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Both pseudo-octahedral and pseudo-square pyramidal bis-iminoxolene complexes trans -(Diso) 2 RuCl 2 and trans -(Diso) 2 Ru(PPh 3 ) are structurally distorted, with the ruthenium atom slipping off the twofold axis of the idealized coordination polyhedra. These distortions take place because they allow or enhance π interactions between ruthenium and the iminoxolene π orbitals. 

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. 

The dioxomolybdenum( vi ) complex MoO 2 Cl 2 (dmf) 2 reacts with Pb(DOPO Q ) 2 (DOPO = 2,4,6,8-tetra- tert -butyl-1,9-dioxophenoxazinate) to give MoO 2 (DOPO Q ) 2 , which has an eight-coordinate structure with normal molybdenum-oxo bond distances and angles but elongated distances to the dioxophenoxazine ligand. The dioxo complex is deoxygenated by phosphines to produce octahedral Mo(DOPO Cat ) 2 , in which reduction has taken place at the ancillary ligands. This compound in turn reacts with trimethylamine- N -oxide to regenerate MoO 2 (DOPO Q ) 2 , allowing a catalytic cycle for phosphine oxidation. This represents an example of four-electron nonclassical oxygen atom transfer in which both the oxidized and reduced forms of the metal complexes can be observed. 

Reaction of the 9,9-dimethylxanthene-bis(imine)-bis(catechol) ligand XbicH 4 with half an equivalent of Zr(acac) 4 affords the neutral tetracatecholate complex (XbicH 2 ) 2 Zr, containing four iminium ions hydrogen bonded to the catecholates. The heteroleptic bis(catecholate)-tetraphenylporphyrin complex (TPP)Zr(XbicH 2 ) is formed from reaction of (TPP)Zr(OAc) 2 with XbicH 4 in the presence of base. Both compounds adopt an eight-coordinate square antiprismatic geometry around the zirconium center. NMR spectra of (TPP)Zr(XbicH 2 ) show that it is fluxional at room temperature, with homoleptic (XbicH 2 ) 2 Zr showing fluxionality at higher temperatures. Calculations and kinetic isotope effect measurements suggest that the motions involve dissociation of a single catecholate oxygen and subsequent twisting of the seven-coordinate species. The compounds show reversible one-electron oxidations of each of the bound catecholates to bound semiquinones. 

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. 

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.