Triethylsilyl Perfluoro-Tetraphenylborate, [Et(3)Si][F(20)-BPh(4)], a widely used Non-Existent Compound

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.

Isolable fluorinated triphenylmethyl cation salts of [HCB11Cl11]-: demonstration of remarkable hydride affinity

Significantly fluorinated triarylmethyl cations have long attracted attention as potentially accessible highly reactive carbocations, but their isolation in a convenient form has proved elusive. We show that abstraction of chloride with a cationic silylium reagent leads to the facile formation of di-, tetra-, and hexafluorinated trityl cations, which could be isolated as analytically pure salts with the [HCB₁₁Cl₁₁]^- counterion and are compatible with (halo)arene solvents. The F₆Tr⁺ cation carrying six meta-F substituents was computationally predicted to possess up to 20% higher hydride affinity than the parent triphenylmethyl cation Tr⁺. We report that indeed F₆Tr⁺ displays reactivity unmatched by Tr⁺. F₆Tr⁺ at ambient temperature abstracts hydrides from the C-H bonds in tetraethylsilane, mesitylene, methylcyclohexane, and catalyzes Friedel-Crafts alkylation of arenes with ethylene, while Tr⁺ does none of these.

Development of Transition-Metal-Free Lewis Acid-Initiated Double Arylation of Aldehyde: A Facile Approach Towards the Total Synthesis of Anti-Breast-Cancer Agent

This work describes a mild and robust double hydroarylation strategy for the synthesis of symmetrical /unsymmetrical diaryl- and triarylmethanes in excellent yields using Lambert salt (0.2-1.0 mol%). Despite the anticipated challenges associated with controlling selective product formation, unsymmetrical diaryl- and triarylmethanes products are obtained unprecedentedly. A highly efficient gram scale reaction has also been reported (TON for symmetrical product=475 and for unsymmetrical product=390). The synthetic utility of the methodology is demonstrated by the preparation of several unexplored diaryl- and triarylmethane-based biologically relevant molecules, such as arundine, vibrindole A, turbomycin B, and certain anti-inflammatory agents. A total synthesis of an anti-breast-cancer agent is also demonstrated. Control experiments, Hammett analysis, HRMS and GC-MS studies reveal the reaction intermediates and reaction mechanism.

Ga+-catalyzed hydrosilylation? About the surprising system Ga+/HSiR3/olefin, proof of oxidation with subvalent Ga+ and silylium catalysis with perfluoroalkoxyaluminate anions

Already 1 mol% of subvalent [Ga(PhF)2]+[pf]- ([pf]- = [Al(ORF)4]-, RF = C(CF3)3) initiates the hydrosilylation of olefinic double bonds under mild conditions. Reactions with HSiMe3 and HSiEt3 as substrates efficiently yield anti-Markovnikov and anti-addition products, while bulkier substrates such as HSiiPr3 are less reactive. Investigating the underlying mechanism by gas chromatography and STEM analysis, we unexpectedly found that H2 and metallic Ga0 formed. Without the addition of olefins, the formation of R3Si-F-Al(ORF)3 (R = alkyl), a typical degradation product of the [pf]- anion in the presence of a small silylium ion, was observed. Electrochemical analysis revealed a surprisingly high oxidation potential of univalent [Ga(PhF)2]+[pf]- in weakly coordinating, but polar ortho-difluorobenzene of E 1/2(Ga+/Ga0; oDFB) = +0.26-0.37 V vs. Fc+/Fc (depending on the scan rate). Apparently, subvalent Ga+, mainly known as a reductant, initially oxidizes the silane and generates a highly electrophilic, silane-supported, silylium ion representing the actual catalyst. Consequently, the [Ga(PhF)2]+[pf]-/HSiEt3 system also hydrodefluorinates C(sp3)-F bonds in 1-fluoroadamantane, 1-fluorobutane and PhCF3 at room temperature. In addition, both catalytic reactions may be initiated using only 0.2 mol% of [Ph3C]+[pf]- as a silylium ion-generating initiator. These results indicate that silylium ion catalysis is possible with the straightforward accessible weakly coordinating [pf]- anion. Apparently, the kinetics of hydrosilylation and hydrodefluorination are faster than that of anion degradation under ambient conditions. These findings open up new windows for main group catalysis.

Lambert Salt-Initiated Development of Friedel-Crafts Reaction on Isatin to Access Distinct Derivatives of Oxindoles

Herein, a mild metal-free and efficacious route for the synthesis of biologically important 3-aryl oxindole derivatives is described. Using Lambert salt-initiated hydroarylation of isatin, a diverse array of monoarylated products, symmetrical/unsymmetrical double-arylated products, and deoxygenated hydroarylated products could be synthesized from the single starting substrate in good to excellent yields. A preliminary mechanistic study revealed that the reaction proceeds via a monoarylated product followed by a nucleophilic attack by another electron-rich arene nucleophile under mild conditions. The potential of newly synthesized symmetric/unsymmetric 3,3-disubstituted oxindole, 3-substituted 3-hydroxy oxindoles, 3,3-di(indolyl)indolin-2-ones, and α-aryl oxindoles as valuable building blocks is further illustrated.

Hydrogen-Bridged Oligosilanylsilyl Mono- and Oligosilanylsilyl Dications

Hydrogen‐bridged oligosilanylsilyl borates 8 [B(C₆F₅)₄], 9[B(C₆F₅)₄] and diborates 10 [B(C₆F₅)₄]₂ have been prepared by hydride transfer between α‐ω‐dihydrido‐ (11) and branched tetrahydrido‐oligosilanes (13) and trityl cation. The obtained cyclic intramolecularly stabilized silylium ions 8, 9 and bissilylium ion 10 were characterized by low temperature NMR spectroscopy supported by the results of density functional calculations. The branched Si−H−Si monocation 9 undergoes at low temperatures a fast degenerate rearrangement, which exchanges the Si−H groups with a barrier of 31 kJ mol⁻¹ via an antarafacial transition state. Reaction of the branched monocation 9 with a second equivalent of trityl cation or of the branched oligosilane 13 with two equivalents of trityl cation, gives at −80 °C the corresponding bissilylium ion 10, an example for a new class of highly reactive poly‐Lewis acids.

The influence of ring strain on the formation of Si-H-Si stabilised oligosilanylsilyl cations

Hydride transfer between Si(SiMe₂H)₄ (2) and [Ph₃C][B(C₆F₅)₄] in 3-fluorotoluene yields the intermolecularly silane-stabilised silylium ion [((HMe₂Si)₃SiSiMe₂)₂H]⁺ ([5]+), independently of the amount of [Ph₃C][B(C₆F₅)₄] (0.5, 1.0 or 2.0 equiv.) used. The cyclic silane-stabilised silylium ion [4]+ is not detected by NMR spectroscopy. This result demonstrates the influence of ring strain effects on the formation of intra- ([4]+) or intermolecularly ([5]+) Si-H-Si bridged silyl cations.

Synthesis and Catalytic Activity of Atrane-type Hard and Soft Lewis Superacids with a Silyl, Germyl, or Stannyl Cationic Center

The synthesis and isolation of atrane-type molecules 1E⁺ (E=Si, Ge, or Sn) having a cationic group 14 elemental center are reported. The cations 1E⁺ act as hard and soft Lewis superacids, which readily interact with various hard and soft Lewis basic substrates. The rigid atrane framework stabilizes the localized positive charge on the elemental center and assists the formation of the well-defined highly coordinated states of 1E⁺ . The cations were applied to the hydrodefluorination, Friedel-Crafts reaction, alkyne cyclization, and carbonyl reduction as Lewis acid catalysts. Most notably, [1Si][ClO₄ ] exhibits unique chemoselectivity that depends on a solvent in the competitive reaction of silyl enol ether with a mixture of benzaldehyde dimethyl acetal and benzaldehyde. Our findings indicate the potential of hard and soft Lewis superacids in organic synthesis.

Switching between X-Pyrano-, X-Furano-, and Anhydro-X-pyranoside Synthesis (X = C, N) under Lewis acid Catalyzed Conditions

A variety of C-glycosides can be obtained from the fluoroarylborane (B(C6F5)3) or silylium (R3Si+) catalyzed functionalization of 1-MeO- and per-TMS-sugars with TMS-X reagents. A one-step functionalization with a change as simple as the addition order and/or Lewis acid and TMS-X enables one to afford chiral synthons that are common (C-pyranosides), have few viable synthetic methods (C-furanosides), or are virtually unknown (anhydro-C-pyranosides), which mechanistically arise from whether a direct substitution, isomerization/substitution, or substitution/isomerization occurs, respectively.

Silylium Ions: From Elusive Reactive Intermediates to Potent Catalysts

The history of silyl cations has all the makings of a drama but with a happy ending. Being considered reactive intermediates impossible to isolate in the condensed phase for decades, their actual characterization in solution and later in solid state did only fuel the discussion about their existence and initially created a lot of controversy. This perception has completely changed today, and silyl cations and their donor-stabilized congeners are now widely accepted compounds with promising use in synthetic chemistry. This review provides a comprehensive summary of the fundamental facts and principles of the chemistry of silyl cations, including reliable ways of their preparation as well as their physical and chemical properties. The striking features of silyl cations are their enormous electrophilicity and as such reactivity as super Lewis acids as well as fluorophilicity. Known applications rely on silyl cations as reactants, stoichiometric reagents, and promoters where the reaction success is based on their steady regeneration over the course of the reaction. Silyl cations can even be discrete catalysts, thereby opening the next chapter of their way into the toolbox of synthetic methodology.

Reversible Silylium Transfer between P-H and Si-H Donors

The Mo=PR₂ π* orbital in a Mo phosphenium complex acts as acceptor in a new P^III -based Lewis superacid. This Lewis acid (LA) participates in electrophilic Si-H abstraction from E₃ SiH to give a Mo-bound secondary phosphine ligand, Mo-PR₂ H. The resulting Et₃ Si⁺ ion remains associated with the Mo complex, stabilized by η¹ -P-H donation, yet undergoes rapid exchange with an η¹ -Si-H adduct of free silane in solution. The equilibrium between these two adducts presents an opportunity to assess the role of this new LA in catalytic reactions of silanes: is the LA acting as a catalyst or as an initiator? Preliminary results suggest that a cycle including the Mo-bound phosphine-silylium adduct dominates in the catalytic hydrosilylation of acetophenone, relative to a putative cycle involving the silane-silylium adduct or "free" silylium.

Towards Naked Zinc(II) in the Condensed Phase: A Highly Lewis Acidic ZnII Dication Stabilized by Weakly Coordinating Carborate Anions

The employment of the hexyl-substituted anion [HexCB₁₁ Cl₁₁ ]^- allowed the synthesis of a Zn^II species, Zn[HexCB₁₁ Cl₁₁ ]₂ , 3, in which the Zn²⁺ cation is only weakly coordinated to two carborate counterions and that is soluble in low polarity organic solvents such as bromobenzene. DOSY NMR studies show the facile displacement of at least one of the counterions, and this near nakedness of the cation results in high catalytic activity in the hydrosilylation of 1-hexene and 1-methyl-1cyclohexene. Fluoride ion affinity (FIA) calculations reveal a solution Lewis acidity of 3 (FIA=262.1 kJ mol^-1 ) that is higher than that of the landmark Lewis acid B(C₆ F₅ )₃ (FIA=220.5 kJ mol^-1 ). This high Lewis acidity leads to a high activity in catalytic CO₂ and Ph₂ CO reduction by Et₃ SiH and hydrogenation of 1,1-diphenylethylene using 1,4-cyclohexadiene as the hydrogen source. Compound 3 was characterized by multinuclear NMR spectroscopy, mass spectrometry, single crystal X-ray diffraction, and DFT studies.

Synthesis of a Counteranion-Stabilized Bis(silylium) Ion

The preparation of a molecule with two alkyl‐tethered silylium‐ion sites from the corresponding bis(hydrosilanes) by two‐fold hydride abstraction is reported. The length of the conformationally flexible alkyl bridge is crucial as otherwise the hydride abstraction stops at the stage of a cyclic bissilylated hydronium ion. With an ethylene tether, the open form of the hydronium‐ion intermediate is energetically accessible and engages in another hydride abstraction. The resulting bis(silylium) ion has been NMR spectroscopically and structurally characterized. Related systems based on rigid naphthalen‐n,m‐diyl platforms can only be converted into the dications when the positively charged silylium‐ion units are remote from each other (1,8 versus 1,5 and 2,6).

On Silylated Oxonium and Sulfonium Ions and Their Interaction with Weakly Coordinating Borate Anions

Attempts have been made to prepare salts with the labile tris(trimethylsilyl)chalconium ions, [(Me3 Si)3 E]+ (E=O, S), by reacting [Me3 Si-H-SiMe3 ][B(C6 F5 )4 ] and Me3 Si[CB] (CB- =carborate=[CHB11 H5 Cl6 ]- , [CHB11 Cl11 ]- ) with Me3 Si-E-SiMe3 . In the reaction of Me3 Si-O-SiMe3 with [Me3 Si-H-SiMe3 ][B(C6 F5 )4 ], a ligand exchange was observed in the [Me3 Si-H-SiMe3 ]+ cation leading to the surprising formation of the persilylated [(Me3 Si)2 (Me2 (H)Si)O]+ oxonium ion in a formal [Me2 (H)Si]+ instead of the desired [Me3 Si]+ transfer reaction. In contrast, the expected homoleptic persilylated [(Me3 Si)3 S]+ ion was formed and isolated as [B(C6 F5 )4 ]- and [CB]- salt, when Me3 Si-S-SiMe3 was treated with either [Me3 Si-H-SiMe3 ][B(C6 F5 )4 ] or Me3 Si[CB]. However, the addition of Me3 Si[CB] to Me3 Si-O-SiMe3 unexpectedly led to the release of Me4 Si with simultaneous formation of a cyclic dioxonium dication of the type [Me3 Si-μO-SiMe2 ]2 [CB]2 in an anion-mediated reaction. DFT studies on structure, bonding and thermodynamics of the [(Me3 Si)3 E]+ and [(Me3 Si)2 (Me2 (H)Si)E]+ ion formation are presented as well as mechanistic investigations on the template-driven transformation of the [(Me3 Si)3 E]+ ion into a cyclic dichalconium dication [Me3 Si-μE-SiMe2 ]2 2+ .

Silylium cation initiated sergeants-and-soldiers type chiral amplification of helical aryl isocyanide copolymers

Silylium cations act as new highly efficient metal-free single-component cationic initiators for the cationic polymerization and copolymerization of chiral or achiral aryl isocyanides, preparing optically active polymers and copolymers obeying “sergeants-and-soldiers” rule.

Nonclassical Applications of closo-Carborane Anions: From Main Group Chemistry and Catalysis to Energy Storage

Classically closo-carborane anions, particularly [HCB₁₁H₁₁]^- and [HCB₉H₉]^-, and their derivatives have primarily been used as weakly coordinating anions to isolate reactive intermediates, platforms for stoichiometric and catalytic functionalization, counteranions for simple Lewis acid catalysis, and components of materials like liquid crystals. The aim of this article is to educate the reader on the contemporary nonclassical applications of these anions. Specifically, this review will cover new directions in main group catalysis utilized to achieve some of the most challenging catalytic reactions such as C-F, C-H, and C-C functionalizations that are difficult or impossible to realize with transition metals. In addition, the review will cover the utilization of the clusters as dianionic C σ-bound ligands for coordination chemistry, ligand substituents for coordination chemistry and advanced catalyst design, and covalently bound spectator substituents to stabilize radicals. Furthermore, their applications as solution-based and solid-state electrolytes for Li, Na, and Mg batteries will be discussed.

Hydrosilylation of carbonyl and carboxyl groups catalysed by Mn(i) complexes bearing triazole ligands

Manganese(i) complexes bearing readily accessible triazole ligands are effective catalysts for the hydrosilylation of carbonyl and carboxyl compounds.

Tris(dimethylamino)silylium ion: structure and reactivity of a dimeric silaguanidinium

The formal dimer of an elusive silaguanidinium ion is described. It undergoes spontaneous electrophilic aromatic silylation of electron rich π-systems.

Cationic Complexes of Boron and Aluminum: An Early 21st Century Viewpoint

Boron and aluminum are lighter Group 13 elements, found in daily life commodities, and considered environmentally benign. Nevertheless, they markedly differ in their elemental properties (e.g., metal character, atomic radius). The use of Lewis acidic complexes of boron and aluminum for methods of bond activation and catalysis (e.g., hydrogenation of unsaturated substrates, polymerization of olefins and epoxides) is quickly expanding. The introduction of cationic charge may boost the metalloid-centered Lewis acidity and allow for its fine-tuning particularly with regard to preference for "hard" or "soft" Lewis bases (i.e., substrates). Especially the isolation of low-coordinate cations (number of ligand atoms smaller than four) demands elaborate techniques of thermodynamic and kinetic stabilization (i.e., electronic saturation and steric shielding) by a ligand system. Furthermore, the properties of the solvent and the counteranion must be considered with care. Here, selected examples of boron and aluminum cations are described.

Polymerization of Polar Monomers Mediated by Main-Group Lewis Acid-Base Pairs

The development of new or more sustainable, active, efficient, controlled, and selective polymerization reactions or processes continues to be crucial for the synthesis of important polymers or materials with specific structures or functions. In this context, the newly emerged polymerization technique enabled by main-group Lewis pairs (LPs), termed as Lewis pair polymerization (LPP), exploits the synergy and cooperativity between the Lewis acid (LA) and Lewis base (LB) sites of LPs, which can be employed as frustrated Lewis pairs (FLPs), interacting LPs (ILPs), or classical Lewis adducts (CLAs), to effect cooperative monomer activation as well as chain initiation, propagation, termination, and transfer events. Through balancing the Lewis acidity, Lewis basicity, and steric effects of LPs, LPP has shown several unique advantages or intriguing opportunities compared to other polymerization techniques and demonstrated its broad polar monomer scope, high activity, control or livingness, and complete chemo- or regioselectivity, as well as its unique application in materials chemistry. These advances made in LPP are comprehensively reviewed, with the scope of monomers focusing on heteroatom-containing polar monomers, while the polymerizations mediated by main-group LAs and LBs separately that are most relevant to the LPP are also highlighted or updated. Examples of applying the principles of the LPP and LP chemistry as a new platform for advancing materials chemistry are highlighted, and currently unmet challenges in the field of the LPP, and thus the suggested corresponding future research directions, are also presented.

Thermodynamic versus kinetic control in substituent redistribution reactions of silylium ions steered by the counteranion

An in-depth experimental and theoretical study of the substituent exchange reaction of silylium ions is presented. Apart from the substitution pattern at the silicon atom, the selectivity of this process is predominantly influenced by the counteranion, which is introduced with the trityl salt in the silylium ion generation. In contrast to Müller's protocol for the synthesis of triarylsilylium ions under kinetic control, the use of Reed's carborane anions leads to contact ion pairs, allowing selective formation of trialkylsilylium ions under thermodynamic control. DFT calculations finally revealed an unexpected mechanism for the rate-determining alkyl exchange step, which is initiated by an unusual 1,2-silyl migration in the intermediate ipso-disilylated arenium ion. The resulting ortho-disilylated arenium ion can then undergo an alkyl transfer via a low-barrier five-centered transition state.

Mono- and dinuclear Ni(i) products formed upon bromide abstraction from the Ni(i) ring-expanded NHC complex [Ni(6-Mes)(PPh3)Br]

New T- and Y-shaped Ni(i) complexes are reported and analysed by DFT and EPR.

Electrochemical Oxidation of [1-X-12-I-CB11Me10-] Anions: Formation of Borenium Ylides [12-Dehydro-1-X-CB11Me10] and Iodonium Ylide Anions [{12-(1-X-CB11Me10-)}2I+]

Cyclic voltammograms of 12-iodinated icosahedral carborane anions [1-X-12-I-CB₁₁Me₁₀^-] (X = H, CH₃, C₂H₅, C₃H₇, C₄H₉, C₆H₁₃, and COOCH₃) show two one-electron anodic oxidation peaks at the Pt electrode in liquid SO₂. Oddly, the first is irreversible and the second partially reversible. Mass spectrometry of the principal anionic product of preparative anodic oxidation of [1-H-12-I-CB₁₁Me₁₁^-], identical with the anionic product of its reaction with [Et₃Si-H-SiEt₃]⁺ and/or Et₃Si⁺, allows it to be identified as the iodonium ylide anion [{12-(1-H-CB₁₁Me₁₀^-)}₂I⁺]. Its reversible oxidation to a neutral ylide radical [{12-(1-H-CB₁₁Me₁₀^•)}{12-(1-H-CB₁₁Me₁₀^-)}I⁺] is responsible for the second peak. A DFT geometry optimization suggests that both the ylide anion and the ylide radical are very crowded and have an unusually large C-I-C valence angle of ∼132°; they are the first compounds with two bulky highly methylated CB₁₁ cages attached to the same atom. Molecular iodine is another product of the electrolysis. We propose an electrode mechanism in which initial one-electron oxidation of [1-X-12-I-CB₁₁Me₁₀^-] is followed by a transfer of an iodine atom from the B-I bond to SO₂ to yield a weakly bound radical ISO₂^• which disproportionates into SO₂ and I₂. The other product is the borenium ylide [12-dehydro-1-X-CB₁₁Me₁₀], which has a strongly Lewis acidic naked vertex in position 12 that rapidly adds to another [1-X-12-I-CB₁₁Me₁₀^-] anion to form the observed stable ylide anion [{12-(1-X-CB₁₁Me₁₀^-)}₂I⁺]. In acetonitrile, where it presumably exists as a solvent adduct, [12-dehydro-1-X-CB₁₁Me₁₀] has been trapped with H₂O and, to a small extent, with MeOH, but not with several other potential trapping agents.

Brønsted Acid-Promoted Formation of Stabilized Silylium Ions for Catalytic Friedel-Crafts C-H Silylation

A counterintuitive approach to electrophilic aromatic substitution with silicon electrophiles is disclosed. A strong Brønsted acid that would usually promote the reverse reaction, i.e., protodesilylation, was found to initiate the C-H silylation of electron-rich (hetero)arenes with hydrosilanes. Protonation of the hydrosilane followed by liberation of dihydrogen is key to success, fulfilling two purposes: to generate the stabilized silylium ion and to remove the proton released from the Wheland intermediate.

Dispersion-Energy-Driven Wagner-Meerwein Rearrangements in Oligosilanes

The installation of structural complex oligosilanes from linear starting materials by Lewis acid induced skeletal rearrangement reactions was studied under stable ion conditions. The produced cations were fully characterized by multinuclear NMR spectroscopy at low temperature, and the reaction course was studied by substitution experiments. The results of density functional theory calculations indicate the decisive role of attractive dispersion forces between neighboring trimethylsilyl groups for product formation in these rearrangement reactions. These attractive dispersion interactions control the course of Wagner-Meerwein rearrangements in oligosilanes, in contrast to the classical rearrangement in hydrocarbon systems, which are dominated by electronic substituent effects such as resonance and hyperconjugation.

Cationic Si-H-Si Bridges in Polysilanes: Their Detection and Targeted Formation in Stable Ion Studies

The ionization of 1,1-dihydridocyclopentasilane 7 has been found to yield the cyclic polysilanylsilyl cation 8 instead of the expected hydrogen-substituted silylium ion 6. The silyl cation 8 is stabilized by the formation of an intramolecular Si-H-Si bridge, which also provides the thermodynamic driving force for its formation. In general, the preference for the formation of Si-H-Si bridges can be used to scavenge and identify transient intermediates in the Lewis acid induced rearrangement of polysilanes. The validity of this concept has been demonstrated for one central step in this chemistry, the ring-contraction reaction of cyclohexasilanes to form silylcyclopentasilanes.

Reactive p-block cations stabilized by weakly coordinating anions

The chemistry of the p-block elements is a huge playground for fundamental and applied work. With their bonding from electron deficient to hypercoordinate and formally hypervalent, the p-block elements represent an area to find terra incognita. Often, the formation of cations that contain p-block elements as central ingredient is desired, for example to make a compound more Lewis acidic for an application or simply to prove an idea. This review has collected the reactive p-block cations (rPBC) with a comprehensive focus on those that have been published since the year 2000, but including the milestones and key citations of earlier work. We include an overview on the weakly coordinating anions (WCAs) used to stabilize the rPBC and give an overview to WCA selection, ionization strategies for rPBC-formation and finally list the rPBC ordered in their respective group from 13 to 18. However, typical, often more organic ion classes that constitute for example ionic liquids (imidazolium, ammonium, etc.) were omitted, as were those that do not fulfill the - naturally subjective -"reactive"-criterion of the rPBC. As a rule, we only included rPBC with crystal structure and only rarely refer to important cations published without crystal structure. This collection is intended for those who are simply interested what has been done or what is possible, as well as those who seek advice on preparative issues, up to people having a certain application in mind, where the knowledge on the existence of a rPBC that might play a role as an intermediate or active center may be useful.