Control of Substrates Beyond the Catalyst Active Site

Efficacy analysis of compartmentalization for ambient CH4 activation mediated by a RhII metalloradical in a nanowire array electrode

Compartmentalization is a viable approach for ensuring the turnover of a solution cascade reaction with ephemeral intermediates, which may otherwise deactivate in the bulk solution. In biochemistry or enzyme-relevant cascade reactions, extensive models have been constructed to quantitatively analyze the efficacy of compartmentalization. Nonetheless, the application of compartmentalization and its quantitative analysis in non-biochemical reactions is seldom performed, leaving much uncertainty about whether compartmentalization remains effective for non-biochemical reactions, such as organometallic, cascade reactions. Here, we report our exemplary efficacy analysis of compartmentalization in our previously reported cascade reaction for ambient CH₄-to-CH₃OH conversion, mediated by an O₂-deactivated Rh^II metalloradical with O₂ as the terminal oxidant in a Si nanowire array electrode. We experimentally identified and quantified the key reaction intermediates, including the Rh^II metalloradical and reactive oxygen species (ROS) from O₂. Based on such findings, we experimentally determined that the nanowire array enables about 81% of the generated ephemeral intermediate Rh^II metalloradical in air, to be utilized towards CH₃OH formation, which is 0% in a homogeneous solution. Such an experimentally determined value was satisfactorily consistent with the results from our semi-quantitative kinetic model. The consistency suggests that the reported CH₄-to-CH₃OH conversion surprisingly possesses minimal unforeseen side reactions, and is favorably efficient as a compartmentalized cascade reaction. Our quantitative evaluation of the reaction efficacy offers design insights and caveats into application of nanomaterials to achieve spatially controlled organometallic cascade reactions.

We integrated theory with experiment to evaluate the catalytic cycle of seemingly incompatible steps enabled by nanowire array for CH₄-to-CH₃OH conversion, and determined the array’s efficacy in the context of microscopic compartmentalization.