A mixed-valence dinuclear ruthenium complex composed of Ru(II)-acetylide and Ru(III)-tropolonato units: Acetylide–vinylidene interconversion in solution and solid state

A dinuclear Ru(II)–Ru(III) complex, [Ru(acac)2(μ2-tropC2)RuCp(dppe)] (2a, acac = acetylacetonato, Cp = cyclopentadienyl, dppe = 1,2-bis(diphenylphosphino)ethane, HtropC2H = 5-acetylenyltropolone), has been newly synthesized and fully characterized. 2a is composed of two hetero units, [RuIICp(dppe)] and [RuIII(acac)2(trop)], and it showed a broad absorption in the NIR region, indicating the electronic communication between the two hetero units. 2a quantitatively converted to the vinylidene form [2aH](TsO) by the addition of p-toluenesulfonic acid monohydrate (TsOH·H2O) to the chloroform solution of 2a. The weak NIR absorption exhibited by 2a disappeared in [2aH](TsO). [2aH](TsO) re-converted to the acetylide 2a after the addition of triethylamine to the acetonitrile solution of [2aH](TsO). 1H NMR and UV–vis–NIR spectroscopy indicated the mutual interconversion and on/off behavior of the electronic communication between the two hetero units. Moreover, structural interconversion also proceeded in the solid state. 2a swiftly converted to [2aH](TsO) after grinding with solid TsOH·H2O for 5 min. The conversion yield estimated from IR measurements was 70%. [2aH](TsO) re-converted to 2a after re-grinding with AcONa with a conversion yield of 84%. These results indicate the usability of 2a as a molecular switch triggered by protonation/deprotonation both in solution and solid state.