Catalytic oxidations using cobalt(II) complexes - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 308

An efficient catalytic system for oxygenation of phenols to p- or o-
quinones with molecular oxygen was achieved by utilization of a catalyst
consisting of and the multidentate N-heterocyclic podand ligand,
N,N '-bis-2-(2-pyridyl)ethyl)-2,6-pyridinedicarboxamide, 2-BPEPA (Figure
54) 155 .

In acetonitrile the bipyridinecobalt(II) complex
activates dioxygen via the reversible formation of a complex 156 ,
which dehydrogenates (oxidizes) N -methylanilines, benzyl alcohol, and
aldehydes (with subsequent autoxidation). In the absence of substrate, the
complex reduces dioxygen via residual water in the solvent to

generate HOOH.

9. COBALT-FENTON SYSTEMS

According to recent reports 157 , Fenton chemistry involves the formation
of hydroperoxide (ROOH) adducts (A) of reduced transition metal ions
[iron(II), copper(I), and cobalt(II)] via nucleophilic addition, e.g.

=pyor
These reactive intermediates (A) bind dioxygen to form adducts of the
type

where B

(B), which react selectively with methylenic

carbon centers of hydrocarbons to form ketones:

and with arylolefins to form dioxygenation products: