Comparison of coordination mode of some biphosphine ligands in cyclometalated organoplatinum(II) complexes

The reaction of the cyclometalated complexes [PtR(CˆN)(SMe2)], 1, in which R is Me or 4-MeC6H4, and CˆN is either ppy (deprotonated 2-phenylpyridine) or bhq (deprotonated benzo-h-quinoline), with 1,2-bis[bis(pentafluorophenyl)phosphino]ethane (dfppe), were studied. When 0.5 equiv of dfppe was added, the binuclear cyclometalated Pt(II) complexes [Pt2R2(CˆN)2(μ-dfppe)], 2i–l, were formed, which are the first examples of diplatinum complexes with bridging dfppe ligands. When the ligand dfppe was reacted with complex 1 in the ratio of 1:1, only in the case of R = Me and CˆN = ppy, the complex [Pt(Me)(κ1-ppy)(κ2-dfppe)], 4d, was obtained, in which the ppy ligand is monodentate and dfppe is chelating, and in other cases the dimers 2j–l were formed. The results were compared, using density functional theory (DFT), with other diphosphine ligands, 1,1-bis(diphenylphosphino)methane (dppm) and 1,2-bis(diphenylphosphino)ethane (dppe) to clarify the electronic and steric effects of diphosphine ligands on their coordination mode ability.