Synthesis, structural characterization, and catalytic activity of chiral diamine and diimine Pd(II)-complexes

A combined catalytic and crystallographic investigation on the effectiveness of chiral diamino-bithiophene (2) and the corresponding diimino molecules (1) as chiral ligands for Pd(II) catalyzed transformations is presented. In particular, a systematic X-ray characterization of the [Pd]-pre-catalytic species provided valuable rationales for the different behavior of the two classes of ligands, underlining the key role played by sterical as well as electronic factors in controlling the oxidative addition of the starting racemic allylcarbonate to the chiral Pd(0) intermediate. Moreover, the versatility of the synthetic strategy for the preparation of enantiopure oligothienyl systems allowed us to synthesize a new type of mixed thiophene/pyridine ligands (2d) that have been effectively employed in asymmetric allylic alkylations (AAA). (c) 2006 Elsevier B.V. All rights reserved.