Comparison of the molecular structures and infrared spectra of titanocene and niobocene chelate trimethylacetates

An X-ray structural study (λ(Mo-K α ), θ2θ scanning, 2θ ⩽ 46°, T = −120°C) of Cp 2 TiOOCCMe 3 (I) has been performed. The cyclopentadienyl ligands form π-bonds with the Ti atom (mean TiC mean 2.40(1) A, mean CC 1.48(2) A, the dihedral angle between the rings being 45(1)°. The chelate OOCCMe 3 ligands is located in a bisecting plane with equivalent TiO bonds equal to 2.13(1) A (Ti⋯C OCO 2.51(1) A, OCO angle 116(1)°). The geometry of I has been compared to the previously investigated structure of Cp 2 NbOOCCMe 3 (II) which has the carboxylate group farther from the metal atom (NbO 2.23(1) A, Nb⋯C OCO 2.61(1) A, OCO angle 118(1)°). The effect of d 1 and d 2 metal electronic configurations on the geometry and IR spectra of I and II is discussed in terms of the nature of the MOCO bonding.