Search

The alkylation of 3‐/4‐bromo‐ and ‐iodopyridine with methyl triflate smoothly affords the corresponding N‐methylpyridinium triflate salts. An anion exchange with NaI or [PPh4]Y (Y=Cl, Br, I) yields the corresponding halide salts. Most of them could be structurally characterized and their strong halogen bonds were investigated. While the halogen atom of 4‐halogenopyridinium is susceptible to nucleophilic substitution, 3‐halogenopyridinium ions are far more stable against nucleophilic attacks. Due to the comparable interaction strength of halogen bonds and hydrogen bonds, the latter of which is widely used in chromatography, the potential of 3‐halogenopyridinium moieties for an application in chromatography is obvious and was successfully employed in affinity chromatography of different proteins. [ABSTRACT FROM AUTHOR]

The renaissance of Brønsted superbases is primarily based on their pronounced capacity for a large variety of chemical transformations under mild reaction conditions. Four major set screws are available for the selective tuning of the basicity: the nature of the basic center (N, P, ...), the degree of electron donation by substituents to the central atom, the possibility of charge delocalization, and the energy gain by hydrogen bonding. Within the past decades, a plethora of neutral electron‐rich phosphine and phosphazene bases have appeared in the literature. Their outstanding properties and advantages over inorganic or charged bases have now made them indispensable as auxiliary bases in deprotonation processes. Herein, an update of the chemistry of basic phosphines and phosphazenes is given. In addition, due to widespread interest, their use in catalysis or as ligands in coordination chemistry is highlighted. [ABSTRACT FROM AUTHOR]

In this work, the syntheses of non‐coordinated electron‐rich phenolate anions via deprotonation of the corresponding alcohols with an extremely powerful perethyl tetraphosphazene base (Schwesinger base) are reported. The application of uncharged phosphazenes renders the selective preparation of anionic phenol‐phenolate and phenolate hydrates possible, which allows for the investigation of hydrogen bonding in these species. Hydrogen bonding brings about decreased redox potentials relative to the corresponding non‐coordinated phenolate anions. The latter show redox potentials of up to −0.72(1) V vs. SCE, which is comparable to that of zinc metal, thus qualifying their application as organic zinc mimics. We utilized phenolates as reducing agents for the generation of radical anions in addition to the corresponding phenoxyl radicals. A tetracyanoethylene radical anion salt was synthesized and fully characterized as a representative example. We also present the activation of sulfur hexafluoride (SF6) with phenolates in a SET reaction, in which the nature of the respective phenolate determines whether simple fluorides or pentafluorosulfanide ([SF5]−) salts are formed. [ABSTRACT FROM AUTHOR]

The reaction of the strong monophosphazene base with the weakly acidic phenol leads to the formation of a phenol–phenolate anion with a moderately strong hydrogen bond. Application of the more powerful tetraphosphazene base (Schwesinger base) renders the isolation of the corresponding salt with a free phenolate anion possible. This compound represents the first species featuring the free phenolate anion [H5C6‐O]−. The deprotonation of phenol derivatives with tetraphosphazene bases represents a great way for the clean preparation of salts featuring free phenolate anions and in addition allows the selective syntheses of hydrogen bonded phenol‐phenolate salts. This work presents a phosphazenium phenolate salt with a redox potential of −0.72 V and its capability for the selective activation of the chemically inert greenhouse gas SF6. The performed two‐electron reduction of SF6 leads to phosphazenium pentafluorosulfanide ([SF5]−) and fluoride salts. [ABSTRACT FROM AUTHOR]

The reaction of a saline phosphazenium hydroxide hydrate with siloxanes led to a novel kind of silanol‐silanolate anions. The weakly coordinating behavior of the cation renders the formation of silanol‐silanolate hydrogen bonds possible, which otherwise suffer from detrimental silanolate–oxygen cation interactions. We investigated the influence of various weakly coordinating cations on silanol‐silanolate motifs, particularly with regard to different cation sizes. While large cations favor the formation of intramolecular hydrogen bonds resulting in cyclic structures, the less bulky tetramethyl ammonium cation encourages the formation of polyanionic silanol‐silanolate chains in the solid state. [ABSTRACT FROM AUTHOR]

In this contribution we present an account on pentafluoroethylated compounds of silicon, germanium and tin. The pronounced electron‐withdrawing effect of the pentafluoroethyl group leads to a markedly increased Lewis acidity at the central atom which results in the stabilization of hypervalent complexes, anionic element(II) species as well as remarkable reactivities of element‐element and element‐hydrogen bonds. By addition to unsaturated C−C bonds or by reaction with organic halides as well as transition‐metal complexes the molecules bearing a pentafluoroethyl‐element group are readily accessible. Moreover, the utilization of pentafluoroethyl groups facilitates the formation of donor‐stabilized germylenes and stannylenes. A series of such compounds serves as suitable pentafluoroethylation reagents. Conversely to the well‐studied trifluoromethyl derivatives these compounds frequently exhibit a higher thermostability, which allows a more convenient handling. The introduction of electron‐withdrawing pentafluoroethyl groups into organosilicon, organogermanium and organotin compounds creates a pronounced electron‐deficiency at the central atom, which leads to a significantly different chemical behavior with respect to non‐fluorinated derivatives. These characteristics facilitate the formation of hypervalent complexes, stabilization of low‐valent species as well as main group and transition‐metal complexes. [ABSTRACT FROM AUTHOR]

In this contribution the syntheses of transition metal complexes of the electron‐withdrawing Sn(C2F5)3 ligand are presented. The reaction of HSn(C2F5)3 with organometallics LnM–R (M = Zn, W, Mo; R = Et, Me; L = CO, Cp), metal carbonyls [Ni(CO)4], and [{Fe(CO)2Cp}2], as well as chloro complexes such as [TiCl2Cp2], furnished the corresponding stannylated compounds. The electron‐deficient Sn(C2F5)3 ligand significantly influences the IR spectroscopic and structural features with respect to related non‐fluorinated stannyl complexes. [ABSTRACT FROM AUTHOR]

The treatment of phenyl‐protected pentafluoroethylstannanes, Sn(C2F5)4–nPhn (n = 1–3), with anhydrous HF results in the formation of the corresponding fluorostannanes which are associated in the solid state but form monomeric and dimeric fluoride complexes in solution. Due to the pronounced Lewis acidity caused by the electron‐withdrawing pentafluoroethyl groups, these stannanes represent suitable precursors for the synthesis of neutral, monoanionic and dianionic hexacoordinate tin(IV) complexes. The employment of an excess of cesium fluoride and 1,10‐phenanthroline exclusively leads to the octahedral complexes [Sn(C2F5)nF6–n]2– (n = 2–4) and [Sn(C2F5)nF4–n(phen)] (n = 1–3). The addition of bases, donating solvents as well as LiF, on the other hand, selectively affords salts containing dinuclear anions of the form [(C2F5)3Sn(µ‐F)3Sn(C2F5)3]– and [(C2F5)2F2Sn(µ‐F)2SnF2(C2F5)2]2–. [ABSTRACT FROM AUTHOR]

A versatile two-step synthesis of tris(pentafluoroethyl)stannane, HSn(C2F5)3, is presented. Electron-withdrawing C2F5 groups significantly influence the polarity of the tin–hydrogen bond, which allows facile deprotonation of the compound, even in water. The utility of this electron-deficient stannane was illustrated in hydrostannylations of alkenes and alkynes, as well as in dehalogenation reactions. The remarkably high reactivity of HSn(C2F5)3 is demonstrated in fast hydrostannylations, even in the absence of activators, whereby the regioselectivity of this process turns out to be solvent dependent. It is of great advantage that in dehalogenation reactions volatile halogenotris(pentafluoroethyl)stannanes, XSn(C2F5)3 (X=I, Br), are formed that allow facile separation of the tin-containing byproducts from the reaction mixtures. [ABSTRACT FROM AUTHOR]

Cover Feature: Non-coordinated and Hydrogen Bonded Phenolate Anions as One-Electron Reducing Agents (Chem. Eur. J. 21/2021) Hydrogen bond, phenol, phenolate, radical anion, SF6 activation Keywords: hydrogen bond; phenol; phenolate; radical anion; SF6 activation EN hydrogen bond phenol phenolate radical anion SF6 activation 6356 6356 1 04/16/21 20210412 NES 210412 B The superbasic tetraphosphazene b is a thieving magpie on the hunt for the shiny proton. [Extracted from the article]

Keywords: hydrogen bond; phenol; phosphazene base; SF6 activation; weakly coordinating cation EN hydrogen bond phenol phosphazene base SF6 activation weakly coordinating cation 6357 6357 1 04/16/21 20210412 NES 210412 B The non-coordinated phenolate anion ([H SB 5 sb C SB 6 sb -O] SP - sp b is easily accessible by deprotonation of phenol with the superbasic perethyl tetraphosphazene Schwesinger base, while monophosphazenes only deliver the hydrogen-bonded phenol-phenolate adduct. Hydrogen bond, phenol, phosphazene base, SF6 activation, weakly coordinating cation Cover Feature: Non-Coordinated Phenolate Anions and Their Application in SF6 Activation (Chem. Eur. J. 21/2021). [Extracted from the article]

In this contribution the syntheses of transition metal complexes of the electron‐withdrawing Sn(C2F5)3 ligand are presented. The reaction of HSn(C2F5)3 with organometallics LnM–R (M = Zn, W, Mo; R = Et, Me; L = CO, Cp), metal carbonyls [Ni(CO)4], and [{Fe(CO)2Cp}2], as well as chloro complexes such as [TiCl2Cp2], furnished the corresponding stannylated compounds. The electron‐deficient Sn(C2F5)3 ligand significantly influences the IR spectroscopic and structural features with respect to related non‐fluorinated stannyl complexes. [ABSTRACT FROM AUTHOR]