectroelectrochemistry, and quantum chemical calculations. Single crystal X-ray structures of three of their radical anions and of three of their dianions were obtained.

Abnormal Tin-Boron Exchange in the Attempted Synthesis of a Borylated Borole.

Boroles are important motifs within functional materials. With the aim to prepare a pinacolboryl-substituted derivative, the metallacycle transfer from corresponding zirconium and tin precursors has been explored. We show that the reaction of 1,1-dimethyl-2,3,4,5-tetrapinacolborylstannole with dichloro(phenyl)borane does not provide the desired borole, but instead a stannyl-substituted 1-chloroboracyclopent-3-ene.