2-(Arylamino)-4,6-di- tert -butylphenols containing 4-substituted phenyl groups ( R apH 2 ) react with oxobis(ethylene glycolato)osmium( vi ) in acetone to give square pyramidal bis(amidophenoxide)oxoosmium( vi ) complexes. A mono-amidophenoxide complex is observed as an intermediate in these reactions. Reactions in dichloromethane yield the diolate ( H ap) 2 Os(OCH 2 CH 2 O). Both the glycolate and oxo complex are converted to the corresponding cis -dichloride complex on treatment with chlorotrimethylsilane. The novel bis(aminophenol) ligand EganH 4 , containing an ethylene glycol dianthranilate bridge, forms the chelated bis(amidophenoxide) complex (Egan)OsO, where the two nitrogen atoms of the tetradentate ligand bind in the trans positions of the square pyramid. Structural and spectroscopic features of the complexes are described well by an osmium( vi )-amidophenoxide formulation, with the amount of π donation from ligand to metal increasing markedly as the co-ligands change from oxo to diolate to dichloride. In the oxo-bis(amidophenoxides), the symmetry of the ligand π orbitals results in only one effective π donor interaction, splitting the energy of the two osmium-oxo π* orbitals and rendering the osmium-oxo bonding appreciably anisotropic.
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Highly covalent metal–ligand π bonding in chelated bis- and tris(iminoxolene) complexes of osmium and ruthenium
The bis(aminophenol) 2,2′-biphenylbis(3,5-di- tert -butyl-2-hydroxyphenylamine) (ClipH 4 ) forms trans -(Clip)Os(py) 2 upon aerobic reaction of the ligand with {( p -cymene)OsCl 2 } 2 in the presence of pyridine and triethylamine. A more oxidized species, cis -β-(Clip)Os(OCH 2 CH 2 O), is formed from reaction of the ligand with the osmium( vi ) complex OsO(OCH 2 CH 2 O) 2 , and reacts with Me 3 SiCl to give the chloro complex cis -β-(Clip)OsCl 2 . Octahedral osmium and ruthenium tris-iminoxolene complexes are formed from the chelating ligand tris(2-(3′,5′-di- tert -butyl-2′-hydroxyphenyl)amino-4-methylphenyl)amine (MeClampH 6 ) on aerobic reaction with divalent metal precursors. The complexes’ structural and electronic features are well described using a simple bonding model that emphasizes the covalency of the π bonding between the metal and iminoxolene ligands rather than attempting to dissect the parts into discrete oxidation states. Emphasizing the continuity of bonding between disparate complexes, the structural data from a variety of Os and Ru complexes show good correlations to π bond order, and the response of the intraligand bond distances to the bond order can be analyzed to illuminate the polarity of the bonding between metal and the redox-active orbital on the iminoxolenes. The osmium compounds’ π bonding orbitals are about 40% metal-centered and 60% ligand-centered, with the ruthenium compounds’ orbitals about 65% metal-centered and 35% ligand-centered.
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- Award ID(s):
- 1465104
- NSF-PAR ID:
- 10331411
- Date Published:
- Journal Name:
- Dalton Transactions
- Volume:
- 49
- Issue:
- 21
- ISSN:
- 1477-9226
- Page Range / eLocation ID:
- 7015 to 7027
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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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.more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d0dt01287d
