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

Abstract

The first nonracemic cyclometalated “roll-over” complex of platinum(II), [Pt(L-H)Me(DMSO)], has been synthesized in good yields by reaction of the chiral pinene-derived ligand (5 S,7 S )-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(μ-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.