The palladium-catalyzed allylation of primary amines has been investigated by DFT calculations (B3PW91, PCM method), and two potential mechanisms were studied. The first mechanism relies on the formation of cationic hydridopalladium complexes. Their formation involves a metal-assisted formal (1,3) shift of a proton from the nitrogen atom of an ammonium to the Cbeta carbon atom. The second part of the cycle relies on a ligand exchange through a pentacoordinated 18VE hydridopalladium complex. The last step likely proceeds through a bimolecular pathway and formally consists of a proton transfer from the allylammonium to the alcohol group of the complex. The second mechanism, which is closer to that currently admitted for nucleophilic allylic substitutions, relies on the decomplexation of the coordinated allylammonium and appears to be favored. This catalytic cycle was recomputed on model complexes varying the ligands, and a charge decomposition analysis was carried out to assess the influence of the electronic properties of the ligands. To compare our results with competitive experiments, CDA calculations were also performed on real ligands. In agreement with experimental observations, this process was found to be strongly ligand dependent, decomplexation being favored by strong pi-acceptor ligands. These calculations led us to show experimentally that complex [Pd(P(OPh)(3))(2)(eta(3)-C(3)H(5))][OTf] is an efficient catalyst for this allylation. Finally, this catalytic process proved to be sensitive to the nature of the amine, with poorly basic amines favoring the re-formation of the catalytic precursor.

Reaction of 2,5-diphenylphospholide anion with 2-chloromethylpyridine affords the 1-(2-methylpyridine)phosphole ligand. The corresponding cationic Ru-(cymene)Cl chelate complex catalyzes the hydrogen transfer process of ketones with very high TON and TOF numbers. Due to the presence of two very different binding sites, mixed P, N-chelate ligands possess unusual electronic properties that make them very attractive in both coordination chemistry and catalysis. 1 These ligands, which usually show a pronounced hemilabile character, have found interesting applications in some catalytic processes of recognized importance such as reduction, 2 allylic alkylation, 3 C-C coupling (Heck reaction), 4 and olefin/CO copolymerization. 5 As part of a large research program aimed at incorporating diverse phosphorus heterocycles in mixed heteroditopic chelates and polydentate ligands, 6 we decided to explore the synthesis of 1-phospholyl derivatives of 2-methylpyridine. Herein, we report on the synthesis, the X-ray crystal structure, and the catalytic activity in the transfer hydrogenation of ketones of the cationic cymene RuCl complex of one of these new ligands.Among different possible candidates for the phosphole subunit, we selected the 2,5-diphenylphospholyl ligand, whose P-functional derivatives show a very good stability toward air oxidation. Furthermore, the precursor of these P-functional compounds, the 1,2,5-triphenylphosphole, is cheap and easily available on a multigram scale from the simple reaction of dichlorophenylphosphine with 1,4-diphenyl-1,3-butadiene. 7 Synthesis of the 1-(2-methylpyridine)-2,5-diphenylphosphole ligand 3 was carried out following a classical approach that involves the reaction of the 2,5-diphenylphospholide anion 2 with 2-chloromethylpyridine in THF at room temperature. Interestingly, we found that when the easily available 1,1′-bis(2,5-diphenylphosphole) 8 1 is used as starting precursor of anion 2, no chromatographic separation is needed to isolate 3. Following this procedure, ligand 3 was obtained in 80% yield as an air-stable yellow solid which can be stored without special precautions. The formulation of 3 was conventionally established by NMR and mass spectroscopies and elemental analysis (Scheme 1).As a preliminary study to explore the coordination behavior of 3, we deliberately focused our work on the synthesis of chelate-based (η 6 -arene)ruthenium complexes. Reaction of 3 with half an equivalent of [Ru(η 6 -C 10 H 14 )Cl 2 ] did not produce the cationic chelate complex but the monodentate complex 4, which results from the simple cleavage of the dimer (eq 1). Additionnal heating in different solvents did not allow the displacement of the chloride ligand. Though 4 was fully characterized (1) See for example: (a) Fritz, H. P.; Gordon, I. R.; Schwarzhans, K. E.; Venanzi, L. M. Doux, M.; Bouet, M.; Mézailles, N.; Ricard, L.; Le Floch, P. Organometallics 2002, 21, 2785. (g) Doux, M.; Melaimi, M.; Mézailles, N.; Ricard, L.; Le Floch, P. Chem. Commun. 2002, 1566. (7) Campbell, I. G.; Cook...