NIO2ACTIVATION

O2-Activation at nickel complexes and their use as catalysts for environmentally friendly oxidation technologies

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 Obiettivo del progetto (Objective)

'The goal of the proposed research plan is the preparation of nickel complexes as catalysts for the oxidation of hydrocarbons using environmentally friendly oxidants like molecular oxygen (O2) or hydrogen peroxide (H2O2). The complexes will be prepared using highly robust nitrogen-based ligand scaffolds and carbene N-heterocyclic systems. Different ligands with different architectures (from bidentate to pentadentate) will be used in order to evaluate the most suitable scaffold for nickel and several substrates will be used in order to test the activity of the prepared catalysts in oxidation reactions of inactivated organic compounds. Moreover, their ability to perform stereospecific reactions using more complicated targets (natural products) bearing several non-equivalent C-H bonds will also be tested. This subject is specially relevant and interesting due to the importance of selectively incorporate oxidized functionality into organic frameworkds. The performance of asymmetric oxdiation processes may be achieved by the use of chiral ligands. Moreover, the active species implicated in the oxidation processes will be studied. In this sense, the preparation of nickel complexes based on carbene N-heterocyclic ligands may allow the access to low-valent complexes (Ni0 or NiI) which may be capable of direct activation of molecular O2 leading to the formation and detection of Ni-O2 species which may be responsible for the oxidation reactions. Relevant aspects to be considered are their electronic structure, the reversibility of the interaction, the basicity and electrophilicity of these species and their ability to oxidize organic substrates. These Ni-O2 species may possess different oxidation profiles towards exogenous substrates depending on the ligand architecture.'

Introduzione (Teaser)

Oxidation catalysis of organic compounds is a common chemical reaction used to produce fine and commodity chemicals. EU-funded researchers developed a novel environmentally friendly compound exhibiting excellent catalytic activity as an alternative to the more hazardous and expensive ones conventionally used.

Descrizione progetto (Article)

Catalysts are compounds that speed the rate of chemical reactions without themselves being altered by the reaction. Thus, they can be used again and again.

Oxidation catalysis of organic substrates is a main field of research given that oxidation, typically mediated by a transition metallic compound and using hydrocarbons (organic compounds) as a feed-stock, is a common step in the production of commodity and fine chemicals.

Metal complexes can activate molecular oxygen (O2 or dioxygen) for catalytic oxidations. While iron and copper systems have been studied extensively, other metal complexes have not.

Studying the ability of nickel (Ni) to activate molecular oxygen and of the catalytic potential of the resulting Ni-O2 species toward organic substrates was the motivation for the EU-funded NiO2activation project.

Researchers focused on an isolatable and thermally stable superoxo compound, [NiII(beta-diketiminato)(O2)] (LNiO2).

LNiO2 showed unprecedented dioxygenase-like activity in the oxidation of 2,4,6-tri-tert-butylphenol, an industrial chemical used as a fuel, oil, gasoline or lubricant additive. No example of such a reaction appears in the literature and it appears to be specific to Ni as copper- and cobalt-based metal superoxo compounds do not exhibit this behaviour.

In addition, scientists found that LNiO2 interacted with an iron(I) complex to form a highly reactive compound with a NiO2Fe core exhibiting mono-oxygenase activity.

NiO2activation project results supported the powerful oxidising potential of Ni-dioxygen compounds and their viability as environmentally friendly alternatives to heavy metal counterparts palladium and platinum for use in industrially relevant oxidation catalysis reactions.