Die Schöne (WCA) und das (kationische) Biest: Neues aus der Chemie von und mit schwach koordinierenden Anionen

Abstract

An einen Übersichtsartikel aus dem Jahre 2004 anknüpfend, wird hier über den strukturellen Aufbau, die Stabilität und die Anwendungen moderner schwach koordinierender Anionen (weakly coordinating anions, WCAs) berichtet, aber auch über Fortschritte der “klassischen” WCAs. In tabellarischer Form werden sowohl Ausgangsverbindungen zur Einführung einer Vielzahl von WCAs als auch deren physikochemische Eigenschaften zusammengefasst. Damit lässt sich für mögliche Anwendungen gut beurteilen, wie WCAs am besten in vorgegebene Systeme inkorporiert werden können. Die angeführten Anwendungsbeispiele für WCAs sind breit gestreut, eigene Abschnitte bilden aber die Schwerpunkte Übergangsmetallkomplexe, katalytische Anwendungen und Leitsalze für elektrochemische Anwendungen.

Stable Salts of Heteroleptic Iron Carbonyl/Nitrosyl Cations

“…Furthermore, the close agreement between the experimental vibrations in the solid state and the ideal, non-distorted calculated frequencies of [Fe(CO) 4 (NO)] + (C 2v ) and [Fe(CO)(NO) 3 ] + (C 3v ), indicate that the [F-{Al(OR F ) 3 } 2 ] À anion truly induces pseudo-gasphase conditions in condensed phases. [10] The broad signal in the 14 N NMR spectrum (Figure 2 b, left) and the appearance of only one signal in the 13 C NMR spectrum (see section S2) for 1 indicate a Berry pseudorotation [21] in solution, equilibrating the expected two different sets of CO ligands (Table 1), similar to the related [Co-(CO) 5 ] + . [22] For 2, the 14 N NMR signal is sharper, hinting at a more static structure in solution (Figure 2 b, right).…”

“…With that in mind, we made use of the versatility of carbon monoxide (CO) as a ligand by starting from Fe(CO) 5 as a Fe 0 source in combination with an oxidative approach. In order to compensate for the lability of the Fe À CO bond in the resulting iron cations, we utilized the weakly coordinating anion (WCA) [F-{Al(OR F ) 3 } 2 ] À (R F = C(CF 3 ) 3 ) [9,10] [11] In regard to ternary carbonyl/nitrosyl cations, the only currently known examples are [Cr(CO) 5 -(NO)][WCA], reported by us [12] and [Co(CO) 2 (NO) 2 ]-[WCA]. [13] And although the neutral Fe(CO) 2 (NO) 2 [14] and anionic [Fe(CO) 3 (NO)] À (the Hieber anion) [15] shown in Figure 1 were discovered more than half a decade ago and found their applications as useful starting materials or catalysts, [16] as of yet, their cationic counterparts have been mostly untouched.…”

Why Do Five Ga+ Cations Form a Ligand‐Stabilized [Ga5]5+ Pentagon and How Does a 5:1 Salt Pack in the Solid State?

“…[4] However,r elated chemistry with Ga + did not work and the only published compound which seemed likely to be asuitable starting material for coordination chemistry was the [Ga 2 Cp*] + cluster cation [5] -with the complication of providing one surplus equivalent of neutral GaCp* per used Ga + (Cp* = C 5 Me 5 ). Thes ubsequent facile access to arene complexes of In + and Ga + salts [6,7] with the non-reactive weakly coordinating anion (WCA) [8] [Al(OR F ) 4 ] À opened an ew starting point to interesting coordination chemistry with av ariety of s-donors including phosphines, [6,7] carbenes, [9] pyridines, [10] and also crown ethers. [11] In all of this,[ Al-(OR F ) 4 ] À was very helpful [12] for the elimination of cation-anion interactions and allowed for ap redictable reaction outcome.H owever,d ue to its considerable size (diameter 1.25 nm, V À = 0.76 nm 3 )and the pseudo-gas-phase conditions that the anion provides, [8,13] the overall charge of such coordination compounds was expected to be limited to + 1.…”

“…Thes ubsequent facile access to arene complexes of In + and Ga + salts [6,7] with the non-reactive weakly coordinating anion (WCA) [8] [Al(OR F ) 4 ] À opened an ew starting point to interesting coordination chemistry with av ariety of s-donors including phosphines, [6,7] carbenes, [9] pyridines, [10] and also crown ethers. [11] In all of this,[ Al-(OR F ) 4 ] À was very helpful [12] for the elimination of cation-anion interactions and allowed for ap redictable reaction outcome.H owever,d ue to its considerable size (diameter 1.25 nm, V À = 0.76 nm 3 )and the pseudo-gas-phase conditions that the anion provides, [8,13] the overall charge of such coordination compounds was expected to be limited to + 1. However,w hen changing to bidentate 2,2'-bipyridine (bipy) and phenanthroline (phen) as ligands,u nexpectedly,t he formation of indium-cluster-cation salts with planar triangles (for example,[ In 3 (bipy) 6 ] 3+ )a nd rhomboids (for example, [In 4 (phen) 6 ] 4+ )t hat both feature strong In-In bonding was observed.…”

Structural and Computational Analysis of 2‐Halogeno‐Glycosyl Cations in the Presence of a Superacid: An Expansive Platform

“…Fittingly,asharper doublet peak with alarge coupling (24 Hz) was obtained for C1, in agreement with an unconventional coordination phenomenon triggered by the noncoordinating SbF 6 À (Figure 6b). [36] The transient formation of 16 in HF/SbF 5 was confirmed by [34,35] Thus,i nt he absence of nucleophile in the reaction medium, this superelectrophilic glucosyl cation can be trapped by noncoordinating Sb n F 5n+1 À species.…”