Palladium Chemistry of 2-Ferrocenyl-1,10-phenanthroline Ligand

The synthesis of the 2-ferrocenyl-1,10-phenanthroline ligand 1 has been improved, and its reactivity toward palladium is described. This study allows evidencing that 1 can coordinate to the metal center in an N−N bidentate fashion or undergo ortho metalation, thus acting as a terdentate N−N−C pincer ligand. Examples of the former coordination mode include complexes [Pd(Cl)(Me)(1)] (2) and [Pd(Me)(NCMe)(1)][PF6] (3), whereas cyclometalation is observed in [Pd(1)(O2CCF3)] (5), [Pd(1)(MeCN)][PF6] (6), and [Pd(1)(PPh3)][O2CCF3] (7). These cyclometalated adducts are chiral, racemic compounds. X-ray crystal structures of compounds 5, 6, and 7 have been determined, confirming the presence of a five-membered palladacycle and evidencing that in the solid state packing occurs through weak π−π interactions between the phenanthroline rings of the ligands. The reactivity of the racemic mixture of 5 with the enantiopure phosphine (R)-Ph-BINEPINE (8) affords a kinetic dynamic resolution leading, after two recrystallizations, to the isolation of only one of the two possible diastereoisomers.