FTIR spectroscopy of ethyl benzoate-titanium tetrachloride complexes with application to supported Ziegler-Natta catalysts

Abstract

Abstract. X-ray studies revealed a strong trans-influence in titanium tetrachloride-ethyl benzoate complexes. From FTIR spectra, a very strong complexation is found in a 2:1 complex and in a surface complex on magnesium chloride supported Ziegler-Natta catalysts. In both cases the ester is proposed to be trans to a bridging chlorine. Key words:Ziegler-Natta, ethyl benzoate, titanium tetrachloride, transinfluence, complex.A recent important development in Ziegler-Natta catalysis is the development of the magnesium chloride supported highly active catalyst for the polymerization of olefins. The complexity and the excellent activity of the catalysts challenged our understanding of the system. We therefore initiated a basic research of the compounds which constitute the catalysts in order to obtain a more reliable comprehension of the structure of the active center, In this context the combination of IR-spectroscopy and single crystal X-ray scattering measurements proved to be a powerful tool to elucidate structural information of possible catalyst precursors.Accurate X-ray scattering measurements on single crystals of the 1:2 and 2:2 complexes between titanium tetrachloride and ethyl benzoate revealed important trends in bonding behaviour [1]. A significant transinfluence is observed. Terminal Ti-C1 bonds (2.31 A) trans to another terminal Ti-C1 are significantly longer than terminal Ti-C1 bonds (2.22--2.24 ,~) trans to an ester group or a bridging chlorine. A cis influence is also seen, as the ester complexation through carbonyl is enhanced by an increasing number of weakly bonded neighbours in the octahedral Ti-entity.

MOCVD of TiO2 Thin Films using a Heteroleptic Titanium Complex: Precursor Evaluation and Investigation of Optical, Photoelectrochemical and Electrical Properties

“…The bands in the range 2750 to 2950 cm −1 were characteristic stretching frequencies of the different CH groups present in the molecule. The bands around 600–540 cm −1 were unambiguously assigned to the TiO bond, and were not observed in the ligand spectrum. TiN stretching frequencies, which typically appear below 400 cm −1 , could not be observed .…”

Spectroscopic Evidences for TiCl4/Donor Complexes on the Surface of MgCl2-Supported Ziegler–Natta Catalysts

“…As far as the role and states of the IDs are concerned, several contrasting opinions have been formulated since the early history of these catalysts. According to some authors, the ID coordinates directly on a vacancy of the titanium sites, thus creating new active (and stereo-specific) centers. ,,− This hypothesis is in agreement with many experimental observations on the produced polymer, and with the direct detection of TiCl 4 /ester complexes on MgCl 2 by extended X-ray absorption fine structure (EXAFS) spectroscopy, and it is further corroborated by the fact that homogeneous complexes are formed between TiCl 4 and many Lewis base molecules. However, it is weakened by the finding that the IDs react with the aluminum alkyls, and they can also be extracted from the catalyst in different amounts .…”

Investigation of Planar Ziegler-Natta Model Catalysts Using Attenuated Total Reflection Infrared Spectroscopy

“…IR spectroscopy has been extensively applied to Ziegler-Natta catalysts [17]. With regard to propylene polymerization catalysts, most of the work has focused on the spectral changes in the m C=O of the internal aromatic ester in various stages of catalyst preparation [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31].…”