Proton-Initiated Reversible Chalcogen-Vertex Extrusion in Macropolyhedral Chalcogenaboranes

Area of Science:

• Inorganic Chemistry
• Boron Cluster Chemistry
• Main Group Element Chemistry

Background:

• Chalcogenaborane anions [E2B17H18]- (E = S, Se) feature macropolyhedral structures with two identical arachno-10-vertex subclusters.
• Understanding cluster rearrangements and reactivity is crucial for synthesizing novel boron-containing compounds.

Purpose of the Study:

• To investigate the structural and chemical consequences of protonating chalcogenaborane anions.
• To explore the reactivity and stability of the resulting neutral species.
• To characterize novel boron cluster architectures and transformations.

Main Methods:

• Protonation of [E2B17H18]- anions (E = S, Se).
• Single-crystal X-ray diffraction (SCXRD) for structural determination of 2a.
• Multielement NMR spectroscopy (experimental and DFT-calculated) for characterization.
• Density Functional Theory (DFT) calculations for spectral analysis and mechanistic insights.

Main Results:

• Protonation induces radical cluster rearrangement, yielding metastable neutral E2B17H19 species (2a, 2b) with two distinct nido-10-vertex subclusters.
• One chalcogen atom is extruded, forming a bridging μ2-{EH} unit, and can be reintegrated upon deprotonation.
• Compounds 2a and 2b undergo dehydrogenation to form known E2B17H17 (3), with 2b also yielding SeB17H19 (4) via selenium loss.

Conclusions:

• Protonation of chalcogenaborane anions leads to a unique cluster rearrangement and extrusion of a chalcogen atom.
• The metastable neutral species exhibit reversible deprotonation and subsequent boronotropic dehydrogenation.
• These findings expand the known chemistry of boron clusters and highlight pathways to novel structures and compounds.