Cyclometalated platinum(II) complexes of 2,2'-bipyridine N-oxide containing 1,1'-bis(diphenylphosphino)ferrocene ligand: Structural, computational and electrochemical studies

The preparation and characterization of new heteronuclear-platinum(II) complexes containing 1,1'-bis(diphenylphosphino)ferrocene (dppf) ligand are described. The reaction of the known starting complex [PtMe(κ2N,C-bipyO-H)(SMe₂)], A, in which bipyO-H is a cyclometalated “rollover” 2,2'-bipyridine N-oxide, with the dppf ligand in a 2 : 1 ratio or an equimolar ratio led to the formation of corresponding binuclear complex [Pt₂Me₂(κ²N,C-bipyO-H)₂(µ-dppf)], 1, or mononuclear complex [PtMe(κ¹C-bipyO-H)(dppf)], 2, respectively. According to the reaction conditions, the dppf ligand in 1 and 2 behaves as either a bridging or chelateing ligand. All complexes were characterized by NMR spectroscopy. The solid-state structure of 2 was determined by single-crystal X-ray diffraction method and it was shown that the chelateing dppf ligand in this complex was arranged “synclinal-staggered” conformation. Also, the occurrence of intermolecular C–H_Cp…O_bipyO-H interactions in the solid-state gave rise to an extended 1-D network. The electronic absorption spectra and the electrochemical behavior of these complexes are discussed. Density functional theory (DFT) was used for geometry optimization of the singlet states in solution and for electronic structure calculations. The analysis of the molecular orbital (MO) compositions in terms of occupied and unoccupied fragment orbitals in 2 was performed.