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Bulky alkyls and a hydridoalkyl of zirconium(<scp>IV</scp>): influence of steric constraints upon (i) conformation and the Zr–C rotational barrier and (ii) the Zr–C bond length. X-Ray crystal and molecular structure of [zr(η-C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>{CH(SiMe<sub>3</sub>)<sub>2</sub>}Ph]
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1978
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X-ray CrystallographyCrystal StructureEngineeringChemistryVariable Temperature 1HSpectra-structure CorrelationLow Temperature ConformationStructure ElucidationSteric ConstraintsBiophysicsMaterials ScienceInorganic ChemistryChemical BondActivation Free EnergyPhysical ChemistryQuantum ChemistryMolecular ChemistryCrystallographyCrystal Structure DesignX-ray CrystalNatural SciencesMain Group ChemistryBulky Alkyls
Variable temperature 1H n.m.r. spectra of [Zr(η-C5H5)2{CH(SiMe3)2]}R](R = Me, Prn, CH2SiMe3, Ph, Cl, or H) in [2H8]toluene show that the activation free energy for rotation about the Zr–CH(SiMe3)2 bond is exceptionally high [11·6–15·3 kcal mol–1: R = H (a dimer in vapour or in C6H6) > Cl > alkyl > Ph] with a preference to a low temperature conformation in which the two sets of SiMe3 and η-C5H5 groups are diastereotopic; this is established for the crystalline state (X-ray) in the case of R = Ph [Zr–Ph, 2·324(7)Å], in which the Zr–C(sp3) bond is very long [2·329(6)Å], cf. [Zr(η-C5H5)2(CH2MMe3)2][M = C, 2·29(1); or Si; 2·279(4)Å, respectively].