Pushing the redox potentials of deelectronators to highly positive values using solvent effects and weakly coordinating anions

Abstract

While the development of weakly coordinating anions (WCAs) received much attention, the progress on new weakly coordinating and inert solvents almost stagnated. Here we study the effect of strategic F-substitution on the solvent properties of fluorobenzenes C6FxH6−x (xFB, x = 1–5). Asymmetric fluorination leads to dielectric constants as high as 22.1 for 3FB that exceeds acetone (20.7). Combined with the WCAs [Al(ORF)4]– or [(FRO)3Al-F-Al(ORF)3]– (RF = C(CF3)3), the xFB solvents push the potentials of Ag+ and NO+ ions to +1.50 / +1.52 V vs. Fc+/Fc. This is by +0.85 / +0.40 V higher than any published value. The xFB/WCA-system has electrochemical xFB stability windows that exceed 5 V for all xFBs with positive upper limits between +1.82 V (1FB) and +2.67 V (5FB) vs. Fc+/Fc. High level ab initio calculations with inclusion of solvation energies show that these high potentials result from weak interactions of the ions with solvent and counterion. To access the available positive xFB potential range with stable reagents, the innocent deelectronator salts [anthraceneF]+∙[WCA]– and [phenanthreneF]+∙[WCA]– with potentials of +1.47 and +1.89 V vs. Fc+/Fc are introduced.

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 [Ga(PhF)][pf], the Ga + cation has no Ga-anion contacts, but is coordinated to only one PhF ring in a η 6 coordination mode, with GaÀ C distances ranging from 280.3(4) pm to 288.4(4) pm and a GaÀ C 6centroid distance of 248.68 (18) pm. These values compare well with the GaÀ C distances in previously reported Ga I -fluoroarene complexes, [14] but are significantly longer than in the analogous monoarene complex [Ga(HMB)] + with the more electron-rich hexamethylbenzene (HMB) ligand.…”

“…Notes † It should be noted that, if the reaction between Ga 0 and Ag [pf] is performed in 4FB instead of 3FB, partial decomposition of the [pf] À anion is observed (ESI section 5.1), probably due to the increased reactivity of Ag[pf] in 4FB and due the fact that Ga + is less stabilized by the even weaker coordinating solvent. [18] The [pf] À anion is known to decompose in the presence of very strong electrophiles. [63] In oDFB solutions of Ga + , the [pf] À anion only decomposes under the influence of ultrasound.…”

“…[3,7,[10][11][12] This reactivity results from the less or even unsaturated coordination sphere around the metal ion, increasing its Lewis acidity but also oxidation power. [18] Turning to subvalent group 13 metal ions, both Ga I and In I are prone to disproportionation, making the choice of the counterion and the (solventÀ )ligand crucial. Classical Ga I starting materials are Green's galliumiodide, "GaI" [19] or the formal dihalides "GaX 2 " (X = Cl, Br, I).…”

Gold carbonyl cations and beyond: homoleptic gold(i) complexes with P4 and P4S3 and the half-sandwich cation [Au(C6H6)(CO)]+

“…18 Here, we present a simple synthesis in the commercial organic solvent 1,2,3,4-tetrafluorobenzene (4FB) that is very weakly coordinating, yet polar (e r = 12.6). 19 [Au(CO) 2 ][F{Al(OR F ) 3 } 2 ] 1 was synthesized by oxidation of gold powder with the synergistic Ag + /0.5 I 2 system (eqn (1)). Colorless crystals of 1 were obtained by vapor diffusion of n-pentane into a 4FB solution in 70% crystalline yield.…”