Leaching of palladium species from Pd nanoparticles under C--C coupling conditions was observed for both Heck and Suzuki reactions by using a special membrane reactor. The membrane allows the passage of palladium atoms and ions, but not of species larger than 5 nm. Three possible mechanistic scenarios for palladium leaching were investigated with the aim of identifying the true catalytic species. Firstly, we examined whether or not palladium(0) atoms could leach from clusters under non-oxidising conditions. By using our membrane reactor, we proved that this indeed happens. We then investigated whether or not small palladium(0) clusters could in fact be the active catalytic species by analysing the reaction composition and the palladium species that diffused through the membrane. Neither TEM nor ICP analysis supported this scenario. Finally, we tested whether or not palladium(II) ions could be leached in the presence of PhI by oxidative addition and the formation of [Pd(II)ArI] complexes. Using mass spectrometry, UV-visible spectroscopy and 13C NMR spectroscopy, we observed and monitored the formation and diffusion of these complexes, which showed that the first and the third mechanistic scenarios were both possible, and were likely to occur simultaneously. Based on these findings, we maintain that palladium nanoparticles are not the true catalysts in C--C coupling reactions. Instead, catalysis is carried out by either palladium(0) atoms or palladium(II) ions that leach into solution.

Both symmetric and nonsymmetric bis(aryl)acenaphthenequinonediimine ligands, featured by substituents in meta-positions of the aryl rings, have been applied for the first time as ancillary ligands for the palladiumcatalyzed CO/vinyl arene copolymerization. The nature and the number of substituents affect both the productivity and the molecular weight of the synthesized copolymers. Palladium complexes containing the nonsymmetric ligands are the most efficient catalysts reported so far for the synthesis of atactic polyketones.

[reaction: see text] Ruthenacycles obtained by cyclometalation of enantiopure aromatic primary or secondary amines with [(eta6-benzene)RuCl2]2 or with [(eta6-p-cymene)RuCl2]2 are efficient catalysts for asymmetric transfer hydrogenation (TOF up to 190 h(-1) at room temperature). Enantioselectivities in the transfer hydrogenation of acetophenone ranged from 38% to 89%. It is possible to prepare the catalysts in situ, which allows the use of high throughput experimentation.

The cyclometalation of chiral and achiral primary amines occurred readily with Ru(II), Rh(III), and Ir(III) derivatives. Thus, the metalation of (R)-1-phenylethylamine by [(η 6 -benzene)RuCl 2 ] 2 , [(η 5 -Cp*)-RhCl 2 ] 2 , and [(η 5 -Cp*)IrCl 2 ] 2 was studied. Good yields of the expected cationic products in which the phenyl group was ortho-metalated were obtained for the rhodium and the ruthenium derivatives, whereas a mixture of products was formed in the case of the iridium complex. Benzylamine, (R)-1-phenylpropylamine, (R)-1-(1-naphthyl)ethylamine, and (R)-1-aminotetraline afforded also the cycloruthenation products whose general formula is [(η 6 -benzene)Ru(N-C)(NCMe)]PF 6 where N-C represents the orthometalated ligands. Substitution of the acetonitrile ligand by PMe 2 Ph occurred readily on the ruthenium complexes, affording stable compounds that were characterized by X-ray diffraction studies on single crystals, thus ascertaining the existence of the cycloruthenated five-membered rings. Accurate analyses of the structure of the complexes were implemented in solution and in the solid state. The (S) configuration at the metal was usually associated with a δ conformation of the metallacycle, and conversely, the (R) configuration with the λ conformation. The study of the conformation of the five-membered rings revealed that the orientation of the NH 2 group is such that one NH unit is oriented toward the η 6 -benzene ring (roughly parallel to the Ru-centroid benzene vector), whereas the second NH is parallel to the Ru-L bond, L ) NCMe or PMe 2 Ph.