Understanding the mechanism of direct visible-light-activated [2 + 2] cycloadditions mediated by Rh and Ir photocatalysts: combined computational and spectroscopic studies |
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Authors: | Hoimin Jung Mannkyu Hong Marianna Marchini Marco Villa Philipp S Steinlandt Xiaoqiang Huang Marcel Hemming Eric Meggers Paola Ceroni Jiyong Park Mu-Hyun Baik |
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Institution: | Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141 Republic of Korea.; Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 34141 Republic of Korea.; Department of Chemistry “Giacomo Ciamician”, University of Bologna, via Selmi 2, 40126 Bologna Italy.; Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Strasse 4, 35043 Marburg Germany |
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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.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. |
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