Synthesis and study of tricarbonylchromium complexes of some metalloporphines

Siddiqui, Zahir Uddin (1970) Synthesis and study of tricarbonylchromium complexes of some metalloporphines. Masters thesis, Memorial University of Newfoundland.

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Abstract

The tricarbonylchromium complexes of some metalloporphins have been synthesized and studied. The tricarbonylchromium complexes of 1st transition series metal porphines were prepared by refluxing hexacarbonylchromium and metal porphine in an atmosphere of pure nitrogen for 6 hours. After the preliminary studies by thin-layer chromatography on dried products the purification was done on a florisil column under nitrogen using different eluents for different compounds; in most of the cases the chromatographic technique for purification was successful. The purity of the purified products was tested by ultra violet/visible and infra red spectroscopy. The visible region spectrum of the complex had a blue or red shift in the bands as compared to starting material (metal porphine ): in most cases, if the product was impure bands were mixed and broad. The infra red of pure product always had very distinct carbonyl peaks: if the compound was decomposed no CO stretching vibrations were observed. -- The structures of the complexes were established with the help of infra red, ultra violet and n.m.r.. The elemental analysis confirmed the structure although the elemental analyses were not correct in some compounds due to their unstability. -- Tetraphenylporphine, p-substituted porphine and metalloporphines have been studied spectroscopically (UV/visible lR) and theoretically. Zerner and Gouterman have done extended Hückel calculations on porphine systems with the metals Mn, Fe, Co, Ni, Cu and Zn. These calculations help in understanding the electronic structure of metalporphine. -- The studies on the trend of carbonyl frequencies of arene metal tricarbonyl have been done by Brown and Hughes using different arenes and different transition metals. -- The preparation of tricarbonylchromium complexes of α,β,γ,δ tetraphenylporphine metals and their infra red, ultra violet/visible spectra gives a better understanding of electronic distribution and bonding in metalloporphines. -- The experimental results of CO stretching vibrations trend in the complexes was found in the following decreasing order: Cr⁺²>Mn⁺²∿∿Co⁺²∿∿Zn⁺²∿∿Cu⁺²∿∿Ni⁺²>Mn⁺³. -- The expected trend of CO stretching vibrations in complexes was in the following decreasing order. Cr⁺²>Mn⁺²>Co⁺²>Zn⁺²>Cu⁺²>Ni⁺²>Mn⁺³. -- The CO stretching vibrations in all the complexes depend upon the π electron distribution in the metal porphines. A decrease of π electron distribution will increase the CO stretching vibration values and an increase of π electron distribution will decrease the CO stretching vibration values. As a result the trend in CO stretching vibration gives the qualitative values for π electron distribution in the metal porphine system and also throws light on bonding between central metal and porphine.

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