Chiral cyclometalation of 6-(1-phenylbenzyl)-2,2′-bipyridine

Abstract

A new bipyridine ligand, 6-(1-phenylbenzyl)-2,2′-bipyridine, has been prepared by a multistep synthesis starting from the corresponding substituted pyridine. The coordinating properties of the new ligand have been tested with two d⁸ metal ions, Pt(II) and Pd(II), to give the cyclometalated complexes [Pt(N,N,C)Cl] and [Pd(N,N,C)Cl], where N,N,C is a terdentate deprotonated bipyridine containing a new stereogenic carbon atom directly generated by C–H bond activation. The single-crystal of the platinum complex has been solved by X-ray diffraction. DFT calculations confirm the presence of a Pt⋯H interaction that stabilizes one of the two possible conformers by 14.7 kJ mol⁻¹ for Pt and 12.9 kJ mol⁻¹ for Pd. The energy barrier to pass from one conformer to the other is 25.4 and 23.8 kJ mol⁻¹ respectively. Under different reaction conditions, regioselective activation of a pyridine C–H bond gave the less common cyclometalated rollover complex [Pt(L-H)Me(DMSO)], which was isolated and characterised.