Integrated electrochemical CO2 reduction and hydroformylation.

The development of integrated multi-catalyst processes has become of high interest to transform abundant feedstocks or environmental pollutants to commodity chemicals in a one pot, one pass fashion. Specifically, CO2 poses a large environmental burden and would thus be a desirable, relatively abundant C1 source in multi-step synthetic chemistry. Herein we disclose the synthesis of aldehydes from CO2via the integration of electrochemical CO2 reduction (CO2RR) and hydroformylation, taking advantage of the typically unwanted concomitant hydrogen evolution (HER) to generate the necessary CO and H2 needed for hydroformylation. Though typical hydroformylation catalysts based on Rh would be deactivated under CO2RR conditions, we circumvent this limitation by spatially segregating our CO2RR and hydroformylation systems in a vial-in-vial reactor, while allowing CO and H2 transport between catalyst sites. In this manner, 97% aldehyde yield from CO2RR and styrene was achieved selectively using a classic homogeneous hydroformylation catalyst in HRh(CO)(PPh3)3, and 43% aldehyde yield was obtained using a heterogenized version of this Rh catalyst onto mesoporous silica. This work not only repurposes undesired HER in CO2RR and prepares aldehydes from CO2 without added H2, but expands the scope of processes that transform feedstocks all the way to commodity chemicals in a one pass manner.

A generalized kinetic model for compartmentalization of organometallic catalysis.

Compartmentalization is an attractive approach to enhance catalytic activity by retaining reactive intermediates and mitigating deactivating pathways. Such a concept has been well explored in biochemical and more recently, organometallic catalysis to ensure high reaction turnovers with minimal side reactions. However, the scarcity of theoretical frameworks towards confined organometallic chemistry impedes broader utility for the implementation of compartmentalization. Herein, we report a general kinetic model and offer design guidance for a compartmentalized organometallic catalytic cycle. In comparison to a non-compartmentalized catalysis, compartmentalization is quantitatively shown to prevent the unwanted intermediate deactivation, boost the corresponding reaction efficiency (γ), and subsequently increase catalytic turnover frequency (TOF). The key parameter in the model is the volumetric diffusive conductance (F V) that describes catalysts' diffusion propensity across a compartment's boundary. Optimal values of F V for a specific organometallic chemistry are needed to achieve maximal values of γ and TOF. As illustrated in specific reaction examples, our model suggests that a tailored compartment design, including the use of nanomaterials, is needed to suit a specific organometallic catalytic cycle. This work provides justification and design principles for further exploration into compartmentalizing organometallics to enhance catalytic performance. The conclusions from this work are generally applicable to other catalytic systems that need proper design guidance in confinement and compartmentalization.

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 RhII metalloradical with O2 as the terminal oxidant in a Si nanowire array electrode. We experimentally identified and quantified the key reaction intermediates, including the RhII 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 RhII 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.