A Super-Oxidized Radical Cationic Icosahedral Boron Cluster

Stauber, Julia M.; Schwan, Josef; Zhang, Xinglong; Axtell, Jonathan C.; Jung, Dahee; McNicholas, Brendon J.; Oyala, Paul H.; Martinolich, Andrew J.; Winkler, Jay R.; See, Kimberly A.; Miller, Thomas F., III; Gray, Harry B.; Spokoyny, Alexander M.

doi:10.1021/jacs.0c06159

Published July 29, 2020 | Version Submitted + Supplemental Material

Journal Article Open

A Super-Oxidized Radical Cationic Icosahedral Boron Cluster

While the icosahedral closo-[B₁₂H₁₂]²⁻ cluster does not display reversible electrochemical behavior, perfunctionalization of this species via substitution of all 12 B–H vertices with alkoxy or benzyloxy (OR) substituents engenders reversible redox chemistry, providing access to clusters in the dianionic, monoanionic, and neutral forms. Here, we evaluated the electrochemical behavior of the electron-rich B₁₂(O-3-methylbutyl)₁₂ (1) cluster and discovered that a new reversible redox event that gives rise to a fourth electronic state is accessible through one-electron oxidation of the neutral species. Chemical oxidation of 1 with [N(2,4-Br₂C₆H₃)₃]·⁺ afforded the isolable [1]·⁺ cluster, which is the first example of an open-shell cationic B₁₂ cluster in which the unpaired electron is proposed to be delocalized throughout the boron cluster core. The oxidation of 1 is also chemically reversible, where treatment of [1]·⁺ with ferrocene resulted in its reduction back to 1. The identity of [1]·⁺ is supported by EPR, UV–vis, multinuclear NMR (¹H, ¹¹B), and X-ray photoelectron spectroscopic characterization.

Additional Information

© 2020 American Chemical Society. Received: June 8, 2020; Published: July 10, 2020. This work was supported as part of the Center for Synthetic Control Across Length-scales for Advancing Rechargeables (SCALAR), an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) under Award No. DE-SC0019381 (A.M.S. and K.A.S. synthesis and characterization; T.F.M., computational work and theory). A.M.S. is a Research Corporation for Science Advancement (RCSA) Cottrell Scholar and a Dreyfus Foundation Camille Dreyfus Teacher-Scholar. Acknowledgment is made to the donors of The American Chemical Society Petroleum Research Fund for funding work in the H.B.G. lab (J.S. and H.B.G.). Work in the Beckman Institute at Caltech was supported by the Arnold and Mabel Beckman Foundation (B.J.M., J.R.W.). X.Z. acknowledges the Agency for Science, Technology and Research (Singapore) for an A*STAR fellowship. X.Z. and T.F.M. acknowledge the computational resources from the Extreme Science and Engineering Discovery Environment (XSEDE) Bridges computer at the Pittsburgh Supercomputing Center through allocation TG-MCB160013. A.J.M. acknowledges support through a postdoctoral fellowship from the Resnick Sustainability Institute at Caltech. D.J. acknowledges the UCLA Graduate Division for the Dissertation Year Fellowship. The National Science Foundation (NSF-1531940) and the Dow Next Generation Educator Fund are acknowledged for EPR facility support. The authors declare the following competing financial interest(s): UCLA has patents on several compounds reported in this work from which A.M.S. and current/former co-workers may receive royalty payments. The Cs₂[B₁₂(OH)₁₂] salt (Catalog #902209) is commercially available through the MilliporeSigma catalog.

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Submitted - a-super-oxidized-radical-cationic-icosahedral-boron-cluster.pdf

Supplemental Material - ja0c06159_si_001.pdf

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