Proton-Initiated Reversible Chalcogen-Vertex Extrusion in Macropolyhedral Chalcogenaboranes

High Resolution Image Download MS PowerPoint Slide Protonation of the macropolyhedral chalcogenaborane anions [E 2 B 17 H 18 ] − (E = S, 1a – Se, 1b – ) induces a radical cluster rearrangement, yielding the new metastable isoelectronic neutral species E 2 B 17 H 19 ( 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 μ 2 -{EH} unit. Remarkably, deprotonation of compounds 2 facilitates a boronotropic dehydrogenation, giving reintegration of the extruded {EH} unit and regeneration of the original [E 2 B 17 H 18 ] − 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( 77 Se) values for the two widely separated selenium resonances add further support. Metastable compounds 2 ultimately eliminate dihydrogen to yield the known neutral E 2 B 17 H 17 compounds 3 . For 2b, a competing pathway leads to loss of selenium, to give known SeB 17 H 19 4 .