A Conjugated Diosma-Octacyclic Complex and Its Mixed-Valence Singly Reduced State
Metallaaromatics as a new class of organometallic compounds have attracted considerable attention in recent years. Metallaaromatic compounds where the number of fused rings forming the metalla-polycyclic skeleton exceeds seven have not been reported to date. Likewise, metallaaromatic compounds containing two transition-metal centres are rarely encountered in the literature. In this work two dicationic diosma-octacyclic complexes have successfully been synthesized and fully characterized. One of them, with aromatic osmapentalene termini linked by the non-aromatic osmafuran moiety to the rigid naphthalenediolate bridge, represents the first example of a fused, fully conjugated dimetalla-octacyclic complex. A reference complex with more flexible biphenolate in the bridging position was also prepared. Their redox and electronic properties were investigated by combined methods of cyclic voltammetry and UV-vis-NIR-IR spectroelectrochemistry, supported by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. The rigid octacyclic complex forms a stable singly reduced mixed-valence species with the spin density localized at one the osmapentalene termini.