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      Chemistry of Our Oceans

      editorial
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      Journal of the Brazilian Chemical Society
      Sociedade Brasileira de Química

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          Towards rational design of carbon nitride photocatalysts: Identification of cyanamide "defects" as catalytically relevant sites

          The heptazine-based polymer melon (also known as graphitic carbon nitride, g-C3N4), is a promising photocatalyst for hydrogen evolution. Nonetheless, attempts to improve its inherently low activity are rarely based on rational approaches due to a lack of fundamental understanding of its mechanistic operation. Here, we employ molecular heptazine-based model catalysts to identify the cyanamide moiety as a photocatalytically relevant "defect". We exploit this knowledge for the rational design of a carbon nitride polymer populated with cyanamide groups, yielding a material with 12- and 16-times the hydrogen evolution rate and apparent quantum efficiency (400 nm), respectively, compared to the benchmark melon. Computational modelling and material characterization suggest this moiety improves co-ordination (and, in turn, charge transfer kinetics) to the platinum co-catalyst and enhances the separation of the photo-generated charge carriers. The demonstrated knowledge transfer for rational catalyst design presented here provides the conceptual framework for engineering high performance heptazine-based photocatalysts.
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            Unexpected regioselective carbon-hydrogen bond activation/cyclization of indolyl aldehydes or ketones with alkynes to benzo-fused oxindoles.

            Rhodium-catalyzed carbon-hydrogen bond activation has attracted great interest in the construction of carbon-carbon and carbon-heteroatom bonds. In recent years, transition metal-mediated oxygen transposition through a 'dehydration-rehydration' process has been considered as a promising strategy towards oxygen-functionalized compounds. Here we describe an unexpected rhodium-catalyzed regioselective carbon-hydrogen bond activation/cyclization of easily available indolyl aldehydes or ketones with alkynes to afford benzo-fused oxindoles, involving the sequential carbonyl-assisted carbon-hydrogen activation of the indole ring at the 4-position, [4+2] cyclization, aromatization via dehydration, nucleophilic addition of water to iminium and oxidation. Isotopic labelling experiments disclose the occurrence of apparent oxygen transposition via dehydration-rehydration from the indolyl-3-carbonyl group to the 2-position of pyrrole to forge a new carbonyl bond. The tandem reaction has been used as the key step for the concise synthesis of priolines, a type of alkaloid isolated from the roots of Salvia prionitis.
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              Mar. Chem.

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                Author and article information

                Contributors
                Role: ND
                Journal
                jbchs
                Journal of the Brazilian Chemical Society
                J. Braz. Chem. Soc.
                Sociedade Brasileira de Química (São Paulo )
                1678-4790
                November 2015
                : 26
                : 11
                : 2169-2170
                Affiliations
                [1 ] Universidade Federal da Bahia Brazil
                Article
                S0103-50532015001102169
                10.5935/0103-5053.20150285
                6b3370b6-a848-4ec4-9dfa-f51de2554723

                http://creativecommons.org/licenses/by/4.0/

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                Product

                SciELO Brazil

                Self URI (journal page): http://www.scielo.br/scielo.php?script=sci_serial&pid=0103-5053&lng=en
                Categories
                CHEMISTRY, MULTIDISCIPLINARY

                General chemistry
                General chemistry

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