Highly Active Ethene Polymerization Catalysts with Unusual Imine Ligands - Late Transition Metal Polymerization Catalysis - page 67

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Chart 3.2 1,2-Diimine ligands 20 - 28 .
In the solid state, complex 37 exists as a dimer with a central inversion center. Two
molecules are bridged by two bromo ligands, leaving one terminal bromo ligand at a
five-coordinated Ni center. The coordination sphere of Ni is essentially square pyra-
midal. The peripheral N-substituents are roughly orthogonal to the Ni-acenaphtho-
nechinone diimine backbone, effecting axial steric shielding of the Ni atom. Fig. 3.3
shows a view of the core part of the molecule. The orthogonality of the N-substitu-
ents and the steric similarity between N-2,6-diisopropylphenyl and N-2,5-diisopro-
pylpyrrolyl groups as peripheral steering ligands is easily appreciated. Hence there
is no major structural difference between N-aryl and N-hetaryl Ni-diimine com-
plexes, in accord with the design principle of this family of precatalysts.
3.2.1.4 Diimine Nickel and Palladium Complexes with 2,6-Dibromo-4-methylphenyl
Groups
Another appealing steric congruence exists between 2,6-diisopropylphenyl and 2,6-
dibromophenyl groups (Fig. 3.4). Note though that the isopropyl group has quite
different dynamics.