<p>Oxidation
reactions are fundamental transformations in organic synthesis and chemical
industry. With oxygen or air as terminal oxidant, aerobic oxidation catalysis provides
the most sustainable and economic oxidation processes. Most aerobic oxidation
catalysis employs redox metal as its active center. While nature provides
non-redox metal strategy as in pyrroloquinoline quinone (PQQ)-dependent
methanol dehydrogenases (MDH), such an effective chemical version is unknown.
Inspired by the recently discovered rare earth metal-dependent enzyme Ln-MDH,
here we show that an open-shell semi-quinone anionic radical species in
complexing with lanthanum could serve as a very efficient aerobic oxidation
catalyst under ambient conditions. In this catalyst, the lanthanum metal serves
only as a Lewis acid promoter and the redox process occurs exclusively on the
semiquinone ligand. The catalysis is initiated by 1e<sup>-</sup>-reduction of
lanthanum-activated <i>ortho</i>-quinone to
a semiquinone-lanthanum complex La(<b>SQ<sup>-.</sup></b>)<sub>2</sub>,
which undergoes a coupled O-H/C-H dehydrogenation for aerobic oxidation of
alcohols with up to 330 h<sup>-1</sup> TOF. This study suggests a possible functional
mode of semiquinone radicals, widely observed with quinoproteins in Nature. Moreover,
this unique reductive activation strategy as well as the resulted radical anion
as redox ligand creates a new turning point in the development of efficient aerobic
oxidation catalysis.</p>
A Bio-Inspired Lanthanum-Ortho Quinone Catalyst for Aerobic Oxidation of Alcohol