Electron spin resonance studies on Ziegler catalyst systems: Part III. Some mixtures of aluminium methyl compounds and aluminium chloride with bis‐cyclopentadienyl titanium dichloride and bis‐cyclopentadienyl methyl chlorotitanium

Abstract

The systems (CsH~,)zTiC12 f AI(CH3)3(1), ( C~H & Z T~C I Z + AI(CH3)zCI (II), (C5H5)zTiCHsCI + AICH~CIZ (HI), (CsH5)zTiCl~ -t-AICH3Ch (IV) and (C5H5)2TiCH3CI + AIC13 (V) were studied by means of electron spin resonance a t room temperature. In most cases the concentration of the titanium compounds was approximately 0.8 M ; the AI/Ti ratio of the aluminium and titanium components was normally 1.0 and 2.0. The number of unpaired electrons as function of time, and also the shape of the spectra, was measured over a period of lo00 hours. The g-values of the resonance curves were also determined. From the methyl migration observed by us it could be expected, that the systems 11 and I11 show a close similarity at AI/Ti = 1.0; this also holds for the systems IV and V.In the systems I (AI/Ti = 0.8), 11 (AI/Ti = 1.0 and 2.0) and 111 (AI/Ti = 1.0) the concentration of unpaired electrons reaches a final value within the measuring period ; this value is approximately equal to the concentration of the titanium component. The consequent supposition that the unpaired electron is coupled to a particle containing a trivalent titanium atom is confirmed by the result of a simultaneous measurement of the number of unpaired electrons and the number of trivalent titanium atoms, the latter being determined by titration. When the concentration of unpaired electrons is lower than appr. 10 mmoles/l, the spectra show a more or less complicated hyperfine structure. It appears that the spectra may be considered to be built up of three basic spectra, which can be ascribed to the complexes ( C~H~) Z T~C I A I ( C H~) Z C I , ( C~H~) Z T~C I A~C H~C~Z and (C5H5)Z TiCIAIC13. A suggestion is presented as to the way in which these complexes have been formed. At concentrations above appr. 100 mmoles/l, the spectra contract to form a single, narrow line; upon dilution the original spectrum re-appears.The g-values of the systems all lie around 1.97.Part I1 of this series has been published in Rec. trav. chim. 81, 73 (1962). 226 IntroductionFairly recently various investigators have started to study the esr spectra of (CsH5)zTiClz-Al alkyl systems.For example, Shilov et a1 examined the system ( C E , H~) Z T~C I~-A I (~C~H~ in toluene at a concentration of the Ti-component = 2.10-4 M and lower. From the spectrum they concluded i.a. that the unpaired electron has a finite spin density at the position of the Al-atom.Maki and RandaN examined the esr spectra of mixtures of (CgH5)zTiClz with Al(CH3)3, Al(CzH5)3, Al(iC4H9)3, Al(CzH5)zCI and AlCzHsCh in benzene at a concentration of the Ti-component = 10-3 -10-4 M . For the various systems they found characteristic spectra which did not change in character during the measuring period, except those for the mixtures with AlCzHsCIz.Zejrova et a I 4 studied the spectra of mixtures of (CsHs)zTiCIz, (C5H5)zTiBrz and (C5H5)zTiIz with AI(CzH5)3, AI(CsH5)3, Al(iC3H7)3, AI(CH3)3, Al(iC4Hg)3 and Al(CzH5)zCI, at various Ti concentrations. We performed measurements on the mixtures in toluene mentioned in Table I, at room ...