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) (LH(2)) results in the formation of dimeric complexes [Ti(OiPr)(2)L](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 (ZrL(2))(2) and Zr(2)L(3)(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.

Dioximate‐ and Bis(salicylaldiminate)‐Bridged Titanium and Zirconium Alkoxides: Structure Elucidation by Mass Spectrometry

“…A single peak at m / z 511.2 (calcd 511.2) in the MS/MS spectrum was assigned to [Ti L 5 (O i Pr) 2 +Na] + . Similar fragmentation was previously observed for various bis(β-diketonate)-substituted titanium alkoxide derivatives 8. This fragmentation pathway indicated a type B structure (Scheme 3).…”

“…Low-energy collision-induced dissociation (CID) of the precursor ion, that is, sodiated molecule, resulted in a clear fragmentation to one specific fragment ion [Ti L 2 +Na] + . This contrasts with [(Ti{O i Pr} 2 {bis(diketonate)}) 2 ],8 in which a fragment ion [Ti L (O i Pr) 2 +Na] + was detected. Whereas the bis(β-diketones) formed metallacycles with two bridging ligands and four terminal O i Pr groups (type B in Scheme 3), the dimeric dioximate structures contain two μ 2 -OR and two terminal alkoxo groups (type A in Scheme 3).…”

“…This difference is probably due to the smaller strain of the more flexible L 1 or L 2 ligands if both bridge titanium atoms of the same dimeric unit. There is a noteworthy difference between the cyclic compounds [(Ti{O i Pr} 2 {bis(diketonate)}) 2 ]8 (Scheme 1) and [(Ti{O i Pr} 2 {bis(dioximate)}) 2 ] [Eq. (1)].…”

“…We have recently shown for cyclic [(Ti{O i Pr} 2 {bis(diketonate)}) 2 ] compounds that ESI-MS is a suitable method for structure elucidation of such compounds 8. The mass spectrometric investigations showed that 2 and 3 have the same structure.…”

“…We recently described reactions of various bis(β - diketones) and bis(β-ketoesters) with titanium and zirconium alkoxides, which in each case resulted in cyclic oligomers 8. For example, reaction with Ti(O i Pr) 4 resulted in the cyclic dimers [(Ti{O i Pr} 2 {bis(diketonate)}) 2 ] (see Scheme 1, top left); complexes with a higher degree of substitution were additionally formed with Zr(O i Pr) 4 .…”