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Budagumpi, S.,Kim, K.H.,Kim, I. Elsevier Publishing Company 2011 Coordination chemistry reviews Vol.255 No.23
This review discusses the principles underlying mononucleating N-heterocyclic ligand design, selectivity of metal centers, preparation of organometallic catalysts with a N-heterocyclic backbone, and their catalytic activity in olefin oligo/polymerization. A vast number of N-heterocyclic organometallic compounds have been applied for the polymerization on account of their modest cost, low toxicity, and the large availability of transition metals in stable and variable oxidation states, which makes them versatile precursors for these reactions. The main points of focus in this review are the key advances made over more the past 25 years in the design and development of non-metallocene single-site organometallic catalysts bearing different N-heterocyclic scaffolds as a backbone. These catalysts are applied as precursors for the transformation of ethylene, higher α-olefins, and cyclic olefins into oligo/polymers. Emphasis is placed on the architecture of ligand peripheries for tuning the formed polymer properties and the consequences on product formation of different alkyl or aryl substituents directly attached to the metal center in a N-heterocyclic ligand system.
Budagumpi, S.,Liu, Y.,Suh, H.,Kim, I. Elsevier Sequoia 2011 Journal of organometallic chemistry Vol.696 No.9
Sterically modulated bis-imine ligands (L<SUP>1</SUP>-L<SUP>3</SUP>) were prepared by reacting 4,4'-methylene bis-(2,6-dialkyl aniline) and antipyrine-4-carboxaldehyde in a 1:2 stoichiometric ratio. The reactions of L<SUP>1</SUP>-L<SUP>3</SUP> with dichloro(cycloocta-1.5-diene)palladium(II) [PdCl<SUB>2</SUB>(cod)] yield the corresponding binuclear palladium complexes with the general formula Pd<SUB>2</SUB>Cl<SUB>4</SUB>L (L = L<SUP>1</SUP>, L<SUP>2</SUP>, and L<SUP>3</SUP>). The binucleating ligands bind to the palladium ion via the lone pair on the imine nitrogen and amide oxygen atoms, resulting in a square-planar geometry around the metal center. All the palladium catalysts efficiently oligomerize ethylene to produce C<SUB>4</SUB>-C<SUB>20</SUB> fractions at activities of up to 1308 kg-oligomer mol-Pd<SUP>-1</SUP> bar<SUP>-1</SUP> h<SUP>-1</SUP> at 30 <SUP>o</SUP>C in combination with ethylaluminum sesquichloride. The formation of active sites by the change in geometry of the metal complexes could be traced using spectroscopic and electrochemical techniques.