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(MeC5H4)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)MnC2Mn(dmpe)(C5H4Me)][PF6] ([1][PF6]) 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)MnC2Mn(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)(C5H4Me)][PF6]2 ([1][PF6]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. A singlet/triplet spin equilibrium (see scheme) is exhibited by the C2‐bridged half‐sandwich complex [(MeC5H4)(dmpe)MnC2Mn(dmpe)(C5H4Me)] (1). In addition, the mixed valent monocation 1+ is paramagnetic, while the dication 12+ is diamagnetic; this stresses the fact that the manganese centers are electronically strongly coupled. The interesting electronic properties exhibited by these complexes makes them promising candidates for the purpose of molecular electronics.