meso-to-meso Pt^II-bridged Ni^II-porphyrin dimers

The synthesis and characterization of meso-to-meso Pt^II-bridged Ni^II-porphyrin dimers 5–7 are reported herein. A boron–platinum exchange reaction of meso-pinacolatoborylporphyrin 8 with Pt(cod)Cl₂ afforded the cod-coordinated meso-to-meso Pt^II-linked cis-dimer 5, which was subsequently converted to the 1,3-bis(diphenylphosphino)propane (DPPP)-coordinated cis-dimer 6 and the PPh₃-coordinated trans-dimer 7 upon treatment with DPPP and PPh₃, respectively. On the other hand, a reaction of 5 with tri-tert-butylphosphine induced reductive elimination to give the meso–meso directly linked diporphyrin 9. Comparative studies of these Pt^II-bridged Ni^II-porphyrin dimers were conducted by UV/Vis absorption spectroscopy, electrochemical studies, and theoretical calculations. In the course of these studies, we found that cis-dimers 5 and 6 underwent an unprecedented reductive elimination to give the meso–meso linked dimer 9 upon chemical or electrochemical one-electron oxidation, while trans-dimer 7 was stable under such conditions.