Selective Photocatalytic Hydroxylation of Inert Hydrocarbons Such as Methane Using Air as the Oxidant

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The low-temperature conversion of hydrocarbons into more reactive intermediates, e.g. alcohols, is a great challenge for catalysis. In contrast nature has already proved that reactions of this type can be performed under ambient conditions using enzymes such as methane monooxygenases that are based on iron or copper ions in the active site. Studies on selective oxidations, using low molecular weight iron or copper complexes as model compounds for these enzymes thus far mainly have been performed as thermal processes. In contrast, in our collaborative project, we now want to incorporate photochemical key-steps for the following reasons: a) Excited state molecules are much more powerful oxidants (as well as reductants) than the corresponding ground state species. Thus, a peroxo metal complex for example, that will not oxidize a certain hydrocarbon under ambient conditions, might well be able to perform this reaction upon irradiation. b) It could be possible to photochemically generate new oxygen complexes as reactive species that are otherwise very difficult to obtain through a normal chemical reaction. c) The electron distribution and spin characteristics of metal-oxo fragments and related reactive intermediates may be influenced and controlled by light absorption. Therefore, we plan to study reactions such as the reaction of metal ozonides to form a mononuclear metal-oxo complex releasing dioxygen if activated by light. Such complexes are regarded as extremely powerful oxidants and could be used for selective oxidations in situ. Furthermore, it is well known that several peroxo complexes are light sensitive. Again, investigations will be performed to find out, if such a peroxide can be directly transformed into a metal oxo complex by photoinduced processes. Methane and other hydrocarbons will be reacted with different oxygen complexes , e.g. dinuclear copper peroxo species, dioxygen adducts or metal oxo compounds under exposure to mono- and polychromatic light.