The intermolecular asymmetric Heck reaction: Mechanistic and computationalstudies

Reactive intermediates in the asymmetric Heck reaction between aryl electro philes and 2,3-dihydrofuran have been identified by NMR and mass spectromet ry, with BINAP or the achiral diphosphanes dppp and dppf as ligands. The ma jor cationic species observed is an alkylpalladium produced by addition of PdAr to the alkene followed by two further PdH-mediated isomerisation steps . This last species has been characterised at -60 degrees by H-1-, C-13-, a nd P-31-NMR, including HMQC techniques. The regiochemistry of PdAr and PdH addition to the reactant are opposite as defined by the reaction with (2-H- 2(1))-2,3-dihydrofuran. DFT Calculations on the reaction pathway between [C H2(PH2)]PdPh+ and 2,3-dihydrofuran reveal several structurally interesting intermediates involving agostic beta -atom, ipso-Ph or reactant O-atom bond ed to the Pd-atom, and elucidate the isomerisation pathway.