Ruthenium and osmium bis-homoleptic complexes of two noninnocent ligands, ONO, N-(3,5-di-tert-butyl-2-oxyphenyl)-3,5-di-tert-butylquinoneimine, and DOPO, 2,4,6,8-tetra-tert-butyl-1-oxo-1H-phenoxazin-9-olate, were synthesized by reacting di-μ-chlorobis[(p-cymene)chloroM(II) (M = Os and Ru) with Pb(LQ)2 (ONO and DOPO). The ligands’ consecutive 5-membered chelate rings with all ligand atoms sp2-hybridized encourage it to adopt a meridional geometry in an octahedron. The complexes containing the DOPO ligand were found to be octahedral, whereas the complexes containing the ONO ligand show distortions from the expected octahedral geometry. Ruthenium and osmium bis(ONO) distort towards trigonal prismatic geometries in order to minimize aryloxide-to-metal π* interactions due to donation from the second-highest ligand orbital to the metal, an orbital that is often neglected in π-donor ligands. The degree of distortion directly correlates with the degree of reduction of the redox active ligand. As the metal-ligand π bonding orbitals shift from ligand-centered to metal-centered, and hence the ligand becomes more oxidized, these orbitals become more σ-antibonding in the trigonal prism and restore the geometric preference to octahedral.

Octahedral to trigonal prismatic distortion in Ruthenium and Osmium bis-homoleptic complexes of a noninnocent ligand

249th National Meeting (2015)

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