Rate and Mechanism of the Reversible Formation of Cationic (η3-Allyl)- palladium Complexes in the Oxidative Addition of Allylic Acetate to Palladium(0) Complexes Ligated by Diphosphanes

✍ Scribed by Christian Amatore; Sophie Gamez; Anny Jutand

• Publisher: John Wiley and Sons
• Year: 2001
• Tongue: English
• Weight: 155 KB
• Volume: 7
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/1521-3765(20010316)7:6<1273::aid-chem1273>3.0.co;2-7

✦ Synopsis

The oxidative addition of the allylic acetate, CH 2 CH À CH 2 À OAc, to the palladium(0) complex [Pd 0 (P,P)], generated from the reaction of [Pd(dba) 2 ] with one equivalent of P,P (P,P dppb 1,4-bis(diphenylphosphanyl)butane, and P,P dppf 1,1'-bis(diphenylphosphanyl)ferrocene), gives a cationic (h 3 -allyl)palladium(ii) complex, [(h 3 -C 3 H 5 )Pd(P,P) ], with AcO À as the counter anion. This reaction is reversible and proceeds through two successive equilibria. The overall equilibrium constants have been determined in DMF. Compared with PPh 3 , the overall equilibrium lies more in favor of the cationic (h 3 -allyl)palladium(ii) complex when bidentate P,P ligands are considered in the order: dppb b dppf b PPh 3 . The reac-tion proceeds via a neutral intermediate complex [(h 2 -CH 2 CH À CH 2 À OAc)Pd 0 -(P,P)], which has been kinetically detected. The rate constants of the successive steps have been determined in DMF by UV spectroscopy and conductivity measurements. The overall complexation step of the Pd 0 by the allylic acetate CC bond is faster than the oxidative addition/ionization step which gives the cationic (h 3 -allyl)palladium(ii) complex.