- Award ID(s):
- 1465104
- 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
More Like this
-
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.more » « less
-
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
-
Optically active C 2 -symmetric bis(aminophenols) based on ( R )-2,2′-diaminobinaphthyl (BiniqH 4 ) and ( R , R )-2,3-butanediyldianthranilate (BdanH 4 ) have been prepared by condensation of the diamines with 3,5-di- tert -butylcatechol. Group 10 bis(iminosemiquinone) complexes ( R )-(Biniq)M (M = Pd, Pt) and ( C , R , R )-(Bdan)Pd have been prepared by oxidatively metalating the corresponding ligands. In ( R )-(Biniq)M, the C 2 axis passes through the approximate square plane of the bis(iminosemiquinone)metal core, while in ( C , R , R )-(Bdan)Pd the C 2 axis is perpendicular to this plane. In the latter compound, the ( R , R )-butanediyl strap binds selectively over one enantioface of the metal complex in a conformation where the methyl groups are anti to one another. Osmium oxo complexes with the intrinsically chiral OsO(amidophenoxide) 2 chromophore are obtained by metalation of OsO(OCH 2 CH 2 O) 2 with ( R , R )-BdanH 4 . Both the ( A , R , R ) and ( C , R , R ) diastereomers can be observed, with metalation in refluxing toluene selectively giving the latter isomer. The electronic structures of the complexes are illuminated by the circular dichroism spectra, in conjuction with the optical spectra and TDDFT calculations.more » « less
-
Tris(2-(arylamido)-4,6-di- tert -butylphenoxo)molybdenum( vi ) complexes ( R ap) 3 Mo can be prepared either from (cycloheptatriene)Mo(CO) 3 and the N -aryliminoquinone, or from MoO 2 (acac) 2 and the aminophenol. In contrast to all other reported unconstrained transition metal tris(amidophenoxide) complexes, the molybdenum complexes show a facial geometry in the solid state. In solution, the fac isomer predominates, though a small amount of mer isomer is detectable at room temperature. At elevated temperature the two species interconvert through Rây-Dutt trigonal twists, which are faster than Bailar twists in this system, presumably because of steric effects of the N -aryl groups. Substituents on the N -aryl ring shift the fac / mer equilibrium of the complex, with more electron-withdrawing substituents generally increasing the proportion of the mer isomer. The preference for fac over mer geometry is thus suggested to be due to enhanced π bonding in the fac isomer. In contrast to analogous catecholate complexes, the tris(amidophenoxide) complexes are not Lewis acidic and are inert to nucleophilic oxidants such as amine- N -oxides.more » « less
-
Abstract Understanding what controls the strength of bonding of adsorbed intermediates to transition‐metal surfaces is of central importance in many technologies, especially catalysis and electrocatalysis. Our recently measured bond enthalpies of −OH, −OCH3, −O(O)CH and −CH3to Pt(111) and Ni(111) surfaces are fit well (standard deviation of 7.2 kJ mol−1) by a predictive equation involving only known parameters (gas‐phase ligand–hydrogen bond enthalpies, bond enthalpies of adsorbed H atoms to that surface, electronegativities of the elements, and group electronegativities of the ligands). This equation is based upon Pauling's equation, with improvements introduced by Matcha, derived here following manipulations of Matcha's equation similar to (but going beyond) those introduced by Schock and Marks to explain ligand–metal bond enthalpy trends in organometallic complexes.