Tuning the Electrochemical Potential of Perfunctionalized Dodecaborate Clusters Through Vertex Differentiation

Abstract

We report a new class of redox-­‐active vertex-­‐differentiated dodecaborate clusters featuring pentafluoroaryl groups. These [B12(OR)11NO2] clusters share several unique photophysical properties with their [B12(OR)12] analogues, while exhibiting significantly higher (+0.5 V) redox potentials. This work describes the synthesis, characterization, and isolation of [B12(O-­‐CH2C6F5)11NO2] clusters in all 3 oxidation states (dianion, radical, and neutral). Reactivity to post-­‐functionalization with thiol species via SNAr on the pentafluoroaryl groups is also demonstated.

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“…suggests that the B12 cluster underwent single-electron reduction during the synthetic procedure. It is well documented that perfunctionalized B12 clusters undergo rich redox chemistry, 62,[70][71][72][73][74] and this redox behavior is consistent with the chemistry observed during the preparation of the analogous [B12(OCH2C6H4(Me-DalPhos)AuCl)12] 11+ cluster we have previously reported and likely due to a solvent-based electron transfer process (See SI Section S2.1.8.). 28 It is noted that the one-electron reduction of the B12 core results in an overall 11+ charge for [4] 11+ as opposed to the 12+ charge that would be expected in the absence of any cluster-based redox.…”

“…The 340 nm transition is attributed to ligand-based charge transfer, while the absorption located at 550 nm is diagnostic of hypocloso-B12 clusters in the monoanionic charge state. 62,[70][71][72] The presence of this absorption in addition to the silent 11 B NMR spectrum of purified [4][SbF6]11 (SI Section 2.1.8.) suggests that the B12 cluster underwent single-electron reduction during the synthetic procedure.…”

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“…The broadness of this signal is due to extensive and overlapping hyperfine splitting patterns that result from the delocalization of a single electron across all twelve boron nuclei of the cluster core. 17,19 The signal broadness and isotropic g-factor of this species are consistent with EPR data of hypocloso-dodecaborate radical anion analogues that our group [23][24][25] and others [16][17][18][19] have previously reported, and further support the presence of an unpaired electron that is delocalized throughout the B 12 core.…”

“…This redox boundary poses critical questions concerning the oxidation limit of icosahedral boron clusters, which is not only of fundamental interest, but could also have implications in the use of B 12 -based materials for energy storage and other applications. 2,[21][22][23] As previously established, 2,12,20,21,24,25 the redox potential of alkoxy and benzyloxy-substituted B 12 clusters ([B 12 (OR) 12 ]) can be rationally tuned as a function of their substituents by greater than 1 V for the same redox event. With this in mind, in addition to the high chemical, electrochemical, and Figure 1.…”

“…A: Structures of polyhedral closo-boron clusters as predicted by the Wade-Mingos electron-counting rules. 14,15 2,12,20,21,24,25 and this work, which introduces a third, reversible redox event for the B 12 (O-3-methylbutyl) 12 (1) derivative. structural stability of icosahedral boron clusters, 1,2,5,21,26-28 we envisioned we could tune and expand the redox potential window of B 12 (OR) 12 derivatives through judicious selection of the supporting substituents.…”