Date on Master's Thesis/Doctoral Dissertation

8-2013

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Chemistry

Committee Chair

Burns, Christopher T.

Author's Keywords

Phosphine sulfonate ligands; Catalysis; Transition metal complexes

Subject

Ligands; Transition metal compounds; Complex compounds

Abstract

Transition metal complexes are widely used as homogeneous catalysts mediating a variety of organic reactions, such as s-bond activation/formation, regio-/ enantio-selective reactions, oxygen transfer, homo-/co-polymerization, etc. Among miscellaneous supporting ligands, bidentate ligands bearing a sulfonate donor have drawn considerable attention. Phosphine sufonate ligands have been successfully developed for neutral palladium alkyls that promote incorporation of polar vinyl monomers into polyethylene chains producing highly linear copolymers. In the past decade, extensively investigated sulfonate ligands are mainly three types, phosphine-sulfonate, NHC-sulfonate, and olate-sulfonate. Phosphine-sulfonate ligands support palladium(II) for catalysis of ethylene copolymerization with polar vinyl monomers. They also support ruthenium(II) and (IV) forming complexes that are catalysts in regioselective alkylation reactions. NHC-sulfonate ligands form copper(I) complexes promoting asymmetric conjugate addition with high enantioselectivity. One olate-sulfonate ligand is known. It can stabilize Ru(II) to form a Ru(II) alkenylidene complex to perform ring closure metathesis (RCM). The literature has shown that sulfonate ligands have unique catalytic properties. Pursuing enhanced donor capability and tunable electronic and steric properties while retaining the unique catalytic properties of the sulfonate donor, we have developed a series of phosphinimine-sulfonate ligands which employ phosphinimine as a co-donor. The phosphinimine-sulfonate ligands are synthesized in their zwitterionic forms from commercially available toluidine-sufonic acid and in 7 steps. The synthetic steps include chlorination of sulfonic acid, formation of alkyl sulfonate esters, diazotization of amines, azidation of diazonium salts, formation of phosphazene group via Staudinger reaction, and protonation-deprotection of the phosphazene.The zwitterionic ligands are air-stable and convenient for creation of a ligand library. The desired anionic ligands can be readily generated by deprotonation with sodium hydride. Phosphinimine-sulfonate ligands show good coordination ability with palladium precursors such as (cod)PdMeCl or Py2PdMeCl to form corresponding palladium methyl complexes. Palladium methyl complexes containing triphenyl, methyldiphenyl, di-n-butylphenyl, and tri-n-butylphosphinimine-sulfonate ligands have been synthesized. A thermal behavior study of the synthesized palladium methyl complexes showed that 2,6-positions of the phosphiniminobenzene rings are subjected to orthopalladation. An ethylene reactivity test showed that phosphinimine sulfonate palladium methyl complexes can oligomerize ethylene forming alkanes and are catalyst candidates for polymerization. A study on the introduction of ortho-bulky groups to maintain proper steric properties required for blocking axial faces of the palladium's coordination plane in ethylene polymerization and copolymerization will be required to develop the phosphinimine motif further.

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