An isolable, chelating bis[cyclic (alkyl)(amino)carbene] stabilizes a strongly bent, dicoordinate Ni(0) complex.

Chelating ligands have had a tremendous impact in coordination chemistry and catalysis. Notwithstanding their success as strongly σ-donating and π-accepting ligands, to date no chelating bis[cyclic (alkyl)(amino)carbenes] have been reported. Herein, we describe a chelating, C2-symmetric bis[cyclic (alkyl)(amino)carbene] ligand, which was isolated as a racemic mixture. The isolation and structural characterization of its isostructural, pseudotetrahedral complexes with iron, cobalt, nickel, and zinc dihalides featuring eight-membered metallacycles demonstrates the binding ability of the bis(carbene). Reduction of the nickel(II) dibromide with potassium graphite produces a dicoordinate nickel(0) complex that features one of the narrowest angles measured in any unsupported dicoordinate transition metal complexes.

Synthesis, characterisation and reactivity of a zinc triazenide for potential use in vapour deposition.

In this study, we synthesised and characterised a new zinc(II) triazenide for potential use in vapour deposition of zinc sulphide thin films. The compound is volatile and quantitatively sublimes at 80 °C under vacuum (0.5 mbar). Thermogravimetric analysis showed a one-step volatilisation with an onset temperature at ∼125 °C and 5% residual mass. The compound also reacted with 2 or 4 molar equivalents of triphenylsilanethiol to give dimeric and monomeric zinc thiolates, respectively. The high volatility, thermal stability, and reactivity with sterically hindered thiols makes this compound a potential candidate for use in vapour deposition of zinc containing thin films.

Hydrobismuthation: Insertion of Unsaturated Hydrocarbons into the Heaviest Main Group Element Bond to Hydrogen.

The bismuth hydride (2,6-Mes2H3C6)2BiH (1, Mes = 2,4,6-trimethylphenyl), which has a Bi-H 1H NMR spectroscopic signal at δ = 19.64 ppm, was reacted with phenylacetylene at 60 °C in toluene to yield [(2,6-Mes2C6H3)2BiC(Ph)=CH2] (2) after 15 min. Compound 2 was characterized by 1H, 13C NMR, and UV-vis spectroscopy, single crystal X-ray crystallography, and calculations employing density functional theory. Compound 2 is the first example of a hydrobismuthation addition product and displays Markovnikov regioselectivity. Computational methods indicated that it forms via a radical mechanism with an associated Gibbs energy of activation of 91 kJ mol-1 and a reaction energy of -90 kJ mol-1.

Synthesis of a Carbene-Stabilized (Diphospha)aminyl Radical and Its One Electron Oxidation and Reduction to Nonclassical Nitrenium and Amide Species.

Herein, we report the synthesis of an acyclic carbene-stabilized diphospha(aminyl) PNP radical CAACMePNPCAACMe 4 (CAACMe = 1-[2,6-bis(isopropyl)phenyl]-3,3,5,5-tetramethyl-2-pyrrolidinylidene) by a facile one-pot, seven-electron reduction of hexachlorophosphazene chloride [Cl3PNPCl3][Cl]. The PNP radical 4 features a conjugated framework with spin density primarily localized on the central nitrogen atom as well as the flanking carbenes. Unlike other tripnictogen radicals, 4 undergoes facile one-electron oxidation and reduction to yield nonclassical nitrenium and amide species [5]+ and [6]-, respectively. The cation [5]+ exhibits conformational flexibility in the solution state between the expected W-shaped geometry [5b]+ and a previously unobserved linear heteroallene-type structure [5a]+, which was characterized in the solid state. The equilibrium was explored both computationally and experimentally, showing that [5a]+ is favored over [5b]+ both enthalpically (ΔH = -2.9 × 103 ± 80 J mol-1) and entropically (ΔS = 4.2 ± 0.25 J mol-1 K-1). The formal amide [6]- displays remarkable flexibility in its coordination chemistry due to the presence of multiple Lewis basic centers, as evidenced by the structure of its potassium complex K262, which exhibits µ, κ-P, κ-P, and η3-PNP coordination modes. Protonation of [6]- leads to the formation of an amine 7, which features a trigonal planar geometry around nitrogen.

Computational thermochemistry: extension of Benson group additivity approach to organoboron compounds and reliable predictions of their thermochemical properties.

High-level computational data for standard gas phase enthalpies of formation, entropies, and heat capacities are reported for 116 compounds of boron. A comparison of the results with extant experimental and computational benchmark values reveals important trends and clear outliers. Recommendations are made to revise some of the key quantities, such as the enthalpies of formation of orthoboric acid, trimethylthioborate, and triphenylborane, the last of which is found to be considerably in error. The uncertainties associated with the experimental values are found to exceed those of high-level calculations by a clear margin, prompting the redetermination of Benson group additivity contributions for boron-based groups on purely computational grounds. The applicability of the established group contribution values is demonstrated by estimating thermochemical data for large organoboron compounds that cannot be treated with high-level quantum chemical methods and comparing the results with existing experimental and computational values.

Bis[cyclic (alkyl)(amino)carbene] isomers: Stable trans-bis(CAAC) versus facile olefin formation for cis-bis(CAAC).

Isomeric bis(aldiminium) salts with a 1,4-cyclohexylene framework were synthesized. The first isolable bis(CAAC) was prepared from the trans-stereoisomer and its ditopic ligand competency was proven by conversion to iridium(I) and rhodium(I) complexes. Upon deprotonation, the cis-isomer yielded an electron rich olefin via a classic, proton-catalyzed pathway. The CC bond formation from the desired cis-bis(CAAC) was shown to be thermodynamically very favorable and to involve a small activation barrier. Compounds that can be described as insertion products of the cis-bis(CAAC) into the E-H bonds of NH3, CH3CN and H2O were also identified.

High-Level Ab Initio Predictions of Thermochemical Properties of Organosilicon Species: Critical Evaluation of Experimental Data and a Reliable Benchmark Database for Extending Group Additivity Approaches.

A high-level composite quantum chemical method, W1X-1, is used herein to calculate the gas-phase standard enthalpy of formation, entropy, and heat capacity of 159 organosilicon compounds. The results set a new benchmark in the field that allows, for the first time, an in-depth assessment of existing experimental data on standard enthalpies of formation, enabling the identification of important trends and possible outliers. The calculated thermochemical data are used to determine Benson group additivity contributions for 60 Benson groups and group pairs involving silicon. These values allow fast and accurate estimation of thermochemical parameters of organosilicon compounds of varying complexity, and the data acquired are used to assess the reliability of experimental work of Voronkov et al. that has been repeatedly criticized by Becerra and Walsh. Recent results from other computational investigations in the field are also carefully discussed through the prism of reported advancements.

Haptotropism in a Nickel Complex with a Neutral, π-Bridging cyclo-P4 Ligand Analogous to Cyclobutadiene.

Dedicated to Professor Manfred Scheer on the occasion of his 65th birthday The reaction of (1)Ni(η2 -cod), 2, incorporating a chelating bis(N-heterocyclic carbene) 1, with P4 in pentane yielded the dinuclear complex [(2)Ni]2 (µ2 ,η2 : η2 -P4 ), 3, formally featuring a cyclobutadiene-like, neutral, rectangular, π-bridging P4 -ring. In toluene, the butterfly-shaped complex [(1)Ni]2 (µ2 ,η2 : η2 -P2 ), 4, with a formally neutral P2 -unit was obtained from 2 and either P4 or 3. Computational studies showed that a haptotropic rearrangement involving two isomers of the µ2 ,η2 : η2 -P4 coordination mode and a low-energy µ2 ,η4 : η4 -P4 coordination mode, as previously predicted for related nickel cyclobutadiene complexes, could explain the coalescence observed in the low-temperature NMR spectra of 3. The insertion of the (1)Ni fragment into a P-P bond of P7 (SiMe3 )3 , forming complex 5 with a norbornane-like P7 ligand, was also observed.

Tetracyclic silaheterocycle formed through a pericyclic reaction cascade including a two-fold intramolecular C-C bond activation.

Reductive debromination of the tribromoamidosilane 2 gave the tetracyclic silaheterocycle 3 through a unique reaction cascade involving unprecedented two-fold intramolecular cycloaddition by transient silylenes. Experimental and computational analyses of the reaction mechanism allowed the identification of the key intermediates that lead to the silaheterocycle 3 or, alternatively, to the cyclotrisilene 19.

Room-Temperature Magnetic Bistability in a Salt of Organic Radical Ions.

Cocrystallization of 7,7',8,8'-tetracyanoquinodimethane radical anion (TCNQ-•) and 3-methylpyridinium-1,2,3,5-dithiadiazolyl radical cation (3-MepyDTDA+•) afforded isostructural acetonitrile (MeCN) or propionitrile (EtCN) solvates containing cofacial π dimers of homologous components. Loss of lattice solvent from the diamagnetic solvates above 366 K affords a high-temperature paramagnetic phase containing discrete TCNQ-• and weakly bound π dimers of 3-MepyDTDA+•, as evidenced by X-ray diffraction methods and magnetic susceptibility measurements. Below 268 K, a first-order phase transition occurs, leading to a low-temperature diamagnetic phase with TCNQ-• σ dimer and π dimers of 3-MepyDTDA+•. This study reveals the first example of cooperative interactions between two different organic radical ions leading to magnetic bistability, and these results are central to the future design of multicomponent functional molecular materials.

Low-Valent Germanylidene Anions: Efficient Single-Site Nucleophiles for Activation of Small Molecules.

Rare mononuclear and helical chain low-valent germanylidene anions supported by cyclic (alkyl)(amino)carbene and hypermetallyl ligands were synthesised by stepwise reduction from corresponding germylene precursors via stable and isolable germanium radicals. The electronic structures of the anions can be described with ylidene and ylidone resonance forms with the Ge-C π-electrons capable of binding even weak electrophiles. The germanylidene anions reacted with CO2 to give µ-CO2 -κC:κO complexes, a rare coordination mode for low-valent germanium and inaccessible for the related neutral germylones. These results implicate low-valent germanylidene anions as efficient single-site nucleophiles for activation of small molecules.

A Monomeric Aluminum Imide (Iminoalane) with Al-N Triple-Bonding: Bonding Analysis and Dispersion Energy Stabilization.

The reaction of :AlAriPr8 (AriPr8 = C6H-2,6-(C6H2-2,4,6-iPr3)2-3,5-iPr2) with ArMe6N3 (ArMe6 = C6H3-2,6-(C6H2-2,4,6-Me3)2) in hexanes at ambient temperature gave the aluminum imide AriPr8AlNArMe6 (1). Its crystal structure displayed short Al-N distances of 1.625(4) and 1.628(3) Å with linear (C-Al-N-C = 180°) or almost linear (C-Al-N = 172.4(2)°; Al-N-C = 172.5(3)°) geometries. DFT calculations confirm linear geometry with an Al-N distance of 1.635 Å. According to energy decomposition analysis, the Al-N bond has three orbital components totaling -1350 kJ mol-1 and instantaneous interaction energy of -551 kJ mol-1 with respect to :AlAriPr8 and ArMe6N̈:. Dispersion accounts for -89 kJ mol-1, which is similar in strength to one Al-N π-interaction. The electronic spectrum has an intense transition at 290 nm which tails into the visible region. In the IR spectrum, the Al-N stretching band is calculated to appear at ca. 1100 cm-1. In contrast, reaction of :AlAriPr8 with 1-AdN3 or Me3SiN3 gave transient imides that immediately reacted with a second equivalent of the azide to give AriPr8Al[(NAd)2N2] (2) or AriPr8Al(N3){N(SiMe3)2} (3).

Side-on Coordination in Isostructural Nitrous Oxide and Carbon Dioxide Complexes of Nickel.

A nickel complex incorporating an N2 O ligand with a rare η2 -N,N'-coordination mode was isolated and characterized by X-ray crystallography, as well as by IR and solid-state NMR spectroscopy augmented by 15 N-labeling experiments. The isoelectronic nickel CO2 complex reported for comparison features a very similar solid-state structure. Computational studies revealed that η2 -N2 O binds to nickel slightly stronger than η2 -CO2 in this case, and comparably to or slightly stronger than η2 -CO2 to transition metals in general. Comparable transition-state energies for the formation of isomeric η2 -N,N'- and η2 -N,O-complexes, and a negligible activation barrier for the decomposition of the latter likely account for the limited stability of the N2 O complex.

The Monomeric Alanediyl :AlAriPr8 (AriPr8 = C6H-2,6-(C6H2-2,4,6-Pri3)2-3,5-Pri2): An Organoaluminum(I) Compound with a One-Coordinate Aluminum Atom.

Reduction of the aluminum iodide AlI2AriPr8 (1; AriPr8 = C6H-2,6-(C6H2-2,4,6-Pri3)2-3,5-Pri2) with 5% w/w Na/NaCl in hexanes gave a dark red solution from which the monomeric alanediyl :AlAriPr8 (2) was isolated in ca. 28% yield as yellow-orange crystals. Compounds 1 and 2 were characterized by X-ray crystallography, electronic and NMR spectroscopy, and theoretical calculations. The Al atom in 2 is one-coordinate, and the compound displays two absorptions in its electronic spectrum at 354 and 455 nm. It reacts with H2 under ambient conditions to give the aluminum hydride {AlH(µ-H)AriPr8}2, probably via a weakly bound dimer of 2 as an intermediate.

Molecular Complexes Featuring Unsupported Dispersion-Enhanced Aluminum-Copper and Gallium-Copper Bonds.

The reaction of the copper(I) ß-diketiminate copper complex {(Cu(BDIMes))2(µ-C6H6)} (BDIMes = N,N'-bis(2,4,6-trimethylphenyl)pentane-2,4-diiminate) with the low-valent group 13 metal ß-diketiminates M(BDIDip) (M = Al or Ga; BDIDip = N,N'-bis(2,6-diisopropylphenyl)pentane-2,4-diiminate) in toluene afforded the complexes {(BDIMes)CuAl(BDIDip)} and {(BDIMes)CuGa(BDIDip)}. These feature unsupported copper-aluminum or copper-gallium bonds with short metal-metal distances, Cu-Al = 2.3010(6) Å and Cu-Ga = 2.2916(5) Å. Density functional theory (DFT) calculations showed that approximately half of the calculated association enthalpies can be attributed to London dispersion forces.

Fabrication of Porous Hydrogenation Catalysts by a Selective Laser Sintering 3D Printing Technique.

Three-dimensional selective laser sintering printing was utilized to produce porous, solid objects, in which the catalytically active component, Pd/SiO2, is attached to an easily printable supporting polypropylene framework. Physical properties of the printed objects, such as porosity, were controlled by varying the printing parameters. Structural characterization of the objects was performed by helium ion microscopy, scanning electron microscopy, and X-ray tomography, and the catalytic performance of the objects was tested in the hydrogenation of styrene, cyclohexene, and phenylacetylene. The results show that the selective laser sintering process provides an alternative and effective way to produce highly active and easily reusable heterogeneous catalysts without significantly reducing the catalytic efficiency of the active Pd/SiO2 component. The ability to control the size, porosity, mechanical properties, flow properties, physical properties, and chemical properties of the catalyst objects opens up possibilities to optimize devices for different reaction environments including batch reactions and continuous flow systems.

Boron-nitrogen substituted dihydroindeno[1,2-b]fluorene derivatives as acceptors in organic solar cells.

The electrophilic borylation of 2,5-diarylpyrazines results in the formation of boron-nitrogen doped dihydroindeno[1,2-b]fluorene which can be synthesized using standard Schlenk techniques and worked up and handled readily under atmospheric conditions. Through transmetallation via diarylzinc reagents a series of derivatives were synthesized which show broad visible to near-IR light absorption profiles that highlight the versatility of this BN substituted core for use in optoelectronic devices. The synthesis is efficient, scalable and allows for tuning through changes in substituents on the planar heterocyclic core and at boron. Exploratory evaluation in organic solar cell devices as non-fullerene acceptors gave power conversion efficiencies of 2%.

Oligoamide Foldamers as Helical Chloride Receptors-the Influence of Electron-Withdrawing Substituents on Anion-Binding Interactions.

The anion-binding properties of three closely related oligoamide foldamers were studied using NMR spectroscopy, isothermal titration calorimetry and mass spectrometry, as well as DFT calculations. The 1 H NMR spectra of the foldamers in [D6 ]acetone solution revealed partial preorganization by intramolecular hydrogen bonding, which creates a suitable cavity for anion binding. The limited size of the cavity, however, enabled efficient binding by the inner amide protons only for the chloride anion resulting in the formation of a thermodynamically stable 1:1 complex. All 1:1 chloride complexes displayed a significant favourable contribution of the entropy term. Most likely, this is due to the release of ordered solvent molecules solvating the free foldamer and the anion to the bulk solution upon complex formation. The introduction of electron-withdrawing substituents in foldamers 2 and 3 had only a slight effect on the thermodynamic constants for chloride binding compared to the parent receptor. Remarkably, the binding of chloride to foldamer 3 not only produced the expected 1:1 complex but also open aggregates with 1:2 (host:anion) stoichiometry.

Nickel as a Lewis Base in a T-Shaped Nickel(0) Germylene Complex Incorporating a Flexible Bis(NHC) Ligand.

Flexible, chelating bis(NHC) ligand 2, able to accommodate both cis- and trans-coordination modes, was used to synthesize (2)Ni(η2 -cod), 3. In reaction with GeCl2 , it produced (2)NiGeCl2 , 4, featuring a T-shaped Ni0 and a pyramidal Ge center. Complex 4 could also be prepared from [(2)GeCl]Cl, 5, and Ni(cod)2 , in a reaction that formally involved Ni-Ge transmetalation, followed by coordination of the extruded GeCl2 moiety to Ni. A computational analysis showed that 4 possesses considerable multiconfigurational character and the Ni→Ge bond is formed through σ-donation from the Ni 4s, 4p, and 3d orbitals to Ge. (NHC)2 Ni(cod) complexes 9 and 10, as well as (NHC)2 GeCl2 derivative 11, incorporating ligands that cannot accommodate a wide bite angle, failed to produce isolable Ni-Ge complexes. The isolation of (2)Ni(η2 -Py), 12, provides further evidence for the reluctance of the (2)Ni0 fragment to act as a σ-Lewis acid.