Visible Light-Induced Oxidation of Alcohols by a Luminescent Osmium(VI) Nitrido Complex: Evidence for the Generation of PhIO⁺ as a Highly Active Oxidant in the Presence of PhIO

Abstract

Although alcohols are readily oxidized by a variety of oxidants, their oxidation by metal nitrido complexes is yet to be studied. We report herein visible-light-induced oxidation of primary and secondary alcohols to carbonyl compounds by a strongly luminescent osmium(VI) nitrido complex (OsN). The proposed mechanism involves initial rate-limiting hydrogen-atom transfer (HAT) from the α-carbon of the alcohol to OsN*. Attempts to develop catalytic oxidation of alcohols by OsN* using PhIO as the terminal oxidant resulted in the formation of novel osmium(IV) iminato complexes in which the nitrido ligand is bonded to a δ-carbon of the alcohol. Experimental and theoretical studies suggest that OsN* is reductively quenched by PhIO to generate PhIO + , which is a highly active oxidant that readily undergoes αand δ-C−H activation of alcohols.

Chalcogen atom abstraction from NCE− (E = O, S, Se) and i-Pr2S by the excited state of a luminescent tricyano osmium(vi) nitride

“…In our previous work, we showed that OsN* readily undergoes an initial one-electron oxidation of various substrates, 12–16 hence it is reasonable to propose that the present photoreactions proceed via an initial 1 e − transfer (ET) from NCE − to OsN* to generate Os V N and the NCE˙ radical; this is followed by rapid recombination of the two species to afford the unstable intermediate [Os IV (L)(CN) 3 (N-ECN)] 2− , which then undergoes spontaneous E–CN bond cleavage to produce OsNE and CN − (Fig. 5).…”

“…Indeed, upon irradiation with visible light ( λ > 460 nm), OsN* readily activates the strong C–H bonds of alkanes and arenes, 11 undergoes oxidative N -dealkylation of various tertiary amines 12 and C–O bond cleavage of dihydroxybenzene, 13 exhibits formal N atom transfer to aliphatic secondary amines 14 and ring-nitrogenation of aromatic amines. 15 Recently, we have also found that OsN* could activate both α- and δ-C–H bonds of alcohols in the presence of PhIO, due to the formation of the highly potent oxidant PhIO + 16 (Fig. 1).…”