Solutions to this problem would lead to a selleck inhibitor more sustainable economy bemuse of improved access to energy resources such as natural gas. Although natural gas is still abundant, about a third of methane extracted in distant oil fields currently cannot be used as a chemical feedstock because of a dearth of economically and ecologically viable methodologies for partial methane oxidation. Two readily available “”atom-economical”" “”green”" oxidants are dioxygen and hydrogen peroxide, but few methodologies have utilized these oxidants effectively in selective organic transformations. Hydrocarbon oxidation and C-H functionalization reactions rely on Pd-II and Pt-II complexes. These reagents have practical advantages because they can tolerate moisture and atmospheric oxygen.
But this tolerance for atmospheric oxygen also makes it challenging to develop novel organometallic palladium and platinum-catalyzed C-H oxidation reactions utilizing O-2 or H2O2.
This Account focuses on these challenges: the development of M-C bond (M = Pt-II, Pd-II) functionalation and related selective hydrocarbon C-H oxidations with O-2 or H2O2. Reactions discussed in this Account do not involve mediators, since the latter can impart low reaction selectivity and catalyst instability. As an efficient solution to the problem of direct M-C oxidation and functionalization with O-2 and H2O2, this Account introduces the use of facially chelating semilabile ligands such as di(2-pyridyl)methanesulfonate and the hydrated form of di(2-pyridyl)ketone that enable selective and facile M-II-C(sp(n)) bond functionalization with O-2 (M = Pt, n = 3; M = Pd, n = 3 (benzylic)) or H2O2 (M = Pd, n = 2).
The reactions proceed efficiently in protic solvents such as water, methanol, or acetic add. With the exception of benzylic Pd-II complexes, the organometallic substrates studied form isolable high-valent Pt-IV or Pd-IV intermediates as a result of an Anacetrapib oxidant attack at the M-II atom. The resulting high-valent M-IV intermediates undergo C-O reductive elimination, leading to products in high yields. Guidelines for the synthesis of products containing other C-X bonds (X = OAc, Cl, Br) while using O-2 or H2O2 as oxidants are also discussed. Although the M-II-C bond functionalization reactions including high-valent intermediates are well understood, the mechanism for the aerobic functionalization of benzylic Pd-II complexes will require a more detailed exploration.
Importantly, further optimization of the systems suitable for stoichiometric M-II-C bond functionalization led to the development of catalytic reactions, selleck screening library including selective acetoxylation of benzylic C-H bonds with O-2 as the oxidant and hydroxylation of aromatic C H bonds with H2O2 in acetic acid solutions. Both reactions proceed efficiently with substrates that contain a directing heteroatom.
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