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The C-H bond is the most common linkage in organic chemistry, and also one of the most inert. The ability to selectively activate and functionalize typical (e.g. aryl and alkyl) C-H bonds is accordingly one of the most important challenges in catalysis. Transition-metal-containing molecules or complexes (in either heterogeneous or homogeneous forms) have proven to be the most effective class of catalysts for such selective reactions.
Alkanes are our most abundant organic resource but are famously difficult to exploit for selective chemical reactions. We have found that "pincer"-ligated iridium complexes (e.g. (PCP)Ir) are highly effective for the selective dehydrogenation of alkanes and alkyl groups to give olefins which are, in stark contrast with alkanes, perhaps the most versatile of chemical precursors. We are incorporating this reaction into tandem systems for several catalytic transformations based on dehydrogenation. We are further exploiting the ability of the (PCP)Ir fragment to activate C-H bonds for reactions such as electro¬chemical dehydrogenation, intermolecular coupling dehydrogenative coupling to give C-C or C-O bonds, and the deoxygenation of alcohols.
More recently we have turned attention to iridium Phebox complexes. While (PCP)Ir operates via C-H activation by electron-rich Ir(I), (Phebox)Ir operates via Ir(III) and possibly Ir(V) intermediates. Such a high-oxidation-state catalytic cycle offers many potential advantages. Surprisingly, the (Phebox)Ir-catalyzed reactions of simple hydrocarbons are themselves catalyzed by an even simpler species, the Na+ cation.
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