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Published March 1, 2022 | Supplemental Material + Accepted Version + Submitted
Journal Article Open

Remote Oxidative Activation of a [Cp*Rh] Monohydride


Half-sandwich rhodium monohydrides are often proposed as intermediates in catalysis, but little is known regarding the redox-induced reactivity accessible to these species. Herein, the bis(diphenylphosphino)ferrocene (dppf) ligand has been used to explore the reactivity that can be induced when a [Cp*Rh] monohydride undergoes remote (dppf-centered) oxidation by 1e⁻. Chemical and electrochemical studies show that one-electron redox chemistry is accessible to Cp*Rh(dppf), including a unique quasi-reversible Rh^(II/I) process at −0.96 V vs. ferrocenium/ferrocene (Fc^(+/0)). This redox manifold was confirmed by isolation of an uncommon Rh^(II) species, [Cp*Rh(dppf)]⁺, that was characterized by electron paramagnetic resonance (EPR) spectroscopy. Protonation of Cp*Rh(dppf) with anilinium triflate yielded an isolable and inert monohydride, [Cp*Rh(dppf)H]+, and this species was found to undergo a quasireversible electrochemical oxidation at +0.41 V vs. Fc^(+/0) that corresponds to iron-centered oxidation in the dppf backbone. Thermochemical analysis predicts that this dppf-centered oxidation drives a dramatic increase in acidity of the Rh−H moiety by 23 pK_a units, a reactivity pattern confirmed by in situ ¹H NMR studies. Taken together, these results show that remote oxidation can effectively induce M−H activation and suggest that ligand-centered redox activity could be an attractive feature for the design of new systems relying on hydride intermediates.

Additional Information

© 2022 Wiley-VCH GmbH. Issue Online: 01 March 2022; Version of Record online: 03 February 2022; Accepted manuscript online: 17 January 2022; Manuscript received: 08 December 2021. The authors thank Dr. Justin Douglas and Sarah Neuenswander for assistance with NMR and EPR spectroscopy. This work was supported by the US National Science Foundation through award OIA-1833087. Support for NMR and EPR instrumentation was provided by the US National Institutes of Health (S10OD016360 and S10RR024664) and by the US National Science Foundation (CHE-1625923). The authors declare no conflict of interest. Data Availability Statement: The data that support the findings of this study are available in the supplementary material of this article.

Attached Files

Accepted Version - nihms-1772884.pdf

Submitted - 10.26434_chemrxiv-2021-jv2cc.pdf

Supplemental Material - chem202104389-sup-0001-misc_information.pdf


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August 22, 2023
October 23, 2023