Synthesis of Cyclometallated Pt(II) Complexes of a Bulky Bipyridine Ligand

Treatment of 3,4,5,6-tetraphenyl-2,2′-bipyridine (LH) (7) with [PtCl2(dmso)2] (dmso = dimethyl sulfoxide) in chloroform afforded the cyclometallated square-planar platinum(II) complex [PtCl(L)] (8) and the octahedral Pt(IV) complex mer-[PtCl3(L)] (9) containing an anionic tridentate (C^N^N) ligand. The chloride of (8) can be easily replaced by trifluoroacetate to yield [(L)PtO2CCF3] (10). Reaction of (8) with the alkyne HC≡CC6H4But-4 resulted in the formation of [(L)PtC≡CC6H4But-4] (11). Treatment of (8) with 4-dimetylamino- pyridine (DMAP) and PPh3 in dichloromethane, and the subsequent addition of NH4PF6 in methanol produced the salts [Pt(DMAP)(L)]PF6 (12) and [Pt(PPh3)(L)]PF6 (13), respectively. In a similar manner, reaction of (8) with 0.5 equiv. of bis(diphenyl-phosphino)methane (dppm) formed the dppm-bridged binuclear dicationic salt [(L)Pt(μ-dppm)Pt(L)][PF6]2 (14).