Platinum(II), palladium(II) and gold(III) adducts and cyclometalated derivatives of 6-methoxy-2,2’-bipyridine: A comparative study

Reaction of 6-methoxy-2,20-bipyridine (bpy6OMe) with the electron-rich platinum(II) complex [Pt(Me)2(DMSO)2] gave the rollover cyclometalated complex [Pt(k2-N,C-bpy6OMe-H) (Me) (DMSO)] under mild conditions. The occurrence of rollover cyclometalation was demonstrated by single crystal X-ray diffraction structure determination. In contrast, reaction of bpy6OMe with [Pt(Ph)2(DMSO)2] and [Pt(Cl)2(DMSO)2] under mild conditions gave only adduct species of the type [Pt(X)2(bpy6OMe)] (X ¼ Ph, Cl). Under harsher conditions, activation of a CeH bond in the methoxy substituent yielded the terdentate cyclometalated complex [Pt (k3-N,N,C-bpy6OMe-H)Cl]. Finally, reaction of Pd(II) and Au(III) derivatives invariably gave adduct species, with the exception of the dimeric complex [Pd(k2-N,C-bpy6OMe- H) (OAc)]2, which, however, was not isolated in pure form. The reactivity of bpy6OMe, as emerged from this study, was compared with that of the corresponding disubstituted ligand 6,60-dimethoxy-2,20- bipyridine, previously studied by us.