# Proton-Initiated Reversible Chalcogen-Vertex Extrusion in Macropolyhedral Chalcogenaboranes

## TL;DR

This paper describes a reversible chemical transformation in chalcogenaborane clusters triggered by protonation and deprotonation.

## Contribution

The study reveals a proton-induced reversible structural rearrangement in macropolyhedral chalcogenaborane clusters.

## Key findings

- Protonation converts [E2B17H18]− into metastable E2B17H19 with distinct subcluster architectures.
- Deprotonation regenerates the original anions through boronotropic dehydrogenation.
- Metastable compounds eliminate dihydrogen or selenium to form known neutral products.

## Abstract

Protonation of the
macropolyhedral chalcogenaborane anions [E2B17H18]− (E = S, 1a

–
Se, 1b

–
) induces a radical cluster rearrangement,
yielding the new metastable isoelectronic neutral species E2B17H19 (2a and 2b). This transformation converts the original structure comprising
two identical “arachno” 10-vertex subclusters
into a new architecture with two distinct “nido” 10-vertex subclusters. Notably, one of the chalcogen atoms,
which originally was a triconnected cluster vertex in anions 1

–
, is extruded, forming a
bridging μ2-{EH} unit. Remarkably, deprotonation
of compounds 2 facilitates a boronotropic dehydrogenation,
giving reintegration of the extruded {EH} unit and regeneration of
the original [E2B17H18]− anions 1

–
. Compound 2a is characterized by a single-crystal X-ray diffraction
(SCXRD) study, and by agreement between experimental and density functional
theory (DFT)-calculated multielement NMR spectra. Also, for 2b, the measured and calculated δ­(77Se) values
for the two widely separated selenium resonances add further support.
Metastable compounds 2 ultimately eliminate dihydrogen
to yield the known neutral E2B17H17 compounds 3. For 2b, a competing pathway
leads to loss of selenium, to give known SeB17H19
4.