Facile access to redox-active C₂-bridged complexes with half-sandwich manganese end groups

The dinuclear mixed-valent complex [(MeC₅H₄)(dmpe) MnC₂Mn-(dmpe)(C₅H₄Me)] ⁺[(η²-MeC₅H₄) ₃Mn]^- [1]⁺[2]^- (dmpe = 1,2-bis (dimethylphosphanyl)ethane) was prepared by the reaction of [Mn(MeC ₅H₄)₂] with dmpe and Me₃SnC≡ CSnMe₃. The reactions of [1]⁺[2]^- with K[PF⁶] and Na[BPh₄] yielded the corresponding anion metathesis products [(MeC₅H₄)(dmpe)Mn-C ₂Mn(dmpe)(C₅H₄Me)][PF₆] ([1][PF ₆]) and [(MeC₅H₄)(dmpe)MnC₂Mn(dmpe)- (C₅H₄Me)][BPh₄] ([1][BPh₄]). These mixed-valent species can be reduced to the neutral form by reaction with Na/ Hg. The obtained complex [(MeC₅H₄)-(dmpe)MnC ₂Mn(dmpe)(C₅H₄Me)] (1) displays a triplet/singlet spin equilibrium in solution and in the solid state, which was additionally studied by DFT calculations. The diamagnetic dicationic species [(MeC₅H₄)(dmpe)MnC₂Mn- (dmpe)(C ₅H₄Me)][PF₆]₂ ([1][PF ₆]₂) was obtained by oxidizing the mixed-valent complex [1][PF₆] with one equivalent of [Fe(C₅H₅) ₂][PF₆]. Both redox processes are fully reversible. The dinuclear compounds were characterized by NMR, IR, UV-visible, and Raman spectroscopy, cyclic voltammetry, and magnetic susceptibility measurements. X-ray diffraction studies were performed on [1][2], [1][PF₆], [1][BPh₄], and [1][PF₆]₂.