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Molybdenum(0) Triazolylidenes as Catalysts for Borrowing Hydrogen Processes
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Esta tese descreve a síntese e caracterização de complexos de molibdénio(0) com ligandos
bidentados contendo fragmentos de triazolilideno/piridina/triazole, bem como a sua aplicação catalítica
em processos de borrowing hydrogen (BH) e acceptorless dehydrogenative coupling (ADC), e na
oxidação de aminas primárias a amidas.
O manuscrito da tese está organizado em quatro capítulos. O Capítulo 1 apresenta uma
introdução geral aos carbenos N-heterocíclicos (NHCs) e mesoiónicos (MICs), incluindo uma discussão
sobre as suas propriedades eletrónicas e os métodos sintéticos utilizados para a preparação de 1,2,3-
triazolilidenos (trz). Além disso, está incluído o estado da arte dos complexos de molibdénio contendo
ligandos bidentados NHC e a sua aplicação catalítica em processos BH e ADC. Por fim, são
apresentados o objetivo principal da tese e os objetivos específicos.
O Capítulo 2 descreve a síntese e caracterização de uma nova família de complexos Mo(0)
tetracarbonilo contendo ligandos bidentados 1,2,3-triazolilideno. Todos os complexos foram
caracterizados por espectroscopia de RMN (1H, 13C e 95Mo) e IR, e por análise elementar. Além disso,
a estrutura molecular do complexo Mo contendo o ligando piridil-triazolilideno foi determinada por
estudos de difração de raios-X de cristal único. A capacidade doadora dos ligandos NHC e MIC também
é discutida.
O Capítulo 3 descreve a aplicação dos novos complexos de molibdénio(0) descritos no Capítulo
2 na síntese de quinolinas, N-alquilação de aminas com álcoois, α-alquilação de cetonas com álcoois,
β-alquilação entre álcoois e oxidação de aminas. Entre os diferentes complexos [Mo(CO)4(trz)], o
complexo com o grupo Et como substituinte apresentou a maior atividade catalítica na síntese de
quinolinas e na oxidação de aminas. Em contraste, o complexo Mo contendo o ligando triazolilideno
com grupos fenil nas posições N3 foi mais ativo na α-alquilação de cetonas com álcoois.
Por fim, no Capítulo 4, são apresentadas as conclusões da tese.
This thesis describes the synthesis and characterization of a new family of molybdenum(0) complexes with bidentate ligands containing triazolylidene/pyridine/triazole fragments and different wingtips, as well as their catalytic application in borrowing hydrogen (BH) and acceptorless dehydrogenative coupling (ADC) processes, and in the oxidation of primary amines to amides. The manuscript of the thesis is organized in four chapters. Chapter 1 presents a general introduction to N-heterocyclic (NHCs) and mesoionic carbenes (MICs), including a discussion of their electronic properties and the synthetic methods used for the preparation of 1,2,3-triazolylidenes (trz). In addition, the state-of-the-art of molybdenum complexes bearing bidentate NHC and their catalytic application in BH and ADC processes are included. Finally, the main goal of the thesis and the specific objectives are presented. Chapter 2 describes the synthesis and characterization of a new family of Mo(0) tetracarbonyl complexes containing bis-chelating 1,2,3-triazolylidene ligands. All complexes were characterized by NMR (1H, 13C, and 95Mo) and IR spectroscopy, and by elemental analysis. In addition, the molecular structure of the Mo complex containing the mixed pyridyl-triazolylidene ligand was determined by single- crystal X-ray diffraction studies. The donor capacity of the NHC and MIC ligands is also discussed. Chapter 3 describes the application of the novel molybdenum(0) complexes described in Chapter 2 in the synthesis of quinolines, N-alkylation of amines with alcohols, α-alkylation of ketones with alcohols, β-alkylation between alcohols, and in the oxidation of amines. Among the different [Mo(CO)4(trz)] complexes, the ethyl wingtip-substituted complex showed the highest catalytic activity in the synthesis of quinolines and the oxidation of amines. In contrast, the Mo complex bearing the triazolylidene ligand with phenyl groups at N3 positions was more active in the α-alkylation of ketones with alcohols. Finally, in Chapter 4, the conclusions of the thesis are presented.
This thesis describes the synthesis and characterization of a new family of molybdenum(0) complexes with bidentate ligands containing triazolylidene/pyridine/triazole fragments and different wingtips, as well as their catalytic application in borrowing hydrogen (BH) and acceptorless dehydrogenative coupling (ADC) processes, and in the oxidation of primary amines to amides. The manuscript of the thesis is organized in four chapters. Chapter 1 presents a general introduction to N-heterocyclic (NHCs) and mesoionic carbenes (MICs), including a discussion of their electronic properties and the synthetic methods used for the preparation of 1,2,3-triazolylidenes (trz). In addition, the state-of-the-art of molybdenum complexes bearing bidentate NHC and their catalytic application in BH and ADC processes are included. Finally, the main goal of the thesis and the specific objectives are presented. Chapter 2 describes the synthesis and characterization of a new family of Mo(0) tetracarbonyl complexes containing bis-chelating 1,2,3-triazolylidene ligands. All complexes were characterized by NMR (1H, 13C, and 95Mo) and IR spectroscopy, and by elemental analysis. In addition, the molecular structure of the Mo complex containing the mixed pyridyl-triazolylidene ligand was determined by single- crystal X-ray diffraction studies. The donor capacity of the NHC and MIC ligands is also discussed. Chapter 3 describes the application of the novel molybdenum(0) complexes described in Chapter 2 in the synthesis of quinolines, N-alkylation of amines with alcohols, α-alkylation of ketones with alcohols, β-alkylation between alcohols, and in the oxidation of amines. Among the different [Mo(CO)4(trz)] complexes, the ethyl wingtip-substituted complex showed the highest catalytic activity in the synthesis of quinolines and the oxidation of amines. In contrast, the Mo complex bearing the triazolylidene ligand with phenyl groups at N3 positions was more active in the α-alkylation of ketones with alcohols. Finally, in Chapter 4, the conclusions of the thesis are presented.
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Palavras-chave
molybdenum triazolylidene ligands borrowing hydrogen quinolines