| The ferrocenyl-substituted pyridines have attracted considerable attention due to their distinctive structures and excellent electrochemical reversibility of FeII/FeIII redox couple in ferrocene. These π-conjugated organometallic compounds have been applied in catalysis, electro-active molecular devices and liquid crystal materials. The vast majority of known ferrocenyl pyridines only contain a single ferrocenyl unit, and a few of them have two or more ferrocenyl units. The studies on the synthesis and electrochemical properties of multi-ferrocenyl substituted pyridines are relatively rare, especially for the multi-ferrocenyl substituted pyridines with other substituents. In view of this, my doctoral dissertation focuses on this subject to make a study and analysis.Molecules containing pyridine core with multiple ferrocenyl termini are accessible by C–C cross-coupling reactions, such as Negishi, Suzuki, Stille and Sonogashira ferrocenylation of appropriate pyridylhalides with ferrocenyl metal-salt intermediates or ferrocenylacetylene. However, classic coupling reactions cannot easily accomplish the synthesis of pyridine derivatives bearing multiple different ferrocenyl groups because of the laborious preparation of ferrocenyl metal-salt intermediates and multi-steps coupling reactions.The acetylene-nitrile [2+2+2] cycloaddition reaction is known as an atom economic route to synthesize substituted pyridine derivatives. Four diferrocenyl pyridine derivatives, 4,6-diferrocenyl-2-methylpyridine(2-CH3-4,6-Fc2-C5H2 N, 1) [Fc = Fe(η5-C5H4)(η5-C5H5)], 3,6-diferrocenyl-2-methylpyridine(2-CH3-3,6-Fc2-C5H2 N, 2), 4,6-diferrocenyl-2-phenylpyridine(2-C6H5-4,6-Fc2-C5H2 N, 3) and 3,6-diferrocenyl-2-phenylpyridine(2-C6H5-3,6-Fc2-C5H2 N, 4) were prepared by cobaltl-mediated [2+2+2] cycloaddition reactions of ferrocenylacetylene with acetonitrile or benzonitrile. The byproduct 1,2,4-triferrocenylbenzene(1,2,4-Fc3-C6H3, 5) was obtained along with 1-4. The optimization of cycloaddition reaction focused on the preparation of 3 and 4. The influence of reactant ratio, solvent(organic solvents and supercritical carbon dioxide), reaction temperature and time on the activity and selectivity of five cobalt catalysts, Co, Co Cl2, Co2(CO)8, Cp Co(CO)2, Co2(CO)6(μ2-η2-Fc C≡CFc) was investigated. The optimal reactions were obtained with 15%(mol) catalyst concentration, 1:6 ratio of Fc-C≡CH to Ph CN, toluene used as solvent, 5 h reaction time and reflux reaction temperature.A series of new diferrocenyl-diferrocenylethynyl substituted pyridine derivatives, 4,6-diferrocenyl-3,5-diferrocenylethynyl-2-methylpyridine [2-CH3-4,6-Fc2-3,5-(Fc C≡C)2-C5 N, 6], 3,6-diferrocenyl-4,5-diferrocenylethynyl-2-phenylpyridine [2-C6H5-3,6-Fc2-4,5-(Fc C≡C)2-C5 N, 7], 4,6-diferrocenyl-3,5-diferrocenylethynyl-2-phenylpyridine [2-C6H5-4,6-Fc2-3,5-(Fc C≡C)2-C5 N, 8], 3,5-diferrocenyl-4,6-diferrocenylethynyl-2-phenylpyridine [2-C6H5-3,5-Fc2-4,6-(Fc C≡C)2-C5 N, 9] have been synthesized by [2+2+2] cycloaddition reactions of 1,4-bis(ferrocenyl)butadiyne and acetonitrile or benzonitrile under the optimal cobaltl-mediated cycloaddition reaction conditions, in which ethynyl unit has been introduced to make a rigid bridge linkage between ferrocenyl termini and pyridine core. The ferrocenyl derivatives have ideal electrochemical features. The substituted patterns of ferrocenyl termini on pyridine or benzene ring are closely related with their electrochemical properties, which means electrochemical properties of ferrocenyl derivatives can be used for deducing their molecular structures. Compounds 6-9 belong to the positional isomers of pyridine derivatives, however, the data collected from spectroscopic means were not enough to confirm the exact substituted positions of ferrocenyl and ferrocenylethynyl groups on central pyridine ring in isomers 6-9. Therefore, we firstly used the electrochemical and structural information of analogy compounds to determine the substitutions positons of isomers 2-4. The mechanism of the “Cp Co” catalyzed [2+2+2] cycloaddition reactions of 1,4-bis(ferrocenyl)butadiyne with nitrile was assumed, which explaines the regioselectivity of cycloaddition products.Two new triferrocenyl-diferrocenylethynyl substituted benzene derivatives, 1,3,5-triferrocenyl-2,4-diferrocenylethynylbenzene(1,3,5-Fc3-2,4-(Fc C≡C)2-C6 H, 10), 1,2,4-triferrocenyl-3,5-diferrocenylethynylbenzene(1,2,4-Fc3-3,5-(Fc C≡C)2-C6 H, 11) were synthesized by cycloaddition reactions of ferrocenylacetylene cobalt cluster as catalyst precursor with 1,4-bis(ferrocenyl)butadiyne.The molecular composition and structure of compounds 1-11 were characterized by FT-IR, NMR, MS, CV and Elemental analysis. The molecular and crystal structures of compounds 1, 3, 4, 6, 10 were determined by X-ray single crystal diffraction analysis.The cyclic voltammetry and square wave voltammetry highlight the electrochemical behaviors of compounds 1-4 and 6-11, which indicates multi-step reversible redox processes of ferrocenyl moieties have occurred. The wave splitting and ?E1/2(oxidation potential difference) values in cyclic voltammograms are closely related with the substituted patterns of ferrocenyl termini on pyridine rings, and the electronic communication between ferrocenyl units is electrostatic interactions. The electrochemical properties of five ferrocenyl-subtituted benzene derivatives 10-11 were investigated by cyclic voltammetry and thin-layer cyclic voltammetry, which reveals that the redox reactions of them occur in three distinct steps involving a total of five electrons... |
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