Reactive p-block cations stabilized by weakly coordinating anions

Borate Salts of Aluminum-Alkyl Cations Stabilized by P-, O-, and C-Donors: Synthesis, Characterization and Application as Cocatalysts

Well-defined Al-alkyl borate (AAB) salts {[iBu2(L)Al]2(μ-H)}+[B(C6F5)4]- (AlHAl_L) with L = N-donor ligands have been recently reported as promising "complete" cocatalysts for olefin polymerization. Herein, we explore structural variations of AlHAl_L going beyond the class of N-donors like the prototypical N,N-dimethyl aniline (DMA). Thirteen P-, O-, and C-donor ligands were screened, allowing isolation of AAB salts with mono- and bidentate phosphines, alkyl-, aryl-, and silyl-ethers, and a N-heterocyclic carbene. Except for the diphosphine with the longest spacer between the P atoms [bis(diphenylphosphino)hexane, DPPH], all donors gave well-defined tetracoordinate or tricoordinate molecular species, which were characterized in solution (NMR) and solid state (XRD), and tested as cocatalyst in ethylene/1-hexene copolymerization with an ansa-zirconocene catalyst [rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2]. The vast majority of novel AAB salts provided active catalytic systems, further demonstrating the broad tunability of these species. Consistent with previous studies, variability in productivity upon L variation is primarily related to the efficiency of precatalyst activation, determining the fraction of Zr active sites. Variations in polymer molecular weight and comonomer incorporation observed with some P-, O- and C-donor ligands indicate that also interactions between the L donors and the Zr active species might be relevant in determining catalytic performance in some cases.

Synthesis, Characterization, and Reactivity of Aminotroponiminate-Based Difluoroboranes: A Pathway toward Bore(boro)nium Cations

Aminotroponiminates (ATIs), a well-known monoanionic bidentate ligand, display a wide range of coordination chemistry. To exploit their electronic and steric factors in achieving boron cations, a series of symmetrical, unsymmetrical, and bis(ATI) borane complexes [(C7H5)(NiPr)2BF2] (3a), [(C7H5)(NtBu)2BF2] (3b), [(C7H5)(NiBu)2BF2] (3c), [(C7H5)(NiBu)(NtBu)BF2] (3d), and [(C7H5)(NiPr)(NCH2)BF2]2 (3e) were synthesized in this work. All the ATI borane complexes are highly blue luminescent in the solution, and their fluorescence decay time was recorded in DCM. The observed decay time range was found to exist between 1.7 and 2.8 ns. Complexes 3a and 3b when treated with trimethylsilyl triflate (TMS-OTf) enabled the isolation of tricoordinated borenium cations [(C7H5)(NiPr)2BOH]+ (4a) and [(C7H5)(NtBu)2BOH]+ (4b), respectively. Interestingly, the reaction of bis(ATI) borane 3e and TMS-OTf resulted in a boron dication 4e in which the borenium and boronium cations are bridged via an oxygen atom in a seven-membered ring scaffold. All of the ATI boranes and cations were well characterized by various spectroscopic techniques in solution and X-ray structure diffraction analysis in the solid state. Further, theoretical calculations using density functional theory (DFT) were conducted to understand the electronic structure and bonding scenario of these complexes.

Hexaphenyl-1,2-Diphosphonium Dication [Ph3P-PPh3]2+: Superacid, Superoxidant, or Super Reagent?

The oxidation of triphenylphosphine by perfluorinated phenaziniumF aluminate in difluorobenzene affords hexaaryl-1,2-diphosphonium dialuminate 1. Dication 12+ is valence isoelectronic with elusive hexaphenylethane, where instead the formation of a mixture of the trityl radical and Gomberg's dimer is favored. Quantum-chemical calculations in combination with Raman/IR spectroscopies rationalize the stability of the P-P bonded dimer in 12+ and suggest, akin to the halogens, facile homolytic as well as heterolytic scission. Thus, 12+ serves as a surrogate of both the triphenylphosphorandiylium dication (Ph3P2+) and the triphenylphosphine radical monocation (Ph3P·+). Treating 1 with dimethylaminopyridine (DMAP) or tBu3P replaces triphenylphosphine under heterolytic P-P bond scission. Qualifying as a superoxidant (E vs Fc/Fc+ = +1.44 V), 1 oxidizes trimethylphosphine. Based on halide abstraction experiments (-BF4, -PF6, -SbCl6, -SbF6) as well as the deoxygenation of triethylphosphine oxide, triflate anions as well as toluic acid, 1 also features Lewis superacidity. The controlled hydrolysis affords Hendrickson's reagent, which itself finds broad use as a dehydration agent. Formally, homolytic P-P bond scission occurs with diphenyldisulfide (PhSSPh) and the triple bonds in benzo- and acetonitrile. The irradiation by light cleaves the P-P bond homolytically and generates transient triphenylphosphine radical cations, which engage in H-atom abstraction as well as CH phosphoranylation.

Borenium Ylide-Mediated 12-B Arylation of Carborane Anions

Developing novel approaches for B-vertex modification is significant in the chemistry of icosahedral boron clusters. Here, we report a protocol for the transformation of air-stable 12-aryliodonium carborane anions, which are readily accessible on a gram scale from the corresponding (diacetoxyiodo)arenes (ArI(OAc)2) and carborane anion, to 12-aryl-carborane anions. Mechanistic studies support the idea that the 12-B arylation proceeds via intramolecular reductive C-B bond formation on the carborane 12-borenium ylide, followed by rearomatization. The reaction proceeds under mild conditions in air and is suitable for one-pot synthesis without the need for purification of the 12-aryliodonium carborane anions. B-B coupling reaction at the 12-B vertex affords dumbbell-type carborane anion dimers. This reaction offers an alternative approach for B-C bond formation in closo borates, complementing conventional cross-coupling approaches.

Stable Mg2+ Dication Weakly Stabilized/Coordinated in Solution: Synthesis, Structure, Reactivity, and Use in Catalysis

The first soluble and stable Mg2+ dication stabilized only by weakly coordinating and chemically robust carborate anions [HexCB11Cl11]- is described. Mg[HexCB11Cl11]2 (1), prepared by reaction of Mg(nBu)2 with 2 equiv of [Ph3C][HexCB11Cl11], consists, in the solid state, of a central Mg2+ surrounded by two [HexCB11Cl11]- anions. In solution, experimental and classical molecular dynamics simulations (cMD) agree with cation/anion association being retained, reflecting the high electrophilicity of the Mg center. Yet, reflecting only weak anion/cation interactions, species 1 polymerizes 1-hexene and coordinates alkynes. However, 1 displays no reaction with HSiEt3 at room temperature, consistent with a low hydridicity of the hard (HSAB) Mg2+ center. Contrasting with 1 (FIA = 264 kJ mol-1; FIA: Fluoride Ion Affinity), salt Mg[(nBu)3NB12H4Cl7]2 (2), incorporating the more basic ammoniododecaborate [(nBu)3NB12H4Cl7]- anion, is significantly less Lewis acidic (FIA = 214.7 kJ mol-1) and unreactive with alkenes and alkynes. Salt 1 effectively catalyzes alkene/alkyne hydrosilylation via an initial alkene/alkyne coordination/initiation, as suggested by experimental and computational data. It also efficiently catalyzes (with a catalyst loading down to 0.1 mol%) the hydrosilylation of CO2 to CH4 in the presence of HSiEt3. Salt 1 smoothly promotes the catalytic transfer hydrogenation of 1,1-diphenylethylene, and it is also an active imine hydrogenation catalyst in the presence of H2.

Coexistence of the Perfluorinated Cp* Anion With Oxidizing and Electrophilic Cations

The air- and water-stable perfluorinated Cp* [C5(CF3)5]- is presented as a candidate for the vastly underexplored group of weakly coordinating carbanions (WCCAs). Its extreme electron deficiency, combined with the stabilization of the negative charge within an aromatic system, results in a low basicity, yielding a very weak coordination ability. As Cp anions usually possess a strongly pronounced carbanionic character, the perfluorinated Cp* resembles an extraordinary exception for both the WCA and Cp chemistry. However, the coordination ability remains ambivalent due to the substitution lability of many of its complexes, allowing for the formation of unique ligand-WCA switches. Due to the low reactivity, there is a need for new transfer reagents containing the perfluorinated Cp* in combination with reactive cations. Thus, we report the synthesis and complete characterization of [C5(CF3)5]- salts with hydride-accepting [(C6H5)3C]+, valuable Ag(I) reagents, oxidizing [Fe(C5H5)2]+ or [N(p-C6H4Br)3]+ and Brønsted acidic [H(m,m-NC5H3F2)2]+. Notably, these unprecedented ion pairs are exclusively accessible and stabilized by the low coordination affinity and pronounced oxidative resistance of the perfluorinated Cp*.

Chemocatalytic Conversion of Dinitrogen to Ammonia Mediated by a Tungsten Complex

Whereas molybdenum dinitrogen complexes have played a major role as catalytic model systems of nitrogenase, corresponding tungsten complexes were in most cases found to be catalytically inactive. Herein, we present a modified pentadentate tetrapodal (pentaPod) phosphine ligand in which two dimethylphosphine groups of the pentaPodMe (P5Me) ligand have been replaced with phospholanes (Pln). The derived molybdenum complex [Mo(N2)P5Pln] generates 22 and the analogous tungsten complex [W(N2)P5Pln] 7 equivalents of NH3 from N2 in the presence of 180 equivalents of SmI2(THF)2/H2O, rendering the latter the first tungsten complex chemocatalytically converting N2 to NH3. In contrast, the tungsten complex [W(N2)P5Me] generates ammonia from N2 only in a slightly overstoichiometric fashion. The reasons for these reactivity differences are investigated with the help of spectroscopic and electrochemical methods.

Construction of efficient Pb(II) carboxylate catalysts for the oxygen and hydrogen evolution reactions

The development of cost-effective and efficient electrocatalysts can solve the problems associated with the production of energy via water-splitting reactions. In this work, we have focused on two lead-based coordination polymers (CPs), namely, {[Pb2(TPBN)(HBTC)2]2·2.5H2O}n (CP1) and {[Pb2(TPBN)(NDC)2]·H2O}n (CP2), that were synthesized by self-assembly method at room temperature in good yields. The two-dimensional structures of CP1 and CP2 were determined by single-crystal X-ray diffraction studies. Their phase purity and thermal stability were confirmed by powder X-ray diffraction and TGA analysis, respectively. In addition to this, Hirshfeld surface analysis of CP1 and CP2 revealed the key differences in their intermolecular interactions. Both CP1 and CP2 were employed for HER and OER. It has been found that the change in the carboxylate from BTC to NDC resulted in better electrocatalytic activity towards water-splitting reactions. This may be attributed to the presence of more π character in NDC compared to BTC, which makes the electron flow much easier for HER process. CP1 and CP2 showed overpotential values of -0.58 V and -0.55 V, respectively, in 1 M H2SO4 to reach a 10 mA cm-2 current density with Tafel slopes of 31 mV dec-1 and 25 mV dec-1, respectively. For the OER process, CP1 and CP2 exhibited overpotentials of 590 mV and 470 mV, respectively, in 1 M KOH at a current density of 50 mA cm-2 with Tafel slope values of 81 mV dec-1 and 56 mV dec-1, respectively. Turnover frequency (TOF) values of CP1 and CP2 were 1.05 s-1 and 3.21 s-1 for OER and 1.97 s-1 and 9.65 s-1 for HER, respectively. These results indicate that both CPs can act as highly efficient electrocatalysts for clean energy production.

Nucleophilic Functionalization of a Cationic Pentaphosphole Complex-A Systematic Study of Reactivity

The systematic nucleophilic functionalization of the cationic pentaphosphole ligand complex [Cp*Fe(η4-P5Me)][OTf] (A) with group 16/17 nucleophiles is reported. This method represents a highly reliable and versatile strategy for the design of novel transition-metal complexes featuring twofold substituted end-deck cyclo-P5 ligands, bearing unprecedented hetero-element substituents. By the reaction of A with classical group 16 nucleophiles, complexes of the type [Cp*Fe(η4-P5MeE)] (E=OEt (1), OtBu (2), SPh (3), SePh (4)) are obtained. By transferring this protocol to group 17 nucleophiles, the highly sensitive complexes [Cp*FeP5(η4-P5MeX)] (X=F (5), Cl (6), Br (7), I (8)) could be isolated. All products show exclusively 1,1'-substitution at the cyclo-P5 ring. Interestingly, further studies on the reactivity of the halogenated species revealed their ability to undergo ring-opening reactions with cyclic ethers such as THF and ethylene oxide yielding [Cp*FeP5(η4-P5MeOC4H8X)] (X=Br (9), I (10)) or [Cp*FeP5(η4-P5MeOC2H4X)] (X=Br (11), I (12)), respectively. Furthermore, the use of acyclic ethers such as dimethoxyethane led to the formation of [Cp*FeP5(η4-P5MeOC2H4OCH3)] (13) mediated by C-O bond cleavage, followed by subsequent P-O bond formation, as further enlightened by DFT calculations.

Development of the design and synthesis of metal-organic frameworks (MOFs) - from large scale attempts, functional oriented modifications, to artificial intelligence (AI) predictions

Owing to the exceptional porous properties of metal-organic frameworks (MOFs), there has recently been a surge of interest, evidenced by a plethora of research into their design, synthesis, properties, and applications. This expanding research landscape has driven significant advancements in the precise regulation of MOF design and synthesis. Initially dominated by large-scale synthesis approaches, this field has evolved towards more targeted functional modifications. Recently, the integration of computational science, particularly through artificial intelligence predictions, has ushered in a new era of innovation, enabling more precise and efficient MOF design and synthesis methodologies. The objective of this review is to provide readers with an extensive overview of the development process of MOF design and synthesis, and to present visions for future developments.

Cationic Group 13 and 14 Element Clusters

Anionic and neutral clusters dominate the cluster chemistry of group 13 and 14 elements, many of which have become classic textbook examples of main group element clusters. However, facilitated by the development of unreactive, weakly coordinating anions, the number of known group 13 and 14 cationic cluster compounds has risen rapidly in recent years. Hence, this review aims to give an overview over this research field, which arouses increasing interest owing to the often unusual structures of the cationic clusters, as well as their application in bond activation chemistry. Challenges of the cluster formation are discussed and suitable starting materials are presented, as well as syntheses, structures and the rich follow-up chemistry of (also mixed) group 13 and 14 cluster cations.

Corrolato(oxo)antimony(V) Dimer with Hydrogen-Bond Donor Groups in Secondary Coordination Sphere as a Catalyst for Hydrogen Evolution Reaction

The focus is on developing alternative molecular catalysts using main-group elements and implementing strategic improvements for sustainable hydrogen production. For this purpose, a FB corrole with a (2-(2-((4-methylphenyl)sulfonamido)ethoxy)phenyl) group inserted into the meso position (C-10) of the corrole, along with its high-valent (corrolato)(oxo)antimony(V) dimer, was synthesized. In the crystal structure analysis of the FB corrole and the (corrolato)(oxo)antimony(V) dimer complex, it was noted that the sulfonamido group in the ligand periphery sits atop the corrole ring. The electrochemical hydrogen evolution reaction (HER) of the (corrolato)(oxo)antimony(V) dimer was studied and compared with a previously reported (corrolato)(oxo)antimony(V) complex, which lacks hydrogen-bond donor groups in the secondary coordination sphere. The newly designed molecules, featuring hydrogen-bond donor groups in the secondary coordination sphere, demonstrated clear superiority in the electrochemical HER. Controlled potential electrolysis was employed to evaluate the charge accumulation associated with hydrogen generation in a homogeneous three-electrode system in the presence of 50 mM TFA. The produced hydrogen exhibits a Faradaic efficiency of approximately 80.96%, a turnover frequency (TOF) of 0.44 h-1, and a production rate of 52.83 μL h-1, highlighting the effective catalytic activity of the (corrolato)(oxo)antimony(V) dimer in hydrogen evolution.

Carbon-Based Weakly Coordinating Anions: Molecular Design, Synthesis and Applications

Although carbanions, which are usually regarded as reactive species and powerful metalation reagents, can be stabilized through choice of the substitution pattern, they have rarely been considered for the design of weakly coordinating anions (WCA). Here, we report on an evaluation of the potential of a series of differently substituted carbanions to serve as WCA by computational methods. This led us to the synthesis of the water- and air-stable allyl anion 1 with triflyl and 3,5-bis(trifluoromethyl)phenyl (ArF) moieties, which can be isolated in high yields even on a gram-scale. Single crystal X-ray crystallography and NMR studies confirmed the weak coordination ability of the anion by showing negligible or only weak interactions with different cations. This property enabled the application of 1 in the stabilization of reactive group 14 and 15 cations. In addition to the crystallization of a phosphenium cation, the first all-carbon salt with a non-aromatic carbanion is reported, which revealed to be a convenient reagent for hydride abstraction such as from silanes. Overall, this work demonstrates the so far untapped potential of carbanions as WCA, that are accessible with a variety of different cations for various applications.

Diverse Functionality of Molecular Germanium: Emerging Opportunities as Catalysts

Fundamental research on germanium as the central element in compounds for bond activation chemistry and catalysis has achieved significant feats over the last two decades. Designing strategies for small molecule activations and the ultimate catalysts established capitalize on the orbital modalities of germanium, apparently imitating the transition-metal frontier orbitals. There is a growing body of examples in contemporary research implicating the tunability of the frontier orbitals through avant-garde approaches such as geometric constrained empowered reactivity, bimetallic orbital complementarity, cooperative reactivity, etc. The goal of this Perspective is to provide readers with an overview of the emerging opportunities in the field of germanium-based catalysis by perceiving the underlying key principles. This will help to convert the discrete set of findings into a more systematic vision for catalyst designs. Critical exposition on the germanium's frontier orbitals participations evokes the key challenges involved in innovative catalyst designs, wherein viewpoints are provided. We close by addressing the forward-looking directions for germanium-based catalytic manifold development. We hope that this Perspective will be motivational for applied research on germanium as a constituent of pragmatic catalysts.

A Redox-Active Phenothiazine-based Pd2L4-Type Coordination Cage and Its Isolable Crystalline Polyradical Cations

Polyradical cages are of great interest because they show very fascinating physical and chemical properties, but many challenges remain, especially for their synthesis and characterization. Herein, we present the synthesis of a polyradical cation cage 14⋅+ through post-synthetic oxidation of a redox-active phenothiazine-based Pd2L4-type coordination cage 1. It's worth noting that 1 exhibits excellent reversible electrochemical and chemical redox activity due to the introduction of a bulky 3,5-di-tert-butyl-4-methoxyphenyl substituent. The generation of 14⋅+ through reversible electrochemical oxidation is investigated by in situ UV/Vis-NIR and EPR spectroelectrochemistry. Meanwhile, chemical oxidation of 1 can also produce 14⋅+ which can be reversibly reduced back to the original cage 1, and the process is monitored by EPR and NMR spectroscopies. Eventually, we succeed in the isolation and single crystal X-ray diffraction analysis of 14⋅+, whose electronic structure and conformation are distinct to original 1. The magnetic susceptibility measurements indicate the predominantly antiferromagnetic interactions between the four phenothiazine radical cations in 14⋅+. We believe that our study including the facile synthesis methodology and in situ spectroelectrochemistry will shed some light on the synthesis and characterization of novel polyradical systems, opening more perspectives for developing functional supramolecular cages.

Stable and Fully-Oxidized Methylene-Bridged Macrocyclic Phenothiazine Polyradical Cations

Macrocyclic arenes represent one of the most important and intensively investigated entities in supramolecular chemistry. However, research on the redox activities of macrocyclic arenes, especially their isolable and crystalline polyradical analogues, has been rarely reported. Here, we present the synthesis, redox activity, and application of methylene-bridged macrocyclic phenothiazines, where polyradical cations are successfully isolated and unambiguously characterized for the first time. This research provides an effective method for preparing polyradical macrocycles, which expands the scope of investigation into macrocyclic arenes and their potential applications.

Bis(diiminate)-based boron difluoro complexes: effective synthon for bis(borenium) cations

A series of boron difluoro bis(diiminate) complexes have been prepared and used to obtain triflate substituted fluoroborane complexes. The corresponding well-defined bis(borenium) cations were subsequently synthesized and structurally authenticated. We are also presenting the first experimental and theoretical study of bis(borenium) cations that are derivative of cationic borinic acid.

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

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

On the Synthesis and Structure of 'Naked' Ga(I) and In(I) Salts and the Surprising Stability of Simple Ga(I) and In(I) Salts in the Coordinating Solvents Ether and Acetonitrile

In this work, we present the solid-state structures of solvent-free Ga[pf] and In[pf] salts ([pf]-=[Al(ORF)4]-; RF=C(CF3)3), which are very rare examples of salts with truly 'naked' metal cations. Both salts may serve as starting materials for subvalent gallium and indium chemistry with very weakly coordinating ligands providing the freedom of choice for solvents and ligands for the future. On the other hand, we report and rationalize the formation and isolation of [M(OEt2)2][pf] and [M(MeCN)2][pf] (M=Ga, In), underlining the surprising stability of these subvalent group 13 M+ ions against disproportionation. Unexpectedly, dicoordinate and carbene analogous [M(L)2]+ ions with the [pf]- counterion are stable in L=acetonitrile and diethyl ether at room temperature, opening up possible applications for example in organic synthesis and catalysis.

Intramolecularly O,N,O-Coordinated Tin(II) Salts: Syntheses, Structures, Cyclization, and Transition Metal Complexation

We report the syntheses of tin(II) salts of the types [L1SnX]SnX3 [L1=2,6-{(i-PrO)2(O)P}2C5H3N: 1, X=Cl; 2, X=Br], [L2SnCl]SnCl3 [L2=2-{(i-PrO)Ph(O)P}-6-{(i-PrO)2(O)P}C5H3N: 3], [L3SnX]SnX3 [L3=2,6-{MeO(O)C}2C5H3N: 4, X=Cl; 5, X=Br], [L4SnX]SnX3 [L4=2,6-{Et2N(O)C}2C5H3N: 6, X=Cl; 7, X=Br]. These compounds were obtained by addition of SnX2 to the corresponding ligand inducing autoionization of the respective tin(II) halide. The thermal stability of 1, 3, and 4 was elucidated, giving, under ester cleavage and cyclisation, the tin(II) derivatives 8-12. The reaction of [L1SnCl]SnCl3 (1) with W(CO)4(thf)2 afforded the tungsten tetracarbonyl complex [{L1SnCl}{SnCl3}W(CO)4] (13), representing the first example in which a tin(II) stannate anion and a tin(II) stannylium cation simultaneously coordinate to a transition metal centre. The compounds were characterized by single crystal X-ray diffraction analyses and in part by elemental analyses, IR and NMR spectroscopy, electrospray ionization mass spectrometry. DFT calculations accompany the experimental work.

Introducing AFS ([Al(SO3F)3]x) - a thermally stable, readily available, and catalytically active solid Lewis superacid

Common Lewis superacids often suffer from low thermal stability or complicated synthetic protocols, requiring multi-step procedures and expensive starting materials. This prevents their large-scale application. Herein, the easy and comparably cheap synthesis of high-purity aluminium tris(fluorosulfate) ([Al(SO3F)3]x, AFS) is presented. All starting materials are commercially available and no work-up is required. The superacidity of this thermally stable, polymeric Lewis acid is demonstrated using both theoretical and experimental methods. Furthermore, its synthetic and catalytic applicability, e.g. in bond heterolysis reactions and C-F bond activations, is shown.

How to Deal with Charge in the Ranking of Lewis Acidity: Critical Evaluation of an Extensive Set of Cationic Lewis Acids

The quantification of Lewis acidity is of fundamental and applied importance in chemistry. However, if neutral and charged Lewis acids are compared, a coherent ranking has been elusive, and severe uncertainties were accepted. With this study, we present a systematic computational analysis of Lewis base affinities of 784 mono-, di- and tricationic Lewis acids and their comparison with 149 representative neutral Lewis acids. Evaluating vacuum fluoride ion affinities (FIA) reveals a charge-caused clustering that prohibits any meaningful ranking. Instead, solvation-corrected FIAsolv is identified as a metric that overcomes charge sensitivity in a balanced manner, allowing for a coherent evaluation of Lewis acidity across varying charge states. Analyzing the impact of molecular volume on solvation-induced FIA damping provides rationales for fundamental trends and guidelines for the choice or design of neutral and cationic Lewis acids in the condensed phase. Exploring alternative scales, explicit counteranion effects, and selected experimental case studies reaffirms the advantages of solvation-corrected FIAsolv as the most versatile and practical approach for the quantitative ranking of general (thermodynamic) Lewis acidity.

Lewis Acid Decorated Hexacyanodiborane(6) Dianion

First examples of diborane(6) dianions decorated with weakly coordination B(C6F5)3 (BCF) groups and SiEt3 + moieties have been synthesized demonstrating the synthetic potential of the [B2(CN)6]2- dianion. [B2{CNB(C6F5)3}6]2- (1) was isolated as potassium and tetrabutylammonium salt. 1 is a rare example for a weakly coordinating dianion and it was used for the stabilization of the carbocation [Ph3C]+ and the oxonium acid [H(OEt2)2]+. Reaction of [Ph3C]21 with HSiEt3 resulted in the silylated neutral diborane(6) [B2{CNB(C6F5)3}4(CNSiEt3)2] (2) in which two BCF groups have been selectively replaced by SiEt3 + substituents, underscoring the stability and chemical versatility of the [B2(CN)6]2- dianion. The chemical properties and physicochemical data of 1 and 2 provide insight into electronic, coordinating, and steric properties of theses novel diborane(6) compounds.

Counterion influence on near-infrared-II heptamethine cyanine salts for photothermal therapy

Photothermal therapy (PTT) has attracted extensive attention in cancer treatment. Heptamethine cyanine dyes with near-infrared (NIR) absorption performance have been investigated for PTT. However, they are often accompanied by poor photostability, suboptimal photothermal conversion and limited therapeutic efficacy. The photophysical properties of fluorescent organic salts can be tuned through counterion pairing. However, whether the counterion can influence the photostability and photothermal properties of heptamethine cyanine salts has not been clarified. In this work, we investigated the effects of eleven counter anions on the physical and photothermal properties of NIR-II heptamethine cyanine salts with the same heptamethine cyanine cation. The anions have great impacts on the physiochemical properties of dyes in solution including aggregation, photostability and photothermal conversion efficiency. The physical tuning enables the control over the cytotoxicity and phototoxicity of the dyes. The selected salts have been demonstrated to significantly suppress 4T1 breast tumor growth with low toxicity. The findings that the counterion has great effects on the photothermal properties of cationic NIR-II heptamethine cyanine dyes will provide a reference for the preparation of improved photothermal agents through counterion pairing with possible translation to humans.

s-Block metal complexes of superbulky (tBu3Si)2N-: a new weakly coordinating anion?

Sterically hindered amide anions have found widespread application as deprotonation agents or as ligands to stabilize metals in unusual coordination geometries or oxidation states. The use of bulky amides has also been advantageous in catalyst design. Herein we present s-block metal chemistry with one of the bulkiest known amide ligands: (tBu3Si)2N- (abbreviated: tBuN-). The parent amine (tBuNH), introduced earlier by Wiberg, is extremely resistant to deprotonation (even with nBuLi/KOtBu superbases) but can be deprotonated slowly with a blue Cs+/e- electride formed by addition of Cs0 to THF. (tBuN)Cs crystallized as a separated ion-pair, even without cocrystallized solvent. As salt-metathesis reactions with (tBuN)Cs are sluggish and incomplete, it has only limited use as an amide transfer reagent. However, ball-milling with LiI led to quantitative formation of (tBuN)Li and CsI. Structural characterization shows that (tBuN)Li is a monomeric contact ion-pair with a relatively short N-Li bond, an unusual T-shaped coordination geometry around N and extremely short Li⋯Me anagostic interactions. Crystal structures are compared with Li and Cs complexes of less bulky amide ligands (iPr3Si)2N- (iPrN-) and (Me3Si)2N- (MeN-). DFT calculations show trends in the geometries and electron distributions of amide ligands of increasing steric bulk (MeN- < iPrN- < tBuN-) and confirm that tBuN- is a rare example of a halogen-free weakly coordinating anion.

The Field of Main Group Lewis Acids and Lewis Superacids: Important Basics and Recent Developments

New developments in the field of Lewis acidity are highlighted, with the focus of novel Lewis acids and Lewis superacids of group 2, 13, 14, and 15 elements. Several important basics, illustrated by modern examples (classification of Donor-Acceptor (DA) complexes, amphoteric nature of any compound in terms of DA interactions, reorganization energies of main group Lewis acids and the role of the energies of frontier orbitals) are presented and discussed. It is emphasized that the Lewis acidity phenomena are general and play vital role in different areas of chemistry: from weak "atomophilic" interactions to the complexes of Lewis superacids.

Intramolecular donor-stabilized tetra-coordinated germanium(iv) di-cations and their Lewis acidic properties

We report the first examples of intramolecular phosphine-stabilized tetra-coordinated germanium(iv) di-cationic compounds: [LiPr2Ge][CF3SO3]23iPr and [LPh2Ge][CF3SO3]23Ph (LiPr = 6-(diisopropylphosphanyl)-1,2-dihydroacenaphthylene-5-ide; LPh = 6-(diphenylphosphanyl)-1,2-dihydroacenaphthylene-5-ide). The step wise synthetic strategy involves the isolation of neutral and mono-cationic Ge(iv) precursors: [LiPr2GeCl][X] (X = GeCl31iPr, OTf 2iPr), [LPh2GeCl2] 1Ph and [LPh2GeCl][OTf] 2Ph. Both 3iPr and 3Ph exhibit constrained spiro-geometry. DFT studies reveal the dispersion of di-cationic charges over P-Ge-P sites. Anion or Lewis base binding occurs at the Ge site resulting in relaxed distorted trigonal bipyramidal/tetrahedral geometry. 3iPr and 3Ph activate the Si-H bond initially at the P-site. The hydride ultimately migrates to the Ge-site rapidly giving [LPh2GeH][CF3SO3] 3PhH, while sluggishly forming [LiPr2GeH][CF3SO3] 3iPrH. Compounds 3iPr and 3Ph were tested as catalysts for the hydrosilylation of aromatic aldehydes. While catalytic hydrosilylation proceeded via the initial Et3Si-H bond activation in the case of 3iPr, compound 3Ph as a catalyst showed a masked Frustrated Lewis Pair (FLP) type reactivity in the catalytic cycle.

Structures, Bonding Analyses and Reactivity of a Dicationic Digallene and Diindene Mimicking trans-bent Ditetrylenes

The reaction of bisdicyclohexylphosphinoethane (dcpe) and the subvalent MI sources [MI (PhF)2 ][pf] (M=Ga+ , In+ ; [pf]- =[Al(ORF )4 ]- ; RF =C(CF3 )3 ) yielded the salts [{M(dcpe)}2 ][pf]2 , containing the first dicationic, trans-bent digallene and diindene structures reported so far. The non-classical MI ⇆MI double bonds are surprisingly short and display a ditetrylene-like structure. The bonding situation was extensively analyzed by quantum chemical calculations, QTAIM (Quantum Theory of Atoms in Molecules) and EDA-NOCV (Energy Decomposition Analysis with the combination of Natural Orbitals for Chemical Valence) analyses and is compared to that in the isoelectronic and isostructural, but neutral digermenes and distannenes. The dissolved [{Ga(dcpe)}2 ]2+ ([pf]- )2 readily reacts with 1-hexene, cyclooctyne, diphenyldisulfide, diphenylphosphine and under mild conditions at room temperature. This reactivity is analyzed and rationalized.

Aluminum(III) Cations [(NHC) ⋅ AlMes2 ]+ : Synthesis, Characterization, and Application in FLP-Chemistry

The three-coordinate aluminum cations ligated by N-heterocyclic carbenes (NHCs) [(NHC) ⋅ AlMes2 ]+ [B(C6 F5 )4 ]- (NHC=IMeMe 4, IiPrMe 5, IiPr 6, Mes=2,4,6-trimethylphenyl) were prepared via hydride abstraction of the alanes (NHC) ⋅ AlHMes2 (NHC=IMeMe 1, IiPrMe 2, IiPr 3) using [Ph3 C]+ [B(C6 F5 )4 ]- in toluene as hydride acceptor. If this reaction was performed in diethyl ether, the corresponding four-coordinate aluminum etherate cations [(NHC) ⋅ AlMes2 (OEt2 )]+ [B(C6 F5 )4 ]- 7-9 (NHC=IMeMe 7, IiPrMe 8, IiPr 9) were isolated. According to a theoretical and experimental assessment of the Lewis-acidity of the [(IMeMe ) ⋅ AlMes2 ]+ cation is the acidity larger than that of B(C6 F5 )3 and of similar magnitude as reported for Al(C6 F5 )3 . The reaction of [(IMeMe ) ⋅ AlMes2 ]+ [B(C6 F5 )4 ]- 4 with the sterically less demanding, basic phosphine PMe3 afforded a mixed NHC/phosphine stabilized cation [(IMeMe ) ⋅ AlMes2 (PMe3 )]+ [B(C6 F5 )4 ]- 10. Equimolar mixtures of 4 and the sterically more demanding PCy3 gave a frustrated Lewis-pair (FLP), i.e., [(IMeMe ) ⋅ AlMes2 ]+ [B(C6 F5 )4 ]- /PCy3 FLP-11, which reacts with small molecules such as CO2 , ethene, and 2-butyne.

Anions featuring an aluminium-silicon core with alumanyl silanide and aluminata-silene characteristics

Molecular species containing multiple bonds to aluminium have long been challenging synthetic targets. Despite recent landmark discoveries in this area, heterodinuclear Al-E multiple bonds (where E is a group-14 element) have remained rare and limited to highly polarized π-interactions (Al=E ↔ +Al-E-). Here we report the isolation of three alumanyl silanide anions that feature an Al-Si core stabilized by bulky substituents and a Si-Na interaction. Single-crystal X-ray diffraction studies, spectroscopic analysis and density functional theory calculations show that the Al-Si interaction possesses partial double bond character. Preliminary reactivity studies support this description of the compounds through two resonance structures: one that displays a predominant nucleophilic character of the sodium-coordinated silicon centre in the Al-Si core, as shown by silanide-like reactivity towards halosilane electrophiles and the CH-insertion of phenylacetylene. Moreover, we report an alumanyl silanide with a sequestered sodium cation. Cleavage of the Si-Na bond by [2.2.2]cryptand increases the double bond character of the Al-Si core to produce an anion with high aluminata-silene (-Al=Si) character.

From Sn(II) to Sn(IV): Enhancing Lewis Acidity Via Oxidation

We demonstrate the increased Lewis acidity on going from Sn(II) to Sn(IV) by oxidizing TpMe2SnOTf (OTf = SO3CF3) to TpMe2SnF(OTf)2. Replacement of the fluoride ion in TpMe2SnF(OTf)2 by a triflate, resulting in TpMe2Sn(OTf)3 further enhances the Lewis acidity at tin. 119Sn NMR spectroscopy, modified Gutmann-Beckett test, computational analysis, and catalytic phosphine oxide deoxygenation support the claims.

Planar bismuth triamides: a tunable platform for main group Lewis acidity and polymerization catalysis

Geometric deformation in main group compounds can be used to elicit unique properties including strong Lewis acidity. Here we report on a family of planar bismuth(iii) complexes (cf. typically pyramidal structure for such compounds), which show a geometric Lewis acidity that can be further tuned by varying the steric and electronic features of the triamide ligand employed. The structural dynamism of the planar bismuth complexes was probed in both the solid and solution phase, revealing at least three distinct modes of intermolecular association. A modified Gutmann-Beckett method was used to assess their electrophilicity by employing trimethylphosphine sulfide in addition to triethylphosphine oxide as probes, providing insights into the preference for binding hard or soft substrates. Experimental binding studies were complemented by a computational assessment of the affinities and dissection of the latter into their intrinsic bond strength and deformation energy components. The results show comparable Lewis acidity to triarylboranes, with the added ability to bind two bases simultaneously, and reduced discrimination against soft substrates. We also study the catalytic efficacy of these complexes in the ring opening polymerization of cyclic esters ε-caprolactone and rac-lactide. The polymers obtained show excellent dispersity values and high molecular weights with low catalyst loadings used. The complexes retain their performance under industrially relevant conditions, suggesting they may be useful as less toxic alternatives to tin catalysts in the production of medical grade materials. Collectively, these results establish planar bismuth complexes as not only a novel neutral platform for main group Lewis acidity, but also a potentially valuable one for catalysis.

The perfluoroadamantoxy aluminate as an ideal weakly coordinating anion? - synthesis and first applications

Weakly coordinating anions (WCAs) facilitate the stabilization and isolation of highly reactive and almost "naked" cations. Alkoxyaluminate-based WCAs such as [Al(OC(CF₃)₃)₄]^- ([pf]^-) are widely used due to their synthetic accessibility and their high stability. However, small cations are still able to coordinate the oxygen atoms of the [pf]^- anion or even to abstract an alkoxy ligand. The novel WCA [Al(OC₁₀F₁₅)₄]^- ([pfAd]^-; OC₁₀F₁₅ = perfluoro-1-adamantoxy) is characterized by a very rigid core framework, thus indicating a higher stability towards fluoride-ion abstraction (DFT calculations) and providing hope to generate less disordered crystal structures. The [pfAd]^- anion was generated by the reaction of the highly acidic alcohol perfluoro-1-adamantanol C₁₀F₁₅OH with LiAlH₄ in o-DFB. Li[pfAd] could not be synthesized free of impurities (and still contains unreacted alcohol). Yet, starting from contaminated Li[pfAd], the very useful pure salts Ag[pfAd], [Ph₃C][pfAd] and [H(OEt₂)₂][pfAd] could be synthesized. The salts were characterized by NMR spectroscopy, single-crystal X-ray diffraction and IR spectroscopy. Additionally, [NO][pfAd] could be synthesized containing alcohol impurities but nonetheless enabled the synthesis of the salt P₉⁺[pfAd]^-. The synthesis of Tl[pfAd] in a mixture of H₂O/acetone/o-DFB demonstrated the water stability of the [pfAd]^- anion.

Cationic Triarylchlorostibonium Lewis Acids

Organopnictogen cations show promise as powerful, tunable main-group Lewis acid catalysts. The synthesis, solid-state structures, and reactivity of a series of weakly coordinated triarylchlorostibonium salts [Ar₃SbCl][B(C₆F₅)₄] (Ar = Ph, 3-FC₆H₄, 4-FC₆H₄, 3,5-F₂C₆H₃, 2,4,6-F₃C₆H₂) are reported. The cation in each adopts a tetrahedral coordination environment of antimony, with near complete separation from the anion. Structural, computational, and reactivity studies reveal that the Lewis acidity of [Ar₃SbCl]⁺ generally increases with increased fluorination of the Ar substituents, with a secondary quenching effect from para fluorination. [Ar₃SbCl]⁺ is reduced to Ar₃Sb in the presence of Et₃SiH, and the mechanism of this reaction has been modeled computationally. Preliminary studies demonstrate that they are useful catalysts for the dimerization of 1,1-diphenylethylene and the Friedel-Crafts alkylation of benzene.

An easy-to-perform evaluation of steric properties of Lewis acids

Steric and electronic effects play a very important role in chemistry, as these effects influence the shape and reactivity of molecules. Herein, an easy-to-perform approach to assess and quantify steric properties of Lewis acids with differently substituted Lewis acidic centers is reported. This model applies the concept of the percent buried volume (%V _Bur) to fluoride adducts of Lewis acids, as many fluoride adducts are crystallographically characterized and are frequently calculated to judge fluoride ion affinities (FIAs). Thus, data such as cartesian coordinates are often easily available. A list of 240 Lewis acids together with topographic steric maps and cartesian coordinates of an oriented molecule suitable for the SambVca 2.1 web application is provided, together with different FIA values taken from the literature. Diagrams of %V _Bur as a scale for steric demand vs. FIA as a scale for Lewis acidity provide valuable information about stereo-electronic properties of Lewis acids and an excellent evaluation of steric and electronic features of the Lewis acid under consideration. Furthermore, a novel LAB-Rep model (Lewis acid/base repulsion model) is introduced, which judges steric repulsion in Lewis acid/base pairs and helps to predict if an arbitrary pair of Lewis acid and Lewis base can form an adduct with respect to their steric properties. The reliability of this model was evaluated in four selected case studies, which demonstrate the versatility of this model. For this purpose, a user-friendly Excel spreadsheet was developed and is provided in the ESI, which works with listed buried volumes of Lewis acids %V _{Bur_LA} and of Lewis bases %V _{Bur_LB}, and no results from experimental crystal structures or quantum chemical calculations are necessary to evaluate steric repulsion in these Lewis acid/base pairs.

Utilization of a Tris(carbene)borate Ligand for Umpolung Reactivity of a Nucleophilic Tin(II) Cation Salt

We show that a tris(carbene)borate (TCB) ligand, namely [PhB(^tBuIm)₃]^- ([PhB(^tBuIm)₃]^- = phenyltris(3-tert-butylimidazol-2-ylidene)borato), is capable of stabilizing an unprecedented nucleophilic Sn(II) cation salt. Unlike known Sn(II) cations, the strong electron-donating ability of [PhB(^tBuIm)₃]^- makes the cationic tin atom electron-rich, σ-donating yet slightly π-accepting, which allows for the ensuing facile oxidation with o-chloranil and S₈ as well as coordination with coinage metals. The former oxidations give the Sn(IV) cation salts, while the latter reactions produce the metal complexes. The electronic structures of these species are thoroughly probed by quantum chemical computations. These results uncover an added role for TCB ligands in isolating unprecedented p-block species.

A germanimidoyl chloride: synthesis, characterization and reactivity

The first germanimidoyl chloride M^sFluind^tBu-Ge(Cl)NMes (2, where M^sFluind^tBu is a bulky hydrindacene skeleton) was synthesized through the reaction of M^sFluind^tBu-GeCl (1) and mesityl azide (MesN₃). In contrast, treatment of 1 with a less bulky azide ArN₃ (Ar = 4-^tBuC₆H₄) produced a germatetrazole chloride M^sFluind^tBu-Ge(Cl)N₄Ar₂ (3), and a salt [M^sFluind^tBu-GeN₄Ar₂]⁺[BAr^F₄]^- (4; Ar^F = 3,5-(CF₃)₂C₆H₃) followed by chloride abstraction with NaBAr^F₄, both bearing a five-membered GeN₄ ring. Functionalization of 2 with Ar'Li (Ar' = 3,5-^tBu₂C₆H₃) or MeLi furnished a germanimine M^sFluind^tBu-Ge(Ar')NMes (5) or an amide lithium salt M^sFluind^tBu-Ge(Me)₂-N(Mes)Li(thf) (6).

How long are Ga⇆Ga double bonds and Ga-Ga single bonds in dicationic gallium dimers?

Syntheses and characterization of two salts [(L)GaGa(L)][pf]₂ ([pf]^- = [Al(OR^F)₄]^-; R^F = C(CF₃)₃) are reported. They include the first dicationic digallene [(L)Ga⇆Ga(L)]²⁺ (L = CDP^Ph = C(PPh₃)₂) and a digallane [(L)Ga-Ga(L)]²⁺ (L = [NacNac^Mes]^-). The CDP^Ph-supported digallene dication includes a trans-bent [L-GaGa-L]²⁺ bond that is analogous to neutral R-GaGa-R molecules and related to Robinson's famous "Digallyne" [R-GaGa-R]^2-. The dicationic digallane [(L)Ga-Ga(L)]²⁺ is analogous to the widely used "Jones magnesium dimer", but includes a very short Ga^II-Ga^II single bond.

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.

Experimental and Computational Studies of Ruthenium Complexes Bearing Z-Acceptor Aluminum-Based Phosphine Pincer Ligands

Reaction of [Ru(C₆H₄PPh₂)₂(Ph₂PC₆H₄AlMe(THF))H] with CO results in clean conversion to the Ru-Al heterobimetallic complex [Ru(AlMePhos)(CO)₃] (1), where AlMePhos is the novel P-Al(Me)-P pincer ligand (o-Ph₂PC₆H₄)₂AlMe. Under photolytic conditions, 1 reacts with H₂ to give [Ru(AlMePhos)(CO)₂(μ-H)H] (2) that is characterized by multinuclear NMR and IR spectroscopies. DFT calculations indicate that 2 features one terminal and one bridging hydride that are respectively anti and syn to the AlMe group. Calculations also define a mechanism for H₂ addition to 1 and predict facile hydride exchange in 2 that is also observed experimentally. Reaction of 1 with B(C₆F₅)₃ results in Me abstraction to form the ion pair [Ru(AlPhos)(CO)₃][MeB(C₆F₅)₃] (4) featuring a cationic [(o-Ph₂PC₆H₄)₂Al]⁺ ligand, [AlPhos]⁺. The Ru-Al distance in 4 (2.5334(16) Å) is significantly shorter than that in 1 (2.6578(6) Å), consistent with an enhanced Lewis acidity of the [AlPhos]⁺ ligand. This is corroborated by a blue shift in both the observed and computed ν_CO stretching frequencies upon Me abstraction. Electronic structure analyses (QTAIM and EDA-ETS) comparing 1, 4, and the previously reported [Ru(ZnPhos)(CO)₃] analogue (ZnPhos = (o-Ph₂PC₆H₄)₂Zn) indicate that the Lewis acidity of these pincer ligands increases along the series ZnPhos < AlMePhos < [AlPhos]⁺.

One-step Oxidative Monofluorination of Electron-Deficient Sulfoxides to Access Highly Lewis Acidic Sulfur(VI) Cations

The strongly oxidizing, powerful electrophilic fluorination reagent [FXe][OTf] is shown to effect direct oxidative monofluorination of sulfoxides. This one-step, chloride promoter-free methodology provides access to so far inaccessible, yet highly desirable strongly Lewis acidic fluorosulfoxonium cations from electron-deficient and/or sterically demanding sulfoxides that are shown to be practically unreactive towards the previously reported XeF₂ /NEt₄ Cl system. Experimental and density functional theory studies have been conducted to assess the Lewis acidities of the prepared sulfur(VI) cations. Preliminary results obtained with chiral sulfoxides provide early insights into the mechanism of these fluorination reactions.

Oxidative Fluorination of Selenium and Tellurium Compounds using a Thermally Stable Phosphonium SF5 - Salt Accessible from SF6

Fluorinated group 16 moieties are attractive building blocks in synthetic chemistry but only few synthetic methods are available to prepare them. Herein, we report a new oxidative fluorination reagent capable of stabilizing reactive fluorinated anions. It consists of an SF5 - anion and a chemically inert phosphonium cation and is exceptionally thermally stable. Accordingly, it was used to generate the SeF5 - and TeF5 - anions from the elemental chalcogens and to prepare the unknown tetrafluoro(phenyl)-λ5 -selenate PhSeF4 - and -tellurate PhTeF4 - from the corresponding diphenyl dichalcogenides. In addition, we show that further derivatization of [PhTeF4 ]- by oxidation to trans-PhTeF4 O- and subsequent alkylation gives access to a new class of trans-(alkoxy)(phenyl)tetrafluoro-λ6 -tellanes (trans-PhTeF4 OR), thus providing an approach to introduce the functional group into organic molecules.

Small molecule activation with bimetallic systems: a landscape of cooperative reactivity

There is growing interest in the design of bimetallic cooperative complexes, which have emerged due to their potential for bond activation and catalysis, a feature widely exploited by nature in metalloenzymes, and also in the field of heterogeneous catalysis. Herein, we discuss the widespread opportunities derived from combining two metals in close proximity, ranging from systems containing multiple M-M bonds to others in which bimetallic cooperation occurs even in the absence of M⋯M interactions. The choice of metal pairs is crucial for the reactivity of the resulting complexes. In this context, we describe the prospects of combining not only transition metals but also those of the main group series, which offer additional avenues for cooperative pathways and reaction discovery. Emphasis is given to mechanisms by which bond activation occurs across bimetallic structures, which is ascribed to the precise synergy between the two metal atoms. The results discussed herein indicate a future landscape full of possibilities within our reach, where we anticipate that bimetallic synergism will have an important impact in the design of more efficient catalytic processes and the discovery of new catalytic transformations.

Crystallographic evidence for a continuum and reversal of roles in primary-secondary interactions in antimony Lewis acids: applications in carbonyl activation

Primary and secondary interactions form the basis of substrate activation in Lewis-acid mediated catalysis, with most substrate activations occurring at the secondary binding site. We explore two series of antimony cations, [(NMe₂CH₂C₆H₄)(mesityl)Sb]⁺ (A) and [(NMe₂C₆H₄)(mesityl)Sb]⁺ (B), by coordinating ligands with varying nucleophilicity at the position trans to the N-donor. The decreased nucleophilicity of the incoming ligands leads to reversal from a primary bond to a secondary interaction in A, whereas a constrained N-coordination in B diminishes the border between primary and secondary bonding. Investigations on carbonyl olefin metathesis reactions and carbonyl reduction demonstrate increased reactivity of a Lewis acid when the substrate activation occurs at the primary binding site.

An Iridium-Stabilized Borenium Intermediate

Exploration of new organometallic systems based on polyhedral boron clusters has the potential to solve challenging chemical problems such as the stabilization of reactive intermediates and transition-state-like species postulated for E-H (E = H, B, C, Si) bond activation reactions. We report on facile and clean B-H activation of a hydroborane by a new iridium boron cluster complex. The product of this reaction is an unprecedented and fully characterized transition metal-stabilized boron cation or borenium. Moreover, this intermediate bears an unusual intramolecular B···H interaction between the hydrogen originating from the activated hydroborane and the cyclometallated metal-bonded boron atom of the boron cluster. This B···H interaction is proposed to be an arrested insertion of hydrogen into the B_cage-metal bond and the initiation step for iridium "cage-walking" around the upper surface of the boron cluster. The "cage-walking" process is supported by the hydrogen-deuterium exchange observed at the boron cluster, and a mechanism is proposed on the basis of theoretical methods with a special focus on the role of noncovalent interactions. All new compounds were isolated and fully characterized by NMR spectroscopy and elemental analysis. Key compounds were studied by single crystal X-ray diffraction and X-ray photoelectron spectroscopy.

Direct Comparison of Subvalent, Polycationic Group 13 Cluster Compounds: Lessons learned on Isoelectronic DMPE Substituted Gallium and Indium Tetracation Salts

The tetracationic, univalent cluster compounds [{M(dmpe)}4 ]4+ (M=Ga, In; dmpe=bis(dimethylphosphino)ethane) were synthesized as their pf salts ([pf]- =[Al(ORF )4 ]- ; RF =C(CF3 )3 ). The four-membered ring in [{M(dmpe)}4 ]4+ is slightly puckered for M=Ga and almost square planar for M=In. Yet, although structurally similar, only the gallium cluster is prevalent in solution, while the indium cluster forms temperature dependent equilibria that include even the monomeric cation [In(dmpe)]+ . This system is the first report of one and the same ligand inducing formation of isoelectronic and isostructural gallium/indium cluster cations. The system allows to study systematically analogies and differences with thermodynamic considerations and bonding analyses, but also to outline perspectives for bond activation using cationic, subvalent group 13 clusters.