| Summary: | Rare-earth complexes are attractive catalyst systems due to their low cost, low toxicity
and high reactivity. Modular ligand sets are ideal for complex formation since the steric and
electronic properties of the resultant metal complexes can be easily varied. This thesis
explores the structure and reactivity of new yttrium amidate complexes, which combine the
highly reactive metal with the modular amidate ligand set. A library of tris, bis and
mono(amidate) yttrium complexes have been directly synthesized from yttrium
tris(trimethylsilyl)amidate and simple amide proligands.
The tris(amidate) yttrium complexes are highly active initiators of ring-opening
polymerization of Ɛ-caprolactone, yielding some of the largest molecular weight values for
poly(Ɛ-caprolactone) reported. The initiation of this polymerization is proposed to be ligand
initiated; however, a side-reaction is postulated where formation of a Ɛ-caprolactone-enolate
yttrium complex results in broad polydispersity values of the resultant polymers.
The bis(amidate) yttrium complexes are also excellent precatalysts for the
hydroamination of aminoalkenes. Simple modification to the amidate backbone to include
electron-withdrawing groups was found to significantly enhance reaction efficiency. These
catalysts can mediate cyclohydroamination with both primary and secondary amine
containing substrates.
The mono(amidate) yttrium complexes were also investigated as novel precursors for the
synthesis of the elusive terminal yttrium imido complex. Mixed anilido/amidate yttrium
complexes were synthesized in high yield and a-H abstraction and deprotonation reactions
were attempted in the hopes of isolating a crystalline compound. The addition of monodentate and neutral donors was required for isolation and characterization of the key
reactive intermediates.
This new family of yttrium complexes has proven to be very successful in preliminary
catalytic studies. The ease with which the complexes can be synthesized and their steric and
electronic properties make these complexes ideal for further catalytic investigations.
|
|---|
