Tetranuclear Rollover Cyclometalated Organoplatinum-Rhenium Compound; C-I Oxidative Addition and C-C Reductive Elimination Using a Rollover Cycloplatinated Dimer

The novel tetranuclear Pt(IV)-Re(VII) complex [Pt2Me4(OReO3)2(PMePh2)2(µ–bpy-2H)], 4, is synthesized through the reaction of silver perrhenate with new rollover cycloplatinated(IV) complex [Pt2Me4I2(PMePh2)2(µ–bpy-2H)], 3. In complex 4, while 2,2ʹ-bipyridine (bpy) acts as a linker between two Pt metal centers, oxygen acts as a mono-bridging atom between Pt and Re centers through unsupported Pt(IV)–O–Re(VII) bridge. The precursor rollover cycloplatinated(IV) complex 3 is prepared by MeI oxidative addition reaction on the rollover cycloplatinated(II) complex [Pt2Me2(PMePh2)2(µ–bpy-2H)], 2. Complex 2 has a metal-to-ligand charge-transfer band in the visible region, which was used to investigate the kinetics and mechanism of its double MeI oxidative addition reaction. Based on the experimental findings, the classical SN2 mechanism was suggested for both steps and supported by computational studies. All complexes are fully characterized using multinuclear NMR spectroscopy and elemental analysis. Attempts to grow crystals of the rollover cycloplatinated(IV) dimer 3 yielded a new dimer rollover cyclometalated complex [Pt2I2(PMePh2)2(µ–bpy-2H)], 5, presumably from C-C reductive elimination of ethane. The identity of complex 5 is confirmed by single crystal X-ray diffraction analysis.