Osmium(IV) tetraaryl complexes formed from pre-functionalized ligands

Metal(IV) tetraaryl, M(aryl)4, complexes hold great promise as functional building blocks for complex organometallic materials, yet their widespread utility depends on the development of improved synthetic protocols and a deeper understanding of their chemical structure-property relationship(s). Here we show that Os(aryl)4 complexes with pre-installed functional groups (-F, -Cl, -Br, -I, and -SMe) can be prepared from reactions between (Oct4N)2[OsBr6] and Grignard reagents formed by halogen/magnesium insertion or exchange. This approach provides access to compounds that may otherwise prove challenging to prepare through post-functionalization strategies, such as those comprising halogens in the 2- or 5-positions. Furthermore, we show that these tetrahedral complexes can be stabilized by ortho-chloride substituents, moving beyond the alkyl groups that have previously been exploited for this purpose. We characterize these, as well as previously reported, materials using single-crystal X-ray diffraction, solution voltammetry, and UV-vis spectroscopy. We find these compounds, while typically appearing as black or darkly colored in the solid state, yield differently colored CH2Cl2 solutions due to small changes in the λmax and variations in the relative intensity of their four primary absorbance features. Through a comparison of 13 differently substituted complexes, we identify correlations between their electrochemical and optical gaps, and between the E1/2 of their 0/1+ redox event and an adjusted Hammett parameter that accounts for all aryl ligand substituents. This work provides a foundation for advancing new preparative methods to further derivatize such species, and a robust experimental dataset to help benchmark future experimental and computational compound characterization.