Apparent Allyl Rotation and Pd−N Bond Rupture in Allylpalladium Complexes with N‐Donor Ligands − Evidence of an Associative Mechanism

Abstract

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

Liquid crystal behaviour of ionic allylpalladium complexes containing 2-pyrazolylpyridine as bidentate N,N′-ligand

“…4.3 (Hs), 3.6 (Hs + Ha) and 3.1 (Ha) ppm, as a characteristic of a dynamic behaviour from the allyl group. There are many examples in the literature describing the dynamic behaviour of allylpalladium complexes [21][22][23][24]. A multiplet at 5.67 ppm for the meso proton, from which are determined the corresponding coupling constants, is also observed.…”

Pyrazole-based allylpalladium complexes: Supramolecular architecture and liquid crystal behaviour

“…This behaviour can be explained on the basis of the existence of different isomers related with the relative orientation of the allyl group and the two pyrazoles, which can interchange through a rotation of the allyl group or a tautomeric equilibrium. Many examples in the literature support this proposal [11].…”

Pyrazolyl-pyrimidine based ligands in palladium catalyzed copolymerization and terpolymerization of CO/olefins

“…1 H NMR shows the signals corresponding to coordinated pyrazolyl-pyrimidine ligands and the rbonded palladium methyl group. Spectroscopic data also suggested that H 6 is sensitive to coordination being the 1 H NMR signal considerably downfield shifted with respect to the corresponding one in the free ligand [29]. This suggest that chloride is cis coordinated [30] to the pyrimidine ring in all neutral complexes (1a-3a).…”

“…Solvents were purified prior to use by conventional methods [40]. The ligands 1-3 [29,41], the palladium complexes [28,30,42] and the NaBAr 0 4 [43] salt were prepared accord- ing to reported methods. Carbon monoxide (CP grade 99.99%) was supplied by Air Liquide.…”