Title

Syntheses and structural survey of novel alkaline earth and rare earth metal complexes

Date of Award

2004

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor(s)

Karin Ruhlandt-Senge

Keywords

Alkaline earth, Earth metal, Pyrazolate, Ytterbium, Europium

Subject Categories

Chemistry | Physical Sciences and Mathematics

Abstract

The work delineated here represents a variety of novel synthetic schemes towards alkaline earth metal complexes based on direct synthesis from the metals; namely redox transmetallation, redox transmetallation/ligand exchange, and direct metallation at elevated temperatures. The feasibility of metal based, direct synthesis for Group 2 complexes is strengthened with the results obtained in this work, and shows outstanding synthetic utility in addition to the more widely employed alkane elimination reaction from dibutylmagnesium as well as direct metallation by ammonia activated metals. This work proves the latter scheme not only useful for the heavy Group 2 elements, but also for the rare earth metals ytterbium and europium, a synthetic pathway rarely considered towards divalent lanthanide complexes. Part one of this work investigates the reactivity of the two groups of metals on the basis of feasibility of synthetic schemes towards pyrazolate complexes (3,5-di- tert -butylpyrazolate, 3,5-di- iso -propylpyrazolate, 3-methyl-5-phenylpyrazolate, 3,5-diphenylpyrazolate). Similarities are dominant, as expected from the high electropositive character of both groups, but differences are seen in the slightly increased reactivity of the alkaline earth metals and the potential formation of trivalent species for the rare earth metals. The resulting complexes from this survey nicely demonstrate structural similarities based on closely related charge/size ratios and highly ionic bonding in the pyrazolate compounds, often showing isostructural behavior for metals of comparable size (Ca 2+ /Yb 2+ ; Sr 2+ /Eu 2+ /Sm 2+ ). The second part of the thesis explores the proposed intermediate in the redox transmetallation/ligand exchange pathway M(C 6 F 5 ) 2 (M = Ca, Sr, Ba), and the formation of cationic complexes as solvent separated ion pairs of type [M(thf) n ][BPh 4 ] 2 (M = Ca, Sr) and also [Ba(BPh 4 )(thf) 4 ][BPh 4 ]. The metal-based reaction schemes established in the first part of this study are also applied towards the formation of alkaline earth 3,5-di- tert -butylphenolates, revealing the preferential formation of cluster species with less bulky ligand systems. In summary, the results presented in this work greatly extend the synthetic schemes available towards alkaline earth metal complexes and further the understanding of structural preferences and similarities between alkaline earth and rare earth metal compounds.

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