Linear and Bent Cp*2 Si: Reversible Phase Transition of a Key Molecule.

The solid-state structure of decamethylsilicocene Cp*2 Si with a bent and a linear molecule in the same unit cell was so far considered an exception in relation to the structures of its all-bent heavier analogues Cp*2 E with E=Ge, Sn, Pb. Here, we present the solution to this conundrum by reporting a low-temperature phase, where all three symmetrically independent molecules are present in a bent formation. This reversible enantiotropic phase transition occurs in the temperature range between 80 K and 130 K and provides a rationale for the unexpected linear molecule based in entropy beyond hand-waving explanations such as electronic reasons or packing effects.

Insertion Reaction of Me3SiN3 with Bis(germylene).

Herein, we describe the redox reaction of bis(germylene) PhC(NtBu)2Ge-Ge(NtBu)2CPh with different equivalents of Me3SiN3 affording two distinct products. The reaction of Me3SiN3 with bis-germylene in a 1:1 molar ratio results in compound 1 at -78 °C; however, treatment of bis-germylene with a 2.1 equiv of Me3SiN3 at room temperature results in compound 2. The formation of 1 and 2 can be rationalized by two successive 3 + 1 cycloadditions of Me3SiN3 with the germanium center of bis(germylene) and N2 elimination. All of the compounds are well-characterized by various spectroscopic techniques and single-crystal X-ray structural analyses. Density functional theory (DFT) calculations suggest that compound 2 has a dicoordinated nitrogen atom, which is stabilized by hyperconjugative interactions, resulting in pseudo-germylimine moiety. However, the dicoordinated nitrogen atom shows high basicity as indicated by proton affinity values. These are rare examples of isolated products that show insertion as well as simultaneous redox properties of bis(germylene).

Trapping X-ray Radiation Damage from Homolytic Se-C Bond Cleavage in BnSeSeBn Crystals (Bn=benzyl, CH2 C6 H5 ).

Irradiation of dibenzyl diselenide BnSeSeBn with X-ray or UV-light cleaves the Se-C and the Se-Se bonds, inducing stable and metastable radical states. They are inevitably important to all natural and life sciences. Structural changes due to X-ray-induced Se-C bond-cleavage could be pin-pointed in various high-resolution X-ray diffraction experiments for the first time. Extended DFT methods were applied to characterize the solid-state structure and support the refinement of the observed residuals as contributions from the BnSeSe⋅ radical species. The X-ray or UV-irradiated crystalline samples of BnSeSeBn were characterized by solid-state EPR. This paper provides insight that in the course of X-ray structure analysis of selenium compounds not only organo-selenide radicals like RSe⋅ may occur, but also organo diselenide BnSeSe⋅ radicals and organic radicals R⋅ are generated, particularly important to know in structural biology.

Stabilization of Reactive Nitrene by Silylenes without Using a Reducing Metal.

Herein, we report the stabilization of nitrene reagents as the source of a nitrogen atom to synthesize nitrogen-incorporated R1 LSi-N←SiLR2 (1) [L=PhC(NtBu)2 ; R1 =NTMS2 , R2 =NTMS]. Compound 1 is synthesized by reacting LSi(I)-SiI L with 3.1 equivalents of Me3 SiN3 at low temperature to afford a triene-like structural framework. Whereas the reaction of the LSi(I)-SiI L with 2.1 equivalents of Me3 SiN3 at room temperature produced silaimine 2 with a central four-membered Si2 N2 ring which is accompanied by a silylene LSi and a cleaved silylene fragment. 1 further reacts with AgOTf at room temperature to yield compound 3 which shows coordination of nitrene to silver with the triflate salt. The compounds 1 and 2 were fully characterized by NMR, mass spectrometry, and X-ray crystallographic analysis. The quantum mechanical calculations reveal that compounds 1 and 2 have dicoordinated monovalent N atoms having two active lone pairs of electrons. These lone pairs are stabilized by hyperconjugative interactions.

Analysis of Solid-State Luminescence Emission Amplification at Substituted Anthracenes by Host-Guest Complex Formation.

Invited for the cover of this issue are Dietmar Stalke and coworkers from the Georg-August Universität at Göttingen. The image symbolizes the organization of small arenes in the pocket of thiophosphoranyl substituted anthracene like the construction of a stable wall from a loose pile of bricks, shifting the emission to the green and amplifying it by a factor of five. Read the full text of the article at 10.1002/chem.202003017.

Analysis of Solid-State Luminescence Emission Amplification at Substituted Anthracenes by Host-Guest Complex Formation.

Small robust organic molecules showing solid-state luminescence are promising candidates for optoelectronic materials. Herein, we investigate a series of diphenylphosphanyl anthracenes [9-PPh2 -10-R-(C14 H8 )] and their sulfur oxidised analogues. The oxidation causes drastic changes in the molecular structure as the new orientation of the bulky (S)PPh2 substituent induces a strong butterfly bent structure of the anthracene core, which triggers a strong bathochromic shift resulting in a green solid-state fluorescence. As the emission properties change only slightly upon aggregation the origin of the emission is attributed to a typical monomer fluorescence. The host-guest complexes of [9-(S)PPh2 -10-Ethyl-(C14 H8 )] with four basic arenes reveal an emission enhancement up to five-times higher quantum yields compared to the pure host. Less interchromophoric interactions and a restriction of intramolecular motion within the host molecules due to fixation by weak C-H⋅⋅⋅π interactions with the co-crystallised arene are responsible for that emission enhancement.

Isolation of Transient Acyclic Germanium(I) Radicals Stabilized by Cyclic Alkyl(amino) Carbenes.

Despite the notable progress in the stabilization of main group radicals by NHCs and cAACs, no germanium radicals have been isolated so far due to synthetic challenges. Stabilization of neutral [:EIR]• (E = Si, Ge) radicals is an uphill task, as these reactive transient species are highly susceptible to dimerization. Herein, we report the synthesis of acyclic neutral germanium(I) radicals Cy-cAAC:GeN(SiMe3)Dip (1) and Me-cAAC:GeN(SiPh3)Mes (2) obtained by the reduction of [Ar(SiR3)NGeCl3] with KC8 in the presence of cAAC. Compounds 1 and 2 are well characterized by single crystal X-ray structural analysis, cyclic voltammetry, and EPR spectroscopy. Furthermore, the structure and bonding of compounds 1 and 2 have been investigated by theoretical methods.

A Neutral "Aluminocene" Sandwich Complex: η1 - versus η5 -Coordination Modes of a Pentaarylborole with ECp* (E=Al, Ga; Cp*=C5 Me5 ).

The pentaaryl borole (Ph*C)4 BXylF [Ph*=3,5-tBu2 (C6 H3 ); XylF =3,5-(CF3 )2 (C6 H3 )] reacts with low-valent Group 13 precursors AlCp* and GaCp* by two divergent routes. In the case of [AlCp*]4 , the borole reacts as an oxidising agent and accepts two electrons. Structural, spectroscopic, and computational analysis of the resulting unprecedented neutral η5 -Cp*,η5 -[(Ph*C)4 BXylF ] complex of AlIII revealed a strong, ionic bonding interaction. The formation of the heteroleptic borole-cyclopentadienyl "aluminocene" leads to significant changes in the 13 C NMR chemical shifts within the borole unit. In the case of the less-reductive GaCp*, borole (Ph*C)4 BXylF reacts as a Lewis acid to form a dynamic adduct with a dative 2-center-2-electron Ga-B bond. The Lewis adduct was also studied structurally, spectroscopically, and computationally.

Synthesis and Ring Strain of a Benzoborirene-N-Heterocyclic Carbene Adduct.

The reduction of an N-heterocyclic carbene (1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene, IiPr Me 2 ) adduct of dichloro(ortho-bromophenyl)borane by tert-butyl lithium at low temperature yields the IiPr Me 2 adduct A of parent benzoborirene, a highly strained boron-containing bicyclic compound. A is unstable at room temperature and dimerizes at low temperature to the bis-IiPr Me 2 adduct of 9,10-dihydro-9,10-diboraanthracene, characterized by single-crystal X-ray crystallography.

Silanylidene and Germanylidene Anions: Valence-Isoelectronic Species to the Well-Studied Phosphinidene.

The reduction of TipMCl3 (Tip=2,4,6-triisopropylphenyl) (M=Si, Ge) with KC8 in the presence of cyclic alkyl(amino) carbene (cAAC) afforded the acyclic silanylidene and germanylidene anions in the form of potassium salt [K(cAAC)MTip]2 (M=Si (1); Ge (2)). The silanylidene and germanylidene anions are valence-isoelectronic to the well-studied phosphinidene and are a new class of acyclic anions of Group 14. Compounds 1 and 2 were isolated and well characterized by NMR and single-crystal X-ray structure analysis. Furthermore, the structure and bonding of compounds 1 and 2 was investigated by computational methods.

Ruthenium(II)-Catalyzed meta C-H Mono- and Difluoromethylations by Phosphine/Carboxylate Cooperation.

Ruthenium(II)-catalyzed meta-selective C-H (di)fluoromethylation was accomplished by phosphine and carboxylate cooperation. The remote C-H functionalization was characterized by ample substrate scope, thereby setting the stage for meta-(di)fluoromethylation through facile C-H cleavage.

Indium Kα radiation from a MetalJet X-ray source: comparison of the Eiger2 CdTe and Photon III detectors.

The MetalJet source makes available new Kα radiation wavelengths for use in X-ray diffraction experiments. The purpose of this paper is to demonstrate the application of indium Kα radiation in independent-atom model refinement, as well as approaches using aspherical atomic form factors. The results vary greatly depending on the detector employed, as the energy cut-off of the Eiger2 CdTe provides a solution to a unique energy contamination problem of the MetalJet In radiation, which the Photon III detector cannot provide.

Indium Kα radiation from a MetalJet X-ray source: the long way to a successful charge-density investigation.

The MetalJet X-ray source provides indium Kα radiation with a wavelength even shorter than Ag radiation. This paper reports on problematic spectral impurities and presents possible countermeasures so that collection of data with excellent quality up to a high resolution is possible. It is demonstrated that these data can be used in the refinement of a multipole model, the results of which are used for a topological analysis to assess the bonding situation in a sulfur ylide compound.

A donor-supported silavinylidene and silylium ylides: boroles as a flexible platform for versatile Si(ii) chemistry.

Electron-deficient, anti-aromatic 2,5-disilyl boroles are shown to be a flexibly adaptive molecular platform with regards to SiMe3 mobility in their reaction with the nucleophilic donor-stabilised precursor dichloro silylene SiCl2(IDipp). Depending on the substitution pattern, selective formation of two fundamentally different products of rivalling formation pathways is achieved. Formal addition of the dichlorosilylene gives the 5,5-dichloro-5-sila-6-borabicyclo[2.1.1]hex-2-ene derivatives. Under kinetically controlled conditions, SiCl2(IDipp) induces 1,3-trimethylsilyl migration and adds exocyclically to the generated carbene fragment giving an NHC-supported silylium ylide. In some cases interconversion between these compound classes was triggered by temperature or NHC-addition. Reduction of silaborabicyclo[2.1.1]hex-2-ene derivatives under forcing conditions gave clean access to recently described nido-type cluster Si(ii) half-sandwich complexes of boroles. Reduction of a NHC-supported silylium ylide gave an unprecedented NHC-supported silavinylidene which rearranges to the nido-type cluster at elevated temperatures.

One silicon atom of bis(silylene) functions as a selective Lewis base under adduct formation with a Lewis acid.

Herein, we describe the facile and selective one-pot synthetic route to silylene-aluminum and silylene-gallium adducts. Reduction of silylene LSiCl (L = PhC(NtBu)2) with KC8 in the presence of bulky and sterically hindered cyclopentadienyl aluminum Cp'''AlCl2 (Cp''' = 1,2,4-tBu3C5H2) and gallium [η1-Cp'''Ga(µ-Cl)Cl]2 to afford the Lewis acid-base adducts η1-Cp'''M(Cl2) ← Si(L)-SiL (M = Al, 1; M = Ga, 3). To confirm the formation of the Lewis acid-base adduct, the bis(silylene) LSi(I)-Si(I)L reacts with Cp'''AlI2 to form η1-Cp'''Al(I2) ← Si(L)-SiL (2). These are the first examples where one Si atom in the bis(silylene) is a Lewis base and coordinates with aluminum or gallium to form a Lewis acid-base adduct, while the other Si atom in the bis(silylene) still maintains the characteristics of silylene. Compound 3 was heated to 70 °C in toluene for 4 hours and decomposed into the silylene LSiCl and Cp'''GaI. Compounds 1-3 are well characterized with NMR spectroscopic methods and single-crystal X-ray structural analysis.

Hirshfeld atom refinement based on projector augmented wave densities with periodic boundary conditions.

Hirshfeld atom refinement (HAR) is an X-ray diffraction refinement method that, in numerous publications, has been shown to give H-atom bond lengths in close agreement with neutron diffraction derived values. Presented here is a first evaluation of an approach using densities derived from projector augmented wave (PAW) densities with three-dimensional periodic boundary conditions for HAR. The results show an improvement over refinements that neglect the crystal environment or treat it classically, while being on a par with non-periodic approximations for treating the solid-state environment quantum mechanically. A suite of functionals were evaluated for this purpose, showing that the SCAN and revSCAN functionals are most suited to these types of calculation.

Pentamethyl- and 1,2,4-tri(tert-butyl)cyclopentadienyl containing p-block complexes - differences and similarities.

The sterically encumbered cyclopentadienyl ligand 1,2,4-(Me3C)3C5H2 (Cp''') was used to stabilize efficiently the main group metals of Al, Ga, In, Ge and Sn, respectively. The σ-bonded gallium compounds [η1-Cp'''Ga(µ-X)X]2 (X = Cl, 2; X = I, 3) and indium compound [η1-Cp'''In(µ-Br)nBu]2 (7) exhibit dimers through halogen bridges. Reduction of 2 with 2 equivalents of KC8 leads almost to the same amount of η1-Cp'''Ga(THF)Cl2 (4) and η5-Cp'''Ga (5), respectively. The exception is compound 5, which is obtained by reducing 2 or 3 with 4 equivalents of KC8. Compound 5 as Lewis base reacts with GaI3 readily forming the Lewis acid-base adduct product η5-Cp'''Ga → GaI3 (6). Moreover, compounds with the Cp''' ligand stabilize heavier low-valent group 14 elements for example [η5-Cp'''EII]+[EIICl3]- (E = Ge 8, Sn 9), which are π-bonded ionic compounds that possess a low-valent cation and an anion. In the cation of [η5-Cp'''EII]+, the Cp''' ligand adopts an η5-coordination mode with germanium and tin, respectively, which present half-sandwich complexes. While the EII fragment interacts with five π electrons from the Cp''' unit to generate an electron-octet arrangement at the respective element. All new reported structures are comparing well with the corresponding compounds containing the pentamethylcyclopentadienyl (Cp*) ligand.

Three colour solid-state luminescence from positional isomers of facilely modified thiophosphoranyl anthracenes.

Three positional isomers of thiophosphoranyl anthracene were synthesized and their photophysical properties were investigated. By varying the position of the substituents, blue, green and yellow solid-state fluorescence with differences in the emission wavelength of over 100 nm, assigned to the intra- and intermolecular effects, could be established.