Study on the effect of substituents on the structure, volatility, and fluorescence of N-(Alkyl or TMS)-2-pyridinamine diethyl aluminum complexes

Abstract

A series of N-(Alkyl or TMS)-2-pyridinamine ethyl aluminum complex with different substituents were prepared and characterized. When the substituent is n-propyl and n-butyl, the N-(Alkyl or TMS)-2-pyridinamine diethyl aluminum complexes agglomerate at -30 °C. On the contrary, when the substituent is isopropyl and trimethylsilyl, the agglomerate is not easily observed. Compared with the N-(Alkyl or TMS)-2-pyridinamine diethyl aluminum complexes of isopropyl, trimethylsilyl, and isopropyl, the 1H NMR spectra of the pyridine part of N-(n-propyl)-2-pyridinaminoe diethyl aluminum have three sets of peaks. The extra peak may come from the dimer and trimer. Due to the high tension of the quaternary ring and pyridine's influence on the bonding, pyridine did not participate in the coordination, and the optimized monomer structure determines that the monomer is not a quaternary ring structure. Considering the rapid condensation of the liquid product of N-(n-propyl)-2-pyridinaminoe diethyl aluminum at -30 °C, the existence form of compound 2 at different temperatures was determined by variable temperature NMR and simulated NMR. When the temperature reaches 60 °C, the structure of N-(n-propyl)-2-pyridinaminoe diethyl aluminum is a monomer (a stable structure formed with toluene). At -30 °C, the monomer dissociates from the stable structure formed with toluene, and the dimer increases with it. The thermodynamic properties of ethyl aluminum complexes with different substituents were studied by thermal analysis. It was found that the ethyl aluminum complexes with two substituents, isopropyl and trimethylsilyl and difficult to dimerize, were more volatile. The maximum fluorescence wavelength of the complex is affected by the substituents. The spatial and electronic absorption effects of trimethylsilyl make the fluorescence spectrum of the complex 6 blue shift to 406nm. On the contrary, due to the small steric hindrance of n-Propyl, and the easy bonding between Al-N, the fluorescence spectrum of complex 2 shifts to 464nm.