Synthesis, characterization and reactivity studies of group 2, 3 and 4 metal complexes bearing chelating amino siloxide and alkoxide ligands




Shao, Pengcheng Patrick

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A series of chelating amino siloxide and alkoxide ligands have been prepared. Barium, lanthanide and zirconium complexes bearing these new ligands have been synthesized and characterized by NMR or X-ray crystallography. Reactivity of the zirconium complexes has been studied. The tris(siloxide) lanthanide(III) complexes are all monomeric in both solution and solid-state. A yttrium tris(siloxide) and a zwitterionic ytterbium tetrakis(siloxide) complexes have been characterized by X-ray crystallography. The yttrium complexes have shown high volatility. Mono(siloxide) barium(II) silamide complexes are dimeric as determined by X-ray crystallography, and barium bis(siloxide) exists as a monomer-dimer equilibrium in hydrocarbon solvents. Although highly soluble in hydrocarbon solvents, the barium complexes are non-volatile. A new aryl(siloxide) ligand has been synthesized and used as an ancillary ligand for the preparation of lanthanide dialkyl complexes. Although ligand redistribution was not observed, “ate”-complexes were isolated instead of neutral dialkyl complexes. Zirconium bis(aminodiolate) complexes were synthesized by reaction of tetrabenzyl zirconium and two equivalents of the ligands. The substituents on nitrogen were found to have a great effect on the structure. Mono(aminodiolate) zirconium dialkyl complexes were successfully synthesized by three different methods: protonolysis, ligand redistribution and metathesis. Thermal decomposition of these zirconium dialkyl complexes was found to show a marked dependence on the substituents at nitrogen. The α-methyl benzyl derivative decomposed by ortho-metallation of phenyl group exclusively and resulted in clean formation of a metallacyclic complex. The reaction of primary amines with the metallacycle allowed isolation of amide intermediates protonolysis of the benzyl group, and eventually resulted in formation of bridging imide complexes. The insertion reaction of carbonyl groups (C=O) into the metallacycle Zr-carbon bond proceeds regio- and stereoselectively. The first insertion products of carbonyl insertion were isolated, and the β-naphthaldehyde insertion product was characterized by X-ray crystallography. The metallacycle exhibited catalytic activity towards alkyne cyclotrimerization without preactivation. Zirconium cationic complexes were generated by alkyl abstraction using [special characters omitted]. The cationic complexes generated from the zirconium dibenzyl derivatives showed catalytic activity towards both ethylene and 1-hexene polymerization. A new cyclopentadienyl ligand bearing pendant fluorinated alkoxide functionality was synthesized. The zirconium complexes bearing this ligand exhibited remarkably high Lewis acidity, and the dichloride complex was shown to be catalytically active towards vinylether polymerization.



Metal complexes, Solution (Chemistry)