Platinum(II)-Cyclometalated Roll-over Complexes with a Chiral Pinene-Derived 2,2′-Bipyridine

The first nonracemic cyclometalated roll-over complex of platinum(H), [Pt(L-H)Me(DMSO)], has been synthesized in good yields by reaction of the chiral pinene-derived ligand (5S,7S)-5,7-methane-6,6-dimethyl-2-(pyridin-2-yl)5,6,7,8-tetrahydroquinoline, L, with the electron-rich platinum complex [Pt(DMSO)(2)Me-2]. Adducts have also been obtained, namely, [Pt(L)(Me)Cl] and [Pt(L)Cl-2], when electron-poorer platinum complexes such as [Pt(DMSO)(2)(Me)Cl] or [Pt(DMSO)(2)Cl-2] were used as reagents. The structure of [Pt(L)Cl-2] has been solved by X-ray diffraction. Reaction of the mononuclear species [Pt(L-H)Me(DMSO)] with [Pt(Me)(2)(DMSO)(2)] under strictly controlled reaction conditions gives the dinuclear double roll-over complex [(DMSO)(Me)Pt(mu-L-2H)Pt(Me)-(DMSO)], in which the doubly deprotonated ligand L-2H acts as a bridging dianionic ligand with a four fused ring core. Protonation of the uncoordinated nitrogen ligand in [Pt(L-H)Me(DMSO)] gives the uncommon [Pt(L*)Me(DMSO)](+) cationic species, in which L* is the zwitterionic ligand originated from L-H by protonation of the uncoordinated nitrogen atom. Some aspects of the reactivity of the mononuclear roll-over species [Pt(L-H)Me(DMSO)] with acids and neutral ligands are also discussed.