Dataset Information

Understanding the mechanism of direct visible-light-activated [2 + 2] cycloadditions mediated by Rh and Ir photocatalysts: combined computational and spectroscopic studies.

ABSTRACT: The mechanism of [2 + 2] cycloadditions activated by visible light and catalyzed by bis-cyclometalated Rh(iii) and Ir(iii) photocatalysts was investigated, combining density functional theory calculations and spectroscopic techniques. Experimental observations show that the Rh-based photocatalyst produces excellent yield and enantioselectivity whereas the Ir-photocatalyst yields racemates. Two different mechanistic features were found to compete with each other, namely the direct photoactivation of the catalyst-substrate complex and outer-sphere triplet energy transfer. Our integrated analysis suggests that the direct photocatalysis is the inner working of the Rh-catalyzed reaction, whereas the Ir catalyst serves as a triplet sensitizer that activates cycloaddition via an outer-sphere triplet excited state energy transfer mechanism.

SUBMITTER: Jung H

PROVIDER: S-EPMC8293808 | biostudies-literature | 2021 Jul

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Understanding the mechanism of direct visible-light-activated [2 + 2] cycloadditions mediated by Rh and Ir photocatalysts: combined computational and spectroscopic studies.

Jung Hoimin H Hong Mannkyu M Marchini Marianna M Villa Marco M Steinlandt Philipp S PS Huang Xiaoqiang X Hemming Marcel M Meggers Eric E Ceroni Paola P Park Jiyong J Baik Mu-Hyun MH

Chemical science 20210623 28

The mechanism of [2 + 2] cycloadditions activated by visible light and catalyzed by bis-cyclometalated Rh(iii) and Ir(iii) photocatalysts was investigated, combining density functional theory calculations and spectroscopic techniques. Experimental observations show that the Rh-based photocatalyst produces excellent yield and enantioselectivity whereas the Ir-photocatalyst yields racemates. Two different mechanistic features were found to compete with each other, namely the direct photoactivation ...[more]

PMID: 34349938

Similar Datasets

Project description:In this study, comprehensive density functional theory calculations were conducted to investigate the molecular mechanism of electrocatalytic proton reduction using group 9 transition metal bpaqH (2-(bis(pyridin-2-ylmethyl)amino)-N-(quinolin-8-yl)acetamide) complexes. The goal was to explore how variations in the structural and electronic properties among the three metal centers might impact the catalytic activity. All three metal complexes were observed to share a similar mechanism, primarily characterized by three key steps: heterolytic cleavage of H2 (HEP), reduction protonation (RPP), and ligand-centered protonation (LCP). Among these steps, the heterolytic cleavage of H2 (HEP) displayed the highest activation barrier for cobalt, rhodium, and iridium catalysts compared to those of the RPP and LCP pathways. In the RPP pathway, hydrogen evolution occurred from the MII-H intermediate using acetic acid as a proton donor at the open site. Conversely, in the LCP pathway, H-H bond formation took place between the hydride and the protonated bpaqH ligand, while the open site acted as the spectator. The enhanced activity of the cobalt complex stemmed from its robust σ-bond donation and higher hydride donor ability within the metal hydride species. Additionally, the cobalt complex demonstrated a necessary negative potential in the first (MIII/II) and second (MII/I) reduction steps in both pathways. Notably, MIII/II-H exhibited a more crucial negative potential for the cobalt complex compared to those of the other two metal complexes. Through an examination of kinetics and thermodynamics in the RPP and LCP processes, it was established that cobalt and rhodium catalysts outperformed the iridium ligand scaffold in producing molecular hydrogen after substituting cobalt metal with rhodium and iridium centers. These findings distinctly highlight the lower-energy activation barrier associated with LCP compared to alternative pathways. Moreover, they offer insights into the potential energy landscape governing hydrogen evolution reactions involving group 9 transition metal-based molecular electrocatalysts.

Project description:The preparation of visible-light-driven photocatalysts has become highly appealing for environmental remediation through simple, fast and green chemical methods. The current study reports the synthesis and characterization of graphitic carbon nitride/titanium dioxide (g-C3N4/TiO2) heterostructures through a fast (1 h) and simple microwave-assisted approach. Different g-C3N4 amounts mixed with TiO2 (15, 30 and 45 wt. %) were investigated for the photocatalytic degradation of a recalcitrant azo dye (methyl orange (MO)) under solar simulating light. X-ray diffraction (XRD) revealed the anatase TiO2 phase for the pure material and all heterostructures produced. Scanning electron microscopy (SEM) showed that by increasing the amount of g-C3N4 in the synthesis, large TiO2 aggregates composed of irregularly shaped particles were disintegrated and resulted in smaller ones, composing a film that covered the g-C3N4 nanosheets. Scanning transmission electron microscopy (STEM) analyses confirmed the existence of an effective interface between a g-C3N4 nanosheet and a TiO2 nanocrystal. X-ray photoelectron spectroscopy (XPS) evidenced no chemical alterations to both g-C3N4 and TiO2 at the heterostructure. The visible-light absorption shift was indicated by the red shift in the absorption onset through the ultraviolet-visible (UV-VIS) absorption spectra. The 30 wt. % of g-C3N4/TiO2 heterostructure showed the best photocatalytic performance, with a MO dye degradation of 85% in 4 h, corresponding to an enhanced efficiency of almost 2 and 10 times greater than that of pure TiO2 and g-C3N4 nanosheets, respectively. Superoxide radical species were found to be the most active radical species in the MO photodegradation process. The creation of a type-II heterostructure is highly suggested due to the negligible participation of hydroxyl radical species in the photodegradation process. The superior photocatalytic activity was attributed to the synergy of g-C3N4 and TiO2 materials.

Dataset Information

Understanding the mechanism of direct visible-light-activated [2 + 2] cycloadditions mediated by Rh and Ir photocatalysts: combined computational and spectroscopic studies.

Publications

Understanding the mechanism of direct visible-light-activated [2 + 2] cycloadditions mediated by Rh and Ir photocatalysts: combined computational and spectroscopic studies.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets