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Organo(chloro)silanes are essential chemicals, but the synthesis of compounds of the formula RnSiCl4‒n with defined values of n is usually laborious. Herein, we first disclose that a [4+2]-cycloaddition between readily available Cl3SiC≡CSiCl3 and selected dienes provides facile access to vicinal bis(trichlorosilylated) benzenes and bicyclo[2.2.2]octa-2,5-dienes. Second, we show how the number of six Si‒Cl bonds in 1,2-(Cl3Si)2C6H2Me2 (1) can be selectively reduced to four or two by reaction with pinacol (H2pin) or catechol (H2cat), which act as Si···Si'-bridging and/or Si-chelating ligands. Third, we demonstrate that the thermolysis of compound 6, which contains a benzannulated eight-membered C2(SiCl2)2(μ-pin) ring with Si···Si'-bridging pin moiety, furnishes 13 with a benzannulated five-membered C2(SiCl2)2O ring via the release of pinacolone. Such cyclic disiloxanes are valuable building blocks for specialty silicones; an alternative assembly of the Si‒O‒Si unit by controlled hydrolysis of 1 is not feasible if the four valuable Si‒Cl functionalities are to be retained for further derivatization. Substitution of one Cl atom per Si site of 13 gives the rac-1,3-disila-2-oxaindane rac-15 with high selectivity., (© 2024 Wiley‐VCH GmbH.)

An air-stable B 3 ,N 3 -containing dibenzobisanthene (8) was prepared in 29% yield by heating a 1,3,5-tri(azasilaanthryl)benzene (5) with BBr 3 (180 °C). Under these conditions, the reaction does not stop after threefold SiMe 2 /BBr exchange but proceeds further via two rearrangement and two intramolecular C-H borylation steps. Some mechanistic details were unveiled by using smaller model systems and applying lower reaction temperatures. According to X-ray crystallography, compound 8 has a helically distorted scaffold. Due to its multiple resonance structure, it shows a narrow-band blue-green emission ( λ em = 493 nm; Φ PL = 84%; FWHM = 0.20 eV; THF); samples measured in PMMA gave prompt and delayed fluorescence lifetimes of 10.7 ns and 136 μs, respectively. The optical properties of 8 and of structurally related species were also investigated by quantum-chemical means: most of these compounds exhibit a small energy gap Δ E ST between the lowest excited singlet (S 1 ) and triplet (T 1 ) states and a non-negligible spin-orbit coupling (SOC) between S 1 and T 1 /T 2 , demonstrating their potential as thermally activated delayed fluorescence (TADF) emitters.

NBN- and BNB-doped phenalenyls are isoelectronic to phenalenyl anions and cations, respectively. They represent a pair of complementary molecules that have essentially identical structures but opposite properties as electron donors and acceptors. The NBN-phenalenyls 1-4 considered here were prepared from N,N'-dimethyl-1,8-diaminonaphthalene and readily available boron-containing building blocks (i. e., BH 3 ⋅SMe 2 (1), p-CF 3 -C 6 H 4 B(OH) 2 (2), C 6 H 5 B(OH) 2 (3), or MesBCl 2 /iPr 2 NEt (4)). Treatment of 1 with 4-Me 2 N-2,6-Me 2 -C 6 H 2 Li gave the corresponding NBN derivative 5. The BNB-phenalenyl 6 was synthesized from 1,8-naphthalenediyl-bridged diborane(6), PhNH 2 , and MesMgBr. A computational study reveals that the photoemission of 1, 4, and 5 originates from locally excited (LE) states at the NBN-phenalenyl fragments, while that of 2 is dominated by charge transfer (CT) from the NBN-phenalenyl to the p-CF 3 -C 6 H 4 fragment. Depending on the dihedral angle θ between its Ph and NBN planes, compound 3 emits mainly from a less polar LE (θ >55°) or more polar CT state (θ <55°). In turn, the energetic preference for either state is governed by the polarity of the solvent used. An equimolar aggregate of the NBN- and BNB-phenalenyls 3 and 6 (in THF/H 2 O) shows a distinct red-shifted emission compared to that of the individual components, which originates from an intermolecular CT state., (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Two (BE) 8 -[16]annulenes were prepared and fully characterized by experimental and quantum-chemical means ( 1 , E = N; 2 , E = O). The 1,8-naphthalenediyl-bridged diborane(6) 3 served as their common starting material, which was treated with [Al(NH 3 ) 6 ]Cl 3 to form 1 (91% yield) or with 1,8-naphthalenediboronic acid anhydride to form 2 (93% yield). As a result, the heteroannulenes 1 and 2 are supported by four aromatic "clamps" and may also be viewed as NH- or O-bridged cyclic tetramers of BNB- or BOB-doped phenalenyls. X-ray crystallography on mono-, di-, and tetraadducts 2 ·thf, 2 ·py 2 , and 2 ·py 4 showed that 2 is an oligotopic Lewis acid (thf/py: tetrahydrofuran/pyridine donor). The applicability of 2 also as a Lewis basic ligand in coordination chemistry was demonstrated by the synthesis of the mononuclear Ag + complex [Ag(py) 2 ( 2 ·py 4 )] + and the dinuclear Pb 2+ complex 6 . During the assembly of 6 , the rearrangement of 2 led to the formation of two (BO) 9 -macrocycles linked by two BOB-phenalenyls to form a nanometer-sized cage with four negatively charged, tetracoordinated B atoms. Both 1 and 2 show several redox waves in the cathodic regions of the cyclic voltammograms. An in-depth assessment of the consequences of electron injection on the aromaticity of 1 and 2 was achieved by electronic structure calculations. 1 and 2 are proposed to exhibit aromatic switching capabilities in the [16]annulene motif.

An air-stable B 3 ,N 2 -PAH ( B 3 N 2 ; nine annulated six-membered rings) was synthesized from 1-X-2,6-di(azasilaanthryl)benzenes (X = Cl, I) via lithiation/borylation, electrophilic aromatic borylation, and Si/B exchange. The heteroatom distribution in B 3 N 2 meets the requirements for multiple resonance thermally activated delayed fluorescence (MR-TADF). Indeed, B 3 N 2 emits green light (λ em = 523 nm; Φ PL = 85%; CHCl 3 ) with a small fwhm of 0.15 eV. Lifetimes for prompt (7.8 ns) and delayed (60 μs) fluorescence were measured in PMMA.

A joint theoretical and experimental study on 32 endohedral silafullerane derivatives [X@Si20Y20]- (X- = F- -I- ; Y = F-I, H, Me, Et) and Th-[Cl@Si20H12Y8]- (Y = F-I) is presented. First, we evaluated the structure-determining template effect of Cl- in a systematic series of concave silapolyquinane model systems. Second, we investigated the X- →Si20 interaction energy (Eint) as a function of X- and Y and found the largest Eint values for electron-withdrawing exohedral substituents Y. Given that X- ions can be considered as Lewis bases and empty Si20Y20 clusters as Lewis acids, we classify our inseparable host-guest complexes [X@Si20Y20]- as "confined Lewis pairs". Third, 35Cl NMR spectroscopy proved to be highly diagnostic for an experimental assessment of the Cl- →Si20 interaction as the paramagnetic shielding and, in turn, δ(35Cl) of the endohedral Cl- ion correlate inversely with Eint. Finally, we disclose the synthesis of [PPN][Cl@Si20Y20] (Y = Me, Et, Br) and provide a thorough characterization of these new silafulleranes., (© 2023 Wiley-VCH GmbH.)

The B 2 ,N 4 -doped heptacene H4 in which two N , N '-dihydrophenazine units are linked by two BMes bridges (Mes = mesityl) was synthesized via fourfold Buchwald-Hartwig coupling between 2,3,6,7-tetrachloro-9,10-dimesityl-9,10-dihydro-9,10-diboraanthracene and o -phenylenediamine ( t BuXPhos-Pd-G3, DBU/NaOTf, 2-MeTHF, 50 °C, 16 h). Upon exposure to ambient air, H4 is oxidized to its N , N '-dihydro form H2 ; further oxidation with MnO 2 furnishes the di(phenazine) derivative H0 . Stirring under a blanket of H 2 in the presence of Pd/C hydrogenates H0 back to H2 and ultimately H4 . Yellow-colored H0 is a remarkably good electron acceptor with a LUMO-energy level of -3.9 eV; upon irradiation with a 405 nm LED in the presence of THF or 1,4-cyclohexadiene, H0 accepts two H atoms to furnish H2 . One-electron reduction of H0 yields the isolable radical-anion salt Li[ H0 ] (lithium naphthalenide, THF, -30 °C to rt). The ambipolar compounds H2 and H4 possess a navy blue and deep purple color, respectively, due to charge-transfer interactions from the electron-rich N , N '-dihydrophenazine donor(s) to the electron-accepting B 2 C 4 core.

Silylated and halogenated benzenes 1,2-(Me 3 Si) 2 -4,5-X 2 -C 6 H 2 [X = Br ( 3 ), I ( 4 )] are versatile synthetic building blocks. 3 was prepared from known 1,2-(Me 3 Si) 2 -4,5-Cl 2 -C 6 H 2 via C-Cl borylation/bromodeboronation; CuI-catalyzed Br/I exchange on 3 affords 4 . 3 or 4 and BBr 3 yield 9,10-dibromo-9,10-dihydro-9,10-diboraanthracenes (DBAs) 7 or 8 . The B centers were protected with mesityl (Mes; 9 , 10 ) or 2,4,6-tris(trifluoromethyl)phenyl ( F Mes; 11 , 12 ) groups. Heck coupling of 9 and styrene/2,3,4,5,6-pentafluorostyrene furnishes the two tetravinyl-substituted green/blue emitters 13 / 14 .

Starting from the perhydrogenated silafullerane [ n Bu 4 N][Cl@Si 20 (SiH 3 ) 12 H 8 ], treatment with BBr 3 leads to partially and exhaustively brominated clusters, [ n Bu 4 N][Cl@Si 20 (SiBr 2 H) 12 Br 8 ] (120 eq. BBr 3 , room temperature, 30 min) and [ n Bu 4 N][Cl@Si 20 (SiBr 3 ) 12 Br 8 ] (300 eq. BBr 3 , 130 °C, 3 d). Perbromination is accompanied by a massively increased steric strain on the cluster surface, which explains why our approach achieves regioselective derivatization of the Si 32 framework when mild conditions are maintained. Partial Br/H exchange on [ n Bu 4 N][Cl@Si 20 (SiBr 2 H) 12 Br 8 ] (30 eq. iBu 2 AlH, room temperature, 16 h) affords [ n Bu 4 N][Cl@Si 20 (SiH 3 ) 12 Br 8 ].

Silafulleranes with endohedral Cl - ions are a unique, scarcely explored class of structurally well-defined silicon clusters and host-guest complexes. Herein, we report regioselective derivatization reactions on the siladodecahedrane [ n Bu 4 N][Cl@Si 20 (SiCl 3 ) 12 Cl 8 ] ([ n Bu 4 N][ 1 ]), which has its cluster surface decorated with 12 SiCl 3 and 8 Cl substituents in perfect T h symmetry. The room-temperature reaction of [ n Bu 4 N][ 1 ] with excess i Bu 2 AlH in ortho -difluorobenzene ( o DFB) furnishes perhydrogenated [ n Bu 4 N][Cl@Si 20 (SiH 3 ) 12 H 8 ] ([ n Bu 4 N][ 2 ]) in 50% yield; the non-pyrophoric [ 2 ] - is the largest structurally authenticated (by X-ray diffraction) hydridosilane known to date. A simple switch from pure o DFB to an o DFB/Et 2 O solvent mixture suppresses core hydrogenation and results in the formation of [ n Bu 4 N][Cl@Si 20 (SiH 3 ) 12 Cl 8 ] ([ n Bu 4 N][ 3 ]). In addition to the exhaustive Cl/H exchange at all 44 Si-Cl bonds of [ 1 ] - and the regioselective 36-fold silyl group hydrogenation, we achieved the simultaneous introduction of Me substituents at all 8 SiCl vertices along with the conversion of all 12 SiCl 3 to SiH 3 groups by treating [ n Bu 4 N][ 1 ] with Me 2 AlH/Me 3 Al in o DFB ([ n Bu 4 N][Cl@Si 20 (SiH 3 ) 12 Me 8 ], [ n Bu 4 N][ 4 ]; 73%). Quantum-chemical free-energy calculations find an S N 2-Si-type hydrogenation of the exohedral SiCl 3 moieties in [ 1 ] - (trigonal-bipyramidal intermediate) slightly preferred over metathesis-like S N i-Si substitutions (four-membered transition state). Cage hydrogenation likely occurs via S N i-Si processes. The experimentally demonstrated influence of an Et 2 O co-solvent, which drastically increases the respective reaction barriers, is attributed to the increased stability of the resulting i Bu 2 AlH-OEt 2 adduct and its higher steric bulk compared to free i Bu 2 AlH.

Diboration and silaboration reactions are prominent tools to introduce valuable functional groups into organic substrates. To date, most diboranes(4) and silylboranes used for this purpose are electronically and/or kinetically stabilized and require activation by a catalyst. We show here that the tetraaryl (μ-hydrido)diborane(4) anion [3] - and the silyl (hydrido)borate ([4] - )/Me 3 SiBr system react spontaneously with the archetypal olefin ethylene in the absence of a catalyst. The actual active species in both cases are the valence isoelectronic intermediates [FluB-B(H)Flu] - ([1] - ) and FluB-Si(H)Flu (2), which consist of two 9-heterofluorenyl halves that get attached to the 1 and 2 positions of ethylene. At room temperature, [1] - is present in a dynamic equilibrium with its isolable isomer [3] - , while 2 has to be released in situ at low temperatures by H - abstraction from [4] - . Quantum-chemical calculations show qualitatively identical reaction mechanisms for [1] - and 2. Since the reactions start with π coordination of the ethylene molecule to a vacant B(p z ) orbital, the high Lewis acidity and low steric hindrance of the 9-borafluorenyl fragments are the keys to success. As the reaction proceeds, back-donation from the B-E bond into the ethylene π* orbital becomes increasingly important (E = B, Si). The scope of the reactions has been extended to t Bu(H)C[double bond, length as m-dash]CH 2 and t BuC[triple bond, length as m-dash]CH on the one hand and FluB-Si(Cl)Flu as well as FluB-Si(Cl)Ph 2 on the other., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The title compound, di-μ 3 -chlorido-tetra-μ 2 -chlorido-tetra-kis-(diethyl ether-κ O )bis-(1,1-di-methyl-eth-yl)tetra-magnesium, [Mg 4 (C 4 H 9 ) 2 Cl 6 (C 4 H 10 O) 4 ], features an Mg 4 Cl 6 open-cube cluster. The two four-coordinate Mg 2+ ions show an almost tetra-hedral coordination, whereas the two six-coordinate Mg 2+ ions have their ligands in an octa-hedral environment. The Mg-Cl bond lengths differ depending on the coordination number (2 or 3) of the bridging μ-Cl - ligands. There are few comparable structures deposited in the Cambridge Structural Database., (© Metzler et al. 2023.)

9,10-Diboratatriptycene salts M 2 [RB(μ-C 6 H 4 ) 3 BR] (R = H, Me; M + = Li + , K + , [ n -Bu 4 N] + ) have been synthesized via [4 + 2] cycloaddition between doubly reduced 9,10-dihydro-9,10-diboraanthracenes M 2 [DBA] and benzyne, generated in situ from C 6 H 5 F and C 6 H 5 Li or LiN( i -Pr) 2 . [HB(μ-C 6 H 4 ) 3 BH] 2- reacts with CH 2 Cl 2 to form quantitatively the bridgehead-derivatized [ClB(μ-C 6 H 4 ) 3 BCl] 2- , while twofold H - abstraction with B(C 6 F 5 ) 3 in the presence of SMe 2 leads cleanly to the diadduct (Me 2 S)B(μ-C 6 H 4 ) 3 B(SMe 2 ). Photoisomerization of K 2 [HB(μ-C 6 H 4 ) 3 BH] (THF, medium-pressure Hg lamp) provides facile access to diborabenzo[ a ]fluoranthenes, a little explored form of boron-doped polycyclic aromatic hydrocarbons. According to DFT calculations, the underlying reaction mechanism consists of three main steps: (i) photoinduced di-π-borate rearrangement, (ii) "walk reaction" of a BH unit, and (iii) boryl anion-like C-H activation., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The mixed heteroadamantanes Si 6 Ge 4 and Si 6 Sn 4 are readily accessible from Me 2 ECl 2 /Si 2 Cl 6 /cat. Cl - (4 × EMe 2 , 2 × SiCl 2 , 4 × Si-SiCl 3 vertices; E = Ge, Sn). Different from Si 6 Ge 4 , two skeletal isomers are formed in the case of Si 6 Sn 4 . Site-selective SiCl 3 -methylation of Si 6 Ge 4 was achieved, leaving the SiCl 2 groups untouched.

Helicenes combine two central themes in chemistry: extended π-conjugation and chirality. Hetero-atom doping preserves both characteristics and allows modulation of the electronic structure of a helicene. Herein, we report the (BO) 2 -doped tetrathia[7]helicene 1, which was prepared from 2-methoxy-3,3'-bithiophene in four steps. 1 is formally derived by substituting two (Mes)B-O moieties in place of (H)C=C(H) fragments in two benzene rings of the parent tetrathia[7]helicene. X-ray crystallography revealed a dihedral angle of 50.26(9)° between the two terminal thiophene rings. The (P)-/(M)-1 enantiomers were separated by chiral HPLC and are configurationally stable at room temperature. The experimentally determined enantiomerization barrier of 27.4±0.1 kcal mol -1 is lower than that of tetrathia[7]helicene (39.4±0.1 kcal mol -1 ). The circular dichroism spectra of (P)- and (M)-1 show a perfect mirror-image relationship. 1 is a blue emitter (λ em =411 nm) with a photoluminescence quantum efficiency of Φ PL =6 % (cf. tetrathia[7]helicene: λ em ≈405 nm, Φ PL =5 %)., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The B-nucleophilic 9H-9-borafluorene dianion reacts with 9-chloro-9-silafluorene to afford air- and moisture-stable silylborate salts M[Ar 2 (H)B-Si(H)Ar 2 ] (M[HBSiH], M=Li, Na). Li[HBSiH] and Me 3 SiCl give the B-pyridine adduct Ar 2 (py)B-Si(H)Ar 2 ((py)BSiH) or the chlorosilane Li[Ar 2 (H)B-Si(Cl)Ar 2 ] (Li[HBSiCl]) in C 6 H 6 -pyridine or THF. In both cases, the first step is H - abstraction at the B center. The resulting free borane subsequently binds a py or thf ligand. While the py adduct is stable at room temperature, the thf adduct undergoes a 1,2-H shift via the cyclic B(μ-H)Si intermediate BHSi, which is afterwards attacked at the Si atom by a Cl - ion to give Li[HBSiCl]. DFT calculations were employed to support the proposed reaction mechanism and to characterize the electronic structure of BHSi. Treatment of Li[HBSiCl] with the N-heterocyclic carbene IMe introduces the neutral donor at the Si atom and leads to Ar 2 (H)B-Si(IMe)Ar 2 (HBSi(IMe)), a donor-acceptor-stabilized silylene., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The Cl - diadduct [ n Bu 4 N] 2 [A·2Cl] of the mixed cyclohexatetrelane (SiCl 2 ) 5 (GeMe 2 ), A, is accessible from Me 2 GeCl 2 , 6 eq. Si 2 Cl 6 , and 2 eq. [ n Bu 4 N]Cl in one step (96%). Free, tenfold functionalized A can be released from the primary product by decomplexation with AlCl 3 (78%). Insight into the assembly mechanism of [ n Bu 4 N] 2 [A·2Cl] and the reactivity of A is provided.

Alkali-metal salts of 9,10-dimethyl-9,10-dihydro-9,10-diboraanthrancene (M 2 [DBA-Me 2 ]; 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 M 2 [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-Me 2 unit to another equivalent of HBpin to afford Li[5]. Although Li[5] might commonly be considered a [Bpin] - adduct of neutral DBA-Me 2 , it donates a [Bpin] + cation to Li[SiPh 3 ], generating the silyl borane Ph 3 Si-Bpin; Li 2 [DBA-Me 2 ] with an aromatic central B 2 C 4 ring acts as the leaving group. Furthermore, Li 2 [DBA-Me 2 ] 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]N t Bu, the reaction requires elevated temperatures of 100 °C, starts with H-Bpin activation which subsequently generates Li[BH 4 ], so that the mechanism eventually turns into "hidden borohydride catalysis". Ph(H)C[double bond, length as m-dash]NPh, Ph 2 C[double bond, length as m-dash]O, Ph 2 C[double bond, length as m-dash]CH 2 , and i PrN[double bond, length as m-dash]C[double bond, length as m-dash]N i Pr undergo hydroboration already at room temperature. Here, the active hydroboration catalyst is the [4 + 2] cycloadduct between the respective substrate and Li 2 [DBA-Me 2 ]: 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., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

2,3-Difluoro-5,14-dihydro-5,14-diborapentacene (DBP) was endowed with two vicinal Ph 2 P groups by an S N Ar reaction at both CF sites using Ph 2 PSiMe 3 . 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 Ph 2 P(O) species PO. With S 8 or [Me 3 O][BF 4 ], P furnishes the Ph 2 P(S) or Ph 2 P(Me) + derivatives PS or [PMe][BF 4 ] 2 . Along the series P, PO, PS, and [PMe][BF 4 ] 2 , the redox potentials shift anodically from E 1/2 =-1.89 V to -1.02 V (CH 2 Cl 2 ). Thus, derivatization of the Ph 2 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][BF 4 ] 2 red (622 nm) fluorescence in C 6 H 6 , 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., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

A series of new mixed-substituted heteronuclear precursors with preformed Si-Ge bonds has been synthesized via a two-step synthesis protocol. The molecular sources combine convenient handling with sufficient thermal lability to provide access to group IV alloys with low carbon content. Differences in the molecule-material conversion by chemical vapor deposition (CVD) techniques are described and traced back to the molecular design. This study illustrates the possibility of tailoring the physical and chemical properties of single-source precursors for their application in the CVD of Si 1- x Ge x coatings. Moreover, partial crystallization of the Si 1- x Ge x has been achieved by Ga metal-supported CVD growth, which demonstrated the potential of the presented precursor class for the synthesis of crystalline group IV alloys.

Regioselective di- and tetrabrominations of the (B,O) 2 -perylene 1 afford derivatives 2-4. Despite their poor solubility, 2 and 4 could be used in Stille-type coupling reactions to introduce two CCMe (5) or four CC( p -C 6 H 4 t Bu) substituents (6), respectively. The alkynylated derivatives show blue-green photoluminescence with appreciable quantum efficiencies.

Polycyclic aromatic hydrocarbons (PAHs) are prominent lead structures for organic optoelectronic materials. This work describes the synthesis of three B,S-doped PAHs with heptacene-type scaffolds via nucleophilic aromatic substitution reactions between fluorinated arylborane precursors and 1,2-(Me 3 SiS) 2 C 6 H 4 /1,8-diazabicyclo[5.4.0]undec-7-ene (72-92% yield). All compounds contain tricoordinate B atoms at their 7,16-positions, kinetically protected by mesityl (Mes) substituents. PAHs 1 / 2 feature two/four S atoms at their 5,18-/5,9,14,18-positions; PAH 3 is a 6,8,15,17-tetrafluoro derivative of 2 . For comparison, we also prepared the skewed naphtho[2,3- c ]pentaphene-type isomer 4 . The simultaneous presence of electron-accepting B atoms and electron-donating S atoms results in a redox-ambiphilic behavior; the radical cations [ 1 • ] + and [ 2 • ] + were characterized by electron paramagnetic resonance spectroscopy. Several low-lying charge-transfer states exist, some of which (especially S-to-B and Mes-to-B transitions) compete on the excited-state potential-energy surface. Consistent with the calculated state characters and oscillator strengths, this competition results in a spread of fluorescence quantum yields (2-27%). The optoelectronic properties of 1 change drastically upon addition of Ag + ions: while the color of 1 in CH 2 Cl 2 changes bathochromically from yellow to red (λ max from 463 to 486 nm; -0.13 eV), the emission band shifts hypsochromically from 606 to 545 nm (+0.23 eV), and the fluorescence quantum yield increases from 12 to 43%. According to titration experiments, higher order adducts [Ag n 1 m ] n + are formed. As a suitable system for modeling Ag + complexation, our calculations predict a dimer structure ( n = m = 2) with Ag 2 S 4 core, approximately linear S-Ag-S fragments, and Ag-Ag interaction. The computed optoelectronic properties of [Ag 2 1 2 ] 2+ agree well with the experimentally observed ones.

Two challenging but rewarding topics in chemical synthesis are C-F-bond activation and the development of B-centered nucleophiles. We have now tackled both subjects simultaneously by forming aryl-B bonds via S N Ar-type reactions on fluorobenzenes under mild conditions using Na 2 [FluBBFlu], Li 2 [HBFlu], and Li 2 [Me 2 DBA] (BFlu = 9-borafluorenyl, Me 2 DBA = 9,10-dimethyl-9,10-dihydro-9,10-diboraanthracene).

Bicyclic pyrazabole-bridged ferrocenes with BH groups at their bridgehead positions were prepared from [Li(thf)] 2 [1,1'-fc(BH 3 ) 2 ] and pyrazole or 3,5-dimethylpyrazole in the presence of Me 3 SiCl (1 or 1Me, respectively; 1,1'-fc = 1,1'-ferrocenylene); Me 3 SiH and H 2 are released as byproducts. Treatment of 1 or 1Me with 1 eq. of the hydride scavenger [Ph 3 C][B(C 6 F 5 ) 4 ] afforded the borenium salts [2][B(C 6 F 5 ) 4 ] (72%) and [2Me][B(C 6 F 5 ) 4 ] (77%). According to X-ray crystallography, [2Me] + contains one trigonal-planar borenium cation, the cyclopentadienyl (Cp) rings of the 1,1'-fc fragment remain parallel to each other, but the Cp-B bond vector is bent out of the Cp plane by an unprecedentedly large dip angle α * of 40.6°. The Fe⋯B(sp 2 ) distance is very short (2.365(4) Å) and the 11 B NMR signal of the cationic B(sp 2 ) center is remarkably upfield shifted (23.4 ppm), suggesting a direct Fe(3d) → B(2p) donor-acceptor interaction. Although this interpretation is confirmed by quantum-chemical calculations, the coupling between the associated orbitals corresponds to an energy of only 12 kJ mol -1 . Accordingly, both the experimental ( e.g. , Gutmann-Beckett acceptor number AN = 111) and theoretical assessment ( e.g. , Et 3 PO and F - -ion affinities) of the Lewis acidity proves that [2] + is among the strongest boron-based Lewis acids available to date., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

(Cl 3 Si) 4 Ge (1; 91%) is accessible from GeCl 4 , the Si 2 Cl 6 /[ n Bu 4 N]Cl silylation system, and excess SiCl 4 . A key intermediate step involves Cl - sequestration with AlCl 3 in the course of the reaction between the first-formed germanide [(Cl 3 Si) 3 Ge] - and SiCl 4 . The related adduct Cl 2 (Me 2 EtN)SiGe(SiCl 3 ) 2 (2; quantitative conversion) was prepared either by amine-induced cleavage of 1 or by a bottom-up synthesis starting from GeCl 4 and Si 2 Cl 6 .

Si x Ge y alloys are emerging materials for modern semiconductor technology. Well-defined model systems of the bulk structures aid in understanding their intrinsic characteristics. Three such model clusters have now been realized in the form of the Si x Ge y heteroadamantanes [0], [1], and [2] through selective one-pot syntheses starting from Me 2 GeCl 2 , Si 2 Cl 6 , and [nBu 4 N]Cl. Compound [0] contains six GeMe 2 and four SiSiCl 3 vertices, whereas one and two of the GeMe 2 groups are replaced by SiCl 2 moieties in compounds [1] and [2], respectively. Chloride-ion-mediated rearrangement quantitatively converts [2] into [1] at room temperature and finally into [0] at 60 °C, which is not only remarkable in view of the rigidity of these cage structures but also sheds light on the assembly mechanism., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Two subvalent, redox-active diborane(4) anions, [3] 4- and [3] 2- , carrying exceptionally high negative charge densities are reported: Reduction of 9-methoxy-9-borafluorene with Li granules without stirring leads to the crystallization of the B(sp 3 )-B(sp 2 ) diborane(5) anion salt Li[5]. [5] - contains a 2,2'-biphenyldiyl-bridged B-B core, a chelating 2,2'-biphenyldiyl moiety, and a MeO substituent. Reduction of Li[5] with Na metal gives the Na + salt of the tetraanion [3] 4- in which two doubly reduced 9-borafluorenyl fragments are linked via a B-B single bond. Comproportionation of Li[5] and Na 4 [3] quantitatively furnishes the diborane(4) dianion salt Na 2 [3], the doubly boron-doped congener of 9,9'-bis(fluorenylidene). Under acid catalysis, Na 2 [3] undergoes a formal Stone-Wales rearrangement to yield a dibenzo[g,p]chrysene derivative with B=B core. Na 2 [3] shows boron-centered nucleophilicity toward n-butyl chloride. Na 4 [3] produces bright blue chemiluminescence when exposed to air., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Treatment of hexachloropropene (Cl 2 C[double bond, length as m-dash]C(Cl)-CCl 3 ) with Si 2 Cl 6 and [ n Bu 4 N]Cl (1 : 4 : 1) in CH 2 Cl 2 results in a quantitative conversion to the trisilylated, dichlorinated allyl anion salt [ n Bu 4 N][Cl 2 C[double bond, length as m-dash]C(SiCl 3 )-C(SiCl 3 ) 2 ] ([ n Bu 4 N][ 1 ]). Tetrachloroallene Cl 2 C[double bond, length as m-dash]C[double bond, length as m-dash]CCl 2 was identified as the first intermediate of the reaction cascade. In the solid state, [ 1 ] - adopts approximate C s symmetry with a dihedral angle between the planes running through the olefinic and carbanionic fragments of [ 1 ] - of C[double bond, length as m-dash]C-Si//Si-C-Si = 78.3(1)°. One-electron oxidation of [ n Bu 4 N][ 1 ] with SbCl 5 furnishes the distillable blue radical 1 ˙. The neutral propene Cl 2 C[double bond, length as m-dash]C(SiCl 3 )-C(SiCl 3 ) 2 H ( 2 ) was obtained by (i) protonation of [ 1 ] - with HOSO 2 CF 3 (HOTf) or (ii) H-atom transfer to 1 ˙ from 1,4-cyclohexadiene. Quantitative transformation of all three SiCl 3 substituents in 2 to Si(OMe) 3 ( 2 OMe ) or SiMe 3 ( 2 Me ) substituents was achieved by using MeOH/NMe 2 Et or MeMgBr in CH 2 Cl 2 or THF, respectively. Upon addition of 2 equiv. of t BuLi, 2 Me underwent deprotonation with subsequent LiCl elimination, 1,2-SiMe 3 migration and Cl/Li exchange to afford the allenyl lithium compound Me 3 Si(Li)C[double bond, length as m-dash]C[double bond, length as m-dash]C(SiMe 3 ) 2 (Li[ 4 ]), which is an efficient building block for the introduction of Me, SiMe 3 , or SnMe 3 ( 5 ) groups. The trisilylated, monochlorinated allene Cl 3 Si(Cl)C[double bond, length as m-dash]C[double bond, length as m-dash]C(SiCl 3 ) 2 ( 6 ), was obtained from [ n Bu 4 N][ 1 ] through Cl - -ion abstraction with AlCl 3 and rearrangement in CH 2 Cl 2 ( 1 ˙ forms as a minor side product, likely because the system AlCl 3 /CH 2 Cl 2 can also act as a one-electron oxidant)., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Fullerenes and diamondoids are at the core of nanoscience. Comparable monodisperse silicon analogues are scarce. Herein, we report the synthesis of the parent siladodecahedrane, which represents the largest Platonic solid. It shares its pattern of pentagonal faces with the smallest fullerene, C 20 , and its saturated, H-terminated skeleton with diamondoids. Similar to endofullerenes, the silicon cage encapsulates a chloride ion ([Cl@Si 20 H 20 ] - ); similar to diamondoids, its Si-H termini offer a wealth of opportunities for further functionalization. Mere treatment with chloromethanes leads to the perchlorinated cluster [Cl@Si 20 Cl 20 ] - . Both compounds were characterized by mass spectrometry, X-ray crystallography, NMR spectroscopy, and quantum-chemical calculations. The experimentally determined 35 Cl resonances of the endohedral chloride ions are particularly diagnostic to probe the Cl - → Si 20 interaction strength as a function of the different surface substituents, as we have proven by high-level computational analyses.

The intriguing (μ-hydrido)diboranes(4) with their prominent pristine representative [B 2 H 5 ] - have mainly been studied theoretically. We now describe the behavior of the planarized tetraaryl (μ-hydrido)diborane(4) anion [1H] - in cycloaddition reactions with the homologous series of heterocumulenes CO 2 , iPrNCO, and iPrNCNiPr. We show that a C=O bond of CO 2 selectively activates the B-B bond of [1H] - , while the μ-H ligand is left untouched ([2H] - ). The carbodiimide iPrNCNiPr, in contrast, neglects the B-B bond and rather adds the B-bonded H - ion to its central C atom to generate a formamidinate bridge across the B 2 pair ([3] - ). As a hybrid, the isocyanate iPrNCO combines the reactivity patterns of both its congeners and gives two products: one of them ([4H] - ) is related to [2H] - , the other ([5] - ) is an analog of [3] - . We finally propose a mechanistic scenario that rationalizes the individual reaction outcomes and combines them to a coherent picture of B-B vs. B-H bond activation., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The isoelectronic replacement of C[double bond, length as m-dash]C bonds with - B[double bond, length as m-dash]N + bonds in polycyclic aromatic hydrocarbons (PAHs) is a widely used tool to prepare novel optoelectronic materials. Far less well explored are corresponding B,O-doped PAHs, although they have a similarly high application potential. We herein report on the modular synthesis of B,N- and B,O-doped PAHs through the [Au(PPh 3 )NTf 2 ]-catalyzed 6- endo -dig cyclization of BN-H and BO-H bonds across suitably positioned C[triple bond, length as m-dash]C bonds in the key step. Readily available, easy-to-handle o -alkynylaryl boronic and borinic acids serve as starting materials, which are either cyclized directly or first converted into the corresponding aminoboranes and then cyclized. The reaction even tolerates bulky mesityl substituents on boron, which later kinetically protect the formed B,N/O-PAHs from hydrolysis or oxidation. Our approach is also applicable for the synthesis of rare doubly B,N/O-doped PAHs. Specifically, we prepared 1,2-B,E-naphthalenes and -anthracenes, 1,5-B 2 -2,6-E 2 -anthracenes (E = N, O) as well as B,O 2 -containing and unprecedented B,N,O-containing phenalenyls. Selected examples of these compounds have been structurally characterized by X-ray crystallography; their optoelectronic properties have been studied by cyclic voltammetry, electron spectroscopy, and quantum-chemical calculations. Using a new unsubstituted (B,O) 2 -perylene as the substrate for late-stage functionalization, we finally show that the introduction of two pinacolatoboryl (Bpin) substituents is possible in high yield and with perfect regioselectivity via an Ir-catalyzed C-H borylation approach., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The crystal structures are reported of the 6,6-di-fluoro-6 H -dibenzo[ c , e ][1,2]oxaborinin-6-ide (or 9,9-di-fluoro-10-oxa-9-boraphenanthren-9-ide) anion with two different cations, namely, potassium 6,6-di-fluoro-6 H -dibenzo[ c , e ][1,2]oxaborinin-6-ide, K + ·C 12 H 8 BF 2 O - , ( II ), featuring a polymeric structure, and bis-(tetra-phenyl-phospho-nium) bis-(6,6-di-fluoro-6 H -dibenzo[ c , e ][1,2]oxaborinin-6-ide) aceto-nitrile tris-olvate, 2C 24 H 20 P + ·2C 12 H 8 BF 2 O - ·3CH 3 CN, ( III ), which is composed of discrete cations, anions and aceto-nitrile solvent mol-ecules linked by C-H⋯O, C-H⋯N and C-H⋯F hydrogen bonds. There are only minor differences in the geometrical parameters of the anions in these structures., (© Budanow et al. 2020.)

The exhaustive trichlorosilylation of hexachloro-1,3-butadiene was achieved in one step by using a mixture of Si 2 Cl 6 and [nBu 4 N]Cl (7:2 equiv) as the silylation reagent. The corresponding butadiene dianion salt [nBu 4 N] 2 [1] was isolated in 36 % yield after recrystallization. The negative charges of [1] 2- are mainly delocalized across its two carbanionic (Cl 3 Si) 2 C termini (α-effect of silicon) such that the central bond possesses largely C=C double-bond character. Upon treatment with 4 equiv of HCl, [1] 2- is converted into neutral 1,2,3,4-tetrakis(trichlorosilyl)but-2-ene, 3. The Cl - acceptor AlCl 3 , induces a twofold ring-closure reaction of [1] 2- to form a six-membered bicycle 4 in which two silacyclobutene rings are fused along a shared C=C double bond (84 %). Compound 4, which was structurally characterized by X-ray crystallography, undergoes partial ring opening to a monocyclic silacyclobutene 2 in the presence of HCl, but is thermally stable up to at least 180 °C., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

In the title hemisolvate, C 27 H 36 BI 3 N 2 . 0.5C 6 H 6 , the dihedral angles between the central heterocyclic ring and pendant benzene rings are 82.9 (8) and 88.7 (9)° and the complete benzene solvent mol-ecule of crystallization is generated by a crystallographic centre of inversion. In the crystal, one very weak C-H⋯I inter-action links the mol-ecules into [001] chains., (© Schödel et al. 2020.)

A highly modular synthesis of BNB- and BOB-doped phenalenyls is presented. Treatment of the 1,8-naphthalenediyl-bridged boronic acid anhydride 1 with LiAlH 4 /Me 3 SiCl afforded the corresponding 1,8-naphthalenediyl-supported diborane(6) 2 , which served as the starting material for all subsequent transformations. Upon addition of MesMgBr/Me 3 SiCl, 2 was readily converted to the tetraorganyl diborane(6) 5 . The further heteroatoms were finally introduced through the reaction of 2 with (Me 3 Si) 2 NR' or 5 with H 2 NR' or H 2 O (R' = H, Me, p -Tol). A helically twisted, fully BNB-embedded PAH 11 was prepared by combining 2 with a dibrominated m -terphenylamine, followed by a Grignard-mediated double ring-closure reaction. All compounds devoid of B-H bonds show favorable optoelectronic properties, such as luminescence and reversible reduction behavior. In the case of the BNB-phenalenyl 7 (BMes, NMe), the radical-anion salt K[ 7 • ] was generated through chemical reduction with K metal and characterized by EPR spectroscopy. K[ 7 • ] is not long-term stable in a THF/ c -hexane solution, but abstracts an H atom with formation of the diamagnetic BNB-doped 1 H -phenalene K[ 7 H].

The tetraaryl μ-hydridodiborane(4) anion [2H] - possesses nucleophilic B-B and B-H bonds. Treatment of K[2H] with the electrophilic 9-H-9-borafluorene (HBFlu) furnishes the B 3 cluster K[3], with a triangular boron core linked through two BHB two-electron, three-center bonds and one electron-precise B-B bond, reminiscent of the prominent [B 3 H 8 ] - anion. Upon heating or prolonged stirring at room temperature, K[3] rearranges to a slightly more stable isomer K[3 a]. The reaction of M[2H] (M + =Li + , K + ) with MeI or Me 3 SiCl leads to equimolar amounts of 9-R-9-borafluorene and HBFlu (R=Me or Me 3 Si). Thus, [2H] - behaves as a masked [:BFlu] - nucleophile. The HBFlu by-product was used in situ to establish a tandem substitution-hydroboration reaction: a 1:1 mixture of M[2H] and allyl bromide gave the 1,3-propylene-linked ditopic 9-borafluorene 5 as sole product. M[2H] also participates in unprecedented [4+1] cycloadditions with dienes to furnish dialkyl diaryl spiroborates, M[R 2 BFlu]., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Double reduction of the THF adduct of 9H-9-borafluorene (1⋅THF) with excess alkali metal affords the dianion salts M 2 [1] in essentially quantitative yields (M=Li-K). Even though the added charge is stabilized through π delocalization, [1] 2- acts as a formal boron nucleophile toward organoboron (1⋅THF) and tetrel halide electrophiles (MeCl, Et 3 SiCl, Me 3 SnCl) to form B-B/C/Si/Sn bonds. The substrate dependence of open-shell versus closed-shell pathways has been investigated., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

A new pseudopolymorph of dodeca-chloro-penta-silane, namely a benzene monosolvate, Si 5 Cl 12 ·C 6 H 6 , is described. There are two half mol-ecules of each kind in the asymmetric unit. Both Si 5 Cl 12 mol-ecules are completed by crystallographic twofold symmetry. One of the benzene mol-ecules is located on a twofold rotation axis with two C-H groups located on this rotation axis. The second benzene mol-ecule has all atoms on a general position: it is disordered over two equally occupied orientations. No directional inter-actions beyond normal van der Waals contacts occur in the crystal., (© Tillmann et al. 2020.)

Substitutional doping of perylene with two boron atoms at the 6b/12b positions and two oxygen or nitrogen atoms at the 1/7 positions has been achieved. The modular synthesis route developed for these bis-BO- (3) and bis-BN-perylenes (5) starts from the readily accessible borinic acid derivative of the doubly brominated 9,10-dihydro-9,10-diboraanthracene (DBA), 1,5-Br 2 DBA(OH) 2 . A Stille-type reaction first furnishes the alkynyl-substituted species 1,5-(RCC) 2 DBA(OH) 2 (2), which undergo double ring closure to afford 3 via the gold-catalyzed addition of the O-H bonds to the C≡C bonds. Treatment of 2 with MeN(SiMe 3 ) 2 leads to aminoborane intermediates 1,5-(RCC) 2 DBA(N(H)Me) 2 , which can be ring-closed to give 5 in a similar manner as in the case of 3. Different substituents R (such as Me, tBuPh) can be introduced at the 2/8 positions of the perylene core. The products obtained undergo reversible reduction and are efficient blue/turquoise emitters., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The well-known red emitter tetrabenzo[ de , hi , op , st ]pentacene ( TBPA ) has been transformed into a bright blue emitter ( B 2 -TBPA ; λ em = 472 nm; c-hexane) via substitutional doping with two boron atoms. In contrast to the electron-rich TBPA , which forms endo -peroxides with O 2 under daylight, the benchtop-stable B 2 -TBPA is a good electron acceptor and undergoes reversible reduction at a moderate half-wave potential of E 1/2 = -1.73 V ( vs. FcH/FcH + ; THF). Although the size of B 2 -TBPA falls within the nanoscale, the helically twisted compound readily dissolves in c-hexane and does not require solubilizing substituents. The synthesis of B 2 -TBPA is based on the nickel-mediated Yamamoto-type dehalogenation of tetrabrominated 9,10-di(naphth-1-yl)-9,10-dihydro-9,10-diboraanthracene. This intramolecular C-C heterocoupling reaction shows a remarkable solvent dependence: B 2 -TBPA forms only in pyridine (79% yield), whereas an oxadiborepin is obtained from THF solutions ( ODBE , 81%; the reaction mixture is quenched with air in both cases). Insight into the corresponding reaction mechanism was gained from the isolation of intermediates and an investigation of their chemical properties. ODBE is an interesting blue emitter in its own right. Furthermore, it can be ring-opened with excess BBr 3 at the B-O-B moiety to afford a dimeric borabenzo[ de ]anthracene., (This journal is © The Royal Society of Chemistry 2019.)

The addition of 2 eq. of MesLi to the biphenylene-containing 9,10-dihydro-9,10-diboraanthracene (DBA) 2 results in the formation of the corresponding oxaboraphenanthrene 3 after column chromatography under ambient conditions. In the initial step, the anionic B-Mes monoadduct of 2 is generated, which eliminates a formal [Mes 2 B:] - ion with concomitant C-C-bond formation (room temperature, 18 h). The resulting biphenylene-containing borafluorene 4 is still sufficiently Lewis acidic to add the second equivalent of MesLi ([4Mes] - ). Using pristine 9-mesityl-9-borafluorene as a model system, we confirmed that both 4 and [4Mes] - should be capable of inserting an oxygen atom to furnish the observed oxaboraphenanthrene scaffold. The biphenylene-containing oxaboraphenanthrene 3 is a yellow compound with an absorption maximum at λ max = 450 nm. Similar to its DBA analogue 2, 3 shows no photoluminescence.

We have encountered two polymorphs of the title compound, C 24 H 16 B 2 OS 2 , both of which display almost the same unit-cell parameters. Compound (I) crystallizes in the non-centrosymmetric space group P 2 1 with four mol-ecules in the asymmetric unit. These mol-ecules are related by pseudosymmetry. As a result, the space group looks like P 2 1 / c , but the structure cannot be refined successfully in that space group. Compound (II) on the other hand crystallizes in the centrosymmetric space group P 2 1 / c with only two mol-ecules in the asymmetric unit. The crystals studied for (I) and (II) were both non-merohedral twins.

Doubly reduced 9,10-dihydro-9,10-diboraanthracenes (DBAs) are introduced as catalysts for hydrogenation as well as hydride-transfer reactions. The required alkali metal salts M 2 [DBA] are readily accessible from the respective neutral DBAs and Li metal, Na metal, or KC 8 . In the first step, the ambiphilic M 2 [DBA] activate H 2 in a concerted, metal-like fashion. The rates of H 2 activation strongly depend on the B-bonded substituents and the counter cations. Smaller substituents (e.g., H, Me) are superior to bulkier groups (e.g., Et, pTol), and a Mes substituent is even prohibitively large. Li + ions, which form persistent contact ion pairs with [DBA] 2- , slow the H 2 -addition rate to a higher extent than more weakly coordinating Na + /K + ions. For the hydrogenation of unsaturated compounds, we identified Li 2 [4] (Me substituents at boron) as the best performing catalyst; its substrate scope encompasses Ph(H)C═N tBu, Ph 2 C═CH 2 , and anthracene. The conversion of E-Cl to E-H bonds (E = C, Si, Ge, P) was best achieved by using Na 2 [4]. The latter protocol provides facile access also to Me 2 Si(H)Cl, a most important silicone building block. Whereas the H 2 -transfer reaction regenerates the dianion [4] 2- and is thus immediately catalytic, the H - -transfer process releases the neutral 4, which has to be recharged by Na metal before it can enter the cycle again. To avoid Wurtz-type coupling of the substrate, the reduction of 4 must be performed in the absence of the element halide, which demands an alternating process management (similar to the industrial anthraquinone process).

Trichlorosilylated tetrelides [(Cl 3 Si) 3 E] - have been prepared by adding 1 equiv of a soluble Cl - salt to (Cl 3 Si) 4 Si (E=Si) or 4 Si 2 Cl 6 /GeCl 4 (E=Ge). To assess their donor qualities, the anions [(Cl 3 Si) 3 E] - (E=C, Si, Ge) have been treated with BCl 3 , AlCl 3 , and GaCl 3 . Both BCl 3 and GaCl 3 give 1:1 adducts with the anionic centers. AlCl 3 leads to Cl - abstraction from [(Cl 3 Si) 3 E] - with formation of (Cl 3 Si) 4 E (E=Si or Ge). (Cl 3 Si) 4 Ge is cleanly converted to the perhydrogenated (H 3 Si) 4 Ge by use of Li[AlH 4 ]. Another case of Cl - abstraction was observed for [(Cl 3 Si) 3 Ge⋅GaCl 3 ] - , which reacts with GaCl 3 to afford the neutral dimer [(Cl 3 Si) 3 Ge-GaCl 2 ] 2 ., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Doubly boron-doped anthracenes and pentacenes have been longitudinally and laterally expanded through annulation of thiophene or benzene rings. The obtained series of closely related compounds allowed an assessment of key structure-property relationships with a focus on optoelectronic characteristics. Most of the products are benchtop-stable blue emitters and capable of accepting two electrons in a reversible manner. The syntheses involved late-stage modifications through photocyclization or stepwise oxidative C-C coupling (DDQ/BF 3 ·Et 2 O) as well as cyclocondensation of ortho-disilylated or -diborylated aryl building blocks.

Alkali metal salts M 2 [1] (M=Li, Na) of doubly reduced 9,10-dimethyl-9,10-dihydro-9,10-diboraanthracene (1) instantaneously add the C=O bond of CO 2 across their boron centers to furnish formal [4+2]-cycloadducts M 2 [2]. If only 1 equiv of CO 2 is supplied, these products are stable. In the presence of excess CO 2 , however, C-O bond cleavage occurs and an O 2- equivalent is transferred to CO 2 to furnish CO and [CO 3 ] 2- . With M=Li, Li 2 CO 3 precipitates and the neutral 1 is liberated such that it can be reduced again to establish a catalytic cycle. With M=Na, [CO 3 ] 2- remains coordinated to both boron atoms in a bridging mode (Na 2 [4]). A mechanistic scenario is proposed, based on isolated intermediates and model reactions., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

9,10-Dihydro-9,10-diboraanthracenes (DBAs) have low-energy LUMOs and narrow HOMO-LUMO gaps and are thus attractive electron-transporting and light-emitting materials in optoelectronic devices. A systematic series of ten C-halogenated 9,10-(Mes) 2 -DBAs was synthesized and studied by cyclic voltammetry, UV/Vis absorption and emission spectroscopy, and quantum-chemical calculations (Mes=mesityl). We probed the influence of the nature of the halogen atoms and the halogen substitution patterns on key optoelectronic properties of the DBAs. All 9,10-(Mes) 2 derivatives can be reversibly reduced at the DBA cores and at electrode potentials between E 1/2 Red1 =-1.84 and -1.26 V (vs. FcH/FcH + ). The most bathochromic UV/Vis absorption and the fluorescence emission of each DBA correspond to an ICT transition between the Mes rings and the DBA core. Br substituents lower the DBA LUMO energy and narrow the energy gap to the highest degree along the series F6 H 6 solutions and in the solid state. The sterically congested 1,5-(ThMe) 2 -9,10-(Mes) 2 -DBA was prepared in 74 % yield from 1,5-(Br) 2 -9,10-(Mes) 2 -DBA and Me 3 Sn-ThMe through a Stille-type C-C coupling reaction (ThMe=5-Me-2-thienyl)., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The Cl - -induced heterolysis of the Si-Si bond in Si 2 Cl 6 generates an [SiCl 3 ] - ion as reactive intermediate. When carried out in the presence of CCl 4 or Cl 2 C═CCl 2 (CH 2 Cl 2 solutions, room temperature or below), the reaction furnishes the monocarbanion [C(SiCl 3 ) 3 ] - ([A] - ; 92%) or the vicinal dianion [(Cl 3 Si) 2 C-C(SiCl 3 ) 2 ] 2- ([B] 2- ; 85%) in excellent yields. Starting from [B] 2- , the tetrasilylethane (Cl 3 Si) 2 (H)C-C(H)(SiCl 3 ) 2 (H 2 B) and the tetrasilylethene (Cl 3 Si) 2 C═C(SiCl 3 ) 2 (B; 96%) are readily available through protonation (CF 3 SO 3 H) or oxidation (CuCl 2 ), respectively. Equimolar mixtures of H 2 B/[B] 2- or B/[B] 2- quantitatively produce 2 equiv of the monoanion [HB] - or the blue radical anion [B • ] - , respectively. Treatment of B with Cl - ions in the presence of CuCl 2 furnishes the disilylethyne Cl 3 SiC≡CSiCl 3 (C; 80%); in the presence of [HMe 3 N]Cl, the trisilylethene (Cl 3 Si) 2 C═C(H)SiCl 3 (D; 72%) is obtained. Alkyne C undergoes a [4+2]-cycloaddition reaction with 2,3-dimethyl-1,3-butadiene (CH 2 Cl 2 , 50 °C, 3d) and thus provides access to 1,2-bis(trichlorosilyl)-4,5-dimethylbenzene (E1; 80%) after oxidation with DDQ. The corresponding 1,2-bis(trichlorosilyl)-3,4,5,6-tetraphenylbenzene (E2; 83%) was prepared from C and 2,3,4,5-tetraphenyl-2,4-cyclopentadien-1-one under CO extrusion at elevated temperatures (CH 2 Cl 2 , 180 °C, 4 d). All closed-shell products were characterized by 1 H, 13 C{ 1 H}, and 29 Si NMR spectroscopy; an EPR spectrum of [ nBu 4 N][B • ] was recorded. The molecular structures of [ nBu 4 N][A], [ nBu 4 N] 2 [B], B, E1, and E2 were further confirmed by single-crystal X-ray diffraction. On the basis of detailed experimental investigations, augmented by quantum-chemical calculations, plausible reaction mechanisms for the formation of [A] - , [B] 2- , C, and D are postulated.

The photoreactivity of 9-borafluorene-based, C,C-chelated organoborates was investigated. Unlike the related tetraarylborates, the charge-transfer transitions imparted by the biphenyl chelate lead to selective insertion of one aryl substituent into the endocyclic B-C bond of the 9-borafluorene moiety, resulting in the formation of boratanorcaradienes. This photoreaction likely proceeds according to a Zimmerman rearrangement, which is analogous to one of the initially proposed mechanisms for tetraarylborates and provides additional insight into these long-debated photochemical reactions.

Organoboranes are among the most versatile and widely used reagents in synthetic chemistry. A significant further expansion of their application spectrum would be achievable if boron-containing reactive intermediates capable of inserting into C-H bonds or performing nucleophilic substitution reactions were readily available. However, current progress in the field is still hampered by a lack of universal design concepts and mechanistic understanding. Herein we report that the doubly arylene-bridged diborane(6) 1 H 2 and its B[double bond, length as m-dash]B-bonded formal deprotonation product Li 2 [ 1 ] can activate the particularly inert C(sp 3 )-H bonds of added H 3 CLi and H 3 CCl, respectively. The first case involves the attack of [H 3 C] - on a Lewis-acidic boron center, whereas the second case follows a polarity-inverted pathway with nucleophilic attack of the B[double bond, length as m-dash]B double bond on H 3 CCl. Mechanistic details were elucidated by means of deuterium-labeled reagents, a radical clock, α,ω-dihaloalkane substrates, the experimental identification of key intermediates, and quantum-chemical calculations. It turned out that both systems, H 3 CLi/ 1 H 2 and H 3 CCl/Li 2 [ 1 ], ultimately funnel into the same reaction pathway, which likely proceeds past a borylene-type intermediate and requires the cooperative interaction of both boron atoms., (This journal is © The Royal Society of Chemistry 2018.)