Making Use of Obstacles: Alternative Synthetic Approaches towards Osmium(II)‐Based Photochemical Molecular Devices

Abstract

Two synthetic approaches towards the mononuclear complex [(tbbpy)2OsII(tpphz)]2+ (tbbpy = 4,4′‐di‐tert‐butyl‐2,2′‐bipyridine; tpphz = tetrapyrido[3,2‐a:2′,3′‐c:3′′,2′′‐h:2′′′,3′′′‐j]phenazine) based on the precursor [(tbbpy)2OsIICl2] and its oxidized side product [(tbbpy)2OsIIICl2]+ are presented. The first route is analogous to that for the isostructural ruthenium complex, whereas the second strategy efficiently uses the oxidized OsIII complex under reducing conditions to obtain so‐called virtual dilution, which avoids the formation of the dinuclear complex [(tbbpy)2OsII(tpphz)OsII(tbbpy)2]. Concentration‐dependent NMR investigations were performed, and a dimerization constant (KD = 400) could be calculated due to π–π interactions of the tpphz moiety. Solid‐state structures of all synthesized complexes show comparable bond lengths and angles with respect to each other and their ruthenium analogues. Photophysical investigations show the expected absorption in the UV/Vis region and a single emission at 758 nm for [(tbbpy)2OsII(tpphz)]2+. Electrochemical measurements show comparable behavior to the structurally similar complexes [(bpy)2M(tpphz)]2+ (M = Os, Ru).