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(P i Pr 3 ) 2 } 2 ( μ ‐(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 Δ E ½ 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° 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≡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.