Characterizing unusual reactive intermediates with density functional theory: Mechanistic insights for clean energy technologies and organic transformations.

摘要

Developing alternative energy resources is essential to address increasing global energy demands and greenhouse gas levels. Water oxidation, nitric oxide reduction, and organic light-emitting diodes are important technologies for a sustainable future. However, improving these technologies is slow-paced as identifying the critical species responsible for reactivity is often difficult because these reactive species are typically short-lived, high-energy intermediates that evade detection experimentally. Computational models, including density functional theory, can provide important insights into the electronic structure of these fleeting species enabling rational design improvements. The models are benchmarked against experiments for accuracy and facilitate the generation of complete mechanisms for chemical reactivity in accord with experiments.;The electrochemical behavior and mechanisms of mononuclear water oxidation catalysts based on cobalt and manganese are investigated. O--O bond formation occurs via high-spin states, above the electronic ground state, a unique feature of the first-row metals. For cobalt, the high-valent metal-oxo is better described as an electron-deficient, diradicaloid CoII--oxene rather than CoIV--oxo. For manganese, O--O bond formation is promoted by intramolecular radical coupling between antiferromagnetically coupled oxyls.;Cu-doped SSZ-13 zeolite is capable of selectively reducing NOx in oxidizing conditions to N2. An unusual peak, tentatively assigned to an NO+ intermediate, is observed in the infrared spectra is around 2170 cm--1. Our model identifies the structure of a zeolite-stabilized NO+ species matching the experimental vibrational frequency in a complete mechanism for the catalytic reduction.;Blue-emitting phosphorescent iridium(III) complexes exhibit short lifetimes due to population of thermally accessible metal-centered triplet states. The kinetic barriers to metal-ligand bond dissociation to access these non-radiative states are mapped computationally and reveal that heteroleptic complexes introduce a second deactivation pathway via cleavage of the ancillary ligand. Alternative ligands to prevent this dissociation are proposed.;Computational models are used to explain the regiodivergence in the synthesis of bicyclohexa-1,3-dienes from 1,6-enynes with alkyl-substituted methyl propiolates using PPh3 and (S)-xyl-binap as ancillary ligands. In contrast to the original proposal, alkyne insertion occurs into the rhodium--alkenyl bond in both cases. A steric clash of the alkyne's ester terminus with the xyl-binap backbone forces the change in regioselectivity.