Synthesis, characterization and reactivity studies of group 2, 3 and 4 metal complexes bearing chelating amino siloxide and alkoxide ligands
Date
2018-07-26
Authors
Shao, Pengcheng Patrick
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Abstract
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.
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Keywords
Metal complexes, Solution (Chemistry)