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The solution behavior of the cationic complexes [Pd(η³-allyl)(P−N)]⁺ (P−N = o-(PPh2)C6H4CH&dbd;NR (R = C6H4OMe-4, Me, CMe3, (R)-bornyl); allyl = propenyl (1a−4a) and 3-methyl-2-butenyl (1b−4b)) consists essentially of three dynamic processes:  (i) a very fast conformational change of the P−N chelate ring, which moves above and below the P−Pd−N coordination plane, (ii) a relatively fast η³−η¹−η³ interconversion which brings about a syn−anti exchange only for the allylic protons cis to phosphorus; (iii) a slower apparent rotation of the η³-allyl ligand around its bond axis. For 1b−3b, two geometrical isomers are observed, the predominant one having the allyl CMe2 group trans to phosphorus. The complexes 4a and 4b, containing the chiral (R)-bornyl group, are present in solution with two and four diastereomeric species, respectively. The X-ray structural analysis of 4b(ClO4) shows the presence of two diastereomeric molecules in the unit cell, both having distorted-square-planar coordination geometries, characterized by rather elongated Pd−CMe2 bonds trans to phosphorus and by a marked distortion of the allyl ligand, which is rotated away from the PPh2 group. The complexes [Pd(η³-allyl)(P−N)]⁺ react with secondary amines HY in the presence of fumaronitrile, yielding [Pd(η²-fn)(P−N)] and allylamines. Under pseudo-first-order conditions the amination rates obey the laws kobs = k2[HY] + k3[HY]² for 1a−4a and kobs = k2[HY] for 1b, 3b, and 4b. The k2 term is related to direct bimolecular attack on a terminal allyl carbon of the substrate, whereas the k3 term is ascribed to parallel attack by a further amine molecule on the intermediate [Pd(allyl)(P−N)(HY)]⁺. The k2 values increase with increasing basicity and decreasing steric hindrance of the amine, and with increasing electron-withdrawing ability and increasing bulkiness of the P−N nitrogen substituent. The higher amination rates for [Pd(η³-allyl)(P−N)]⁺, compared to [Pd(η³-allyl)(α-diimine)]⁺, are essentially due to lack of displacement equilibria of the P−N ligand by amines.

The complexes [Pd(η³-allyl)(N-N‘)]ClO4 [allyl = 2-butenyl or 3-methyl-2-butenyl, N-N‘ = C5H3(6-R)N-2-CH&dbd;NR‘ (R = H, R‘ = Me, CMe3, C6H4OMe-4; R = Me, R‘ = C6H4OMe-4) and C5H4N-2-CH2NMe2] are present in solution with different isomers, the structures of which may be assigned by an ¹H NMR criterion based on chemical shift changes of the pyridine H(6) and/or of the allylic methyl protons, as confirmed also by 2D ¹H NMR spectra. The isomer distribution depends mainly on the steric requirements of both the allyl and N-N‘ ligands:  for [Pd(η³-3-methyl-2-butenyl)(N-N‘)]ClO4 the predominant isomer (ca. 100%) has a structure with the allylic methyl groups cis to the coordinated pyridine nitrogen when N-N‘ = C5H4N-2-CH&dbd;NCMe3 and cis to the coordinated imino nitrogen when N-N‘ = C5H3(6-Me)N-2-CH&dbd;NC6H4OMe-4. In chlorinated solvents (dichloromethane-d2 or 1,1,2,2-tetrachloroethane-d2) the isomers undergo mutual interconversion through a mechanism involving an apparent rotation of the η³-allyl ligand around its bond axis to the metal. The interconversion rates depend on the nature of allyl and N-N‘ ligands and increase considerably when the compounds are dissolved in dimethyl-d6 sulfoxide. The apparent allyl rotation also occurs for the analogous (η³-2-methyl-2-propenyl)palladium(II) derivatives. For [Pd(η³-2-methyl-2-propenyl)(N-N‘)]ClO4 [N-N‘ = C5H3(6-Me)N-2-CH&dbd;NC6H4OMe-4] the allyl rotation rate increases with increasing concentration up to a limiting constant value. This behavior is interpreted on the basis of a mechanism involving a fast and reversible association of the cationic complex with the perchlorate anion to form a loose ion pair which undergoes a rate-determining molecular geometry rearrangement upon coordination of ClO4^-. For a solution of [Pd(η³-3-methyl-2-butenyl)(N-N‘)]ClO4 (N-N‘ = C5H4N-2-CH2NMe2) in 1,1,2,2-tetrachloroethane-d2, the 2-D ROESY spectrum suggests that the apparent allyl rotation at 28 °C does not involve Pd−NMe2 bond breaking. The rupture of this bond takes place when the temperature is raised to ca. 90 °C or when the complex is dissolved in dimethyl-d6 sulfoxide at ambient temperature.

Novel palladium(II) derivatives containing metal-metal bonds of the type trans-[Pd(RNC)2(M′X3)2] and [Pd(C6H5NC)(L)(M′Cl3)Cl] (RNC = phenyl, cyclohexyl- and p-nitrophenylisocyanide; L = triphenylphosphine and triphenylarsine; M′ = Sn and Ge; X = Cl and Br) have been prepared. These compounds have been characterized by elemental analysis, molecular weight measurements, i.r. spectra, X-ray powder diffraction patterns and cleavage of PdSn and PdGe bonds by reaction with iodine. Their structure was assigned, where possible, on the basis or i.r. data. An attempt to identify the PdSn and PdGe stretching frequencies has been made: the ν(PdSnCl3) appears to fall in the range 199–226 cm−1; ν(PdSnBr3) in the range 156–180 cm−1, and ν(PdGeCl3) in the range 228–240 cm−1.