Electronically Weakly Coupled 4,4′‐Divinylazoarylenes‐Bridged Diruthenium Complexes Featuring Two Ru(CO)Cl(PⁱPr₃)₂ Entities

Abstract

We report here on four novel 4,4′‐divinylazoarylenes‐bridged diruthenium complexes featuring two Ru(CO)Cl(PiPr3)2 entities with a general formula of [{Ru(CO)Cl(PiPr3)2}2(μ‐{CH=CH−Ar}2‐N=N‐4,4′)]; Ar=C6H4; [1 azo], C6H3‐2‐Me; [2 azo], C6H3‐(Me)2‐2,6; [3 azo], and C6H2‐(iPr)2‐2,6; [4 azo]. Those five‐coordinated, square‐pyramidal, 16‐valence electrons (VEs) type‐complexes [1 azo]–[4 azo] were successfully synthesized by the stereo‐and regiospecific insertion of the Ru−H bond of the hydrido substrate HRu(CO)Cl(PiPr3)2 into the two terminal acetylenic bonds of the corresponding 4,4′‐diethynylated azoarylenes [L1]–[L4]. They were routinely characterized in their neutral state by traditional IR, UV/Vis and NMR spectroscopic techniques, and in their two‐closely accessible oxidized states by IR, UV/Vis/NIR spectroelectrochemistry along with electrochemical techniques as well as by (TD)‐DFT calculations. Detailed electrochemical studies on these complexes and IR, UV/Vis/NIR spectro(electro)scopic characterization of their oxidized forms along with (TD)‐DFT calculations revealed to massive 4,4′‐divinylazobenzene linker contributions to the two redox processes in addition to the noteworthy negligible electronic interaction “communication” between the two remote redox‐active end‐groups, rendering them as unique weakly coupled borderline class I/II MV systems in accordance with the Robin and Day classification. Incorporating the four bulky iPr substituents into the ortho‐positions of the 4,4′‐divinylazobenzene linker results to a significant decrease in the tendency of the co‐planarity of the bridge.