Tuning Main Group Element-based Metal-Organic Framework to Boost Electrocatalytic Nitrogen Reduction Under Ambient Conditions

Main group element-based materials are emerging catalysts for ammonia (NH3 ) production via a sustainable electrochemical nitrogen reduction reaction (N2 RR) pathway under ambient conditions. However, their N2 RR performances are less explored due to the limited active behavior and unclear mechanism. Here, an aluminum-based defective metal-organic framework (MOF), aluminum-fumarate (Al-Fum), is investigated. As a proof of concept, the pristine Al-Fum MOF is synthesized by the solvothermal reaction process, and the defect engineering method namely solvent-assisted linker exchange, is applied to create the defective Al sites. The defective Al sites play an important role in ensuring the N2 RR activity for defective Al-Fum. It is found that only the defective Al-Fum enables stable and effective electrochemical N2 RR, in terms of the highest production rate of 53.9 µg(NH3 ) h-1 mgcat -1 (in 0.4 m K2 SO4 ) and the Faradaic efficiency of 73.8% (in 0.1 m K2 SO4 ) at -0.15 V vs reversible hydrogen electrode) under ambient conditions. Density functional theory calculations confirm that the N2 activation can be achieved on the defective Al sites. Such sites also allow the subsequent protonation process via the alternating associative mechanism. This defect characteristic gives the main group Al-based MOFs the ability to serve as promising electrocatalysts for N2 RR and other attractive applications.

NHC-Supported 2-Sila and 2-Germavinylidenes: Synthesis, Dynamics, First Reactivity and Theoretical Studies

2-tetrelavinylidenes (C=EH2 ; E=Si, Ge) are according to quantum chemical studies the least stable isomers on the [E,C,2H] potential energy hypersurface isomerizing easily via the trans-bent tetrelaacetylenes HE≡CH to the thermodynamically most stable 1-tetrelavinylidenes (E=CH2 ). Consequently, experimental studies on 2-tetrelavinylidenes (C=ER2 ) and their derivatives are lacking. Herein we report experimental and theoretical studies of the first N-heterocyclic carbene (NHC) supported 2-silavinylidene (NHC)C=SiBr(Tbb) (1-Si: NHC=C[N(Dipp)CH]2 , Dipp=2,6-diisopropylphenyl, Tbb=2,6-bis[bis(trimethylsilyl)methyl]-4-tert-butylphenyl) and the isovalent 2-germavinylidenes (NHC)C=GeBr(R) (1-Ge, 1-GeMind: R=Tbb, Mind (1,1,3,3,5,5,7,7-octamethyl-s-hydrindacene-4-yl)). The NHC-supported 2-tetrelavinylidenes were obtained selectively from the 1,2-dibromoditetrelenes (E)-(R)BrE=EBr(R) using the diazoolefin (NHC)CN2 as vinylidene transfer reagent. 1-E (E=Si, Ge) have a planar vinylidene core, a bent-dicoordinated vinylidene carbon atom (CVNL ), a very short E=CVNL bond and an almost orthogonal orientation of the NHC five-membered ring to the vinylidene core. Quantum chemical analysis of the electronic structures of 1-E suggest a significantly bent 1-tetrelaallene and tetrelyne character. NMR studies shed light into the dynamics of 1-E involving NHC-rotation around the CVNL -CNHC bond with a low activation barrier. Furthermore, the synthetic potential of 1-E is demonstrated by the synthesis and full characterization of the unprecedented NHC-supported bromogermynes BrGe=C(EBr2 Tbb)(NHC) (2-SiGe: E=Si; 2-GeGe: E=Ge).

Probing Radical Addition to 1-Phosphabutadienes by Employing Muonium as a "Light Isotope" of Hydrogen

Understanding free radical addition to multiple bonds is important to elucidating the mechanistic details of addition polymerization reactions, albeit the fleeting radical intermediates are very difficult to detect by conventional methodologies. Muon spin spectroscopy (μSR) is a highly sensitive method that can detect radical species at 106 spins (cf. EPR: 1012 spins, NMR: 1018 spins). Herein, we employ μSR to detect the radical-addition products from three 1-phosphabutadiene monomers, P-analogues of isoprene. We show that muonium (Mu), a "light" H-atom surrogate, adds predominantly at the C4 position of the P1 =C2 -C3 =C4 moiety to give unprecedented 1-phosphaallyl radicals as the major products. Our structural assignments are supported by assignment of muon, phosphorus and proton hyperfine coupling constants using DFT-calculations. A minor radical product is also detected that is tentatively assigned to an PC3 -heterocyclic free radical. On the basis of DFT-predictions, we speculate that its formation may involve initial addition of Mu+ at the C3 position followed by electron capture. These studies provide rare insights into the prospective radical (or cationic) polymerization of 1-phosphabutadienes, which have previously been polymerized using anionic initiation.

A Guanidine-Supported π-Complex of Germanium Amenable to Intramolecular C-C Cleavage in Arene and Ge Atom Transfer

The germylone dimNHCGe (dimNHC=diimino N-heterocyclic carbene) reacts with azides N3 R (R=SiMe3 or p-tolyl) to furnish the first examples of germanium π-complexes, i. e. guanidine-ligated compounds (dimNHI-SiMe3 )Ge (NHI=N-heterocyclic imine, R=SiMe3 ) and (dimNHI-Tol)Ge (R=p-tolyl). DFT calculations suggest that these species are formed by a Staudinger type replacement of dinitrogen in the azide by a nucleophilic germylone, leading to a transient carbene adduct of iminogermylidene. Heating a solution of compound (dimNHI-SiMe3 )Ge to 70 °C results in extrusion of the iminogermylidene that further aggregates to produce the known [Me3 SiNGe]4 tetramer, whereas the imidazolylidene fragment transforms into an unusual heptatriene species that can be considered as a product of carbene insertion into the C-C bond of a pendant Ar substituent at the imidazolylidene nitrogen of the dimNHC. Reaction of (dimNHI-SiMe3 )Ge with tetrachloro-o-benzoquinone results in the net transfer of a germanium atom and formation of the free diimino-guanidine ligand. This ligand also forms when (dimNHI-SiMe3 )Ge is treated with azide N3 (p-Tol), with the germanium product being [(p-Tol)NGe]n.

Precursors for the Development of π-Conjugated Low-Coordinate Phosphorus Compounds

The synthesis of a novel monomeric precursor and its butadiyne-bridged dimeric form for the preparation of novel π-conjugated organophosphorus compounds is presented. The precursors are synthesized from commercially available starting materials, and based on a Dmp (2,6-dimesitylphenyl) group for kinetic stabilization of the P-functionality, a bromo substituent for the introduction of the phosphorus center, and an acetylene unit at the para position of the Dmp moiety. Such acetylenic units are synthetically versatile, and can be explored for the construction of larger phosphorus-containing π-conjugates. The precursors are utilized to prepare Dmp-stabilized C,C-dibromophosphaalkenes, and butadiyne-bridged dimeric species thereof. The effect of the low-coordinate phosphorus centers and the extent of π-conjugation on the spectroscopic and electronic properties is evaluated by NMR and UV/Vis spectroscopy, as well as cyclic voltammetry. In addition to the phosphaalkenes, the successful syntheses of two new diphosphenes are presented, indicating a broad applicability of the precursor.

Synthesis and Properties of B4 N4 -Heteropentalenes Fused with Polycyclic Hydrocarbons

Hybrid molecules of π-conjugated carbon rings and BN-heterocyclic rings (h-CBNs) fused with each other have been a rare class of compounds due to the limited availability of their synthetic methods. Here we report the synthesis of new h-CBNs featuring a B₄ N₄ -heteropentalene core and polycyclic aromatic hydrocarbon wings. Using 1,2-azaborinine derivatives as a building block, we developed a rational synthetic protocol that allows the formation of a B₄ N₄ ring in a stepwise manner, resulting in the fully fused ABA-type triblock molecules. Thus, three derivatives of 1 bearing naphthalene (1_Naph ), anthracene (1_Anth ), or phenanthrene (1_Phen ) wings fused with the B₄ N₄ core were synthesized and characterized. Among them, 1_Phen , which displays the highest triplet-state energy, was found to serve a host material for phosphorescent OLED devices, for which a maximum external quantum efficiency of 13.7 % was recorded. These findings may promote the synthesis of various types of h-CBNs aiming at new properties arising from the synergy of two different π-electronic systems.

Oxidations of N-coordinated Arsinidene and Stibinidene by Substituted Quinones: A Remarkable Follow-Up Reactivity

The reactivity of pnictinidenes [2-(DippN=CH)-6-(DippNHCH₂ )C₆ H₃ ]E (where E=As (1) or Sb (2)) toward substituted ortho- and para-quinones is reported. The central pnictogen atom is easily oxidized by ortho-quinones closing five-membered EO₂ C₂ ring. The oxidized antimony derivatives are stable species, while in the case of arsenic compounds the hydrogen of the pendant amino NHCH₂ group cleaves one newly formed As-O bonds leading to the closure of a new azaarsole ring. Furthermore, a heating of these arsenic heterocycles resulted in a C-H bond activation at the NCH₂ group involved in this heterocycle followed by a reductive elimination of corresponding catechols and arsinidene [2,6-(DippN=CH)C₆ H₃ ]As. Using of para-quinones, resulted in the oxidation of the central atom with a concomitant hydrogen migration from NHCH₂ group even in the case of the antimony derivatives. The reductive elimination of hydroquinones is in this case feasible for all compounds. Studied compounds were characterized by multi-nuclear NMR, IR and Raman spectroscopy and single-crystal X-ray diffraction analysis. The theoretical study focusing the key compounds and reactions is also included.

Structure and bonding of proximity-enforced main-group dimers stabilized by a rigid naphthyridine diimine ligand

The development of ligands capable of effectively stabilizing highly reactive main-group species has led to the experimental realization of a variety of systems with fascinating properties. In this work, we computationally investigate the electronic, structural, energetic, and bonding features of proximity-enforced group 13-15 homodimers stabilized by a rigid expanded pincer ligand based on the 1,8-naphthyridine (napy) core. We show that the redox-active naphthyridine diimine (NDI) ligand enables a wide variety of structural motifs and element-element interaction modes, the latter ranging from isolated, element-centered lone pairs (e.g., E = Si, Ge) to cases where through-space π bonds (E = Pb), element-element multiple bonds (E = P, As) and biradical ground states (E = N) are observed. Our results hint at the feasibility of NDI-E₂ species as viable synthetic targets, highlighting the versatility and potential applications of napy-based ligands in main-group chemistry.

Coordination of Pnictogenylboranes Towards Tl(I) Salts and a Tl- Mediated P-P Coupling

The coordination chemistry of only Lewis-base (LB)-stabilized pnictogenylboranes EH₂ BH₂ ⋅NMe₃ (E=P, As) towards Tl(I) salts has been studied. The reaction of Tl[BAr^Cl ] (BAr^Cl =[B(3,5-C₆ H₃ Cl₂ )₄ ]^- ) with the corresponding pnictogenylborane results in the formation of [Tl(EH₂ BH₂ ⋅NMe₃ )][BAr^Cl ] (1 a: E=P; 1 b: E=As). Whereas the Tl ion in 1 a/b is monocoordinated, the exchange of the weakly coordinating anion (WCA) in the Tl(I) salt leads to the formation of a trigonal pyramidal coordination mode at the Tl atom by coordination of three equivalents of EH₂ BH₂  ⋅ NMe₃ in [Tl(EH₂ BH₂  ⋅ NMe₃ )₃ ][WCA] (2 a: E=P, WCA=TEF^Cl ; 2 b: E=As, WCA=TEF) (TEF=[Al{OC(CF₃ )₃ }₄ ]^- , TEF^Cl =[Al{(OC(CF₃ )₂ (CCl₃ )}₄ ]^- ). Furthermore, by using two equivalents of PH₂ BH₂ ⋅NMe₃ , a Tl(I)-mediated P-P coupling takes place in CH₂ Cl₂ as solvent resulting in [Me₃ N⋅BH₂ PH₂ PHBH₂ ⋅NMe₃ ][WCA] (WCA=TEF, 3 a; BAr^Cl , 3 b; TEF^Cl , 3 c). In contrast, for the arsenic derivatives 1 b and 2 b, no coupling reaction is observed. The underlying chemical processes are elucidated by quantum chemical computations.

THF-solvated Heavy Alkali Metal Benzyl Compounds (Na, Rb, Cs): Defined Deprotonation Reagents for Alkali Metal Mediation Chemistry

The incorporation of heavy alkali metals into substrates is both challenging and essential for many reactions. Here, we report the formation of THF‐solvated alkali metal benzyl compounds [PhCH₂M ⋅ (thf)_n] (M=Na, Rb, Cs). The synthesis was carried out by deprotonation of toluene with the bimetallic mixture n‐butyllithium/alkali metal tert‐butoxide and selective crystallization from THF of the defined benzyl compounds. Insights into the molecular structure in the solid as well as in solution state are gained by single crystal X‐ray experiments and NMR spectroscopic studies. The compounds could be successfully used as alkali metal mediating reagents. The example of caesium showed the convenient use by deprotonating acidic C−H as well as N−H compounds to gain insight into the aminometalation using these reagents.

An NHC-Stabilized H2 GeBH2 Precursor for the Preparation of Cationic Group 13/14/15 Hydride Chains

The synthesis, characterization and reactivity studies of the NHC‐stabilized complex IDipp ⋅ GeH₂BH₂OTf (1) (IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) are reported. Nucleophilic substitution of the triflate (OTf) group in 1 by phosphine or arsine donors provides access to the cationic group 13/14/15 chains [IDipp ⋅ GeH₂BH₂ERR¹R²]⁺ (2 E=P; R, R¹=H; R²=^tBu; 3 E=P; R=H; R¹, R²=Ph; 4 a E=P; R, R¹, R²=Ph; 4 b E=As; R, R¹, R²=Ph). These novel cationic chains were characterized by X‐ray crystallography, NMR spectroscopy and mass spectrometry. Moreover, the formation of the parent complexes [IDipp ⋅ GeH₂BH₂PH₃][OTf] (5) and [IDipp ⋅ GeH₃][OTf] (6) were achieved by reaction of 1 with PH₃. Accompanying DFT computations give insight into the stability of the formed chains with respect to their decomposition.

Cyclo-Dipnictadialanes

Using the AlI precursor Cp3t Al in conjunction with triphosphiranes (PAr)3 (Ar=Mes, Dip, Tip) we have succeeded in preparing Lewis base-free cyclic diphosphadialanes with both the Al and P atoms bearing three substituents. Using the sterically more demanding Dip and Tip substituents the first 1,2-diphospha-3,4-dialuminacyclobutanes were obtained, whereas with Mes substituents [Cp3t Al(μ-PMes)]2 is formed. This divergent reactivity was corroborated by DFT studies, which indicated the thermodynamic preference for the 1,2-diphospha-3,4-dialuminacyclobutane form for sterically more demanding groups on phosphorus. Using Cp*Al we could extend this concept to the corresponding cyclic diarsadialanes [Cp*Al(μ-AsAr)]2 (Ar=Dip, Tip) and additionally add the phosphorus variants [Cp*Al(μ-PAr)]2 (P=Mes, Dip, Tip). The reactivity of one variant [Cp3t Al(μ-PPh)]2 towards NHCs was tested and resulted in double NHC-stabilised [Cp3t (IiPr2 )Al(μ-PPh)]2 .

Metathesis of P=C Bonds Catalyzed by N-Heterocyclic Carbenes

The catalytic metathesis of C=C bonds is a textbook reaction that has no parallel in the widely studied area of multiple bonds involving heavier p-block elements. A high-yielding P=C bond metathesis of phosphaalkenes (ArP=CPh₂ , Ar=Mes, o-Tol, Ph) has been discovered that is catalyzed by N-heterocyclic carbenes (NHC=Me₂ IMe, Me₂ Iⁱ Pr). The products are cyclic oligomers formally derived from ArP=PAr [i. e. cyclo-(ArP)_n ; n=3, 4, 5, 6] and Ph₂ C=CPh₂ . Preliminary mechanistic studies of this remarkable transformation have established NHC=PAr (Ar=Mes, o-Tol, Ph) as key phosphinidene transfer agents. In addition, novel cyclic intermediates, such as, cyclo-(ArP)₂ CPh₂ and cyclo-(ArP)₄ CPh₂ have also been observed. This work represents a rare application of non-metal-based catalysts for transformations involving main-group elements.

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.

Contrasting the Mechanism of H2 Activation by Monomeric and Potassium-Stabilized Dimeric AlI Complexes: Do Potassium Atoms Exert any Cooperative Effect?

Aluminyl anions are low-valent, anionic, and carbenoid aluminum species commonly found stabilized with potassium cations from the reaction of Al-halogen precursors and alkali compounds. These systems are very reactive toward the activation of σ-bonds and in reactions with electrophiles. Various research groups have detected that the potassium atoms play a stabilization role via electrostatic and cation ⋯ π interactions with nearby (aromatic)-carbocyclic rings from both the ligand and from the reaction with unsaturated substrates. Since stabilizing K⋯H bonds are witnessed in the activation of this class of molecules, we aim to unveil the role of these metals in the activation of the smaller and less polarizable H₂ molecule, together with a comprehensive characterization of the reaction mechanism. In this work, the activation of H₂ utilizing a NON-xanthene-Al dimer, [K{Al(NON)}]₂ (D) and monomeric, [Al(NON)]^- (M) complexes are studied using density functional theory and high-level coupled-cluster theory to reveal the potential role of K⁺ atoms during the activation of this gas. Furthermore, we aim to reveal whether D is more reactive than M (or vice versa), or if complicity between the two monomer units exits within the D complex toward the activation of H₂ . The results suggest that activation energies using the dimeric and monomeric complexes were found to be very close (around 33 kcal mol^-1 ). However, a partition of activation energies unveiled that the nature of the energy barriers for the monomeric and dimeric complexes are inherently different. The former is dominated by a more substantial distortion of the reactants (and increased interaction energies between them). Interestingly, during the oxidative addition, the distortion of the Al complex is minimal, while H₂ distorts the most, usually over 0.77 Δ E d i s t ≠ . Overall, it is found here that electrostatic and induction energies between the complexes and H₂ are the main stabilizing components up to the respective transition states. The results suggest that the K⁺ atoms act as stabilizers of the dimeric structure, and their cooperative role on the reaction mechanism may be negligible, acting as mere spectators in the activation of H₂ . Cooperation between the two monomers in D is lacking, and therefore the subsequent activation of H₂ is wholly disengaged.

Reversible and Irreversible [2+2] Cycloaddition Reactions of Heteroallenes to a Gallaphosphene

[2+2] Cycloaddition reactions of gallaphosphene L(Cl)GaPGaL 1 (L=HC[C(Me)N(2,6-i-Pr2 C6 H3 )]2 ) with carbodiimides [C(NR)2 ; R=i-Pr, Cy] and isocyanates [RNCO; R=Et, i-Pr, Cy] yielded four-membered metallaheterocycles LGa(Cl)P[μ-C(X)NR]GaL (X=NR, R=i-Pr 2, Cy 3; X=O, R=Et 4, i-Pr 5, Cy 6). Compounds 4-6 reversibly react with CO2 via [2+2] cycloaddition at ambient temperature to the six-membered metallaheterocycles LGa(Cl)P[μ-C(O)O]-μ-C(O)N(R)GaL (R=Et 7, i-Pr 8, Cy 9). Compounds 2-9 were characterized by IR and heteronuclear (1 H, 13 C{1 H}, 31 P{1 H}) NMR spectroscopy and elemental analysis, while quantum chemical calculations provided a deeper understanding on the energetics of the reactions.

Acid-Base Free Main Group Carbonyl Analogues

Main group carbonyl analogues (R2 E=O) derived from p-block elements (E=groups 13 to 15) have long been considered as elusive species. Previously, employment of chemical tricks such as acid- and base-stabilization protocols granted access to these transient species in their masked forms. However, electronic and steric effects inevitably perturb their chemical reactivity and distinguish them from classical carbonyl compounds. A new era was marked by the recent isolation of acid-base free main group carbonyl analogues, ranging from a lighter boracarbonyl to the heavier silacarbonyls, phosphacarbonyls and a germacarbonyl. Most importantly, their unperturbed nature elicits exciting new chemistry, spanning the vista from classical organic carbonyl-type reactions to transition metal-like oxide ion transfer chemistry. In this Review, we survey the strategies used for the isolation of such systems and document their emerging reactivity profiles, with a view to providing fundamental comparisons both with carbon and transition metal oxo species. This highlights the emerging opportunities for exciting "crossover" reactivity offered by these derivatives of the p-block elements.

Selective Cross-Coupling of Unsaturated Substrates on AlI

The Al^I compound NacNacAl (1, NacNac = [ArNC(Me)CHC(Me)NAr]^- , Ar = 2,6-iPr₂ C₆ H₃ ) serves as a template for the chemoselective coupling between carbonyls (benzophenone, fenchone, isophorone, p-tolyl benzoate, N,N-dimethylbenzamide, (1-phenylethylidene)aniline) and pyridine. With the CH-acidic ketone (1R)-(+) camphor, the reaction affords a hydrido alkoxide compound of Al, formed as the result of enolization, whereas an enolizable imine, (1-phenylethylidene)aniline, and the bulky ketone isophorone, still chemoselectively couple with pyridine. In contrast, reaction with the ester p-tolyl benzoate results in cleavage of the ester bond together with replacement of the alkoxy group by a hydrogen atom of the pyridine moiety. This study demonstrates that for carbonyl substrates featuring phenyl substituents, the reaction proceeds via intermediate formation of η² (C,X)-coordinated (X = O, N) carbonyl adducts, whereas the reaction of 1 with (R)-(-)-fenchone in the absence of pyridine leads to CH activation in the pendant isopropyl group of the Ar substituent of the NacNac ligand.

Isolation and Structural Determination of a Hexacoordinated Antimony(V) Dication

The hexacoordinated antimony(V) dication [(ppy)₃ Sb]²⁺ ([1]²⁺ ; ppy=2-(2-pyridyl)phenyl), stabilized by three intramolecular donor-acceptor interactions, has been isolated as its hexachloroantimonate salt [1][SbCl₆ ]₂ , prepared by the oxidative addition of chlorine to the neutral stibine [(ppy)₃ Sb] (1), followed by the abstraction of chloride. Air-stable [1][SbCl₆ ]₂ exhibits remarkable thermal stability and the three ppy ligands on the antimony atom are shown to be magnetically inequivalent in the ¹ H and ¹³ C NMR spectra. A hexacoordinated, meridional octahedral bonding geometry has been determined for [1][SbCl₆ ]₂ by X-ray crystallographic analysis. Theoretical calculations were performed to investigate why the meridional form was generated preferentially over the facial form. In addition, the dynamics of the ppy ligands were investigated by variable-temperature ¹ H NMR spectroscopy. The potential to generate dications by using a single-electron-transfer reagent has also been investigated. The dication [1]²⁺ is the first [12-Sb-6]²⁺ chemical species to have been structurally determined.

Reversible Addition of Carbon Dioxide to Main Group Metal Complexes at Temperatures about 0 °C

The reaction of dialane [LAl-AlL] (1; L=dianion of 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene, dpp-bian) with carbon dioxide results in two different products depending on solvent. In toluene at temperatures of about 0 °C, the reaction gives cycloadduct [L(CO₂ )Al-Al(O₂ C)L] (2), whereas in diethyl ether, the reaction affords oxo-bridged carbamato derivative [L(CO₂ )(Et₂ O)Al(μ-O)AlL] (3). The DFT and QTAIM calculations provide reasonable explanations for the reversible formation of complex 2 in the course of two subsequent (2+4) cycloaddition reactions. Consecutive transition states with low activation barriers were revealed. Also, the DFT study demonstrated a crucial effect of diethyl ether coordination to aluminium on the reaction of dialane 1 with CO₂ . The optimized structures of key intermediates were obtained for the reactions in the presence of Et₂ O; calculated thermodynamic parameters unambiguously testify the irreversible formation of the product 3.

(o-Phenylenediamino)borylstannanes: Efficient Reagents for Borylation of Various Alkyl Radical Precursors

(o-Phenylenediamino)borylstannanes were newly synthesized to achieve radical boryl substitutions of a variety of alkyl radical precursors. Dehalogenative, deaminative, decharcogenative, and decarboxylative borylations proceeded in the presence of a radical initiator to give the corresponding organic boron compounds. Radical clock experiments and computational studies have provided insights into the mechanism of the homolytic substitution (S_H 2) of the borylstannanes with alkyl radical intermediates. DFT calculation disclosed that the phenylenediamino structure lowered the LUMO level including the vacant p-orbital on the boron atom to enhance the reactivity to alkyl radicals in S_H 2. Moreover, C(sp³ )-H borylation of THF was accomplished using the triplet state of xanthone.

Synthesis and Coordination Ability of a Donor-Stabilised Bis-Phosphinidene

Chelating phosphines have long been a mainstay as efficient directing ligands in transition-metal catalysis. Low-valent derivatives, namely chelating phosphinidenes, are to date unknown, and could lead to chelating complexes containing more than one metal centre due to the intrisic capacity of phosphinidenes to bind two metal fragments at one P-centre. Here we describe the synthesis of the first such chelating bis-phosphinidene ligand, XantP2 (2), generated by the reduction of a diphosphino xanthene derivative, Xant(PH2 )2 (1) with iPr NHC (iPr NHC=[:C{N(iPr)C(H)}2 ]). Initial studies have shown that this novel chelating ligand can act as a bidentate ligand towards element dihalides (i.e. FeCl2 , ZnI2 , GeCl2 , SnBr2 ), forming cationic complexes with the tetryl elements. In contrast, XantP2 demonstrates an ability to bind multiple metal centres in the reaction with CuCl, leading to a cationic Cu3 P3 ring complex, with Cu centres bridged by phosphinidene arms. Density Functional Theory calculations show that 2 indeed holds 4 lone pairs of electrons, shedding further light on the coordination capacity for this novel ligand class through observation of directionality and hybridisation of these electron pairs.

Completing the Redox-Series of Silicon Trisdioxolene: ortho-Quinone and Lewis Superacid Make a Powerful Redox Catalyst

Quinones are mild oxidants, the redox potentials of which can be increased by supramolecular interactions. Whereas this goal has been achieved by hydrogen bonding or molecular encapsulation, a Lewis acid-binding strategy for redox amplification of quinones is unexplored. Herein, the redox chemistry of silicon tris(perchloro)dioxolene 1 was studied, which is the formal adduct of ortho-perchloroquinone Q^Cl with the Lewis superacid bis(perchlorocatecholato)silane 2. By isolating the anionic monoradical 1^.- , the redox-series of a century-old class of compounds was completed. Cyclic voltammetry measurements revealed that the redox potential in 1 was shifted by more than 1 V into the anodic direction compared to Q^Cl , reaching that of "magic blue" or NO⁺ . It allowed oxidation of challenging substrates such as aromatic hydrocarbons and could be applied as an efficient redox catalyst. Remarkably, this powerful reagent formed in situ by combining the two commercially available precursors SiI₄ and Q^Cl .

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.

Multicomponent Reactions in Polymer Chemistry Utilizing Heavier Main Group Elements

Herein, a concise overview of the use of heavier main group elements in multicomponent reactions and their use in polymer chemistry is provided. Incorporating heavier elements into macromolecular structures via multicomponent reactions allows for the rapid development of materials with unique properties that are not readily achieved using carbon, nitrogen, and/or oxygen. Elements in Group 13, Group 14, Group 15, and Group 16 are specifically covered examining both the familiar and unfamiliar properties of these elements and how they are used in multicomponent chemistry. Furthermore, elements that both take part in the reaction mechanism and remain in the macromolecular structure upon completion are only briefly explored. Some of the state-of-the-art work going into developing these heavier element multicomponent reactions are highlighted and it is hoped to inspire other polymer chemists to explore other parts of the periodic table.

Design of a Single-Atom Indiumδ+ -N4 Interface for Efficient Electroreduction of CO2 to Formate

Main-group element indium (In) is a promising electrocatalyst which triggers CO₂ reduction to formate, while the high overpotential and low Faradaic efficiency (FE) hinder its practical application. Herein, we rationally design a new In single-atom catalyst containing exclusive isolated In^δ+ -N₄ atomic interface sites for CO₂ electroreduction to formate with high efficiency. This catalyst exhibits an extremely large turnover frequency (TOF) up to 12500 h^-1 at -0.95 V versus the reversible hydrogen electrode (RHE), with a FE for formate of 96 % and current density of 8.87 mA cm^-2 at low potential of -0.65 V versus RHE. Our findings present a feasible strategy for the accurate regulation of main-group indium catalysts for CO₂ reduction at atomic scale.

Divergent and Multi-Stage Photoisomerization of Four-Coordinated Boron Compounds with a Naphthyl-Pyridyl/Thiazolyl Backbone

Examination of the photoreactivity of a new class of N,C-chelate organoboron compounds, including a series of unsymmetrically substituted boron molecules, B(naph-pyridyl)(Ar¹ )(Ar² ) and B(naph-thiazolyl)(Ar¹ )(Ar² ), led to the discovery of new and divergent photothermal isomerization phenomena. These include the clean and regioselective photoisomerization by unsymmetrical boron, forming borepin isomers, some of which further isomerize to the corresponding boratanorcaradiene diastereomer pairs as a result of the generation of two chiral centers. Significantly, the boratanorcaradienes involving a 3-thienyl substituent on boron were found to thermally convert to BN-fluoranthene annulated borapentalene via an unprecedented reversible boratacyclopropane-boratacyclopentene rearrangement. Changing the pyridyl donor to a thiazolyl donor on the boron was found to provide the B(naph-thiazolyl)(Mes)₂ compounds with a distinct new photoisomerization pathway-instead of borepin, forming new blue fluorescent polycyclic azaborinine species. This work illustrates the richness and complexity of boron photochemistry.

A Mechanistic Study on Reactions of Group 13 Diyls LM with Cp*SbX2 : From Stibanyl Radicals to Antimony Hydrides

Oxidative addition of Cp*SbX₂ (X=Cl, Br, I; Cp*=C₅Me₅) to group 13 diyls LM (M=Al, Ga, In; L=HC[C(Me)N (Dip)]₂, Dip=2,6‐iPr₂C₆H₃) yields elemental antimony (M=Al) or the corresponding stibanylgallanes [L(X)Ga]Sb(X)Cp* (X=Br 1, I 2) and ‐indanes [L(X)In]Sb(X)Cp* (X=Cl 5, Br 6, I 7). 1 and 2 react with a second equivalent of LGa to eliminate decamethyl‐1,1’‐dihydrofulvalene (Cp*₂) and form stibanyl radicals [L(X)Ga]₂Sb^. (X=Br 3, I 4), whereas analogous reactions of 5 and 6 with LIn selectively yield stibanes [L(X)In]₂SbH (X=Cl 8, Br 9) by elimination of 1,2,3,4‐tetramethylfulvene. The reactions are proposed to proceed via formation of [L(X)M]₂SbCp* as reaction intermediate, which is supported by the isolation of [L(Cl)Ga]₂SbCp (11, Cp=C₅H₅). The reaction mechanism was further studied by computational calculations using two different models. The energy values for the Ga‐ and the In‐substituted model systems showing methyl groups instead of the very bulky Dip units are very similar, and in both cases the same products are expected. Homolytic Sb−C bond cleavage yields van der Waals complexes from the as‐formed radicals ([L(Cl)M]₂Sb^. and Cp*^.), which can be stabilized by hydrogen atom abstraction to give the corresponding hydrides, whereas the direct formation of Sb hydrides starting from [L(Cl)M]₂SbCp* via concerted β‐H elimination is unlikely. The consideration of the bulky Dip units reveals that the amount of the steric overload in the intermediate I determines the product formation (radical vs. hydride).

Systematic DFT Studies on Binary Pseudo-tetrahedral Zintl Anions: Relative Stabilities and Reactivities towards Protons, Trimethylsilyl Groups, and Iron Complex Fragments

Binary pseudo-tetrahedral Zintl anions composed of (semi)metal atoms of the p-block elements have proven to be excellent starting materials for the synthesis of a variety of heterometallic and intermetalloid transition metal-main group metal cluster anions. However, only ten of the theoretically possible 48 anions have been experimentally accessed to date as isolable salts. This brings up the question whether the other species are generally not achievable, or whether synthetic chemists just have not succeeded in their preparation so far. To contribute to a possible answer to this question, global minimum structures were calculated for all anions of the type (TrTt3 )5- , (TrPn3 )2- , and (Tt2 Pn2 )2- , comprising elements of periods 3 to 6 (Tr: triel, Al⋅⋅⋅Tl; Tt: tetrel, Si⋅⋅⋅Pb; Pn: pnictogen, P⋅⋅⋅Bi). By analyzing the computational results, a concept was developed to predict which of the yet missing anions should be synthesizable and why. Additionally, the results of an electrophilic attack by protons or trimethylsilyl groups or a nucleophilic attack by transition metal complex fragments are described. The latter yields butterfly-like structures that can be viewed as a new form of adaptable tridentate chelating ligands.

Catalytic Nitrile Hydroboration: A Route to N,N-Diborylamines and Uses Thereof

Catalytic reduction of nitriles is considered as an attractive and atom-economical route to a diversity of synthetically valuable primary amines. Compared to other methods, dihydroboration approach has been developed relatively recently but has already attracted the attention of many research groups due to reasonably mild reaction conditions, selectivity control and the access to N,N-diborylamines, which emerged as powerful reagents for C-N bond forming reactions. Early developments in catalytic dihydroboration of nitriles implied precious metal catalysts along with harsh conditions and prolonged reaction times, whereas recent advances mostly rely on base and main group metal catalytic systems with significantly improved profiles. This minireview aims to provide an overview of advances and challenges of dihydroboration of nitriles with d-, f- and main group metal catalysts. Mechanistic features of different catalytic systems, functional group tolerance and scope of the methods are also presented. The synthetic utility of N,N-diborylamies, beyond simple protodeborylation, is discussed in the aspect of N-arylation, imine and amide synthesis.

π-Complexes of Diborynes with Main Group Atoms

We present herein an in‐depth study of complexes in which a molecule containing a boron‐boron triple bond is bound to tellurate cations. The analysis allows the description of these salts as true π complexes between the B−B triple bond and the tellurium center. These complexes thus extend the well‐known Dewar‐Chatt‐Duncanson model of bonding to compounds made up solely of p block elements. Structural, spectroscopic and computational evidence is offered to argue that a set of recently reported heterocycles consisting of phenyltellurium cations complexed to diborynes bear all the hallmarks of π‐complexes in the π‐complex/metallacycle continuum envisioned by Joseph Chatt. Described as such, these compounds are unique in representing the extreme of a metal‐free continuum with conventional unsaturated three‐membered rings (cyclopropenes, azirenes, borirenes) occupying the opposite end.

Harnessing Plasticity in an Amine-Borane as a Piezoelectric and Pyroelectric Flexible Film

We demonstrate that trimethylamine borane can exhibit desirable piezoelectric and pyroelectric properties. The material was shown to be able operate as a flexible film for both thermal sensing, thermal energy conversion and mechanical sensing with high open circuit voltages (>10 V). A piezoelectric coefficient of d₃₃ ≈10-16 pC N^-1 , and pyroelectric coefficient of p≈25.8 μC m^-2  K^-1 were achieved after poling, with high pyroelectric figure of merits for sensing and harvesting, along with a relative permittivity of ϵ 33 σ ≈ 6.3.

The Thermal Rearrangement of an NHC-Ligated 3-Benzoborepin to an NHC-Boranorcaradiene

An N-heterocyclic-carbene-ligated 3-benzoborepin with a bridged structure has been synthesized by double radical trans-hydroboration of benzo[3,4]cycloundec-3-ene-1,5-diyne with an N-heterocyclic carbene borane. The thermal reaction of the NHC-ligated borepin at 150 °C gives an isolable NHC-boranorcaradiene. Experiments and density functional theory calculations support a mechanism whereby the borepin initially rearranges to a boranorcaradiene by a thermal 6π-electrocyclic reaction. This is followed by 1,5-boron shift to give a rearranged boranorcaradiene. This shift occurs with stereoinversion at boron through a transition state with open-shell diradical character. This is the first example of the isolation of a boranorcaradiene from a thermal reaction of a borepin.

Diverse Catalytic Systems and Mechanistic Pathways for Hydrosilylative Reduction of CO2

Catalytic hydrosilylation of carbon dioxide has emerged as a promising approach for carbon dioxide utilization. It allows the reductive transformation of carbon dioxide into value-added products at the levels of formate, formaldehyde, methanol, and methane. Tremendous progress has been made in the area of carbon dioxide hydrosilylation since the first reports in 1981. This focus review describes recent advances in the design and catalytic performance of leading catalyst systems, including transition-metal, main-group, and transition-metal/main-group and main-group/main-group tandem catalysts. Emphasis is placed on discussions of key mechanistic features of these systems and efforts towards the development of more selective, efficient, and sustainable carbon dioxide hydrosilylation processes.

Isolation of Carbene-Stabilized Arsenic Monophosphide [AsP] and its Radical Cation [AsP]+. and Dication [AsP]2

Arsenic monophosphide (AsP) species supported by two different N‐heterocyclic carbenes were prepared by reaction of (IDipp)PSiMe₃ (1) (IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) with (IMes)AsCl₃ (2) (IMes=1,3‐bis(2,4,6‐trimethylphenyl)imidazolin‐2‐ylidene) to afford the dichloride [(IMes)As(Cl)P(IDipp)]Cl (3), which upon reduction with KC₈ furnished heteroleptic [(IMes)AsP(IDipp)] (4). The corresponding mono‐ and dications [(IMes)AsP(IDipp)][PF₆], [5]PF₆, and [(IMes)AsP(IDipp)][GaCl₄]_2, [6][GaCl₄]₂, respectively, were prepared by one‐electron oxidation of 4 with ferrocenium hexafluorophosphate, [Fc]PF_6, or by chloride abstraction from 3 with two equivalents of GaCl₃, respectively. Compounds 4–6 represent rare examples of heterodiatiomic interpnictogen compounds, and X‐ray crystal structure determinations together with density functional theory (DFT) calculations reveal a consecutive shortening of the As−P bond lengths and increasing bond order, in agreement with the presence of an arsenic–phosphorus single bond in 4 and a double bond in 6²⁺. The EPR signal of the cationic radical [5]^+. indicates a symmetric spin distribution on the AsP moiety through strong hyperfine coupling with the ⁷⁵As and ³¹P nuclei.

Coordination Chemistry of P4 S3 and P4 Se3 towards the Iron Fragments [Fe(Cp)(CO)2 ]+ and [Fe(Cp)(PPh3 )(CO)]. Chemistry 2019;25:12159-12168. [PMID: 31287589 PMCID: PMC6771638 DOI: 10.1002/chem.201902339]

The complexes Ag(L)n [WCA] (L=P4 S3 , P4 Se3 , As4 S3 , and As4 S4 ; [WCA]=[Al(ORF )4 ]- and [F{Al(ORF )3 }2 ]- ; RF =C(CF3 )3 ; WCA=weakly coordinating anion) were tested for their performance as ligand-transfer reagents to transfer the poorly soluble nortricyclane cages P4 S3 , P4 Se3 , and As4 S3 as well as realgar As4 S4 to different transition-metal fragments. As4 S4 and As4 S3 with the poorest solubility did not yield complexes. However, the more soluble silver-coordinated P4 S3 and P4 Se3 cages were transferred to the electron-poor Fp+ moiety ([CpFe(CO)2 ]+ ). Thus, reaction of the silver salt in the presence of the ligand with Fp-Br yielded [Fp-P4 S3 ][Al(ORF )4 ] (1 a), [Fp-P4 S3 ][F(Al(ORF )3 )2 ] (1 b), and [Fp-P4 Se3 ][Al(ORF )4 ] (2). Reactions with P4 S3 also yielded [FpPPh3 -P4 S3 ][Al(ORF )4 ] (3), a complex with the more electron-rich monophosphine-substituted Fp+ analogue [FpPPh3 ]+ ([CpFe(PPh3 )(CO)]+ ). All complex salts were characterized by single-crystal XRD, NMR, Raman, and IR spectroscopy. Interestingly, they show characteristic blueshifts of the vibrational modes of the cage, as well as structural contractions of the cages upon coordination to the Fp/FpPPh3 moieties, which oppose the typically observed cage expansions that lead to redshifts in the spectra. Structure, bonding, and thermodynamics were investigated by DFT calculations, which support the observed cage contractions. Its reason is assigned to σ and π donation from the slightly P-P and P-E antibonding P4 E3 -cage HOMO (e symmetry) to the metal acceptor fragment.

Beryllium-Induced Conversion of Aldehydes

Aldehydes play a key role in the human metabolism. Therefore, it is essential to know their reactivity with beryllium compounds in order to assess its effects in the body. The reactivity of simple aldehydes towards beryllium halides (F, Cl, Br, I) was studied through solution and solid‐state techniques and revealed distinctively different reactivities of the beryllium halides, with BeF₂ being the least and BeI₂ the most reactive. Rearrangement and aldol condensation reactions were observed and monitored by in situ NMR spectroscopy. Crystal structures of various compounds obtained by Be²⁺‐catalyzed cyclization, rearrangement, and aldol addition reactions or ligation of beryllium halides have been determined, including unprecedented one‐dimensional BeCl₂ chains and the first structurally characterized example of an 1‐iodo‐alkoxide. Long‐term studies showed that only aldehydes without a β‐H can form stable beryllium complexes, whereas other aldehydes are oligo‐ and polymerized or decomposed by beryllium halides.

Gallium "Shears" for C=N and C=O Bonds of Isocyanates

Digallane [L¹ Ga-GaL¹ ] (1, L¹ =dpp-bian=1,2-[(2,6-iPr₂ C₆ H₃ )NC]₂ C₁₂ H₆ ) reacts with RN=C=O (R=Ph or Tos) by [2+4] cycloaddition of the isocyanate C=N bonds across both of its C=C-N-Ga fragments to afford [L¹ (O=C-NR)Ga-Ga(RN-C=O)L¹ ] (R=Ph, 3; R=Tos, 4). The reactions with both isocyanates result in new C-C and N-Ga single bonds. In the case of allyl isocyanate, the [2+4] cycloaddition across one C=C-N-Ga fragment of 1 is accompanied by insertion of a second allyl isocyanate molecule into the Ga-N bond of the same fragment to afford compound [L¹ Ga-Ga(AllN- C=O)₂ L¹ ] (5) (All=allyl). In the presence of Na metal, the related digallane [L² Ga-GaL² ] (2; L² =dpp-dad=[(2,6-iPr₂ C₆ H₃ )NC(CH₃ )]₂ ) is converted into the gallium(I) carbene analogue [L² Ga:]^- (2 A), which undergoes a variety of reactions with isocyanate substrates. These include the cycloaddition of ethyl isocyanate to 2 A affording [Na₂ (THF)₅ ]{L² Ga[EtN-C(O)]₂ GaL² } (6), cleavage of the N=C bond with release of 1 equiv. of CO to give [Na(THF)₂ ]₂ [L² Ga(p-MeC₆ H₄ )(N-C(O))₂ -N(p-MeC₆ H₄ )]₂ (7), cleavage of the C=O bond to yield the di-O-bridged digallium compound [Na(THF)₃ ]₂ [L² Ga-(μ-O)₂ -GaL² ] (8), and generation of the further addition product [Na₂ (THF)₅ ][L² Ga(CyNCO₂ )]₂ (9). Complexes 3-9 have been characterized by NMR (¹ H, ¹³ C), IR spectroscopy, elemental analysis, and X-ray diffraction analysis. Their electronic structures have been examined by DFT calculations.

Isolation of a Diylide-Stabilized Stannylene and Germylene: Enhanced Donor Strength through Coplanar Lone Pair Alignment

The preparation of the first stable diylide‐substituted stannylene and germylene (Y₂E, with E=Ge, Sn and Y=[PPh₃‐C‐SO₂Tol]⁻) is reported. The synthesis is easily accomplished in one step from the sulfonyl‐substituted metalated ylide YNa and the corresponding ECl₂ precursors. Y₂Ge and Y₂Sn exhibit unusual structures in the solid state and in solution, in which the three adjacent lone pairs in the C‐E‐C linkage are arranged coplanar to each other. As shown by DFT studies, this bonding situation is preferred over the typical π‐donation from the ligands into the empty p‐orbital at the metal due to the strong anion‐stabilizing ability of the sulfonyl groups in the ylide backbone and their additional coordination to the metal. The alignment of the three lone pairs leads to a remarkable boost of the HOMO energy and thus of the donor strengths of the tetrylenes. Hence, Y₂Ge and Y₂Sn become stronger donors than their diamino or diaryl congeners and comparable to cyclic alkyl(amino)carbenes. First reactivity studies confirm the high reactivity of Y₂Ge and Y₂Sn, which for example undergo an intramolecular C−H activation reaction via metal–ligand cooperation.

Metal-Free Electrochemical Reduction of Carbon Dioxide Mediated by Cyclic(Alkyl)(Amino) Carbenes

Carbenes are known to activate carbon dioxide to form zwitterionic adducts. Their inherent metal-free redox activity remains understudied. Herein, we demonstrate that zwitterionic adducts of carbon dioxide formed with cyclic(alkyl)(amino) carbenes are not only redox active, but they can mediate the stoichiometric reductive disproportionation of carbon dioxide to carbon monoxide and carbonate. Infrared spectroelectrochemical experiments show that the reaction proceeds through an intermediate radical anion formed by one-electron reduction, ultimately generating a ketene product and carbonate in the absence of additional organic or inorganic reagents.

Atomically Precise Expansion of Unsaturated Silicon Clusters

Small- to medium-sized clusters occur in various areas of chemistry, for example, as active species of heterogeneous catalysis or as transient intermediates during chemical vapor deposition. The manipulation of stable representatives is mostly limited to the stabilizing ligand periphery, virtually excluding the systematic variation of the property-determining cluster scaffold. We now report the deliberate expansion of a stable unsaturated silicon cluster from six to seven and finally eight vertices. The consecutive application of lithium/naphthalene as the reducing agent and decamethylsilicocene as the electrophilic source of silicon results in the expansion of the core by precisely one atom with the potential of infinite repetition.

Ligands Based on Phosphine-Stabilized Aluminum(I), Boron(I), and Carbon(0)

A systematic quantum chemical study of the bonding in d⁶ -transition-metal complexes, containing phosphine-stabilized, main-group-element fragments, (R₃ P)₂ E, as ligands (E=AlH, BH, CH⁺ , C), is reported. By using energy decomposition analysis, it is demonstrated that a strong M-E bond is accompanied by weak P-E bonds, and vice versa. Although the Al-M bond is, for example, found to be very strong, the weak Al-P bond suggests that the corresponding metal complexes will not be stable towards phosphine dissociation. The interaction energies for the boron(I)-based ligand are lower, but still higher than those for two-carbon-based ligands. For neutral ligands, electrostatic interactions are the dominating contributions to metal-ligand bonding, whereas for the cationic ligand a significant destabilization, with weak orbital and even weaker electrostatic metal-ligand interactions, is observed. Finally, for iron(II) complexes, it is demonstrated that different reactivity patterns are expected for the four donor groups: the experimentally observed reversible E-H reductive elimination of the borylene-based ligand (E=BH) exhibits significantly higher barriers for the protonated carbodiphosphorane (CDP) ligand (E=CH) and would proceed through different intermediates and transition states. For aluminum, such reaction pathways are not feasible (E=AlH). Moreover, it is demonstrated that the metal hydrido complexes with CDP ligands might not be stable towards reduction and isomerization to a protonated CDP ligand and a reduced metal center.

Quantum Chemical Calculations on CHOP Derivatives-Spanning the Chemical Space of Phosphinidenes, Phosphaketenes, Oxaphosphirenes, and COP- Isomers

After many decades of intense research in low-coordinate phosphorus chemistry, the advent of Na[OCP] brought new stimuli to the field of CHOP isomers and derivatives thereof. The present theoretical study at the CCSD(T)/def2-TZVPP level describes the chemical space of CHOP isomers in terms of structures and potential energy surfaces, using oxaphosphirene as the starting point, but also covering substituted derivatives and COP- isomers. Bonding properties of the P⁻C, P⁻O, and C⁻O bonds in all neutral and anionic isomeric species are discussed on the basis of theoretical calculations using various bond strengths descriptors such as WBI and MBO, but also the Lagrangian kinetic energy density per electron as well as relaxed force constants. Ring strain energies of the superstrained 1H-oxaphosphirene and its barely strained oxaphosphirane-3-ylidene isomer were comparatively evaluated with homodesmotic and hyperhomodesmotic reactions. Furthermore, first time calculation of the ring strain energy of an anionic ring is described for the case of oxaphosphirenide.

Inorganic Triphenylphosphine

A completely inorganic version of one of the most famous organophosphorus compounds, triphenylphosphine, has been prepared. A comparison of the crystal structures of inorganic triphenylphosphine, PBaz₃ (where Baz=B₃ H₂ N₃ H₃ ) and PPh₃ shows that they have superficial similarities and furthermore, the Lewis basicities of the two compounds are remarkably similar. However, their oxygenation and hydrolysis reactions are starkly different. PBaz₃ reacts quantitatively with water to give PH₃ and with the oxidizing agent ONMe₃ to give the triply-O-inserted product P(OBaz)₃ , an inorganic version of triphenyl phosphite; a corresponding transformation with PPh₃ is inconceivable. Thermodynamically, what drives these striking differences in the chemistry of PBaz₃ and PPh₃ is the great strength of the B-O bond.

Precise Activation of Ammonia and Carbon Dioxide by an Iminodisilene

The activation of NH₃ and CO₂ is still an ambitious target for multiply bonded sub-valent silicon compounds. Now, the precise splitting of the N-H bond of ammonia by (Z)-imino(silyl)disilene 1 to give trans-1,2-adduct 2 a at low temperatures (-78 °C) is presented. According to DFT calculations, the stereospecific hydroamination follows a similar mechanism as the recently reported anti-addition of H₂ to the Si=Si bond of 1. The aminosilane 2 b could also be obtained as the formal silylene addition product under thermodynamic reaction control. By applying low temperatures, the activation of CO₂ with 1 selectively afforded the cis-oxadisilacyclobutanone 7-c as [2+2] cycloadduct. By performing the reaction directly at ambient temperatures, a mixture of three different-sized silacycles (4-6) was observed. Their formation was investigated theoretically and their structures were revealed with separate experiments using 1 and the oxygenation agents N₂ O and O₂ .

Trans-Metal-Trapping: Concealed Crossover Complexes En Route to Transmetallation?

Defined as the transfer of ligands from one metal to another, transmetallation is a common reaction in organometallic chemistry. Its chemical celebrity stems from its role in important catalytic cycles of cross-coupling reactions such as those of Negishi, Sonogashira, Stille, or Suzuki. This article focuses on trans-metal-trapping (TMT), which could be construed as partially complete transmetallations. On mixing two distinct organometallic compounds, of for example lithium with aluminium or gallium, the two metals meet in a crossover co-complex, but the reaction ceases at that point and full transmetallation is not reached. Though in its infancy, trans-metal-trapping shows promise in transforming failed lithiations into successful lithiations and in stabilising sensitive carbanions through cooperative bimetallic effects making them more amenable to onward reactivity.

Cation-Triggered Stannate(II)/Stannylenoid/Stannylene Conversion

The reaction of dipotassio-tetrasilan-1,4-diide (4) with anhydrous SnCl₂ at low temperature results in the formation of a five-membered cyclic potassio chlorostannate(II) ([(18-C-6)K](1)). By careful cation exchange reactions, it was transformed into the sodium chlorostannylenoid 2 (by using Na₂ [B₁₂ Cl₁₂ ]) or into the non-stabilized cyclic bissilylstannylene 3 (through applying Li[Al(OC(CF₃ )₃ )₄ ]). The increasing Lewis basicity of the bissilylstannylene 3 was analyzed by combined methods of DFT calculations and NMR spectroscopy and substantiated by the synthesis of the corresponding iron carbonyl complexes 7 and 8 from the chlorostannate 1 and the stannylene 3, respectively.

A General Route to Metal-Substituted Dipnictenes of the Type [L(X)M]2 E2

Two equivalents of LGa (L=HC[C(Me)N(2,6-iPr₂ C₆ H₃ )]₂ ) reacted with PX₃ (X=Cl, Br) with insertion into two P-X bonds and formation of [L(X)Ga]₂ PX (X=Cl 1, Br 2), whereas the analogous reaction with AsCl₃ occurred with twofold insertion and subsequent elimination of LGaCl₂ and formation of the Ga-substituted diarsene [L(Cl)Ga]₂ As₂ (3). Analogous findings were observed in the reactions with Me₂ NAsCl₂ , yielding the unsymmetrically-substituted diarsene [L(Cl)Ga]As=As[Ga(NMe₂ )L] (4). The reaction of As(NMe₂ )₃ with LGa gave [L(Me₂ N)Ga]₂ As₂ (5) after heating at 165 °C for five days, whereas the reaction with LAl gave [L(Me₂ N)Al]₂ As₂ (6) after heating at only 80 °C for one day. Finally, two equivalents of LGa reacted with Bi(NEt₂ )₃ to give [L(Et₂ N)Ga]₂ Bi₂ (7). Complexes 1-7 were characterized by NMR spectroscopy (¹ H, ¹³ C, ³¹ P), elemental analysis, and single-crystal X-ray diffraction (except for 1 and 5). The bonding situations in 4, 6, and 7 were analyzed by quantum chemical calculations.

Chemoselective and Catalyst-Free O-Borylation of Silanols: A Facile Access to Borasiloxanes

This paper demonstrates the first highly chemoselective syntheses of various borasiloxanes from hydroboranes and silanols, achieved through catalyst-free dehydrogenative coupling at room temperature. This green protocol, which uses easily accessible reagents, allows for the obtaining of borasiloxanes under air atmosphere and solvent-free conditions.

Li+ Ion Conductors with Adamantane-Type Nitridophosphate Anions β-Li10 P4 N10 and Li13 P4 N10 X3 with X=Cl, Br

β-Li₁₀ P₄ N₁₀ and Li₁₃ P₄ N₁₀ X₃ with X=Cl, Br have been synthesized from mixtures of P₃ N₅ , Li₃ N, LiX, LiPN₂ , and Li₇ PN₄ at temperatures below 850 °C. β-Li₁₀ P₄ N₁₀ is the low-temperature polymorph of α-Li₁₀ P₄ N₁₀ and crystallizes in the trigonal space group R3. It is made up of non-condensed [P₄ N₁₀ ]^10- T2 supertetrahedra, which are arranged in sphalerite-analogous packing. Li₁₃ P₄ N₁₀ X₃ (X=Cl, Br) crystallizes in the cubic space group Fm3‾m . Both isomorphic compounds comprise adamantane-type [P₄ N₁₀ ]^10- , Li⁺ ions, and halides, which form octahedra. These octahedra build up a face-centered cubic packing, whose tetrahedral voids are occupied by the [P₄ N₁₀ ]^10- ions. The crystal structures have been elucidated from X-ray powder diffraction data and corroborated by EDX measurements, solid-state NMR, and FTIR spectroscopy. Furthermore, we have examined the phase transition between α- and β-Li₁₀ P₄ N₁₀ . To confirm the ionic character, the migration pathways of the Li⁺ ions have been evaluated and the ion conductivity and its temperature dependence have been determined by impedance spectroscopy. XPS measurements have been carried out to analyze the stability with respect to Li metal.