Metal-Free Peralkylation of the closo-Hexaborate Anion

Abstract

The synthesis of fully alkylated closo-hexaborate dianions is reported. The reaction of [NBu 4 ][B 6 H 6 H fac ], benzyl bromide, and triethylamine under microwave heating conditions affords persubstituted [NBu 4 ][B 6 (CH 2 Ar) 6 H fac ] (Ar = C 6 H 5 , 4−Br-C 6 H 4 ), which have been isolated and characterized by NMR spectroscopy, mass spectrometry, singlecrystal X-ray diffraction, and other spectroscopic techniques. Electrochemical studies of these clusters reveal an irreversible one-electron oxidation, likely indicating degradative cage rupture. The observed metalfree alkylation is proposed to proceed as a consequence of the pronounced nucleophilic character of the hexaborate anion. This work represents the first example of a perfunctionalized hexaborate cluster featuring B−C bonds.

Properties of gaseouscloso-[B6X6]2−dianions (X = Cl, Br, I)

“…10 Much less is known about smaller closo-borate dianions. 30 However, the chemistry of hexaborate dianions has recently received a renewed interest [31][32][33] and their salts have been discussed in the context of hydrogen storage. 34,35 In this study, we explore the gas-phase ion properties of hexaborate dianions (closo-[B 6 X 6 ] 2À ).…”

Hybrid Organic–Inorganic Functionalized Dodecaboranes and Their Potential Role in Lithium and Magnesium Ion Batteries

“…Therefore, these dianions are proposed as better candidates as an electrolyte for the reversible Li and Mg ion batteries. Similar to the previously synthesized organic derivatives, − proposed new dianions in this work can also be synthesized. The main advantage of using hybrid organic–inorganic derivatives is that the solubility of an electrolyte in a suitable less-polar solvent can be tuned through modifying the organic group.…”

“…The main advantage of using hybrid organic−inorganic derivatives is that the solubility of an electrolyte in a suitable less-polar solvent can be tuned through modifying the organic group. 2− , various other organic derivatives of boranes 43,44 and carboranes 45−49 are synthesized in the past few years. Very recently, Hahn and coworkers have shown that the derivatization can enhance the stability of the carba−closo− dodecaborate anion (CB 11 H 11 − ) for the high voltage battery electrolyte.…”

Nucleophilic Boron Reagents: On the Interface of Inorganic and Organic Chemistry

“…2 After investigating this alkylation chemistry further, our group discovered conditions for the peralkylation of the closohexaborate dianion and found evidence for irreversible oxidation of the resulting species. 3 In this issue of Chem, 4 we report our discovery of a reaction sequence involving substitution and cage deconstruction, which ultimately allowed us to form boronic acid pinacol esters without the use of metal catalysis (Figure 1). In contrast to previous nucleophilic boron reagents, the closo-hexaborate anion relies on electron delocalization rather than steric protection.…”

“…Of course, none of this work would be possible without the talented group of people behind it. My advisor, Alex Spokoyny, and one of our postdoctoral researchers, Jon Axtell, had developed some of the fundamental questions around the closo-hexaborate anion long before I joined the group, and the peralkylation work 3…”