Access to cationic polyhedral carboranes via dynamic cage surgery with N-heterocyclic carbenes

Jan Vrána,Maksim A Samsonov,Aleš Růžička,Josef Cvačka,Zdeňka Růžičková,Jindřich Fanfrlík,Drahomír Hnyk,Josef Holub,Michael L Mckee

doi:10.1038/s41467-021-25277-0

Abstract

Polyhedral boranes and heteroboranes appear almost exclusively as neutral or anionic species, while the cationic ones are protonated at exoskeletal heteroatoms or they are instable. Here we report the reactivity of 10-vertex closo-dicarbadecaboranes with one or two equivalents of N-heterocyclic carbene to 10-vertex nido mono- and/or bis-carbene adducts, respectively. These complexes easily undergo a reaction with HCl to give cages of stable and water soluble 10-vertex nido-type cations with protonation in the form of a BHB bridge or 10-vertex closo-type cations containing one carbene ligand when originating from closo-1,10-dicarbadecaborane. The reaction of a 10-vertex nido mono-carbene adduct with phosphorus trichloride gives nido-11-vertex 2-phospha-7,8-dicarbaundecaborane, which undergoes an oxidation of the phosphorus atom to P = O, while the product of a bis-carbene adduct reaction is best described as a distorted C2B6H8 fragment bridged by the (BH)2PCl2+ moiety.

Highlights

Polyhedral boranes and heteroboranes appear almost exclusively as neutral or anionic species, while the cationic ones are protonated at exoskeletal heteroatoms or they are instable
Enough, the number of studies dealing with the reactivity of polyhedral boranes and heteroboranes with N-heterocyclic carbene (NHC) is limited to 12-vertex closo-heteroboranes (o-carborane – 1,2-dicarbadodecaborane(12) and 1-thiadodecaborane(12))[33,34,35] and bridged/ strained 13-vertex heteroboranes[36,37,38,39,40]
We report the reactions of one of the most sterically demanding NHCs with closo-dicarbadecaborane series, as smaller congeners of the most frequently used 12-vertex closo compounds, which yields ten-vertex nido mono- and/or biscarbene adducts, respectively

Summary

Introduction

Polyhedral boranes and heteroboranes appear almost exclusively as neutral or anionic species, while the cationic ones are protonated at exoskeletal heteroatoms or they are instable. The reactions of o-carborane and Xie’s 13-vertex dicarbaboranes mostly lead to deprotonated or deboronated species with one less vertex; in the reactions of thiaborane, cage distortion and the rearrangement of one hydrogen atom from terminal to bridging position have been observed.

Results

Conclusion