Half-sandwich rhodium hydrides are often proposed as intermediates in catalytic processes such as hydrogen evolution, but few of these complexes have been isolated, limiting understanding of their properties and reactivity. Here, a family of Cp*Rh(dppf) rhodium complexes supported by the η5-pentamethylcyclopentadienyl (Cp*) and κ2-bis-diphenylphosphinoferrocene (dppf) ligands have been prepared and studied to reveal their reactivity patterns. Protonation of the formally RhI species, Cp*Rh(dppf), with DMFH+OTf– yielded an isolable monohydride; this monohydride is inert to protonolysis even with strong acids, providing evidence of the stabilizing effect of bidentate diphosphine ligands on the Rh–H bond. Electrochemical studies of the [Cp*Rh(dppf)H]+ complex revealed a quasireversible couple attributable to iron redox cycling in the dppf moiety at +0.41 V vs Fc+/0. The quasireversible nature of this FeIII/II couple enabled rigorous thermochemical analysis, revealing that oxidation of iron in the dppf ligand should result in a dramatic increase in acidity of the Rh–H moiety by 23 pKa units. Reactivity studies carried out via proton nuclear magnetic resonance (1H NMR) experiments will be described, supporting the predicted acidification.

Remote oxidative activation of a [Cp*Rh] hydride promotes Rh–H acidification and bond cleavage

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.