Weakly Coordinating Anions WCAs...

My independent career started with the idea to stabilize reactive cations like, for example, phosphorus cations known from mass spectrometry in the gas phase, also as WCA-salts in condensed phases. As such I was searching for an anion class that should be straight forward to prepare also in larger scale and in addition be thermodynamically stable, or at least be kinetically inert, towards most of the reactive environments provided by any kind of cations. We took up on an idea first published by Steve Strauss in 1996 and published in 2001 our workhorse perfluoroalkoxyaluminate [Al(ORF)4]– (RF = C(CF3)3; Chem. Eur. J. 2001, 7, 490-502). It is available in +100 g scale in one batch, stable in nitric acid and other environments and available with many cations of choice to introduce the WCA to the system.

If [Al(ORF)4]– degrades by very strong Lewis acids, it tends to form the fluoride bridged anion [(FRO)3Al-F-Al(ORF)3]–, which currently bears the title 'Least Coordinating Anion' and withstands even fiercer conditions. Since a few years, salts of [(FRO)3Al-F-Al(ORF)3]– are also available in 10 g batches with a wide selection of cations allowing to introduce the WCA to whatever system relevant (Chemical Science 2018, 9, 7058-7068). 

Fluorinated Carbaborate-WCA: In recent work we also opened the large scale access to the fluorinated carbaborate-WCA [CHB11F11]− and even provide video documentaries for it. Check out our recent preps published with Chem. Methods 2024 described further down this page. The fluorinated carbaborates are more coordinating than the perfluorinated alkoxyaluminates but hold unprecedented stability vs. electrophiles and strong Lewis acids. 

From Fundamentals to Application: The perfluorinated alkoxyaluminates [Al(ORF)4]– and [(FRO)3Al-F-Al(ORF)3]– are WCAs that made their way over the past decades from a means to stabilize unusual cationic systems of fundamental interest to a well-developed class of materials that help to prepare problem case model compounds similarly to being useful in applied research, e.g. for Ionic Liquids (ILs), catalysis, polymerizations, electrochemistry and electrolytes. Currently we are aware of at least 50 groups worldwide that use the favorable properties of this chemically robust and easily in large scale or even commercially at www.iolitec.de available WCA class.

Video Tutorials on Starting Material Preparation: In the section 'Video Tutorials' you will find videos describing all details and equipment to prepare the fluorinated aluminates with a selection of useful countercations.

Review Article: Our last review article on WCAs in general with more than 500 references appeared in 2018:

 

“Taming the Cationic Beast: Novel Developments in the Synthesis and Application of Weakly Coordinating Anions.” 

by Ian Riddlestone*, Anne Kraft, Julia Schaefer, and Ingo Krossing*, Angew. Chem., Int. Ed. 2018, 57, 13982-14024.

 

This Review was selected as a Very Important Paper (VIP-Paper). It is a Web of Science Highly Cited Paper: As of September/October 2018, this paper received enough citations to place it in the top 1% of the academic field of Chemistry based on a highly cited threshold for the field and publication year. It is a Web of Science Hot Paper, published in the past two years and received enough citations in November/December 2018 to place it in the top 0.1% of papers in the academic field of Chemistry.

 

Review on fluorinated Alkoxyaluminates and -borates: More recently, we published a focused full review on the WCAs that derive from work of our group and showed the multitude of possible applications they hold. 

  

“Chemistry with weakly coordinating aluminates [Al(ORF)4]− and borates [B(ORF)4]−: From fundamentals to application.”  by
A. Barthelemy, P. Dabringhaus, Eike Jacob, D. Röhner, M. Schmitt, M. Sellin, and Ingo Krossing*, Compr. Inorg. Chem. 2023, 378-438. https://doi.org/10.1016/B978-0-12-823144-9.00194-1

 

In the meantime more than 100 groups worldwide use these types of WCAs and they evolved for example as the best performing electrolyte salts for Magnesium- or Calcium-Batteries.

 

Upscaled Synthesis to (Fluorinated) Carbaborates...

We present our improved protocols for the single batch syntheses of approximately 32 g of [NHMe3][CB11H12] and 10 g of Na[CHB11F11] as well as salt metathesis reactions, granting access to useful starting materials to introduce the [CHB11F11]− anion. This includes the trityl cation [Ph3C]+ and the bis-1,2-difluorobenzene-silver(I)-complex [Ag(odfb)2]+, as well as some applications of the shown compounds. The described methodology allows the synthesis of large amounts of both the [CB11H12]−, and the [CHB11F11]− anion and therefore making them accessible for further reactions. To facilitate the reproducibility, we present video tutorials of the synthetic steps to Na[CHB11F11].

J. Kulenkampff,  I. Krossing et al., Chem. Methods 2024, accepted. (Link follows a.s.a.p.)