Enhanced Dihydrogen Activation by Mononuclear Iridium(II) Compounds: A Mechanistic Study

Abstract

The organometallic chemistry of 4d and 5d transition metals has been vastly dominated by closed‐shell states. The reactivity of their metalloradical species is though remarkable, albeit yet poorly understood and with limited mechanistic investigations available. In this work we report the synthesis and characterization of two mononuclear IrII species, including the first dinitrogen adduct. These compounds activate dihydrogen at a dissimilar rate, in the latter case several orders of magnitude faster than its IrI precursor. A combined experimental/computational investigation to ascertain the mechanism of this transformation in IrII compounds is reported.

Iridium-Catalyzed Hydrogenation of a Phenoxy Radical to the Phenol: Overcoming Catalyst Deactivation with Visible Light Irradiation

“…The reaction is likely initiated by a PCET event between Ir1 and 1 to generate the 17-electron metalloradical intermediate A , a frequently observed species generated from the reaction of metal hydrides with organic radicals . Detection or characterization of A with spectroscopic methods, including freeze quench EPR spectroscopy, has been unsuccessful, supporting the transient nature of the iridium metalloradical , en route to closed-shell products. Radical coupling between A and 1 generates the proposed iridium phenoxide B , followed by tautomerization by C–H activation, to produce Ir1-Int by either stepwise oxidative addition of the C–H bond, followed by reductive elimination or a concerted pathway .…”