Yttrium complexes containing heteroscorpionate ligands [(3,5-But2C3HN2)2CHC(Ph)2O]– and [o-Me2NC6H4CH2C(NCy)2]–

Abstract

A reaction of benzophenone with bis(3,5-di-tert-butylpyrazolyl)methyllithium (3,5-Bu^t₂C₃HN₂)₂CHLi (obtained in situ by metallation of (3,5-Bu^t₂C₃HN₂)₂CH₂ with n-butyllithium in THF at–70 °C) led to the synthesis of alkoxide lithium complex [(3,5-Bu^t₂-C₃HN₂)₂CHCPh₂O]Li(THF) (1) containing a new monoanionic heteroscorpionate ligand [(3,5-Bu^t₂C₃HN₂)₂CHCPh₂O]^–. Hydrolysis of complex 1 gave 2,2-bis(3,5-di-tert-butylpyrazolyl)-1,1-diphenylethanol (2) in 90% yield. The structure of alcohol 2 was established by X-ray crystallography. A reaction of anhydrous YCl₃ with two molar equivalents of lithium alkoxide 1 in THF furnished yttrium monochloride complex [(3,5-Bu^t₂C₃HN₂)₂CHCPh₂(μ-O)]₂-YCl(THF)[(μ-Cl)Li]₂ (3). According to X-ray diffraction data, chloride 3 is a monomeric ate-complex with one terminal and two bridging chloride ligands. The nitrogen atoms of the pyrazole rings are not involved in the coordination of the ligand with the yttrium ion. The bisalkyl complex [(3,5-Bu^t₂C₃HN₂)₂CHCPh₂O]Y(CH₂SiMe₃)₂(THF)₂ (4) obtained by the reaction of alcohol 2 with an equimolar amount of Y(CH₂SiMe₃)₃(THF)₂ turned out to be unstable and completely decomposed in solution in C₆D₆ at 25 °C within two hours. An exchange reaction of equimolar amounts of YCl₃ and {[o-Me₂NC₆H₄CH₂C(NCy)₂]Li(THF)₂}₂ (5) (Cy is the cyclohexyl) in THF led to the formation of a neutral monochloride complex [o-Me₂NC₆H₄CH₂C(NCy)₂]₂YCl(THF)₂ (6). A reaction of complex 6 with an equimolar amount of o-Me₂NC₆H₄CH₂Li in toluene led to the synthesis of a new yttrium aminobenzyl complex [o-Me₂NC₆H₄CH₂C(NCy)₂]₂Y[CH₂C₆H₄-o-NMe₂] (7). X-ray diffraction studies showed that in complexes 6 and 7 the donor NMe₂ groups of amidinate ligands are not involved in the metal—ligand interaction. Yttrium complexes 4 and 7 exhibited catalytic activity in polymerization of isoprene.