Lewis Superacidic Tellurenyl Cation-Induced Electrophilic Activation of an Inert Carborane.

Martin Hejda,Sergey Makarov,Stefan Mebs,Antonín Lyčka,Zdeněk Černošek,Sergey Ketkov,Jan Macháček,Libor Dostál,Enno Lork,Jens Beckmann,Daniel Duvinage

doi:10.1002/chem.202103181

Abstract

The aryltellurenyl cation [2‐(tBuNCH)C6H4Te]+, a Lewis super acid, and the weakly coordinating carborane anion [CB11H12]−, an extremely weak Brønsted acid (pK a=131.0 in MeCN), form an isolable ion pair complex [2‐(tBuNCH)C6H4Te][CB11H12], in which the Brønsted acidity (pK a 7.4 in MeCN) of the formally hydridic B−H bonds is dramatically increased by more than 120 orders of magnitude. The electrophilic activation of B−H bonds in the carborane moiety gives rise to a proton transfer from boron to nitrogen at slightly elevated temperatures, as rationalized by the isolation of a mixture of the zwitterionic isomers 12‐ and 7‐[2‐(tBuN{H}CH)C6H4Te(CB11H11)] in ratios ranging from 62 : 38 to 80 : 20.

Highlights

In an effort to obtain an essentially isolated [2-(tBuNCH)C6H4Te]+ (I) cation, we turned our attention to an alternative weakly coordinating anions (WCAs), namely, the closocarborane anion [CB11H12]À , which is known as robust entity with a very low reactivity.[4] the salt metathesis reaction of 2-(tBuNCH)C6H4TeCl (II)[5] with Ag[CB11H12][6] provided again a contact ion pair [2-(tBuNCH)C6H4Te][CB11H12] (1), which was isolated as yellow crystals in 99 % yield (Scheme 1, Figure 2).[7] In the solid state, the dative N!Te bond (2.088(2) Å) of 1 is shorter than that of (tBuNCH)C6H4Te][O3SCF3] (2.113(1) Å), but longer than those of (tBuNCH)C6H4Te][SbF6] (2.076(2) Å) and
Besides frustrated Lewis pairs (FLPs), there is a growing number of regular, yet reactive Lewis pairs that are capable of activating small molecules.[2]
In an effort to obtain an essentially isolated [2-(tBuNCH)C6H4Te]+ (I) cation, we turned our attention to an alternative weakly coordinating anions (WCAs), namely, the closocarborane anion [CB11H12]À, which is known as robust entity with a very low reactivity.[4]

Summary

Introduction

In an effort to obtain an essentially isolated [2-(tBuNCH)C6H4Te]+ (I) cation, we turned our attention to an alternative WCA, namely, the closocarborane anion [CB11H12]À , which is known as robust entity with a very low reactivity.[4] the salt metathesis reaction of 2-(tBuNCH)C6H4TeCl (II)[5] with Ag[CB11H12][6] provided again a contact ion pair [2-(tBuNCH)C6H4Te][CB11H12] (1), which was isolated as yellow crystals in 99 % yield (Scheme 1, Figure 2).[7] In the solid state, the dative N!Te bond (2.088(2) Å) of 1 is shorter than that of (tBuNCH)C6H4Te][O3SCF3] (2.113(1) Å), but longer than those of (tBuNCH)C6H4Te][SbF6] (2.076(2) Å) and

Results

Conclusion