322753-18-4Relevant academic research and scientific papers
η1- and η3-Allylpalladium(II) complexes bearing potentially tridentate ligands: Synthesis, solution dynamics, and crystal structures
Barloy, Laurent,Ramdeehul, Shailesh,Osborn, John A.,Carlotti, Claire,Taulelle, Francis,De Cian, Andre,Fischer, Jean
, p. 2523 - 2532 (2007/10/03)
The potentially tridentate ligands 2,2':6',2''-terpyridine (terpy) and 2,6-bis(diphenylphosphanylmethyl)pyridine (PNP) have been used to prepare novel palladium-allyl complexes of general formula [(terpy)Pd(CH2CHCRR')](BF4) [R = R'=H (1); R= H, R'=Me (2); R=R'=Me (3)] and [(PNP)Pd(CH2CHCRR')](BF4) [R = R' = H (4); R = H, R'= Me (5); R = R' = Me (6)], which were characterized by elemental analysis, IR spectroscopy, and 13C, 31P and variable-temperature 1H NMR spectroscopy. The low-temperature 1H NMR spectra show that the configuration of the complexes in solution depends strongly on the nature of the ligand. The terpy complexes 1-3 are η3-allyl species, where terpy is dihapto and one pyridine ring remains uncoordinated, whereas the PNP complexes 4-6 occur as η1-allyl compounds with a trihapto PNP ligand. All complexes are fiuxional through η3-η1 exchange processes. Energy barriers of 47.5-48.6 kJ·mol-1 (243-262 K) are reported for the interconversion of terminal allylic protons (complexes 2-4). ΔG(+) is higher (71.1 kJ·mol-1 at 350 K) for the interconversion of the methyl groups in complex 6. A lower-barrier oscillatory mechanism involving terpy (ΔG(+) = 43.9 kJ·mol-1 at 231 K) is also involved in complex 1. The X-ray structures of complexes [(η3-terpy)Pd(η1-C5H9)](BF4) (3a) and [(η3-PNP)Pd(η1-C4H7)](BF4) (5a) are reported; the structure of 3a corresponds to a species that is not observed in solution.
