Unusually Large Primary (2)H/(1)H Kinetic Isotope Effects Accompanying a syn-beta-H Elimination Reaction in a sigma-Alkyl-Palladium Complex.
The Pd-sigma-alkyl complex 5, is stable in solution for long periods in the absence of base. On addition of simple amine bases, such as 1,8-bis(dimethylamino)naphthalene (7), complex 5 rapidly generates the triene 6 via a beta-H elimination process whose stereochemistry is demonstrated to be syn. In contrast to the low primary kinetic isotope effects (kH/kD) that normally attend syn-beta-H elimination processes from sigma-alkylmetal species, large values are observed on performing inter- and intramolecular competition experiments with 5. However, the substitution of D for H has negligible effect on the absolute rate at low temperatures (-60 degrees C). A mechanism to account for this behavior is presented, and implications for asymmetric Heck reactions are noted.
The Bristol Centre for Organometallic Catalysis, The School of Chemistry, Bristol, BS8 1TS, UK. guy.lloyd-jones@bris.ac.uk
Guy C
GC
Lloyd-Jones
Paul A
PA
Slatford