The Hexahydro-closo-hexaborate Dianion [B6H6]2– and Its Derivatives

Abstract

[B6H6]2– as the smallest known hydro‐closo‐borate is only moderately stable, and therefore its reaction chemistry remained unexplored for quite a long time. Since the mid 1980s some progress has been made in this field, and a considerable number of derivatives has been prepared. The provided structural and spectroscopic data together with the results of more sophisticated theoretical investigations by high level ab initio methods are a good basis for a systematic review on this class of compounds, and may encourage further synthetic and theoretical work. This is the aim of the present article giving a comprehensive survey up to the beginning of 1999.

Metal-Free Peralkylation of thecloso-Hexaborate Anion

“…The facial proton in 1a can be identified by its characteristic upfield shift at δ −3.8 in the 1 H NMR spectrum. This assignment is consistent with previous spectroscopic and structural studies 10,13 of analogous unfunctionalized and partially functionalized B 6 -based clusters as well as computational studies in which electron density maxima are found at each face of the B 6 cluster. 14 Complete boron vertex substitution, which occurs in the absence of metal catalysis, is also strongly suggested by the disappearance of characteristic terminal B−H stretching vibrations at ∼2400 cm −1 in the infrared (IR) spectrum of purified 1a (Figure 2B).…”

“…Preetz has also remarked on this property 10. However, we find [NBu 4 ][B 6 H 6 H fac ] to be an acceptable starting material for the synthesis of the compounds outlined below.Synthetic Procedures.…”

“…In the examples reported by Preetz, it was concluded that that removal of H fac was not possible beyond three B−C bond formations. 10 Given our recent report 12 2A and the Supporting Information). The facial proton in 1a can be identified by its characteristic upfield shift at δ −3.8 in the 1 H NMR spectrum.…”

“…The observed redox irreversibility is consistent with previous reports of hexaborate cluster decomposition under oxidizing conditions (vide inf ra). 10,20 The anodic shift in the oxidative peak potential between 1a and 1b is likely due to the slightly more electron withdrawing nature of the benzyl substituents in 1b; similar substituent effects have been observed in hexaborate 19 and dodecaborate systems. 12 As the scan rate is incrementally raised from 100 mV/s to 750 mV/s for 1a, a reverse reductive wave becomes more pronounced (Figure 4A).…”

Interaction of Hydrogen with MB6 (M = Ba, Ca, La, and Sr) Surfaces from First Principles

“…Examination of the CPMD trajectories suggests the method of travel prior to recombination to be along the octahedral face and bridging sites connecting separate unit cells on the surface. The mobile character of adsorbed hydrogen on the facial sites is also seen on the hexahydro- closo -hexaborate dianion [B 6 H 6 ] 2– , which has an analogous structure to the metal hexaborides described in this work. These trajectories show that the chemisorption phenomenon seems to be governing interactions of hydrogen in nonmetal-terminated regions.…”