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

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.