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Active catalyst for methane hydroxylation by an iridium-oxo complex
Yoshizawa K.a, Ikeda K.a, Mahyuddin M.H.b, Shiota Y.a
a Inst. for Mat. Chem. and Engineering and Integrated Research Consortium on Chemical Science (IRCCS), Kyushu University, Fukuoka, 819-0395, Japan
b Research Group of Advanced Functional Materials, Institut Teknologi Bandung, Bandung, 40132, Indonesia
[vc_row][vc_column][vc_row_inner][vc_column_inner][vc_separator css=”.vc_custom_1624529070653{padding-top: 30px !important;padding-bottom: 30px !important;}”][/vc_column_inner][/vc_row_inner][vc_row_inner layout=”boxed”][vc_column_inner width=”3/4″ css=”.vc_custom_1624695412187{border-right-width: 1px !important;border-right-color: #dddddd !important;border-right-style: solid !important;border-radius: 1px !important;}”][vc_empty_space][megatron_heading title=”Abstract” size=”size-sm” text_align=”text-left”][vc_column_text]© 2020 American Chemical Society. All rights reserved.Motivated by a recent study on [IrV(η5-C5H5){ppy}(O)]2+ (ppy is 2-phenylpryridine), which is able to cleave the C-H bond of decalin but not of methane due to a high activation energy of 25.7 kcal/mol (Zhou, M. et al. Cp∗ iridium Precatalysts for Selective C-H Oxidation via Direct Oxygen Insertion: A Joint Experimental/Computational Study. ACS Catal. 2012, 2, 208 218), in the present study, we perform density functional theory (DFT) calculations on another kind of an Ir-oxo complex, namely, [IrV(η5-C5Me5){bpy(COOH)2}(O)]2+ or OC, where bpy(COOH)2 is 2,2′-bipyridine-4,4′ dicarboxylic acid, to assess its ability to hydroxylate methane to methanol. OC is formed by light-induced oxidation of the Ir-H2O complex to generate electricity. By hydroxylating methane to methanol and inserting H2O, OC can regenerate the Ir-H2O complex and thus create a catalytic loop similar to a fuel cell. Herein, by utilizing intrinsic bond orbital (IBO) analysis, we show detailed mechanisms of how OC efficiently cleaves the strong C-H bond of methane to form methanol in three possible spin states, namely, the triplet, open-shell singlet, and closed-shell singlet states. In the triplet state, the C-H bond cleavage proceeds with an activation energy of only 11.3 kcal/mol via a hydrogen atom transfer mechanism, where an intermediate species involving •CH3 and Ir-OH• is formed in the same spin state, although a spin change to the open-shell singlet state is likely to occur. A subsequent HO-CH3 recombination occurs without a barrier through direct radical coupling in the open-shell singlet state. In contrast, the C-H bond cleavage in the closed-shell singlet state occurs via a hydride transfer (or oxygen insertion) mechanism, where methanol is directly formed without any intermediate states. Although this reaction mechanism requires a lower C-H activation energy (5.6 kcal/mol), OC in the closed-shell singlet state is less stable by 11.9 kcal/mol than that in the triplet state. These results provide a theoretical prediction of an alternative promising catalyst for the direct conversion of methane to methanol and the methane fuel cell.[/vc_column_text][vc_empty_space][vc_separator css=”.vc_custom_1624528584150{padding-top: 25px !important;padding-bottom: 25px !important;}”][vc_empty_space][megatron_heading title=”Author keywords” size=”size-sm” text_align=”text-left”][vc_column_text]Direct radical coupling,Generate electricity,High activation energy,Hydrogen-atom transfer,Intermediate specie,Intermediate state,Methane hydroxylations,Reaction mechanism[/vc_column_text][vc_empty_space][vc_separator css=”.vc_custom_1624528584150{padding-top: 25px !important;padding-bottom: 25px !important;}”][vc_empty_space][megatron_heading title=”Indexed keywords” size=”size-sm” text_align=”text-left”][vc_column_text]Density functional theory,Hydride transfer,Intrinsic bond orbital,Iridium-oxo complex,Methane hydroxylation[/vc_column_text][vc_empty_space][vc_separator css=”.vc_custom_1624528584150{padding-top: 25px !important;padding-bottom: 25px !important;}”][vc_empty_space][megatron_heading title=”Funding details” size=”size-sm” text_align=”text-left”][vc_column_text]The computations in this work were primarily performed using the computer facilities at the Research Institute for Information Technology, Kyushu University. This work was supported by KAKENHI Grant no. JP17H03117 from the Japan Society for the Promotion of Science (JSPS) and the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT), the MEXT projects of Integrated Research Consortium on Chemical Sciences, the Cooperative Research Program of Network Joint Research Center for Materials and Devices, the Elements Strategy Initiative to Form Core Research Center, and JST-CREST JPMJCR15P5 and JST-Mirai JPMJMI18A2.[/vc_column_text][vc_empty_space][vc_separator css=”.vc_custom_1624528584150{padding-top: 25px !important;padding-bottom: 25px !important;}”][vc_empty_space][megatron_heading title=”DOI” size=”size-sm” text_align=”text-left”][vc_column_text]https://doi.org/10.1021/acscatal.0c01610[/vc_column_text][/vc_column_inner][vc_column_inner width=”1/4″][vc_column_text]Widget Plumx[/vc_column_text][/vc_column_inner][/vc_row_inner][/vc_column][/vc_row][vc_row][vc_column][vc_separator css=”.vc_custom_1624528584150{padding-top: 25px !important;padding-bottom: 25px !important;}”][/vc_column][/vc_row]