N-ferrocenyl-substituted planar-chiral N-heterocyclic carbenes and their PdII complexes

The N-ferrocenyl-linked N-heterocyclic carbenes 1a and 1b were obtained by treatment of their imidazolium salts 12a and 12b with potassium tert-butoxide. The latter were shown to be accessible from (R)-1-amino-2-methylferrocene (9) and aminoferrocene, respectively, which were converted into the corresponding formamidines and then subjected to a novel cyclization procedure. Treating the ligand precursors 12a and 12b with [Pd(OAc)(2)](3) under different reaction conditions afforded the trans-pyridine-substituted Pd-II complexes 14a and 14b as well as their trans-triphenylphosphane-substituted counterparts 16a and 16b and, in the case of the chiral ligand precursor, the dinuclear Pd-II complex 15a. Conformational analysis of the ligands based on the X-ray structures of 12a, 12b and 16a revealed the dependence of the two torsion angles between the central imidazolium core and the adjacent ferrocenyl substituents on the steric and electronic properties of the observed systems. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)