Neutral and Cationic Palladium Complexes of P‐Stereogenic Phosphanes Bearing a Heterocyclic Substituent

Abstract

The coordination chemistry of 13 optically pure P‐stereogenic diarylmonophosphanes P(Het)PhR [Het = 4‐dibenzofuranyl (DBF), 4‐dibenzothiophenyl (DBT), 4‐dibenzothiophenyl S,S‐dioxide (DBTO2) and 1‐thianthrenyl (TA); R = OMe, Me, iPr, Fc (ferrocenyl)] to Pd‐allyl moieties is described. Both neutral [PdCl(η3‐(2‐methylallyl)(κP‐P)] and cationic [Pd{η3‐(2‐methylallyl)(κP‐P)2}]PF6 complexes have been prepared. Coordination of the heteroatom of the heterocycle was only possible in the case of TA‐based phosphanes; these furnished complexes of the type [Pd{η3‐(2‐methylallyl)(κ2P,S‐P)}]PF6 after chloride abstraction with TlPF6. The crystal structure of the complex [Pd(η3‐2‐methylallyl)(κ2P,S‐PPh(OMe)(1‐TA)]PF6 is reported. The neutral Pd complexes were found to be highly active in the hydrovinylation of styrene after activation with AgBF4, except for the TA‐based phosphanes. The cationic Pd complexes were evaluated in allylic alkylation and amination with the model substrate rac‐trans‐1,3‐diphenylprop‐2‐enyl acetate (rac‐I), achieving total conversions and up to 70 % ee.