On the border between localization and delocalization: tris(iminoxolene)titanium(iv)Electronic supplementary information (ESI) available: Symmetry-breaking, energy and Cartesian coordinates for calculated structures of (Clamp)Ti and related complexes. CCDC 1845533. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c8dt04528c

• Main Authors: Marshall-Roth, Travis, Yao, Kun, Parkhill, John A, Brown, Seth N
• Format: Journal Article
• Published: 22.01.2019
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c8dt04528c

The tris(aminophenol) ligand tris(4-methyl-2-(3′,5′-di- tert -butyl-2′-hydroxyphenylamino)phenyl)amine, MeClampH 6 , reacts with Ti(O i Pr) 4 to give, after exposure to air, the dark purple, neutral, diamagnetic complex (MeClamp)Ti. The compound is six-coordinate, with an uncoordinated central nitrogen (Ti-N = 2.8274(12) Å), and contains titanium( iv ) and a doubly oxidized ligand, formally a bis(iminosemiquinone)-mono(amidophenoxide). The compound is unsymmetrical in the solid state, though the three ligands are equivalent on the NMR timescale in solution. Ab initio calculations indicate that the ground state is a multiconfigurational singlet, with a low-lying multiconfigurational triplet state. Variable-temperature NMR measurements are consistent with a singlet-triplet gap of 1200 ± 70 cm −1 , in good agreement with calculations. The distortion from threefold symmetry allows a low-lying, partially populated ligand-centered π nonbonding orbital to mix with largely occupied metal-ligand π bonding orbitals. The energetic accessibility of this distortion is inversely related to the strength of the metal-ligand π bonding interaction. An air-stable tris(iminoxolene)titanium( iv ) complex is a ground state singlet best described as intermediate between fully localized and fully delocalized.