Interaction of Trimethylamine and closo-1,6-C2B7H9. Evidence for an “Open” Cage C2B7H9/Amine Adduct

Abstract

Strong evidence for the low-temperature formation of an axially positioned NR3 (R = H, CH3) adduct of an “open” cage C2B7H9 structure is obtained via comparison of the experimentally obtained 13C and 11B NMR data (R = CH3) with that obtained from ab initio/IGLO/NMR and ab initio/GIAO/NMR approaches (R = H, CH3). The amine is positioned at a boron surrounded by the two carborane carbon atoms along a chair arrangement of a six-atom CBCB3 open face belonging to a cluster that can be formally derived by removing a triangular set of three adjacent vertices from a 12-vertex icosahedral unit. Rapid equilibration of the adduct NR3·C2B7H9 with dissociated NR3 and closo-C2B7H9 is proposed to explain the NMR chemical shift observations.