Development of palladium catalysts with nitrogen-donor ligands for controlled copolymerization reactions

The promising results obtained with catalysts having the nonsymmetric Ar,Ar?-BIAN prompted us to study the symmetrically substituted Ar2BIANs featuring one group on the ortho position and one on the meta position of both aryl rings. This is the topic of Chapter 5. Ar2BIAN ligands already known from the literature as well as new molecules have been investigated. The study of their coordination chemistry to palladium points out that syn and anti isomers, depending on the relative position of the substituents on the aryl rings with respect to the square planar plane, are present in solution. The existence of these isomers has been also observed in solid state by X-ray analysis of single crystals of one exponent of this series of complexes. The monocationic palladium derivatives of all the ligands generated active catalysts for the ethylene/MA copolymerisation, but showing modest productivities. The low rate in the catalytic reaction makes them suitable candidates for detailed mechanistic investigations performed by NMR spectroscopy, that allows to correlate the rate of the migratory insertion of the polar monomer into the Pd-alkyl bond to the both electronic and steric effects of the substituents on the aryl rings. In addition, a relationship between the stability of the resting state of the catalytic cycle and the nature of the Ar2BIAN has been established. The synthetic methodology applied for the synthesis of the nonsymmetric Ar,Ar?-BIANs is not so trivial and Chapter 6 deals with the enlargement of this liga