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Síntese de complexos heterolépticos de cobre(I) como potenciais catalisadores da CuAAC
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A procura de processos mais sustentáveis é atualmente um dos maiores impulsionadores da investigação em Química. Entre estes, catálise. Este trabalho foca-se na CuAAC, cicloadição azida-alcino catalisada por cobre, que tem sido alvo de vários estudos nos últimos 20 anos por diversos grupos de investigação. O uso de aditivos, espécies halogenadas e a purificação dos produtos são dos grandes problemas apontados nesta reação que necessitam de solução.1
Tem sido publicado com bons resultados o uso de complexos de cobre contendo ligandos NHC, carbeno N-heterocíclico, ou fosfina em diferentes trabalhos, mas sem uma comparação direta. Com este propósito, foram sintetizadas duas famílias de complexos heterolépticos de cobre(I) contendo ligandos BIAN (bis(aril)acenaftenodiimina) e fosfina, ou BIAN e NHC, de forma a poder comparar a eficiência dos mesmos na CuAAC. Foram também utilizados diferentes contra-iões de forma a averiguar o seu efeito e importância no design de catalisadores.
Partindo de descobertas publicadas anteriormente pelo grupo de investigação,2,3 utilizaram-se ligandos BIAN com grupos eletrodoadores, e trifenilfosfina, por ser um ligando monodentado e facilitar a dissociação, na síntese de nove complexos do tipo [Cu(BIAN)(PPh3)2]X. Prepararam-se ligandos NHC na forma de sais de imidazólio, usualmente utilizados como ligandos neste tipo de complexos, e também um novo contendo 4-iPr-C6H5 como grupo arilo. Estes foram utilizados em conjunto com ligandos BIAN na síntese de cinco complexos do tipo [Cu(BIAN)(NHC)]PF6.
Todos os complexos foram caracterizados por espectroscopia 1D- e 2D-RMN mono e heteronuclear, IV, AE, LC/MS e, quando possível, UV-Vis e difração de raios-X. Foi testada a sua eficiência na reação de CuAAC utilizando diferentes condições, de forma a determinar qual o melhor sistema e o melhor catalisador, que foi posteriormente utilizado na preparação de diferentes 1,2,3-triazoles.
The search for more sustainable processes is currently one of the main drivers of research in Chemistry. Enter, catalysis. This work focuses on CuAAC, copper-catalyzed azide-alkyne cycloaddition, which has been the subject of several studies in the last 20 years by several research groups. The use of additives, halogenated species and the purification of the products are some of the major problems pointed out in this reaction that need a solution.1 It has been published the use of copper complexes containing NHC ligands, N-heterocyclic carbene, or phosphine in different works with good results, but without a direct comparison. For this purpose, two families of heteroleptic copper(I) complexes containing BIAN (bis(aryl)acenaphthenediimine) and phosphine or BIAN and NHC ligands were synthesized, to compare their efficiency in CuAAC. Different counter-ions were also used to ascertain their effect and importance in the catalysts’ design. Based on previous findings by the research group,2,3 BIAN ligands with electron donating groups and triphenylphosphine, which facilitates dissociation, were used in the synthesis of nine complexes of the [Cu(BIAN)(PPh3)2]X type. NHC ligands were prepared in the form of imidazolium salts, commonly used as ligands in this type of complexes, including a new one containing 4-iPr-C6H5 as aryl groups. These were used together with BIAN ligands in the synthesis of [Cu(BIAN)(NHC)]PF6 type complexes. All complexes were characterized by 1D- and 2D-mono and heteronuclear NMR spectroscopy, IR, EA, LC/MS and, when possible, UV-Vis and X-ray diffraction. Their efficiency in the CuAAC reaction was tested under different conditions, in order to determine the best system and the best catalyst, which was later used in the preparation of different 1,2,3-triazoles.
The search for more sustainable processes is currently one of the main drivers of research in Chemistry. Enter, catalysis. This work focuses on CuAAC, copper-catalyzed azide-alkyne cycloaddition, which has been the subject of several studies in the last 20 years by several research groups. The use of additives, halogenated species and the purification of the products are some of the major problems pointed out in this reaction that need a solution.1 It has been published the use of copper complexes containing NHC ligands, N-heterocyclic carbene, or phosphine in different works with good results, but without a direct comparison. For this purpose, two families of heteroleptic copper(I) complexes containing BIAN (bis(aryl)acenaphthenediimine) and phosphine or BIAN and NHC ligands were synthesized, to compare their efficiency in CuAAC. Different counter-ions were also used to ascertain their effect and importance in the catalysts’ design. Based on previous findings by the research group,2,3 BIAN ligands with electron donating groups and triphenylphosphine, which facilitates dissociation, were used in the synthesis of nine complexes of the [Cu(BIAN)(PPh3)2]X type. NHC ligands were prepared in the form of imidazolium salts, commonly used as ligands in this type of complexes, including a new one containing 4-iPr-C6H5 as aryl groups. These were used together with BIAN ligands in the synthesis of [Cu(BIAN)(NHC)]PF6 type complexes. All complexes were characterized by 1D- and 2D-mono and heteronuclear NMR spectroscopy, IR, EA, LC/MS and, when possible, UV-Vis and X-ray diffraction. Their efficiency in the CuAAC reaction was tested under different conditions, in order to determine the best system and the best catalyst, which was later used in the preparation of different 1,2,3-triazoles.
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Palavras-chave
CuAAC BIAN NHC cobre(I) complexos heterolépticos triazoles