Hydrogen Atom Transfer Oxidation by a Gold–Hydroxide Complex

Abstract

Au III -oxygen adducts have been implicated as intermediates in homogeneous and heterogeneous Au oxidation catalysis, but their reactivity is under-explored. Complex 1, ([Au III (OH)-(terpy)](ClO 4 ) 2 , (terpy = 2,2′:6′,2-terpyridine), readily oxidized substrates bearing C−H and O−H bonds. Kinetic analysis revealed that the oxidation occurred through a hydrogen atom transfer (HAT) mechanism. Stable radicals were detected and quantified as products of almost quantitative HAT oxidation of alcohols by 1. Our findings highlight the possible role of Au III -oxygen adducts in oxidation catalysis and the capability of late transition metal−oxygen adducts to perform proton coupled electron transfer.

Comparing Metal–Halide and −Oxygen Adducts in Oxidative C/O–H Activation: AuIII–Cl versus AuIII–OH

“…This reduction event falls at a potential higher than that of the one observed for 2 (−0.13 V). 16 , 21 , 22 …”

“…A dark purple solution was observed at the end of the reaction, which we attribute to the formation of colloidal gold, in analogy to what was previously observed for 2 . 16 …”

“…We have not considered the decay product (presumed to be Au II OH 2 ) as an active oxidant in our calculations of yields because our focus was directed toward the first step of the reaction, where the stoichiometry was assumed to be 1:1. The assumption described above was made for all of the product yields reported in this work and in our previous work, 16 allowing a comparison of the yields of the products between complexes 1 and 2 . An X-band electron paramagnetic resonance (EPR) spectrum taken after 2000 s (maximum yield of 402 nm) showed a signal at g = 2.00 ( Figure 1 ).…”

“…This suggests that the 4-methoxy-2,6-di- ter t-butylphenoxyl radical likely decayed too quickly to be observed. 1 H NMR analysis of this reaction showed 2,6-DTBQ (yield of 96 ± 7% by GC-FID) 16 and C H 3 OH had formed ( Figure S10 ). 16 These compounds are likely formed by PCET oxidation of 4-CH 3 O-2,6-DTBP by 1 .…”

Gold‐Catalyzed Direct C(sp3)−H Acetoxylation of Saturated Hydrocarbons

“…These reports indicate that gold is capable of activating oxidants for the transformation of C−H into C−O bonds and demonstrate the potential for gold to serve as a catalyst for these types of transformations. In stoichiometric experiments, it was also shown that gold(III) hydroxide complexes can oxidize C(sp 3 )−H bonds [8] . Recently, two independent reports by the groups of Wang [9] and Michelet [10] showed that simple gold salts/complexes, when combined with PhI(OAc) 2 , [11] are capable of acetoxylating C(sp 2 )−H bonds in aromatic compounds (Scheme 1b).…”