The Chlorido-Bismuth Dication: A Potent Lewis Acid Captured in a Hepta-Coordinate Species with a Stereochemically Active Lone Pair.

The stabilization of simple, highly reactive cationic species in molecular complexes represents an important strategy to isolate and characterize compounds with uncommon or even unprecedented structural motifs and properties. Here we report the synthesis, isolation, and full characterization of chlorido-bismuth dications, stabilized only by monodentate dimethylsulfoxide (dmso) ligands: [BiCl(dmso)6][BF4]2 (1) and [BiCl(µ2-dmso)(dmso)4]2[BF4]4 (2). These compounds show unusual distorted pentagonal bipyramidal coordination geometries along with high Lewis acidities and have been analyzed by multinuclear NMR spectroscopy, elemental analysis, IR spectroscopy, single-crystal X-ray diffraction, and density functional theory calculations. Attempts to generate the bromido- and iodido-analogs gave dmso-stabilized tricationic bismuth species.

Chemical Aristocracy: He3 Dication and Analogous Noble-Gas-Exclusive Covalent Compounds.

Herein, we predict the first set of covalently bonded triatomic molecular compounds composed exclusively of noble gases. Using a combination of double-hybrid DFT, CCSD(T), and MRCI+Q calculations and a range of bonding analyses, we explored a set of 270 doubly charged triatomics, which included various combinations of noble gases and main group elements. This extensive exploration uncovered nine noble-gas-exclusive covalent compounds incorporating helium, neon, argon, or combinations thereof, exemplified by cases such as He32+ and related systems. This work brings to light a previously uncharted domain of noble gas chemistry, demonstrating the potential of noble gases in forming covalent molecular clusters.

Deciphering the irradiation induced fragmentation-rearrangement mechanisms in valence ionized CF3CH2F.

The increasing presence of 1,1,1,2-tetrafluoroethane (CF3CH2F) in the atmosphere has prompted detailed studies into its complex photodissociation behavior. Experiments focusing on CF3CH2F irradiation have unveiled an array of ions, with the persistent observation of the rearrangement product CHF2+ not yet fully understood. In this work, we combine density functional theory, coupled-cluster calculations with a complete basis set formalism, and atom-centered density matrix propagation molecular dynamics to investigate the energetics and dynamics of different potential pathways leading to CHF2+. We found that the two-body dissociation pathway involving an HF rearrangement, which was previously considered complex for CHF2+ formation, is actually straightforward but not likely due to the facile loss of HF. In contrast, our calculations reveal that the H elimination pathway, once thought of as a potential route to CHF2+, is not only comparably disadvantageous from both thermodynamic and kinetic points of view but also does not align with experimental data, particularly the lack of a rebound peak at m/z 101-102. We establish that the formation of CHF2+ is predominantly via the HF elimination channel, a conclusion experimentally corroborated by studies involving the trifluoroethylene cation CF2CHF+, a key intermediate in this process.

Electrochemical Diselenation of BODIPY Fluorophores for Bioimaging Applications and Sensitization of 1 O2.

Invited for the cover of this issue are the groups of Holger Braunschweig at the Julius-Maximilians-Universität Würzburg, Germany and Eufrânio N. da Silva Júnior at the Universidade Federal de Minas Gerais, UFMG, Brazil. The image depicts the electrochemical synthesis of selenium-containing BODIPY molecules with lightning symbolizing the electrifying synthetic process, while the surrounding elemental chaos hints at the red-shifted absorption and emission and the transformative photophysical properties of these new compounds. Read the full text of the article at 10.1002/chem.202303883.

Synthesis and Reactivity of a Dialane-Bridged Diradical.

Radicals of the lightest group 13 element, boron, are well established and observed in numerous forms. In contrast to boron, radical chemistry involving the heavier group 13 elements (aluminum, gallium, indium, and thallium) remains largely underexplored, primarily attributed to the formidable synthetic challenges associated with these elements. Herein, we report the synthesis and isolation of planar and twisted conformers of a doubly CAAC (cyclic alkyl(amino)carbene)-radical-substituted dialane. Extensive characterization through spectroscopic analyses and X-ray crystallography confirms their identity, while quantum chemical calculations support their open-shell nature and provide further insights into their electronic structures. The dialane-connected diradicals exhibit high susceptibility to oxidation, as evidenced by electrochemical measurements and reactions with o-chloranil and a variety of organic azides. This study opens a previously uncharted class of dialuminum systems to study, broadening the scope of diradical chemistry and its potential applications.

Hydrosilylation of BB triple bonds: catalyst- and reductant-free construction of B-Si bonds and B2Si heterocycles.

Hydrosilanes undergo mild, uncatalyzed single and double 1,2-addition across the B-B triple bonds of diborynes, leading to an unsymmetrical silyldiborene and compounds with novel non-cluster three-membered B2Si rings. The reactions are a new addition to the very few catalyst- and alkali-metal-free methods available for the construction of B-Si bonds.

Stepwise and selective synthesis of chelating, multimetallic and mixed-metal π-diborene complexes.

The reaction of a pyridyl-substituted, doubly Lewis base-stabilised diborene with different amounts of copper(I) precursors led to the formation of the first chelating π-diborene complexes, the first π-diborene complexes in which metals are bound to both faces of the BB bond, and the first mixed-metal π-diborene species.

Electrochemical Diselenation of BODIPY Fluorophores for Bioimaging Applications and Sensitization of 1 O2.

We report a rapid, efficient, and scope-extensive approach for the late-stage electrochemical diselenation of BODIPYs. Photophysical analyses reveal red-shifted absorption - corroborated by TD-DFT and DLPNO-STEOM-CCSD computations - and color-tunable emission with large Stokes shifts in the selenium-containing derivatives compared to their precursors. In addition, due to the presence of the heavy Se atoms, competitive ISC generates triplet states which sensitize 1 O2 and display phosphorescence in PMMA films at RT and in a frozen glass matrix at 77 K. Importantly, the selenium-containing BODIPYs demonstrate the ability to selectively stain lipid droplets, exhibiting distinct fluorescence in both green and red channels. This work highlights the potential of electrochemistry as an efficient method for synthesizing unique emission-tunable fluorophores with broad-ranging applications in bioimaging and related fields.

Cluster-Based Approach Utilizing Optimally Tuned TD-DFT to Calculate Absorption Spectra of Organic Semiconductor Thin Films.

The photophysics of organic semiconductor (OSC) thin films or crystals has garnered significant attention in recent years since a comprehensive theoretical understanding of the various processes occurring upon photoexcitation is crucial for assessing the efficiency of OSC materials. To date, research in this area has relied on methods using Frenkel-Holstein Hamiltonians, calculations of the GW-Bethe-Salpeter equation with periodic boundaries, or cluster-based approaches using quantum chemical methods, with each of the three approaches having distinct advantages and disadvantages. In this work, we introduce an optimally tuned, range-separated time-dependent density functional theory approach to accurately reproduce the total and polarization-resolved absorption spectra of pentacene, tetracene, and perylene thin films, all representative OSC materials. Our approach achieves excellent agreement with experimental data (mostly ≤0.1 eV) when combined with the utilization of clusters comprising multiple monomers and a standard polarizable continuum model to simulate the thin-film environment. Our protocol therefore addresses a major drawback of cluster-based approaches and makes them attractive tools for OSC investigations. Its key advantages include its independence from external, system-specific fitting parameters and its straightforward application with well-known quantum chemical program codes. It demonstrates how chemical intuition can help to reduce computational cost and still arrive at chemically meaningful and almost quantitative results.

Boron Insertion into the N≡N Bond of a Tungsten Dinitrogen Complex.

The 1,3-addition of 1,2-diaryl-1,2-dibromodiboranes (B2Br2Ar2) to trans-[W(N2)2(dppe)2] (dppe = κ2-(Ph2PCH2)2), which is accompanied by a Br-Ar substituent exchange between the two boron atoms, is followed by a spontaneous rearrangement of the resulting tungsten diboranyldiazenido complex to a 2-aza-1,3-diboraallenylimido complex displaying a linear, cumulenic B=N=B moiety. This rearrangement involves the splitting of both the B-B and N=N bonds of the N2B2 ligand, formal insertion of a BAr boranediyl moiety into the N=N bond, and coordination of the remaining BArBr boryl moiety to the terminal nitrogen atom. Density functional theory calculations show that the reaction proceeds via a cyclic NB2 intermediate, followed by dissociation into a tungsten nitrido complex and a linear boryliminoborane, which recombine by adduct formation between the nitrido ligand and the electron-deficient iminoborane boron atom. The linear B=N=B moiety also undergoes facile 1,2-addition of Brønsted acids (HY = HOPh, HSPh, and H2NPh) with concomitant Y-Br substituent exchange at the terminal boron atom, yielding cationic (borylamino)borylimido tungsten complexes.

Gas-phase C60Hn+q (n = 0-4, q = 0,1) fullerenes and fulleranes: spectroscopic simulations shed light on cosmic molecular structures.

The discovery of C60, C60+, and C70 in the interstellar medium has ignited a profound interest in the astrochemistry of fullerene and related systems. In particular, the presence of diffuse interstellar bands and their association with C60+ has led to the hypothesis that hydrogenated derivatives, known as fulleranes, may also exist in the interstellar medium and contribute to these bands. In this study, we systematically investigated the structural and spectroscopic properties of C60Hn+q (n = 0-4, q = 0,1) using an automated global minimum search and density functional theory calculations. Our results revealed novel global minimum structures for C60H2 and C60H4, distinct from previous reports. Notably, all hydrogenated fullerenes exhibited lower ionization potentials and higher proton affinities compared to C60. From an astrochemical perspective, our results exposed the challenges in establishing definitive spectroscopic criteria for detecting fulleranes using mid-infrared and UV-Vis spectroscopies. However, we successfully identified distinct electronic transitions in the near-infrared range that serve as distinctive signatures of cationic fulleranes. We strongly advocate for further high-resolution experimental studies to fully explore the potential of these transitions for the interstellar detection of fulleranes.

Dibenzoberylloles: antiaromatic s-block fluorene analogues.

Among a series of Lewis-base-stabilised antiaromatic dibenzoberylloles (DBBes) the cyclic alkyl(amino)carbene (CAAC) analogue undergoes a complex but highly selective thermal decomposition, involving the breaking and making of four bonds each, which yields a rare beryllium η2-alkene complex. Two-electron reduction of the CAAC-stabilised DBBe analogue yields an aromatic dianion.

Synthesis, bridgehead functionalization, and photoisomerization of 9,10-diboratatriptycene dianions.

9,10-Diboratatriptycene salts M2[RB(µ-C6H4)3BR] (R = H, Me; M+ = Li+, K+, [n-Bu4N]+) have been synthesized via [4 + 2] cycloaddition between doubly reduced 9,10-dihydro-9,10-diboraanthracenes M2[DBA] and benzyne, generated in situ from C6H5F and C6H5Li or LiN(i-Pr)2. [HB(µ-C6H4)3BH]2- reacts with CH2Cl2 to form quantitatively the bridgehead-derivatized [ClB(µ-C6H4)3BCl]2-, while twofold H- abstraction with B(C6F5)3 in the presence of SMe2 leads cleanly to the diadduct (Me2S)B(µ-C6H4)3B(SMe2). Photoisomerization of K2[HB(µ-C6H4)3BH] (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.

Catalyst-free diboration and silaboration of alkenes and alkynes using bis(9-heterofluorenyl)s.

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]-)/Me3SiBr 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(pz) 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 tBu(H)C[double bond, length as m-dash]CH2 and tBuC[triple bond, length as m-dash]CH on the one hand and FluB-Si(Cl)Flu as well as FluB-Si(Cl)Ph2 on the other.

Synthesis, Structural Characterization, and Bonding of Molecular Heavier Beryllium Chalcogenides.

The reactions of a cyclic alkyl(amino)carbene (CAAC)-stabilized beryllium radical with E2 Ph2 (E=S, Se, Te) and of a beryllole with HEPh (E=S, Se) yield the corresponding beryllium phenylchalcogenides, including the first structurally authenticated beryllium selenide and telluride complexes. Calculations show that their Be-E bonds are best described by the interaction between the Be+ and E- fragments, with Coulombic forces accounting for ca. 55 % of the attraction and orbital interactions dominated by the σ component.

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.

Nickel boryl complexes and nickel-catalyzed alkyne borylation.

The first nickel bis-boryl complexes cis-[Ni( i Pr2ImMe)2(Bcat)2], cis-[Ni( i Pr2ImMe)2(Bpin)2] and cis-[Ni( i Pr2ImMe)2(Beg)2] are reported, which were prepared via the reaction of a source of [Ni( i Pr2ImMe)2] with the diboron(4) compounds B2cat2, B2pin2 and B2eg2 ( i Pr2ImMe = 1,3-di-iso-propyl-4,5-dimethylimidazolin-2-ylidene; B2cat2 = bis(catecholato)diboron; B2pin2 = bis(pinacolato)diboron; B2eg2 = bis(ethylene glycolato)diboron). X-ray diffraction and DFT calculations strongly suggest that a delocalized, multicenter bonding scheme dictates the bonding situation of the NiB2 moiety in these square planar complexes, reminiscent of the bonding situation of "non-classical" H2 complexes. [Ni( i Pr2ImMe)2] also efficiently catalyzes the diboration of alkynes using B2cat2 as the boron source under mild conditions. In contrast to the known platinum-catalyzed diboration, the nickel system follows a different mechanistic pathway, which not only provides the 1,2-borylation product in excellent yields, but also provides an efficient approach to other products such as C-C coupled borylation products or rare tetra-borylated compounds. The mechanism of the nickel-catalyzed alkyne borylation was examined by means of stoichiometric reactions and DFT calculations. Oxidative addition of the diboron reagent to nickel is not dominant; the first steps of the catalytic cycle are coordination of the alkyne to [Ni( i Pr2ImMe)2] and subsequent borylation at the coordinated and, thus, activated alkyne to yield complexes of the type [Ni(NHC)2(η2-cis-(Bcat)(R)C[double bond, length as m-dash]C(R)(Bcat))], exemplified by the isolation and structural characterization of [Ni( i Pr2ImMe)2(η2-cis-(Bcat)(Me)C[double bond, length as m-dash]C(Me)(Bcat))] and [Ni( i Pr2ImMe)2(η2-cis-(Bcat)(H7C3)C[double bond, length as m-dash]C(C3H7)(Bcat))].

Group IV heteroadamantanes: synthesis of Si6Sn4 and site-selective derivatization of Si6Ge4.

The mixed heteroadamantanes Si6Ge4 and Si6Sn4 are readily accessible from Me2ECl2/Si2Cl6/cat. Cl- (4 × EMe2, 2 × SiCl2, 4 × Si-SiCl3 vertices; E = Ge, Sn). Different from Si6Ge4, two skeletal isomers are formed in the case of Si6Sn4. Site-selective SiCl3-methylation of Si6Ge4 was achieved, leaving the SiCl2 groups untouched.

Metal-Free Intermolecular C-H Borylation of N-Heterocycles at B-B Multiple Bonds.

Carbene-stabilized diborynes of the form LBBL (L=N-heterocyclic carbene (NHC) or cyclic alkyl(amino)carbene (CAAC)) induce rapid, high yielding, intermolecular ortho-C-H borylation at N-heterocycles at room temperature. A simple pyridyldiborene is formed when an NHC-stabilized diboryne is combined with pyridine, while a CAAC-stabilized diboryne leads to activation of two pyridine molecules to give a tricyclic alkylideneborane, which can be forced to undergo a further H-shift resulting in a zwitterionic, doubly benzo-fused 1,3,2,5-diazadiborinine by heating. Use of the extended N-heteroaromatic quinoline leads to a borylmethyleneborane under mild conditions via an unprecedented boron-carbon exchange process.

Dope it with germanium: selective access to functionalized Si5Ge heterocycles.

The Cl- diadduct [nBu4N]2[A·2Cl] of the mixed cyclohexatetrelane (SiCl2)5(GeMe2), A, is accessible from Me2GeCl2, 6 eq. Si2Cl6, and 2 eq. [nBu4N]Cl in one step (96%). Free, tenfold functionalized A can be released from the primary product by decomplexation with AlCl3 (78%). Insight into the assembly mechanism of [nBu4N]2[A·2Cl] and the reactivity of A is provided.