Electron spin resonance spectra of methyl-substituted titanocene(III) halides

Abstract

Electron spin resonance spectra of [Ti(C₅H_{5 –n}Me_n)₂X](n= 0,1,3,4 or 5; X = Cl, Br or I) have been recorded in toluene and 2-methyltetrahydrofuran (mthf) solution at 77 and 295 K. Anisotopic spectra in frozen glasses were satisfactorily simulated and the parameters interpreted in terms of a generalised molecular orbital energy diagram. The monomeric species were characterised by a highly asymmetric g tensor, the lowest component being strongly dependent on the number of methyl groups (n) and the nature of the halide ligand; it moved to a lower value on going from Cl to I and with an increase in n. The ESR spectra revealed that compounds with n= 3–5 were monomeric in toluene whereas those with n= 0 or 1 were dimers. The latter compounds dissociated in mthf with the co-ordination of the solvent molecule. Mixtures of [Ti(C₅H₂Me₃)₂Cl] or [Ti(C₅H₂Me₃)₂Br] with their co-ordinated solvates were found in mthf at room temperature while [Ti(C₅H₂Me₃)₂I] and all the C₅HMe₄ and C₅Me₅ compounds remained unsolvated. At 77 K the monomer–solvate equilibria were shifted so that all the C₅H₂Me₃ compounds formed only solvates, the C₅HMe₄ compounds were only partly solvated and the C₅Me₅ compounds remained unsolvated.