3,6-Divinyl-N-arylcarbazoles-bridged diruthenium complexes bearing two Ru(CO)Cl(PiPr3)2 moieties: Polyelectrochromism and electronic coupling

A series of five 3,6-divinyl-N-arylcarbazoles-bridged diruthenium complexes with a general formula of [{Ru(CO)Cl((PPr3)-Pr-i)(2)}(2)(mu-(CH=CH)(2)-(N-arylcarbazole)-3,6); aryl = 4-anisyl; [1a], 4-tolyl; [1b], phenyl; [1c], 4-(trifluoromethyl)phenyl; [1d], and 4-nitrophenyl; [1e]] were successfully synthesized. These new square-pyramidal bis(ruthenium-vinyl)-type complexes were characterized in their neutral state via classical NMR, UV/Vis, and IR spectroscopic techniques and in their three various accessible oxidized states via electrochemical techniques and ESR spectroscopy along with UV/Vis/NIR and IR spectroelectrochemistry as well as with DFT calculations. Our obtained results were compared with the closely related bis(ruthenium-vinyl)-appended N-(4-anisyl)diphenylamine TAARu2 counterpart of [1a]. Electrochemical studies on complexes [1a]-[1e] revealed three consecutive, chemically and electrochemically, well-separated, reversible one-electron oxidation processes at low and well-accessible potentials. Their half-wave potential separations Delta E-1/2 between the individual redox waves and the derived comproportionation constants K-c1-K-c3 attribute to noteworthy stability of every oxidized intermediate state. The concert electrochemical and UV/Vis/NIR/IR spectro(electro)scopic results on these rotationally restricted N-arylcarbazoles-bridged bis(ruthenium-alkenyl)-type complexes [1a]-[1e] confirmed the relative weakness influence of altering the para-substituent on the peripheral aryl ring. This is most probably due to the sizable torsion with nearly 55 degrees between the co-planarity of the carbazole heterocycle core and the peripheral N-bound aryl ring. In their mixed-valent (MV) radical states [1a](+)-[1e](+), the observed pattern of two well-separated Ru(C equivalent to O) bands mirrors the uneven distribution of the uni-positive charge over the two chemically equivalent bis(ruthenium-vinyl) moieties as indicated by classical class II of Robin-Day classification of MV states.