Heuristics-Guided Exploration of Reaction Mechanisms

摘要

For the investigation of chemical reaction networks, the efficient andaccurate determination of all relevant intermediates and elementary reactionsis mandatory. The complexity of such a network may grow rapidly, in particularif reactive species are involved that might cause a myriad of side reactions.Without automation, a complete investigation of complex reaction mechanisms istedious and possibly unfeasible. Therefore, only the expected dominant reactionpaths of a chemical reaction network (e.g., a catalytic cycle or an enzymaticcascade) are usually explored in practice. Here, we present a computationalprotocol that constructs such networks in a parallelized and automated manner.Molecular structures of reactive complexes are generated based on heuristicrules derived from conceptual electronic-structure theory and subsequentlyoptimized by quantum chemical methods to produce stable intermediates of anemerging reaction network. Pairs of intermediates in this network that might berelated by an elementary reaction according to some structural similaritymeasure are then automatically detected and subjected to an automated searchfor the connecting transition state. The results are visualized as anautomatically generated network graph, from which a comprehensive picture ofthe mechanism of a complex chemical process can be obtained that greatlyfacilitates the analysis of the whole network. We apply our protocol to theSchrock dinitrogen-fixation catalyst to study alternative pathways of catalyticammonia production.