Optically active bis(aminophenols) and their metal complexes.

Optically active -symmetric bis(aminophenols) based on ()-2,2'-diaminobinaphthyl (BiniqH) and (,)-2,3-butanediyldianthranilate (BdanH) have been prepared by condensation of the diamines with 3,5-di--butylcatechol. Group 10 bis(iminosemiquinone) complexes ()-(Biniq)M (M = Pd, Pt) and (,,)-(Bdan)Pd have been prepared by oxidatively metalating the corresponding ligands. In ()-(Biniq)M, the axis passes through the approximate square plane of the bis(iminosemiquinone)metal core, while in (,,)-(Bdan)Pd the axis is perpendicular to this plane.

Slip to π Ru: structural distortions due to metal-iminoxolene π bonding.

Both pseudo-octahedral and pseudo-square pyramidal bis-iminoxolene complexes -(Diso)RuCl and -(Diso)Ru(PPh) 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.

Modulation of Isomerization and Ligand Exchange Rates by π Bonding in Bis(iminoxolene)iridium Pyridine Complexes.

The bis(iminoxolene)iridium complex (Diso)IrCl (Diso = -(2,6-diisopropylphenyl)-4,6-di--butyl-2-imino--benzoquinone) reacts with pyridine to give -(Diso)Ir(py)Cl as the kinetic product, with -(Diso)Ir(py)Cl formed as the exclusive thermodynamic product upon heating. Electronic spectra and density functional theory calculations point to very similar electronic structures for the cis and trans isomers, with a nonbonding iminoxolene-centered HOMO and a metal-iminoxolene π* LUMO. The triplet states of -(Diso)Ir(py)Cl and -[(Diso)Ir(py)] (but not -(Diso)Ir(py)Cl) are unusually low in energy (1000-1500 cm above the singlets), as shown by variable-temperature NMR spectroscopy.

Mono- and Bis(iminoxolene)iridium Complexes: Synthesis and Covalency in π Bonding.

-(2,6-Diisopropylphenyl)-4,6-di--butyl--iminobenzoquinone (Diso) reacts with the (cyclooctadiene)iridium chloride dimer to form a monoiminoxolene complex, (Diso)Ir(cod)Cl. Reaction of 2 equiv of the iminoquinone with chlorobis(cyclooctene)iridium dimer affords the bis-iminoxolene (Diso)IrCl. This five-coordinate complex adopts a distorted square pyramidal structure with an apical chloride ligand and undergoes halide exchange to form an air-stable iodide complex.

Amphiphilicity in Oxygen Atom Transfer Reactions of Oxobis(iminoxolene)osmium Complexes.

Oxobis(iminoxolene)osmium(VI) compounds (ap)OsO (ap = 2-(4-RCHN)-4,6-BuCHO) are readily deoxygenated by phosphines and phosphites to give five-coordinate (ap)Os(PR') or six-coordinate (ap)Os(PR'). Structural data indicate that this net two-electron reduction is accompanied by apparent oxidation of the iminoxolene ligands due to their greater ability to engage in π donation to the reduced deoxy form of the osmium complex. In (ap)Os(PR'), the HOMO is a ligand-based combination of the iminoxolene redox-active orbitals, while the LUMO is a highly covalent metal-iminoxolene π* orbital.

Synthesis, dynamics and redox properties of eight-coordinate zirconium catecholate complexes.

Reaction of the 9,9-dimethylxanthene-bis(imine)-bis(catechol) ligand XbicH4 with half an equivalent of Zr(acac)4 affords the neutral tetracatecholate complex (XbicH2)2Zr, containing four iminium ions hydrogen bonded to the catecholates. The heteroleptic bis(catecholate)-tetraphenylporphyrin complex (TPP)Zr(XbicH2) is formed from reaction of (TPP)Zr(OAc)2 with XbicH4 in the presence of base. Both compounds adopt an eight-coordinate square antiprismatic geometry around the zirconium center.

High-valent osmium iminoxolene complexes.

2-(Arylamino)-4,6-di-tert-butylphenols containing 4-substituted phenyl groups (RapH2) 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 (Hap)2Os(OCH2CH2O).

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) forms trans-(Clip)Os(py) upon aerobic reaction of the ligand with {(p-cymene)OsCl} in the presence of pyridine and triethylamine. A more oxidized species, cis-β-(Clip)Os(OCHCHO), is formed from reaction of the ligand with the osmium(vi) complex OsO(OCHCHO), and reacts with MeSiCl to give the chloro complex cis-β-(Clip)OsCl. 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) on aerobic reaction with divalent metal precursors.

Deuteration of BTZ043 Extends the Lifetime of Meisenheimer Intermediates to the Antituberculosis Nitroso Oxidation State.

Substituted nitrobenzothiazinones (BTZs) are potent antituberculosis prodrugs that are reductively activated to produce nitroso moieties that form covalent adducts with a cysteine residue of decaprenylphosphoryl-β-d-ribose-2'-oxidase (DprE1) of (). The resulting cell wall synthesis inhibition is lethal to , leading to consideration of development of BTZs for clinical use. The hydride-induced reduction of the nitroaromatic proceeds by reversible formation of the corresponding Meisenheimer complex.

Mono- and bimetallic pentacoordinate silicon complexes of a chelating bis(catecholimine) ligand.

Schiff base condensation of 4,5-diamino-9,9-dimethylxanthene with 4,6-di-tert-butylcatechol-3-carboxaldehyde affords the bis(catecholimine) ligand XbicH, which can bind metals in both a square bis(catecholate) upper pocket and a pentagonal NO lower pocket. Metalation with PhSiCl results in [(XbicH)SiPh][HCl], where the silicon adopts a five-coordinate, square pyramidal geometry in the upper pocket and the lower pocket binds to two protons on the imine nitrogens. Deprotonation of the imines with LiOBu, NaN[SiMe], or AgOAc results in binding of the univalent metal ion in the lower pocket, where it adopts an unusual pentagonal monopyramidal geometry in the solid state.

On the border between localization and delocalization: tris(iminoxolene)titanium(iv).

The tris(aminophenol) ligand tris(4-methyl-2-(3',5'-di-tert-butyl-2'-hydroxyphenylamino)phenyl)amine, MeClampH6, reacts with Ti(OiPr)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).

Molybdenum(vi) tris(amidophenoxide) complexes.

Tris(2-(arylamido)-4,6-di-tert-butylphenoxo)molybdenum(vi) complexes (ap)Mo can be prepared either from (cycloheptatriene)Mo(CO) and the N-aryliminoquinone, or from MoO(acac) 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.

When Do Strongly Coupled Diradicals Show Strongly Coupled Reactivity? Thermodynamics and Kinetics of Hydrogen Atom Transfer Reactions of Palladium and Platinum Bis(iminosemiquinone) Complexes.

The 2,2'-biphenylene-bridged bis(iminosemiquinone) complexes ( BuClip)M [ BuClipH = 4,4'-di- tert-butyl- N, N'-bis(3,5-di- tert-butyl-2-hydroxyphenyl)-2,2'-diaminobiphenyl; M = Pd, Pt] can be reduced to the bis(aminophenoxide) complexes ( BuClipH)M by reaction with hydrazobenzene (M = Pd) or by catalytic hydrogenation (M = Pt). The palladium complex with one aminophenoxide ligand and one iminosemiquinone ligand, ( BuClipH)Pd, is generated by comproportionation of ( BuClip)Pd with ( BuClipH)Pd in a process that is both slow (0.06 M s in toluene at 23 °C) and only modestly favorable ( K = 1.

Group 10 Bis(iminosemiquinone) Complexes: Measurement of Singlet-Triplet Gaps and Analysis of the Effects of Metal and Geometry on Electronic Structure.

Bis(iminosemiquinone) complexes of divalent group 10 metals have been described as having open-shell singlet ground states characteristic of very strong coupling between the two ligand radicals. By using the nonlinear temperature dependence of the chemical shifts of the H NMR spectra, the singlet-triplet gaps in seven of these compounds have been measured, with the nickel compounds having gaps of about 2400 cm and the palladium compounds about 1800 cm. Bis(iminosemiquinone)platinum complexes have singlet-triplet gaps too large to measure by this technique (over 2800 cm, estimated to be about 3000 cm), though bis(3,5-di- tert-butylbenzosemiquinonato)platinum(II) has a measurable singlet-triplet gap of 1850 cm.

A chelating bis(aminophenol) ligand bridged by a 1,1'-ferrocene-bis(para-phenylene) linker.

1,1'-Bis(4-(2-hydroxy-3,5-di-tert-butylphenyl)aminophenyl)ferrocene (pFlipH) is prepared in three steps from commercially available 1,1'-ferrocenediboronic acid or its pinacol ester. The suitability of the ligand to bind as a tetradentate ligand in a cis, planar fashion has been confirmed by formation of a square planar palladium bis-iminosemiquinone (pFlip)Pd. The linker unit appears to be structurally similar to 1,1'-ferrocenediyl, but the electronic interaction of the ferrocene with the aminophenols is minimal.

Intrinsic Bond Energies from a Bonds-in-Molecules Neural Network.

Neural networks are being used to make new types of empirical chemical models as inexpensive as force fields, but with accuracy similar to the ab initio methods used to build them. In this work, we present a neural network that predicts the energies of molecules as a sum of intrinsic bond energies. The network learns the total energies of the popular GDB9 database to a competitive MAE of 0.

The Metal or the Ligand? The Preferred Locus for Redox Changes in Oxygen Atom Transfer Reactions of Rhenium Amidodiphenoxides.

The rhenium(V) oxo complex oxo(triphenylphosphine) (bis(3,5-di-tert-butyl-2-phenoxo)amido)rhenium(V), (ONO)ReO(PPh), reacts with molecular oxygen to give triphenylphosphine oxide and the dimeric rhenium(VII) complex fac,anti-(ONO)Re(O)(μ-O)Re(O)(ONO). The ONO ligand adopts an unusual fac geometry, presumably to maximize π donation to rhenium; strong π donation is substantiated by the intraligand bond distances (metrical oxidation state = -2.24(9)).

Redox activity and π bonding in a tripodal seven-coordinate molybdenum(VI) tris(amidophenolate).

A tris(aminophenol), tris(2-(3',5'-di-tert-butyl-2'-hydroxyphenyl)amino-4-methylphenyl)amine, MeClampH6, is prepared in three steps from tri-p-tolylamine. The ligand reacts with dioxomolybdenum(VI) bis(acetylacetonate) to form an oxo-free heptadentate complex, (MeClamp)Mo, with a capped octahedral geometry. The molybdenum is formally in the +6 oxidation state, with significant π donation of the amidophenolates, as judged by intraligand bond distances.

Mechanism and selectivity of methyl and phenyl migrations in hypervalent silylated iminoquinones.

Chlorosilanes R(X)(Y)SiCl (R = Me, Ph; X, Y = Me, Ph, Cl) have been reported to react with Pb(ONO(Q))2 (ONO(Q) = 3,5-di-tert-butyl-1,2-quinone-(3,5-di-tert-butyl-2-oxy-1-phenyl)imine) to give five-coordinate (X)(Y)Si(ON[R]O), in which the R group has migrated from silicon to nitrogen. This migration is intramolecular, as confirmed by the lack of crossover between (CH3)3SiCl and (CD3)3SiCl in their reaction with Pb(ONO(Q))2. Reaction of PhSiMeCl2 takes place with high kinetic stereoselectivity to produce isomer Ph(Cl)Si(ON[Me]O) in which the phenyl is axial in the trigonal bipyramid, which subsequently isomerizes to the thermodynamic isomer with axial chlorine.

Metal and ligand effects on bonding in group 6 complexes of redox-active amidodiphenoxides.

Group 6 complexes M(ONO)2 (M = Cr, Mo, W; ONO = bis(2-oxy-3,5-di-tert-butylphenyl)amide) are prepared by the reaction of divalent metal halide precursors with Pb(ONO(Q))2. Analogous complexes containing the 2,4,6,8-tetra-tert-butyl-1,9-dioxophenoxazinate ligand (DOPO) are prepared by protonolysis of chromocene with H(DOPO(Q)) or by reaction of Pb(DOPO(Q))2 with M2Br4(CO)8 (M = Mo, W). The molybdenum and tungsten complexes are symmetrical, octahedral compounds for which spectroscopic data are consistent with M(VI) complexes with fully reduced [L(Cat)](3-) ligands.

Octahedral to trigonal prismatic distortion driven by subjacent orbital π antibonding interactions and modulated by ligand redox noninnocence.

Ru(ONO)2 and Os(ONO)2 distort from octahedral towards trigonal prismatic geometry in order to relieve π antibonding due to donation from the second-highest ligand orbital to the metal. Increasing oxidation of the ONO ligand suppresses distortion by increasing σ* interactions in the trigonal prism.

Mixed amidophenolate-catecholates of molybdenum(VI).

The dioxomolybdenum(vi) complex ((t)BuClipH2)MoO2 ((t)BuClipH4 = 4,4'-di-tert-butyl-N,N'-bis(3,5-di-tert-butyl-2-hydroxyphenyl)-2,2'-diaminobiphenyl) reacts with 3,5-di-tert-butylcatechol to form oxo-free ((t)BuClip)Mo(3,5-(t)Bu2Cat). The bis(amidophenoxide)-monocatecholate complex is monomeric and exhibits a cis-β geometry in the solid state. Variable-temperature NMR data are consistent with two fluxional processes, one that interconverts several geometric isomers at low temperature, and a second that interchanges the ends of the (t)BuClip ligand at ambient temperatures.

Nonclassical oxygen atom transfer as a synthetic strategy: preparation of an oxorhenium(V) complex of the bis(3,5-di-tert-butyl-2-phenoxo)amide ligand.

Oxo(triphenylphosphine)[bis(3,5-di-tert-butyl-2-phenoxo)amido]rhenium(V) [(ONO(Cat))ReO(PPh3)] is prepared by the reaction of iododioxobis(triphenylphosphine)rhenium(V) [ReO2(PPh3)2I] with lead bis(3,5-di-tert-butyl-1,2-quinone-1-(2-oxy-3,5-di-tert-butylphenyl)imine) [Pb(ONO(Q))2]. In this reaction, the ONO ligand undergoes a two-electron reduction, with concomitant oxidation of PPh3 to OPPh3 and transformation of the dioxorhenium(V) fragment into a monooxorhenium(V) fragment, constituting a net nonclassical oxygen atom transfer. (ONO(Cat))ReO(PPh3) adopts a square pyramidal geometry with an apical oxo group [d(ReO) = 1.

Nonclassical oxygen atom transfer reactions of oxomolybdenum(VI) bis(catecholate).

Mechanistic studies indicate that the oxomolybdenum(vi) bis(3,5-di-tert-butylcatecholate) fragment deoxygenates pyridine-N-oxides in a reaction where the oxygen is delivered to molybdenum but the electrons for substrate reduction are drawn from the bound catecholate ligands, forming 3,5-di-tert-butyl-1,2-benzoquinone.

Metrical oxidation states of 2-amidophenoxide and catecholate ligands: structural signatures of metal-ligand π bonding in potentially noninnocent ligands.

Catecholates and 2-amidophenoxides are prototypical "noninnocent" ligands which can form metal complexes where the ligands are best described as being in the monoanionic (imino)semiquinone or neutral (imino)quinone oxidation state instead of their closed-shell dianionic form. Through a comprehensive analysis of structural data available for compounds with these ligands in unambiguous oxidation states (109 amidophenolates, 259 catecholates), the well-known structural changes in the ligands with oxidation state can be quantified. Using these correlations, an empirical "metrical oxidation state" (MOS) which gives a continuous measure of the apparent oxidation state of the ligand can be determined based on least-squares fitting of its C-C, C-O, and C-N bond lengths to this single parameter (a simple procedure for doing so is provided via a spreadsheet in the Supporting Information).