Cyclic bis(β-diketonate)- and bis(β-ketoesterate)-bridged titanium and zirconium alkoxide derivatives

Abstract

Reaction of Ti(OiPr)₄ with various bis(β-diketones) and bis(β-ketoesters) (LH₂) results in the formation of dimeric complexes [Ti(OiPr)₂L]₂, where each metal centre is coordinated by two terminal OiPr ligands and two bridging β-diketonate or β-ketoesterate groups (L). Macrocycles containing two M(OiPr)₂ moieties are thus formed. Reaction of Zr(OiPr)₄ with the same bis(β-diketones) and bis(β-ketoesters) results in different compounds, depending on the organic spacer connecting the two functional groups. With shorter spacers, the compounds [ZrL(OiPr)₂]₂·2iPrOH are obtained, with the same structures as the corresponding titanium complexes. With longer spacers, however, complexes with a higher degree of substitution are formed, such as (ZrL₂)₂ and Zr₂L₃(OiPr)₂·2iPrOH. The molecular weight and structure of all compounds was elucidated by ESI-MS. MS/MS of the corresponding [M+Na]⁺ precursor ions confirmed the proposed structures based on structure-specific product ions. Solution NMR experiments and DFT calculations additionally supported the proposed structures.