CO scission and reductive coupling of organic carbonyls by a redox-active diboraanthracene

Boron-Thioketonates: A New Class of S,O-Chelated Boranes as Acceptors in Optoelectronic Devices

Development of new n-type semiconductors with tunable band gap and dielectric constant has significant implication in dissociating bound charge carrier relevant for demonstrating high performance optoelectronic devices. Boron-β-thioketonates (MTDKB), analogues to boron-β-diketonates containing a sulfur atom in the framework of β-diketones were synthesized. Bulk transport measurement exhibited an outstanding bulk electron mobility of ≈0.003 cm²  V^-1  s^-1 , which is among the best values reported till date in these class of semiconducting materials and correspondingly a single junction photo responsivity of upto 6 mA W^-1 was obtained. This new family of O,S-chelated boron compounds exhibited luminescence in the far red/near-infrared region. The remarkable red shift of 89 nm (fluorescence) observed for 4 a in comparison with analogues boron-β-diketonate signifies the importance of sulfur in these molecules. MTDKBs with amine functionality have also been investigated as an ON/OFF fluorescent sensor.

Multifaceted behavior of a doubly reduced arylborane in B-H-bond activation and hydroboration catalysis

Alkali-metal salts of 9,10-dimethyl-9,10-dihydro-9,10-diboraanthrancene (M₂[DBA-Me₂]; M⁺ = Li⁺, Na⁺, K⁺) activate the H-B bond of pinacolborane (HBpin) in THF already at room temperature. For M⁺ = Na⁺, K⁺, the addition products M₂[4] are formed, which contain one new H-B and one new B-Bpin bond; for M⁺ = Li⁺, the H^- ion is instantaneously transferred from the DBA-Me₂ unit to another equivalent of HBpin to afford Li[5]. Although Li[5] might commonly be considered a [Bpin]^- adduct of neutral DBA-Me₂, it donates a [Bpin]⁺ cation to Li[SiPh₃], generating the silyl borane Ph₃Si-Bpin; Li₂[DBA-Me₂] with an aromatic central B₂C₄ ring acts as the leaving group. Furthermore, Li₂[DBA-Me₂] catalyzes the hydroboration of various unsaturated substrates with HBpin in THF. Quantum-chemical calculations complemented by in situ NMR spectroscopy revealed two different mechanistic scenarios that are governed by the steric demand of the substrate used: in the case of the bulky Ph(H)C[double bond, length as m-dash]NtBu, the reaction requires elevated temperatures of 100 °C, starts with H-Bpin activation which subsequently generates Li[BH₄], so that the mechanism eventually turns into "hidden borohydride catalysis". Ph(H)C[double bond, length as m-dash]NPh, Ph₂C[double bond, length as m-dash]O, Ph₂C[double bond, length as m-dash]CH₂, and iPrN[double bond, length as m-dash]C[double bond, length as m-dash]NiPr undergo hydroboration already at room temperature. Here, the active hydroboration catalyst is the [4 + 2] cycloadduct between the respective substrate and Li₂[DBA-Me₂]: in the key step, attack of HBpin on the bridging unit opens the bicyclo[2.2.2]octadiene scaffold and gives the activated HBpin adduct of the Lewis-basic moiety that was previously coordinated to the DBA-B atom.

Charge-Transfer Transitions Govern the Reactivity and Photophysics of Vicinally Diphosphanyl-Substituted Diborapentacenes

2,3-Difluoro-5,14-dihydro-5,14-diborapentacene (DBP) was endowed with two vicinal Ph₂ P groups by an S_N Ar reaction at both CF sites using Ph₂ PSiMe₃ . Computations reveal the ambipolar product P to undergo P-to-B charge transfer under ambient light irradiation. Consequently, P is prone to photooxidation by air, yielding the Ph₂ P(O) species PO. With S₈ or [Me₃ O][BF₄ ], P furnishes the Ph₂ P(S) or Ph₂ P(Me)⁺ derivatives PS or [PMe][BF₄ ]₂ . Along the series P, PO, PS, and [PMe][BF₄ ]₂ , the redox potentials shift anodically from E_1/2 =-1.89 V to -1.02 V (CH₂ Cl₂ ). Thus, derivatization of the Ph₂ P group allows late-stage modulation of the LUMO-energy level of the DBP. Derivatization also influences the emission properties of the compounds, as PO shows green (521 nm) and [PMe][BF₄ ]₂ red (622 nm) fluorescence in C₆ H₆ , while P and PS are dark. With CuBr and AgBr, P forms dimeric [M(μ-Br)]₂ complexes [PCu]₂ and [PAg]₂ , which show pronounced metal-to-ligand charge transfer (MLCT), making P a promising ligand for photocatalysts.

A Three‐Dimensional Inorganic Analogue of 9,10‐Diazido‐9,10‐Diboraanthracene: A Lewis Superacidic Azido Borane with Reactivity and Stability

Herein, we report the facile synthesis of a three‐dimensional (3D) inorganic analogue of 9,10‐diazido‐9,10‐dihydrodiboraantracene, which turned out to be a monomer in both the solid and solution state, and thermally stable up to 230 °C, representing a rare example of azido borane with boosted Lewis acidity and stability in one. Apart from the classical acid‐base and Staudinger reactions, E−H bond activation (E=B, Si, Ge) was investigated. While the reaction with B−H (9‐borabicyclo[3.3.1]nonane) led directly to the 1,1‐addition on N_α upon N₂ elimination, the Si−H (Et₃SiH, PhMe₂SiH) activation proceeded stepwise via 1,2‐addition, with the key intermediates 5_int and 6_int being isolated and characterized. In contrast, the cooperative Ge−H was reversible and stayed at the 1,2‐addition step.

Solid-state 11B NMR studies of coinage metal complexes containing a phosphine substituted diboraanthracene ligand

Transition metal interactions with Lewis acids (M → Z linkages) are fundamentally interesting and practically important. The most common Z-type ligands contain boron, which contains an NMR active ¹¹B nucleus. We measured solid-state ¹¹B{¹H} NMR spectra of copper, silver, and gold complexes containing a phosphine substituted 9,10-diboraanthracene ligand (B₂P₂) that contain planar boron centers and weak M → BR₃ linkages ([(B₂P₂)M][BAr^F₄] (M = Cu (1), Ag (2), Au (3)) characterized by large quadrupolar coupling (C_Q) values (4.4-4.7 MHz) and large span (Ω) values (93-139 ppm). However, the solid-state ¹¹B{¹H} NMR spectrum of K[Au(B₂P₂)]^- (4), which contains tetrahedral borons, is narrow and characterized by small C_Q and Ω values. DFT analysis of 1-4 shows that C_Q and Ω are expected to be large for planar boron environments and small for tetrahedral boron, and that the presence of a M → BR₃ linkage relates to the reduction in C_Q and ¹¹B NMR shielding properties. Thus solid-state ¹¹B NMR spectroscopy contains valuable information about M → BR₃ linkages in complexes containing the B₂P₂ ligand.

Thiophene-fused boracycles as photoactive analogues of diboraanthracenes

The construction of thiophene-fused analogues of diboraanthracenes with different aryl substituents through boron-mercury exchange followed by the nucleophilic replacement of the chlorines of dichlorodiboradithiophene 2 with Grignard reagents is reported. These diboradithiophenes exhibited unusual photophysical and electrochemical properties. They all undergo photoisomerisation, which can be traced using photophysical and ¹H NMR spectroscopy studies.

Direct deoxygenative borylation of carboxylic acids

Carboxylic acids are readily available, structurally diverse and shelf-stable; therefore, converting them to the isoelectronic boronic acids, which play pivotal roles in different settings, would be highly enabling. In contrast to the well-recognised decarboxylative borylation, the chemical space of carboxylic-to-boronic acid transformation via deoxygenation remains underexplored due to the thermodynamic and kinetic inertness of carboxylic C-O bonds. Herein, we report a deoxygenative borylation reaction of free carboxylic acids or their sodium salts to synthesise alkylboronates under metal-free conditions. Promoted by a uniquely Lewis acidic and strongly reducing diboron reagent, bis(catecholato)diboron (B2cat2), a library of aromatic carboxylic acids are converted to the benzylboronates. By leveraging the same borylative manifold, a facile triboration process with aliphatic carboxylic acids is also realised, diversifying the pool of available 1,1,2-alkyl(trisboronates) that were otherwise difficult to access. Detailed mechanistic studies reveal a stepwise C-O cleavage profile, which could inspire and encourage future endeavours on more appealing reductive functionalisation of oxygenated feedstocks.

H2 evolution from H2O via O-H oxidative addition across a 9,10-diboraanthracene

The water reactivity of the boroauride complex ([Au(B₂P₂)][K(18-c-6)]; (B₂P₂, 9,10-bis(2-(diisopropylphosphino)-phenyl)-9,10-dihydroboranthrene) and its corresponding two-electron oxidized complex, Au(B₂P₂)Cl, are presented. Au(B₂P₂)Cl is tolerant to H₂O and forms the hydroxide complex Au(B₂P₂)OH in the presence of H₂O and triethylamine. [Au(B₂P₂)]Cl and [Au(B₂P₂)]OH are poor Lewis acids as judged by the Gutmann-Becket method, with [Au(B₂P₂)]OH displaying facile hydroxide exchange between B atoms of the DBA ring as evidenced by variable temperature NMR spectroscopy. The reduced boroauride complex [Au(B₂P₂)]^- reacts with 1 equivalent of H₂O to produce a hydride/hydroxide product, [Au(B₂P₂)(H)(OH)]^-, that rapidly evolves H₂ upon further H₂O reaction to yield the dihydroxide compound, [Au(B₂P₂)(OH)₂]^-. [Au(B₂P₂)]Cl can be regenerated from [Au(B₂P₂)(OH)₂]^-via HCl·Et₂O, providing a synthetic cycle for H₂ evolution from H₂O enabled by O-H oxidative addition at a diboraanthracene unit.