Crystal and molecular structures of the nido-carborane anions, 7,9- and 2,9-C2B9H12−

Abstract

Deboronation of meta-carborane, closo-1,7-C2B10H12, with refluxing piperidine results in the quantitative formation of [(C5H10NH)2H+](nido-7,9-C2B9H12−) whose structure was determined by X-ray diffraction. Heating under vacuum liberates piperidine to give (C5H10NH2+)(nido-7,9-C2B9H12−). The reaction of meta-carborane with KOH in refluxing ethanol yields K+nido-7,9-C2B9H12− and the cage substituted anion 10-EtO-7,9-C2B9H11−. The protonated Proton Sponge salt (PSH+)(nido-7,9-C2B9H12−) (PS = 1,8-N,N,N′,N′-tetramethylnaphthalenediamine) was obtained by metathesis from the potassium salt, an X-ray crystallographic study located the bridging hydrogen in the anion on the open face between the two adjacent boron atoms. Anaerobic deboronation of para-carborane, closo-1,12-C2B10H12, with KOH in refluxing tetraglyme–toluene gives the potassium salt of nido-2,9-C2B9H12− from which 2,9-C2B9H13 was isolated in 45% yield by protonation. The salt (PSH+)(nido-2,9-C2B9H12−), obtained from nido-2,9-C2B9H13 and PS, was shown by single crystal X-ray crystallography to contain a hydrogen bridging two boron atoms opposite the carbon atom on the open face. Aerobic deboronation of para-carborane with KOH forms closo-1,10-C2B8H10 and 2-HO-closo-1,10-C2B8H9 in low yields. Fully assigned multinuclear NMR (11B, 13C and 1H) data are reported for the isomeric 7,8-, 7,9- and 2,9-nido-C2B9H12− anions and neutral 7,8- and 2,9-C2B9H13, and compared with computed shifts (at the GIAO B3LYP/6-311G* level) from optimized (at MP2/6-31G*) geometries.