Synthesis and stereochemistry of the first chiral (imidazolinylidene)- and (triazolinylidene)palladium(II) complexes

The reaction of three equiv, of a chiral imidazolium or triazolium perchlorate with one equiv, of Pd(OAc)(2), an excess of NaI and a base leads to the corresponding chiral dicarbene-diiodopalladium(II) complexes in chemical yields up to 98% and with the trans isomer as the major product (1, 2). If only one equiv. of the imidazolium or triazolium perchlorate is used, then dinuclear complexes with bridging iodine atoms are formed (3, 4, chemical yield 92-94 %). The latter can add Lewis basic ligands, e.g, amines, phosphanes or other carbenes, to give mononuclear complexes with one carbene ligand coordinated to the PdI2 fragment (5, 6). Preliminary test experiments with these Pd(II) complexes as catalysts for an enantioselective Heck-type reaction have been carried out.