Osmium(IV) Tetraaryl Complexes Formed from Prefunctionalized Ligands

Transition 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 preinstalled 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 postfunctionalization strategies, such as those comprising halogens in the 2- or 5-positions. We characterize these, as well as previously reported, materials using single-crystal X-ray diffraction, solution voltammetry, and UV-vis spectroscopy. Through a comparison of 13 differently substituted complexes, we identify correlations between their electrochemical and optical gaps, and between the E_1/2 of their 0/1+ redox event and an adjusted Hammett parameter that accounts for all aryl ligand substituents. The electronic property trends observed are further rationalized through a series of first-principles calculations based on density functional theory. Together, this work lays a foundation for advancing new preparative methods to further derivatize such species, and a robust experimental data set to help benchmark future experimental and computational compound characterization.