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 H-1 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.

Automated summary

Half-sandwich rhodium monohydrides are often proposed as intermediates in catalysis. In this study, the reactivity induced by remote oxidation of a [Cp*Rh] monohydride with the bis(diphenylphosphino)ferrocene (dppf) ligand was explored. The results show that one-electron redox chemistry is accessible to Cp*Rh(dppf), and the remote oxidation can effectively induce M-H activation.