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The new didentate N-donor ligands 2-(4-methyl-1H-pyrazol-1-yl)pyrimidine (4Me-pzpm, 1) and 2-(4-bromo-1H-pyrazol-1-yl)pyrimidine (4Br-pzpm, 2) have been synthesised and used to obtain the allylpalladium derivatives [Pd(η 3 -2Me-C 3 H 4 )(NNЈ)]X [X = BArЈ 4 − , NNЈ = 1 (3), NNЈ = 2 (4); X = CF 3 SO 3 − , NNЈ = 1 (5), NNЈ = 2 (6)]. In complexes 3−6 two types of fluxional process have been found: apparent allyl rotation that is observed as H syn −H syn , H anti −H anti interconversions and H 4 −H 6 interchange of the pyrimidine protons that must involve Pd−N(pm) bond rupture. The influence of different factors on both processes -such as the nature of

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Abstract:The CO/tert-butylstyrene/ethylene terpolymerization catalyzed by Pd-(N-N') complexes was studied. The results evidence that the olefin preferentially inserted in the terpolymer chain is strictly related to the nature of the nitrogen ligand, mainly to its steric constraints, and not to the kind of ligand. Indeed, slight variations in the backbone of the nitrogen ligands coordinated to palladium allow for the synthesis of terpolymers with a controlled composition.