Peralkylated Hexaborate Cluster

Peralkylated Hexaborate Cluster


Polyhedral boron clusters, for example, dodecaborate (B12H122–), can be stable under harsh conditions such as strong acidity or high temperatures. By functionalizing such compounds, their properties could be tuned for a range of applications, e.g., as photoactive materials, catalysts, or diagnostic agents. The smaller hexaborate cluster B6H62– is less well studied than the B12-based clusters. It has a nucleophilic character and has previously been partially substituted using carbon-based electrophiles. However, it had not been peralkylated so far.

Alexander M. Spokoyny, University of California, Los Angeles, USA, and colleagues have synthesized the first perfunctionalized hexaborate cluster featuring B−C bonds. The team reacted [NBu4][B6H6Hfac] (Hfac = proton on the cluster face) with benzyl bromide and Hünig’s base (N,N-diisopropylethylamine) in acetonitrile under microwave heating. The product was the peralkylated cluster [NBu4][B6(CH2C6H5)6Hfac], which was characterized using NMR spectroscopy. The team also synthesized the analogous cluster [NBu4][B6(CH2C6H4Br)6Hfac] (pictured) using 4-bromobenzyl bromide, which formed crystals that could be characterized using X-ray crystallography.

The synthesized compounds are stable under ambient conditions. The team suggests that this metal-free alkylation reaction is driven by the nucleophilic character of the hexaborate anion. Based on this approach, hexaborate clusters could potentially be functionalized using a range of other electrophiles.


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