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Homopolyatomic cations of the main group elements and of the element sulfur, in particular, are used as tutorial examples to teach structure and bonding in inorganic chemistry. So far, the cations [S4]2+, [S8]2+, [S19]2+, [S5]•+, and [S8]•+ are known experimentally. In this report, the generation and crystal structure determination of the salt Na2[S20]2[B12Cl12]3, containing the new homopolyatomic sulfur cation [S20]2+, is reported. The structure of the latter cation consists of two seven-membered homocycles, which are bridged by a six-membered sulfur chain. This structure is strongly related to that of [S19]2+. The heptasulfur rings show pronounced bond alternation. Comparison with the experimental structures of [S7X]+ (X = I, Br) and the application of quantum chemical calculations show unambiguously that the observed structural features are intrinsic properties of the cationic cyclo-heptasulfur moieties. The latter can occupy different conformations, which only slightly differ in energy. Charge delocalization and negative hyperconjugation contribute to the stability of the observed structures. The discovery of the [S20]2+ cation fits well into range of known homopolyatomic sulfur cations, which can be classified by their averaged oxidation state of sulfur. [ABSTRACT FROM AUTHOR]

Tris(3,5‐dimethylpyrazolyl)borate aluminum dihalides TpMe2AlX2 (X=Cl, Br and I) can be potential precursors for preparing highly electrophilic dications as well as low oxidation state aluminum compounds. However, the coordinative unsaturation in TpMe2AlX2 makes them susceptible to rearrangement to [Tp2Al][AlX4]. In this work, we revisited the synthesis of TpMe2AlX2 by isolating the solvent‐stabilized tris(3,5‐dimethylpyrazolyl)borate aluminum dihalides TpMe2AlX2(L) (X=Cl, Br; L=THF, HPMA). Efforts to isolate TpMe2All2 resulted in the ring opening of THF revealing the mediation of a highly reactive cationic aluminum species. The monocationic, [TpMe2AlCl(THF)2][B{C6H3(CF3)2}4] was prepared from TpMe2AlCl2(THF) via silver salt metathesis. Attempts to prepare the dicationic species [TpMe2Al(THF)3]2+ resulted in the instantaneous ring‐opening polymerization of THF. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Partial ligand substitution at the iron pentacarbonyl radical cation generates novel half‐sandwich complexes of the type [Fe(η6‐arene)(CO)2]⋅+ (arene=1,3,5‐tri‐tert‐butylbenzene, 1,3,5‐trimethylbenzene, benzene and fluorobenzene). Of those, the bulkier 1,3,5‐tri‐tert‐butylbenzene (mes*) derivative [Fe(mes*)(CO)2]⋅+ was fully characterized by XRD analysis, IR, NMR, cw‐EPR, Mössbauer spectroscopy and cyclic voltammetry as the [Al(ORF)4]− (RF=C(CF3)3) salt. Chemical electronation, i. e. the single electron reduction, with decamethylferrocene generates neutral [Fe(mes*)(CO)2], whereas further deelectronation under CO‐pressure leads to a dicationic three‐legged [Fe(mes*)(CO)3]2+ salt with [Al(ORF)4]− counterion. The full substitution of the carbonyl ligands in [Fe(CO)5]⋅+[Al(ORF)4]− mainly resulted in disproportionation reactions, giving solid Fe(0) and the dicationic bis‐arene salts [Fe(η6‐arene)2]2+([Al(ORF)4]−)2 (arene=1,3,5‐trimethylbenzene, benzene and fluorobenzene). Only by employing the very large fluoride bridged anion [F‐{Al(ORF)3}2]−, it was possible to isolate an open shell bis‐arene cation salt [Fe(C6H6)2]⋅+[F‐{Al(ORF)3}2]−. The highly reactive cation was characterized by XRD analysis, cw‐EPR, Mössbauer spectroscopy and cyclic voltammetry. The disproportionation of [Fe(C6H6)2]⋅+ salts to give solid Fe(0) and [Fe(C6H6)2]2+ salts was analyzed by a suitable cycle, revealing that the thermodynamic driving force for the disproportionation is a function of the size of the anion used and the polarity of the solvent. [ABSTRACT FROM AUTHOR]

Although the discovery of the GaI complex salt [Ga(PhF)2‐3][Al(ORF)4] (RF=C(CF3)3, PhF=C6H5F) invoked the preparation of a diverse library of cationic Ga(I) coordination complexes and clusters, studies on small molecule activation with low‐valent GaI cations are scarce. Herein, a first experimental study on the reactivity of a monomeric Ga(I) cation activated with a pyridine–diimine pincer ligand (in [Ga(PDIdipp)][Al(ORF)4]) towards small‐molecules is reported. First controlled oxidative additions of the GaI cation into C−Cl, H−P and P−P bonds are presented. Moreover, the [4+1]cycloaddition to butadienes was achieved. Intriguingly, the isolated, blue insertion product into the P−P bond of P4 allows for the quantitative release of the P4 molecule upon reaction with AlEt3 and butadienes. Reversible P4 insertion of main‐group metals has previously been reported for Ge and Sn, respectively. The experimental study is supported by high‐level computational analysis of the in‐part reversible oxidative additions at the DLPNO‐CCSD(T)/def2‐TZVPP//PBEh‐3c/def2‐mSVP level of theory with COSMO‐RS solvation in 1,2‐difluorobenzene. [ABSTRACT FROM AUTHOR]

Although the discovery of the GaI complex salt [Ga(PhF)2‐3][Al(ORF)4] (RF=C(CF3)3, PhF=C6H5F) invoked the preparation of a diverse library of cationic Ga(I) coordination complexes and clusters, studies on small molecule activation with low‐valent GaI cations are scarce. Herein, a first experimental study on the reactivity of a monomeric Ga(I) cation activated with a pyridine–diimine pincer ligand (in [Ga(PDIdipp)][Al(ORF)4]) towards small‐molecules is reported. First controlled oxidative additions of the GaI cation into C−Cl, H−P and P−P bonds are presented. Moreover, the [4+1]cycloaddition to butadienes was achieved. Intriguingly, the isolated, blue insertion product into the P−P bond of P4 allows for the quantitative release of the P4 molecule upon reaction with AlEt3 and butadienes. Reversible P4 insertion of main‐group metals has previously been reported for Ge and Sn, respectively. The experimental study is supported by high‐level computational analysis of the in‐part reversible oxidative additions at the DLPNO‐CCSD(T)/def2‐TZVPP//PBEh‐3c/def2‐mSVP level of theory with COSMO‐RS solvation in 1,2‐difluorobenzene. [ABSTRACT FROM AUTHOR]

Here we present stable and crystalline chromium(I) tetracarbonyl complexes with pyridyl‐MIC (MIC=mesoionic carbene) ligands and weakly coordinating anions (WCA=[Al(ORF)4]−, RF=C(CF3)3 and BArF=[B(ArF)4]−, ArF=3,5‐(CF3)2C6H3). The complexes were fully characterized via crystallographic, spectroscopic and theoretical methods. The influence of counter anions on the IR and EPR spectroscopic properties of the CrI complexes was investigated, and the electronic innocence versus non‐innocence of WCAs was probed. These are the first examples of stable and crystalline [Cr(CO)4]+ complexes with a chelating π- ${\pi -}$ accepting ligand, and the data presented here are of relevance for both the photochemical and the electrochemical properties of these classes of compounds. [ABSTRACT FROM AUTHOR]

Isolation and characterization of highly reactive intermediates are crucial to understand the nature of chemical reactivity. Accordingly, the reactivity of weakly coordinating anions (WCA), usually used to stabilized cationic super electrophiles are of fundamental interest. When a variety of WCA are known to form stable σ‐complexes with a proton, inducing Brønsted super acidity, bis‐coordinated weak‐coordinated anions are much more elusive and considered as long‐sought reactive species. In this work, the chemistry of borylated sulfate, triflimidate and triflate anions were scouted in details with the aim of synthetizing the unique analogs of protonated Brønsted superacids. Those complexes were formed by successive borylation with a 9‐boratriptycene derived Lewis super acid paired with a weak coordinated anion, characterized in solution and in the solid state and exhibit unique structures and reactivities. [ABSTRACT FROM AUTHOR]

The synthesis of Naumann's AgI/AgIII mixed valence salt [AgI]+[AgIII(CF3)4]− (Ag‐1) is revisited. Ag‐1 is now safely available in half gram scale upon 2e− oxidation of AgF in presence of CF3SiMe3 and ambient air. In addition to its unprecedented crystallographic characterization, the use of Ag‐1 to build the novel AgI/AgIII salts [Ag(bpy)2]‐1, [Ag(18‐crown‐6)2]‐1, [Ag‐crypt‐222]‐1 and [Ag(PCy3)2]‐1 is herein reported, alongside their characterization by NMR, single crystal X‐ray diffraction (Sc‐XRD) and elemental analysis (EA). The utility of the currently affordable Ag‐1 in gold(I) catalysis was demonstrated by the excellent catalytic activity displayed by [{Au(PPh3)}2(μ‐Cl)]‐1 and [Au(PPh3)]‐1 in the 5‐exo‐dig cyclization of N‐propargylbenzamide (2). These cationic AuI catalysts are accessible from (PPh3)AuCl and Ag‐1, and outperform the activity of the well‐known benchmark catalyst (PPh3)AuNTf2. [ABSTRACT FROM AUTHOR]

The synthesis of Naumann's AgI/AgIII mixed valence salt [AgI]+[AgIII(CF3)4]− (Ag‐1) is revisited. Ag‐1 is now safely available in half gram scale upon 2e− oxidation of AgF in presence of CF3SiMe3 and ambient air. In addition to its unprecedented crystallographic characterization, the use of Ag‐1 to build the novel AgI/AgIII salts [Ag(bpy)2]‐1, [Ag(18‐crown‐6)2]‐1, [Ag‐crypt‐222]‐1 and [Ag(PCy3)2]‐1 is herein reported, alongside their characterization by NMR, single crystal X‐ray diffraction (Sc‐XRD) and elemental analysis (EA). The utility of the currently affordable Ag‐1 in gold(I) catalysis was demonstrated by the excellent catalytic activity displayed by [{Au(PPh3)}2(μ‐Cl)]‐1 and [Au(PPh3)]‐1 in the 5‐exo‐dig cyclization of N‐propargylbenzamide (2). These cationic AuI catalysts are accessible from (PPh3)AuCl and Ag‐1, and outperform the activity of the well‐known benchmark catalyst (PPh3)AuNTf2. [ABSTRACT FROM AUTHOR]

Here we present stable and crystalline chromium(I) tetracarbonyl complexes with pyridyl‐MIC (MIC=mesoionic carbene) ligands and weakly coordinating anions (WCA=[Al(ORF)4]−, RF=C(CF3)3 and BArF=[B(ArF)4]−, ArF=3,5‐(CF3)2C6H3). The complexes were fully characterized via crystallographic, spectroscopic and theoretical methods. The influence of counter anions on the IR and EPR spectroscopic properties of the CrI complexes was investigated, and the electronic innocence versus non‐innocence of WCAs was probed. These are the first examples of stable and crystalline [Cr(CO)4]+ complexes with a chelating π- ${\pi -}$ accepting ligand, and the data presented here are of relevance for both the photochemical and the electrochemical properties of these classes of compounds. [ABSTRACT FROM AUTHOR]

Weakly coordinating anions (WCAs) have attracted much attention in recent years due to their ability to stabilise highly reactive cations. It may well be argued, however, that a profound understanding of what truly defines a WCA is still lacking, and systematic studies to unravel counterion effects are scarce. In this work, we investigate a supramolecular pseudorotaxane formation reaction, subject to a selection of anions, ranging from strongly to weakly coordinating, which not only aids in fostering our knowledge about anion coordination properties, but also provides valuable theoretical insight into the nature of the mechanical bond. We employ state-of-the-art DFT-based methods and tools, combined with isothermal calorimetry and 1 H NMR experiments, to compute anion-dependent Gibbs free association energies Δ G a , as well as to evaluate intermolecular interactions. We find correlations between Δ G a and the anions' solvation energies, which are exploited to calculate physico-chemical reaction parameters in the context of coordinating anions. Furthermore, we show that the binding situation within the (pseudo)rotaxanes can be mostly understood by straight-forward electrostatic considerations. However, quantum-chemical effects such as dispersion and charge-transfer interactions become more and more relevant when WCAs are employed. [ABSTRACT FROM AUTHOR]

The coordination chemistry of only Lewis‐base (LB)‐stabilized pnictogenylboranes EH2BH2⋅NMe3 (E=P, As) towards Tl(I) salts has been studied. The reaction of Tl[BArCl] (BArCl=[B(3,5‐C6H3Cl2)4]−) with the corresponding pnictogenylborane results in the formation of [Tl(EH2BH2⋅NMe3)][BArCl] (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 EH2BH2 ⋅ NMe3 in [Tl(EH2BH2 ⋅ NMe3)3][WCA] (2 a: E=P, WCA=TEFCl; 2 b: E=As, WCA=TEF) (TEF=[Al{OC(CF3)3}4]−, TEFCl=[Al{(OC(CF3)2(CCl3)}4]−). Furthermore, by using two equivalents of PH2BH2⋅NMe3, a Tl(I)‐mediated P−P coupling takes place in CH2Cl2 as solvent resulting in [Me3N⋅BH2PH2PHBH2⋅NMe3][WCA] (WCA=TEF, 3 a; BArCl, 3 b; TEFCl, 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. [ABSTRACT FROM AUTHOR]

Weakly coordinating anions (WCAs) are considered promising candidates for application as electrolytes in multivalent post‐lithium batteries. One strong candidate as electrolyte salt for Mg battery application is [Mg(L)x][Al(ORF)4]2 (L=MeCN (acetonitrile), DME (1,2‐dimethoxyethane); x=3, 6; RF=C(CF3)3) that contains [Al(ORF)4]− as one of the least coordinating WCAs known. Here we present a novel synthetic route, for which vibrational, NMR and XRD analyses show the formation of a clean, pristine electrolyte salt without the common contaminants found in published synthetic routes. The electrochemistry of this pristine and pure [Mg(DME)3][Al(ORF)4]2 electrolyte (0.2 m in DME) was investigated via cyclic voltammetry (CV). In contrast to previous publications using impure materials, the CV showed no sign for Mg deposition from the pristine electrolyte for all conditions tested. This also holds when including the additives LiCl, NaCl, MgCl2, Li[BH4] or a mixture of MgCl2/Mg[HMDS]2 (HMDS=hexamethyldisilazide) in THF. Quantum chemical calculations suggested the possibility of anion decomposition at the negative electrode, leading to an electronically insulating MgF2 layer (rutile structure) on all the electrode materials tested. This hypothesis was confirmed by an XPS investigation of electrodes exposed to the electrolytes containing the WCAs [Al(ORF)4]− and [Al(OC(H)(CF3)2)4]− at negative potentials, which only showed the presence of MgF2 for the [Al(ORF)4]− electrolyte, but not for the related [Al(OC(H)(CF3)2)4]− electrolyte (which allowed to deposit magnesium reversibly on the electrode). [ABSTRACT FROM AUTHOR]

The open‐shell iron pentacarbonyl cation [Fe(CO)5].+ was isolated by deelectronation, i.e. the single‐electron oxidation of the parent neutral Fe(CO)5 using [phenazineF].+ as the [Al(ORF)4]− and [F‐{Al(ORF)3}2]− salt (RF=C(CF3)3; phenazineF=perfluoro‐5,10‐bis(perfluorophenyl)‐5,10‐dihydrophenazine). [Fe(CO)5].+[Al(ORF)4]− was fully characterized (scXRD analysis, IR, NMR, EPR, 57Fe spectroscopy, CV and SQUID magnetization study) and, apart from being a compound of fundamental interest, may serve as a precursor for low‐valent iron coordination chemistry. [ABSTRACT FROM AUTHOR]

Herein, we present two different routes for the synthesis of the perfluorinated trityl cation, which allowed the handling of the free, uncoordinated species in organic solvents for the first time. The usage of the weakly coordinating anion [Al(OTeF5)4]− and its derivatives allows the characterization of this species by NMR spectroscopy and most importantly by single‐crystal X‐ray diffraction. The high hydride ion affinity of the cation is shown by hydrogen abstraction from isobutane. Furthermore, cyclic voltammetry reveals its oxidative potential which is supported by the reaction with tris(4‐bromophenyl)amine, giving rise to the formation of the ammoniumyl radical cation, also known as "magic blue". [ABSTRACT FROM AUTHOR]

The CuI salts [Cu(CH3CN)4]PF and [Cu(oDFB)2]PF with the very weakly coordinating anion Al(OC(CF3)3)4− (PF) as well as [Cu(NEt3)2]PF comprising the unique, linear bis‐triethylamine complex [Cu(NEt3)2]+ were synthesized and examined as catalysts for the conversion of monophenols to o‐quinones. The activities of these CuI salts towards monooxygenation of 2,4‐di‐tert‐butylphenol (DTBP‐H) were compared to those of [Cu(CH3CN)4]X salts with "classic" anions (BF4−, OTf−, PF6−), revealing an anion effect on the activity of the catalyst and a ligand effect on the reaction rate. The reaction is drastically accelerated by employing CuII‐semiquinone complexes as catalysts, indicating that formation of a CuII complex precedes the actual catalytic cycle. This result and other experimental observations show that with these systems the oxygenation of monophenols does not follow a dinuclear, but a mononuclear pathway analogous to that of topaquinone cofactor biosynthesis in amine oxidase. [ABSTRACT FROM AUTHOR]

In this Concept article we provide a brief overview of the design and preparation of N‐heterocyclic carbenes carrying weakly coordinating anions (WCA‐NHCs). The anionic charge in these ligand systems is located on an exocyclic group, for example, B(C6F5)3, tethered to the backbone of the imidazole ring, thus resembling a weakly coordinating moiety. With the general guiding principle behind the application of WCA‐NHCs being the conversion of otherwise cationic NHC complexes into their overall neutral congeners, numerous transition metal as well as main group element complexes were isolated during the last decade, which are summarized herein. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of the bis(η6‐benzene)lithium cation, the benzene metallocene of the lightest metal, is reported. The boron compound FmesBCl2 [Fmes: 2,4,6‐tris(trifluoromethyl)phenyl] reacted with three molar equivalents of the lithio‐acetylene reagent Li‐C≡C‐Fmxyl [Fmxyl: 3,5‐bis(trifluoromethyl)phenyl]. Subsequent crystallization from benzene gave the [bis(η6‐benzene)Li]+ cation with the [{FmesB(‐C≡C‐Fmxyl)3}2Li]− anion. This parent [(arene)2Li]+ cation shows an eclipsed arrangement of the pair of benzene ligands at the central lithium cation with uniform carbon‐lithium bond lengths. The corresponding [(η6‐toluene)2Li]+ and [(η6‐durene)2Li]+ containing salts were similarly prepared. The bis(arene)lithium cations were characterized by X‐ray diffraction, by solid‐state 7Li MAS NMR spectroscopy and their bonding features were analyzed by DFT calculations. [ABSTRACT FROM AUTHOR]

We report on a room temperature (RT) sodium‐sulfur (Na−S) battery based on a sodium anode, a sulfurated poly(acrylonitrile) (SPAN) cathode and an electrolyte containing sodium tetrakis(hexafluoroisopropyloxy) borate (Na[B(hfip)4]; hfip=hexafluoroisopropoxide) in a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC) and fluoroethylene carbonate (FEC). The hfip anion as a weakly coordinating anion (WCA) provides high anodic stability, high ionic conductivity, and superior electrochemical performance in carbonate‐based solvents. The Na‐SPAN cell exhibits an initial discharge capacity of 1360 mAhgs-1 and a remarkable reversible capacity of 1072 mAhgs-1 after 1000 cycles at 3 C (C=C‐rate, 5.025 Ags-1) with an insignificant average capacity decay of less than 0.021 % per cycle. A careful choice of the discharge cut‐off potential (DCP) reveals that a DCP of 0.2 V allows for stable cycling for more than 500 cycles while a DCP of 0.5 V results in a constant capacity decay. The excellent cycle stability at a DCP of 0.2 V is likely to be caused by the high conversion of the SPAN‐bound sulfur into Na2S. [ABSTRACT FROM AUTHOR]

We synthesized new imidazolium‐based tunable aryl alkyl ionic liquids (TAAILs) with the weakly coordinating tetrakis(pentafluoroethyl)gallate anion, [Ga(C2F5)4]−. Phenyl and phenyl derivatives (2‐Me, 4‐OMe, 2,4‐F) were combined with varying alkyl chain lengths at the imidazolium core leading to TAAILs, which were investigated with regard to their viscosity, conductivity, and electrochemical window and compared to EMIM and BMIM standard cations. Remarkable low viscosities of 29 cP at 25 °C for [BMIM][Ga(C2F5)4] were achieved. However, the EMIM and BMIM gallates show electrochemical instability, releasing pentafluoroethane at a voltage of 1.5 V. The 2‐Me‐substituted gallate‐TAAILs slowly decompose over several weeks, whereas all other gallate‐TAAILs showed no decomposition at all. With electrochemical windows of up to 5.15 V and low viscosities in a range of 66–162 cP, the gallate‐TAAILs are promising candidates as electrolytes in electrochemical applications. [ABSTRACT FROM AUTHOR]

The reactions of the cyclo‐As5 complex [Cp*Fe(η5‐As5)] (B) with the AgI and CuI salts of the weakly coordinating anion (WCA) [FAl{OC6F10(C6F5)}3]− ([FAl]−) are studied. These reactions allow the synthesis of the mononuclear complexes [M(η5 : η2‐B)2][FAl] (M=Ag (1), Cu (2)) when a ratio of B/M(FAl) 2 : 1 is used. Compound 1 shows an unusual disorder of the central AgI cation between two π‐coordinating cyclo‐As5 ligands, which is absent in 2 pointing to a weak interaction of the Ag center towards the cyclo‐As5 ligands in B. When the ratio of B/Ag(FAl) is changed to 3 : 1 or 1 : 1, the respective coordination compounds [Ag(η2‐B)3][FAl] (3) and [Ag2(η2 : η2‐B)2][FAl]2 (4) are accessible. The coordination modes of the cyclo‐As5 units in 1, 3 and 4 are all different, reflecting the adaptive coordination behavior of B towards AgI ions. The optimized geometries in the gas phase of 1–4 are determined by DFT calculations to support the bonding situation observed in their solid‐state structures. [ABSTRACT FROM AUTHOR]

130 years after Mond discovered the first homoleptic carbonyl complex Ni(CO)4, we report on a [Ni(CO)4].+ salt as the first synthesis of any homoleptic nickel carbonyl cation in the condensed phase. It was prepared by oxidation of nickel metal with the synergistic oxidant Ag[F{Al(ORF)3}2]/0.5 I2 (RF=C(CF3)3) in CO atmosphere. This D2d‐symmetric metalloradical represents the last missing entry among the structurally characterized homoleptic carbonyl cations of Groups 6 to 11. Additionally, the nickel tricarbonyl‐nitrosyl cation [Ni(CO)3(NO)]+ was obtained by usage of NO[F{Al(ORF)3}2] and all products were fully characterized by means of IR, Raman, NMR/EPR, single crystal and powder XRD. [ABSTRACT FROM AUTHOR]

A facile synthesis and isolation of pristine silicon tetrakis(trifluoromethanesulfonate), Si(OTf)4, is reported, acting as the first neutral silicon‐based Lewis superacid suitable towards soft and hard Lewis bases. Its OTf groups have a dual function: they are excellent leaving groups and modulate the degree of reactivity towards soft and hard Lewis bases. Exposed to soft Lewis donors, Si(OTf)4 leads to [L2Si(OTf)4] complexes (L=isocyanide, thioether and carbonyl compounds) with retention of all Si−OTf bonds. In contrast, it can cleave C−X bonds (X=F, Cl) of hard organic Lewis bases with a high tendency to form SiX4 (X=F, Cl) after halide/triflate exchange. Most notable, Si(OTf)4 allows a gentle oxydefluorination of mono‐ and bis(trifluoromethyl)benzenes, resulting in the formation of the corresponding benzoylium species, which are stabilized by the weakly coordinating [Si(OTf)6] dianion. [ABSTRACT FROM AUTHOR]

Fluoride abstraction from different types of transition metal fluoride complexes [LnMF] (M=Ti, Ni, Cu) by the Lewis acid tris(pentafluoroethyl)difluorophosphorane (C2F5)3PF2 to yield cationic transition metal complexes with the tris(pentafluoroethyl)trifluorophosphate counterion (FAP anion, [(C2F5)3PF3]−) is reported. (C2F5)3PF2 reacted with trans‐[Ni(iPr2Im)2(ArF)F] (iPr2Im=1,3‐diisopropylimidazolin‐2‐ylidene; ArF=C6F5, 1 a; 4‐CF3‐C6F4, 1 b; 4‐C6F5‐C6F4, 1 c) through fluoride transfer to form the complex salts trans‐[Ni(iPr2Im)2(solv)(ArF)]FAP (2 a‐c[solv]; solv=Et2O, CH2Cl2, THF) depending on the reaction medium. In the presence of stronger Lewis bases such as carbenes or PPh3, solvent coordination was suppressed and the complexes trans‐[Ni(iPr2Im)2(PPh3)(C6F5)]FAP (trans‐2 a[PPh3]) and cis‐[Ni(iPr2Im)2(Dipp2Im)(C6F5)]FAP (cis‐2 a[Dipp2Im]) (Dipp2Im=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) were isolated. Fluoride abstraction from [(Dipp2Im)CuF] (3) in CH2Cl2 or 1,2‐difluorobenzene led to the isolation of [{(Dipp2Im)Cu}2]2+2 FAP− (4). Subsequent reaction of 4 with PPh3 and different carbenes resulted in the complexes [(Dipp2Im)Cu(LB)]FAP (5 a–e, LB=Lewis base). In the presence of C6Me6, fluoride transfer afforded [(Dipp2Im)Cu(C6Me6)]FAP (5 f), which serves as a source of [(Dipp2Im)Cu)]+. Fluoride abstraction of [Cp2TiF2] (7) resulted in the formation of dinuclear [FCp2Ti(μ‐F)TiCp2F]FAP (8) (Cp=η5‐C5H5) with one terminal fluoride ligand at each titanium atom and an additional bridging fluoride ligand. [ABSTRACT FROM AUTHOR]

The hydride‐bridged silylium cation [Et3Si−H−SiEt3]+, stabilized by the weakly coordinating [Me3NB12Cl11]− anion, undergoes, in the presence of excess silane, a series of unexpected consecutive reactions with the valence‐isoelectronic molecules CS2 and CO2. The final products of the reaction with CS2 are methane and the previously unknown [(Et3Si)3S]+ cation. To gain insight into the entire reaction cascade, numerous experiments with varying conditions were performed, intermediate products were intercepted, and their structures were determined by X‐ray crystallography. Besides the [(Et3Si)3S]+ cation as the final product, crystal structures of [(Et3Si)2SMe]+, [Et3SiS(H)Me]+, and [Et3SiOC(H)OSiEt3]+ were obtained. Experimental results combined with supporting quantum‐chemical calculations in the gas phase and solution allow a detailed understanding of the reaction cascade. [ABSTRACT FROM AUTHOR]

Carbocations have played a central role in the chemical sciences for over a century. In a synthetic setting, most methods utilize stabilized tricoordinate carbocations, while there are far fewer examples of reactions featuring nonstabilized dicoordinate cations. Here, we provide an overview of recent developments in the generation of high-energy carbocations mediated by weakly coordinating anions and the C–H insertion reactions of such carbocations. Moreover, we discuss mechanistic studies of these catalytic C–H insertion reactions aimed at furthering our understanding of the reactive nature of these rarely invoked cationic intermediates. 1 Introduction 2 Background: Phenyl Carbocations 3 Silylium/Carborane-Catalyzed C–H Insertion Reactions of Phenyl Carbocations 4 Silane-Fueled, Weakly Coordinating Anion-Catalyzed, Reductive C–H Insertion Reactions of Vinyl Carbocations 5 C–H Insertion Reactivity of Vinyl Carbocations under Basic Conditions 6 Conclusion and Outlook [ABSTRACT FROM AUTHOR]

The reaction of the organometallic diarsene complex [Cp2Mo2(CO)4(μ,η2‐As2)] (B) (Cp = C5H5) with Ag[FAl{OC6F10(C6F5)}3] (Ag[FAl]) and Ag[Al{OC(CF3)3}4] (Ag[TEF]), respectively, yields three unprecedented supramolecular assemblies [(η2‐B)4Ag2][FAl]2 (4), [(μ,η1:η2‐B)3(η2‐B)2Ag3][TEF]3 (5) and [(μ,η1:η2‐B)4Ag3][TEF]3 (6). These products are only composed of the complexes B and AgI. Moreover, compounds 5 and 6 are the only supramolecular assemblies featuring B as a linking unit, and the first examples of [AgI]3 units stabilized by organometallic bichelating ligands. According to DFT calculations, complex B coordinates to metal centers through both the As lone pair and the As−As σ‐bond thus showing this unique feature of this diarsene ligand. [ABSTRACT FROM AUTHOR]

While perfluorinated aryl, aryloxy and alkoxy aluminum species are well‐established as weakly coordinating anions (WCAs), corresponding perfluoroalkyl aluminum derivatives are virtually unknown. Reaction of Si(C2F5)3CH3 with Li[AlH4] afforded the tetrakis(pentafluoroethyl)aluminate, [Al(C2F5)4]−. Several salts of the [Al(C2F5)4]− ion were synthesized and characterized by NMR spectroscopic methods, mass spectrometry, X‐ray diffraction studies and elemental analysis. [ABSTRACT FROM AUTHOR]

Salts of the tetrakis(pentafluoroethyl)aluminate anion [Al(C2F5)4]− were obtained from AlCl3 and LiC2F5. They were isolated with different counter‐cations and characterized by NMR and vibrational spectroscopy and mass spectrometry. Degradation of the [Al(C2F5)4]− ion was found to proceed via 1,2‐fluorine shifts and stepwise loss of CF(CF3) under formation of [(C2F5)4−nAlFn]− (n=1–4) as assessed by NMR spectroscopy and mass spectrometry and supported by results of DFT calculations. In addition, the [(C2F5)AlF3]− ion was structurally characterized. [ABSTRACT FROM AUTHOR]

A series of neutral iridium(I) complexes of the general type [(WCA−NHC)]IrL(COD)] (COD=1,5‐cyclooctadiene; L=phosphine, pyridine), bearing anionic N‐heterocyclic carbenes (WCA−NHC) with a weakly coordinating anionic (WCA) borate moiety, were prepared by addition of phosphines and pyridine to [(WCA−NHC)]Ir(COD)], in which the available coordination site is stabilized by intramolecular metal‐arene interaction (π‐face donation). The solvent and substrate scope of the neutral complexes as catalysts for H/D exchange was investigated, revealing their suitability for promoting efficient deuteration in nonpolar solvents such as cyclohexane. [ABSTRACT FROM AUTHOR]

An unprecedented cationic supramolecule [(Cp′′Fe(η5‐P5))12{CuNCMe}8]8+ 2.66 nm in diameter was selectively isolated as a salt of the weakly coordinating anion [Al{OC(CF3)3}4]− for the first time and characterized by X‐ray structure analysis, PXRD, NMR spectroscopy, and mass spectrometry. Its metal‐deficient core contains the lowest possible number of Cu atoms to connect 12 pentaphosphaferrocene units, providing a supramolecule with fullerene topology which, topologically, also represents the simplest homologue in the family of metal‐deficient pentaphosphaferrocene‐based supramolecules [{CpRFe(η5‐P5)}12(CuX)20−n]. The 12 vacant metal sites between the cyclo‐P5 rings, the largest number attained to date, make this compound a facile precursor for potential inner and outer modifications of the core as well as for functionalization via the substitution of labile acetonitrile ligands. [ABSTRACT FROM AUTHOR]

The perfluorinated dihydrophenazine derivative (perfluoro‐5,10‐bis(perfluorophenyl)‐5,10‐dihydrophenazine) ("phenazineF") can be easily transformed to a stable and weighable radical cation salt by deelectronation (i.e. oxidation) with Ag[Al(ORF)4]/ Br2 mixtures (RF=C(CF3)3). As an innocent deelectronator it has a strong and fully reversible half‐wave potential versus Fc+/Fc in the coordinating solvent MeCN (E°′=1.21 V), but also in almost non‐coordinating oDFB (=1,2‐F2C6H4; E°′=1.29 V). It allows for the deelectronation of [FeIIICp*2]+ to [FeIV(CO)Cp*2]2+ and [FeIV(CN‐tBu)Cp*2]2+ in common laboratory solvents and is compatible with good σ‐donor ligands, such as L=trispyrazolylmethane, to generate novel [M(L)x]n+ complex salts from the respective elemental metals. [ABSTRACT FROM AUTHOR]

Acid remarks: The anhydrous diprotic boron acids H(2)(B(12)X(12)) (X = Cl, Br; see picture, B orange, X green) are the first examples of diprotic superacids and may be the strongest acids yet isolated. Both protons protonate benzene to give benzenium ion salts that are stable at room temperature. These acids owe their existence to the stability of the icosahedral B(12) cluster with its dinegative charge buried beneath a layer of halide substituents.

Acid remarks: The anhydrous diprotic boron acids H(2)(B(12)X(12)) (X = Cl, Br; see picture, B orange, X green) are the first examples of diprotic superacids and may be the strongest acids yet isolated. Both protons protonate benzene to give benzenium ion salts that are stable at room temperature. These acids owe their existence to the stability of the icosahedral B(12) cluster with its dinegative charge buried beneath a layer of halide substituents.

The reaction of the Ga+ source [Ga(PhF)2]+[Al(ORF)4]− with the neutral σ‐donor ligand dmap (4‐Me2N‐C6H4N) produces the unexpectedly large and fivefold positively charged cluster cation salt [Ga5(dmap)10]5+([Al(ORF)4]−)5. It includes a regular and planar Ga5 pentagon with strong metal–metal bonding. Additionally, the compound represents the first salt in which an ionic 1:5 packing is realized. We discuss the nature of this structure which results from the conversion of the non‐bonding 4s2 lone‐pair orbitals into fully Ga‐Ga‐bonding orbitals and the solid‐state arrangement of the ions constituting the lattice as an almost orthohexagonal AX5 lattice, possibly the aristotype of any 5:1 salt. [ABSTRACT FROM AUTHOR]

Cyanoborate chemistry has emerged to an important topic during the last two decades, beginning with two independent reports on the successful synthesis of the tetracyanoborate anion [B(CN)4]– in 2000. A wealth of cyanoborate anions with different substituents in addition to CN group(s) bonded to boron, i.e. hydrogen, halogen, aryl, alkenyl, alkyl, perfluoroalkyl, and alkoxy, have been developed, which enable the tuning of properties of compounds and materials based on them. The readily accessible alkali metal cyanoborates are convenient starting materials for the preparation of cyanoborates with various organic, inorganic, and metal cations as well as cyanoborate coordination compounds. A focus has been on low‐viscosity room temperature cyanoborate‐ionic liquids that are of interest for various applications, especially for electrochemical devices such as dye sensitized solar cells (DSSC) and supercapacitors. Many other potential applications of these novel substances in chemistry and materials science have been studied. Furthermore, cyanoborates are promising starting compounds for the synthesis of other boron species, for example the weakly coordinating tetrakis(trifluoromethyl)borate anion [B(CF3)4]– and the boron‐centered nucleophile B(CN)32–. In this review the syntheses, chemical and physicochemical properties, and selected applications of cyanoborates are presented and discussed. [ABSTRACT FROM AUTHOR]

The reaction of [GaCl3(OEt2)n] with LiC2F5 surprisingly leads to the formation of the anion [Ga(C2F5)3Cl]–. The obtained lithium and tetraphenylphosphonium salts are useful starting materials for new pentafluoroethylgallium compounds. [PPh4][Ga(C2F5)3Cl] was conveniently transformed into [PPh4][Ga(C2F5)3X] (X = F, Br, I) with HF, NaBr, and NaI. Treatment of [Li(OEt2)n][Ga(C2F5)3Cl] with aqueous hydrogen chloride gives rise to the tris(pentafluoroethyl)gallane adduct [Ga(C2F5)3{(OH2)(OEt2)}]. Thermolysis of [Li(OEt2)n][Ga(C2F5)3Cl] affords another tris(pentafluoroethyl)gallane adduct, [Ga(C2F5)3(OEt2)], which can be converted into [Ga(C2F5)3(dmap)] (dmap = 4‐dimethylaminopyridine). [Ga(C2F5)3(OEt2)] as well as [Ga(C2F5)3(dmap)] react with [PPh4]Cl to [PPh4][Ga(C2F5)3Cl] and with HF to [HDMAP][Ga(C2F5)3F]. Both [Ga(C2F5)3(OEt2)] and [Ga(C2F5)3(dmap)] are precursors for the previously reported weakly coordinating anion [Ga(C2F5)4]–. Characterizations of the new compounds were carried out by NMR and IR spectroscopy, mass spectrometry, X‐ray diffraction and elemental analyses. [ABSTRACT FROM AUTHOR]

Salts of the weakly coordinating anions [Ga(OTeF5)4]− as well as [Ga(Et)(OTeF5)3]− and the neutral Ga2(Et)3(OTeF5)3 were synthesized and characterized by spectroscopic methods and single‐crystal X‐ray diffraction. Ga2(Et)3(OTeF5)3 was formed by treating GaEt3 with pentafluoroorthotelluric acid (HOTeF5) and reacted with PPh4Cl and CPh3Cl to [PPh4][Ga(Et)(OTeF5)3] and [CPh3][Ga(Et)(OTeF5)3]. In contrast, Ag[Ga(OTeF5)4] was prepared from AgOTeF5 and GaCl3 and was used as a versatile starting material for further reactions. Starting with Ag[Ga(OTeF5)4] the substrates [PPh4][Ga(OTeF5)4] and [CPh3][Ga(OTeF5)4] were formed from PPh4Cl and CPh3Cl. [ABSTRACT FROM AUTHOR]

Salts of the weakly coordinating anions [Ga(OTeF5)4]− as well as [Ga(Et)(OTeF5)3]− and the neutral Ga2(Et)3(OTeF5)3 were synthesized and characterized by spectroscopic methods and single‐crystal X‐ray diffraction. Ga2(Et)3(OTeF5)3 was formed by treating GaEt3 with pentafluoroorthotelluric acid (HOTeF5) and reacted with PPh4Cl and CPh3Cl to [PPh4][Ga(Et)(OTeF5)3] and [CPh3][Ga(Et)(OTeF5)3]. In contrast, Ag[Ga(OTeF5)4] was prepared from AgOTeF5 and GaCl3 and was used as a versatile starting material for further reactions. Starting with Ag[Ga(OTeF5)4] the substrates [PPh4][Ga(OTeF5)4] and [CPh3][Ga(OTeF5)4] were formed from PPh4Cl and CPh3Cl. [ABSTRACT FROM AUTHOR]

The NiI salt [Ni(cod)2]+[Al(ORF)4]– {RF = C(CF3)3} is the starting material for ligand exchange reactions with arenes (benzene, mesitylene and hexamethylbenzene) yielding cationic and purely organometallic 19 valence electron [Ni(cod)(arene)]+ complex salts. The reactions are accompanied by fast solution color changes from yellow to intensely green. Single crystal X‐ray structure analysis, EPR, UV/Vis and IR‐spectroscopic investigations confirm the formation of [Ni(cod)(C6Me6)][Al(ORF)4] (2) as well as [Ni(cod)(mes)][Al(ORF)4] (3, mes = mesitylene) with η6‐coordinated arenes and bidentate cod ligands. The reaction with benzene is plausible but remains less characterized. The energetics of these reactions were used to evaluate diverse DFT methods. 16 functionals with and without D3(BJ) dispersion correction failed to describe the reaction energetics correctly. However, correcting the basic reaction energies with a CCSD(T)/TZ→QZ approach and using further isodesmic reactions with inclusion of COSMO‐RS solvation gave reaction energetics in best agreement with all experimental observations. [ABSTRACT FROM AUTHOR]

Lewis acid promoted activation of inert chemical bonds is central to catalysis. The presence of a highly electrophilic central atom having minimum interactions with anions and solvent molecules is a requisite for a reactive Lewis acid. This requirement for a strong Lewis acid is met with by designing a reactive cation of a heavy element, bismuth, bearing the tridentate trispyrazolylborate ligand. The coordination sphere of the electrophilic bismuth dication is stabilized by very weak interactions with the halogen atoms of the weakly nucleophilic tetrakis(pentafluorophenyl)borate anion, chlorobenzene, and ortho‐dichlorobenzene in the solid state. The high electrophilicity at bismuth is demonstrated by the ability of the dication to efficiently catalyze the addition of Si–H to olefins. [ABSTRACT FROM AUTHOR]

We report the synthesis and structural characterization of a neutral PV Lewis acid, P(OC6F5)5, and salts containing the six‐coordinate anions [P(OC6F5)5F]− and [P(OC6F5)6]−. The latter anion exhibits a rare example of F–πarene interactions in both the solid and the solution phase, which has been quantitatively studied by variable‐temperature (VT) NMR spectroscopy. The Lewis acid strength of P(OC6F5)5 has been assessed through experimental fluoride ion competition experiments and quantum‐chemical calculations of its fluoride ion affinity (FIA) and global electrophilicity index (GEI). Our findings highlight the importance of considering solvent effects in electrophilicity calculations, even when neutral Lewis acids are involved, and show a rare divergence between FIA and GEI trends. The coordinating abilities of the [P(OC6F5)6]− and [P(OC6F5)5F]− anions towards the trityl cation, as a prototypical electrophile, have been assessed. [ABSTRACT FROM AUTHOR]

Weakly coordinating anions (WCAs) are important for academic reasons as well as for technical applications. Tetrakis(pentafluoroethyl)gallate, [Ga(C2F5)4]−, a new WCA, is accessible by treatment of [GaCl3(dmap)] (dmap=4‐dimethylaminopyridine) with LiC2F5. The anion [Ga(C2F5)4]− proved to be reluctant towards deterioration by aqueous hydrochloric acid or lithium hydroxide. Various salts of [Ga(C2F5)4]− were synthesized with cations such as [PPh4]+, [CPh3]+, [(O2H5)2(OH2)2]2+, and [Li(dec)2]+ (dec=diethyl carbonate). Thermolysis of [(O2H5)2(OH2)2][Ga(C2F5)4]2 gives rise to a dihydrate of tris(pentafluoroethyl)gallane, [Ga(C2F5)3(OH2)2]. All products were characterized by NMR and IR spectroscopy, mass spectrometry, X‐ray diffraction, and elemental analysis. Furthermore, an outlook for the application of [Li(dec)2][Ga(C2F5)4] as a conducting salt in lithium‐ion batteries is presented. [ABSTRACT FROM AUTHOR]

Weakly coordinating anions (WCAs) are important for academic reasons as well as for technical applications. Tetrakis(pentafluoroethyl)gallate, [Ga(C2F5)4]−, a new WCA, is accessible by treatment of [GaCl3(dmap)] (dmap=4‐dimethylaminopyridine) with LiC2F5. The anion [Ga(C2F5)4]− proved to be reluctant towards deterioration by aqueous hydrochloric acid or lithium hydroxide. Various salts of [Ga(C2F5)4]− were synthesized with cations such as [PPh4]+, [CPh3]+, [(O2H5)2(OH2)2]2+, and [Li(dec)2]+ (dec=diethyl carbonate). Thermolysis of [(O2H5)2(OH2)2][Ga(C2F5)4]2 gives rise to a dihydrate of tris(pentafluoroethyl)gallane, [Ga(C2F5)3(OH2)2]. All products were characterized by NMR and IR spectroscopy, mass spectrometry, X‐ray diffraction, and elemental analysis. Furthermore, an outlook for the application of [Li(dec)2][Ga(C2F5)4] as a conducting salt in lithium‐ion batteries is presented. [ABSTRACT FROM AUTHOR]

The synthesis of mixed arsenic phosphorus cations was investigated on theoretical and experimental grounds by replacing P4 with AsP3 in the known syntheses of [P4NO]+ and [P9]+. Calculations of [AsP3NO]+ and [AsP8]+ showed that 1‐[AsP3NO]+ and 3‐[AsP8]+ should be the most stable isomers. However, 2‐[AsP3NO]+ was prepared by reacting [NO]+[Al(ORF)4]– (RF = C(CF3)3) with AsP3 with a regioselectivity of 45:1. The kinetic control of this reaction was proven by calculation of the complete reaction mechanism. Examination of the formation energetics of the [AsxP4–xNO]+ (x = 0, 1, 4) and [AsxP9‐x]+ (x = 0, 1, 9) cations at the CCSD(T)/complete basis set limit level showed that for [AsxP4–xNO]+ (x = 0, 1, 4), the replacement of phosphorus by arsenic leads to more exergonic formation energetics. For the [AsxP9‐x]+ clusters (x = 0, 1, 9), the reaction to [AsP8]+ is slightly more exergonic compared to the synthesis of [P9]+. The calculation of the reaction to the homopolyatomic arsenic cation [As9]+ suggested that this reaction will at least be very difficult. Attempts to prepare [AsxP9‐x]+ from AsP3 as well as [Asx]+ from gray arsenic led to the formation of [AsP3NO]+, [P4NO]+, [P9]+ and P4 in case of [AsxP9‐x]+ and decomposition products (e.g. novel As(ORF)3) for [Asx]+. [ABSTRACT FROM AUTHOR]

The synthesis of mixed arsenic phosphorus cations was investigated on theoretical and experimental grounds by replacing P4 with AsP3 in the known syntheses of [P4NO]+ and [P9]+. Calculations of [AsP3NO]+ and [AsP8]+ showed that 1‐[AsP3NO]+ and 3‐[AsP8]+ should be the most stable isomers. However, 2‐[AsP3NO]+ was prepared by reacting [NO]+[Al(ORF)4]– (RF = C(CF3)3) with AsP3 with a regioselectivity of 45:1. The kinetic control of this reaction was proven by calculation of the complete reaction mechanism. Examination of the formation energetics of the [AsxP4–xNO]+ (x = 0, 1, 4) and [AsxP9‐x]+ (x = 0, 1, 9) cations at the CCSD(T)/complete basis set limit level showed that for [AsxP4–xNO]+ (x = 0, 1, 4), the replacement of phosphorus by arsenic leads to more exergonic formation energetics. For the [AsxP9‐x]+ clusters (x = 0, 1, 9), the reaction to [AsP8]+ is slightly more exergonic compared to the synthesis of [P9]+. The calculation of the reaction to the homopolyatomic arsenic cation [As9]+ suggested that this reaction will at least be very difficult. Attempts to prepare [AsxP9‐x]+ from AsP3 as well as [Asx]+ from gray arsenic led to the formation of [AsP3NO]+, [P4NO]+, [P9]+ and P4 in case of [AsxP9‐x]+ and decomposition products (e.g. novel As(ORF)3) for [Asx]+. [ABSTRACT FROM AUTHOR]

Abstract In this study we have studied the synthesis, characterization and catalytic activity of phosphinocopper(I) complexes [Cu(PPh 3) 3 (NCCH 3)][B(O 2 C 6 H 4 -4-R) 2 ] (3a : R = H; 3b : R = Me; 3c : R = NO 2) and [Cu(PPh 3) 3 (NCCH 3)][B(O 2 C 6 H 3 -3,5-di- t Bu) 2 ] (3d) containing weakly coordinating arylspiroborate ligands bearing various electronic and sterically defined characteristics. All new compounds have been characterized fully including single crystal X-ray diffraction studies for 3a and 3c and confirm that the arylspiroborate ligands do not coordinate to the copper atoms. Using these new metal complexes as precatalysts in the cyclisation of short chain alkynoic acids gave the corresponding exo -dig cyclic lactones exclusively. Graphical abstract Copper(I) complexes containing phosphine ligands and weakly coordinating arylspiroborate anions derived from substituted catechols have been prepared and examined for their ability to catalyse the cyclisation of alkynoic acids. Image 1 Highlights • Synthesis of novel diboron compounds with substituted catechols. • Phosphinocopper(I) complexes containing weakly coordinating anions. • No evidence of arylspiroborates interacting with copper. • Active precatalysts in the cyclisation of 4-pentynoic acid and 5-hexynoic acid. [ABSTRACT FROM AUTHOR]

Abstract Density Functional Theory (DFT) calculations were employed to study a series of coinage metal-hydrogen associations formulated as [M(Η 2) n ][A] (M = CuI, AgI or AuI, n = 1–5). The [M(Η 2) n ][A] salts utilize both their anions and cations for H 2 storage. The [M(Η 2) n ]+ cations could be stabilized in the solid state by voluminous counter-anions, i.e. the [(H 3 B) (BH 2 NH 2) 5 (NH 2)]-, [B(CNBH 3) 3 ]- and [B 12 H 12 ]- anions. The estimated bond dissociation energies (BDE s) of the M···(η 2-H 2) bonds are 5–17, 4–11 and 1–26 kcal/mol for the [Cu(Η 2) 4 ]+, [Ag (Η 2) 4 ]+ and [Au (Η 2) 4 ]+ cationic species respectively, while the fifth H 2 molecule is estimated to be very loosely associated to the metal center. Four H 2 molecules could be exploited from the [Cu(Η 2) n ][A] and [Ag (Η 2) n ][A] molecules in addition to the amount of H 2 stored in the anion [A]-. Among the [M(Η 2) n ][A] salts optimal gravimetric, kinetic and thermodynamic properties and relatively low cost, are predicted for [Cu(Η 2) n ][(H 3 B) (BH 2 NH 2) 5 (NH 2)]. Highlights • Solid stabilization of metal hydrides with optimal H 2 storage properties. • Weakly Coordinating Anions. • 'Complex hydrides', exploiting both anion and cation for H 2 storage. • Novel 'concept' design of 'complex hydrides'. [ABSTRACT FROM AUTHOR]