10-Fold Increase in Hydrogen Atom Transfer Reactivity for a Series of = 1 Fe═O Complexes Over the = 2 [(TQA)Fe═O] Complex via Entropic Lowering of Reaction Barriers by Secondary Sphere Cycloalkyl Substitution.

Nonheme iron enzymes utilize = 2 iron(IV)-oxo intermediates as oxidants in biological oxygenations. In contrast, corresponding synthetic nonheme Fe═O complexes characterized to date favor the = 1 ground state that generally shows much poorer oxidative reactivity than their = 2 counterparts. However, one intriguing exception found by Nam a decade ago is the = 1 [Fe(O)(MeNTB)] complex (MeNTB = [tris((-methyl-benzimidazol-2-yl)methyl)amine], ) with a hydrogen atom transfer (HAT) reactivity that is 70% that of the = 2 [Fe(O)(TQA)] complex (TQA = tris(2-quinolylmethyl)amine, ).

Bisphosphonium Benzene Diimides.

The incorporation of cationic groups onto electron-poor compounds is a viable strategy for achieving potent electron acceptors, as evidenced by reports of air-stable radical forms of large aromatic diimides such as naphthalene and perylene diimides. These ions have also been observed to exhibit anion-π interaction tendencies of interest in molecular recognition applications. The benefits of phosphonium incorporation, however, have not yet been extended to the smallest benzene diimides.

Crystal structure and synthesis of the bis(anthracene)dicuprate dianion as the dipotassium salt, [K(tetrahydrofuran)][{Cu(9,10-η-anthracene)}], the first anionic arene complex of copper.

Reactions of (tricyclohexylphosphane)copper(I) chloride with two equivalents of potassium anthracene (KAn) in tetrahydrofuran (THF) at 200 K provides air-sensitive but thermally stable (at 293 K) solutions from which yellow crystalline blocks of bis[bis(tetrahydrofuran-κO)potassium] bis(μ-anthracene-κC:C)dicopper, [K(THF)][{Cu(9,10-η-CH)}] or [K(CHO)][Cu(CH)], 1, were isolated in about 50% yield. Single-crystal X-ray crystallographic analysis of 1 confirmed the presence of the first known (arene)cuprate. Also, unlike all previously known homoleptic (anthracene)metallates of d-block elements, which contain metals coordinated only to terminal rings, the organocuprate unit in 1 contains copper bound to the 9,10-carbons of the central ring of anthracene.

Preparation, Characterization, and Mechanistic Considerations for 1,1,1-Tri(thioacetyl)ethane and 1,1-Di(thioacetyl)ethene.

Two new compounds, 1,1,1-tri(thioacetyl)ethane and 1,1-di(thioacetyl)ethene, arose during reactions of acetyl methoxy(thiocarbonyl) sulfide with potassium methyl xanthate. Relevant mechanisms were elucidated, which in turn suggested novel streamlined routes to these same compounds. Several further transformations of the title compounds were demonstrated, suggesting their potential synthetic utility.

Exploring opportunities for tuning phenyltris(pyrazol-1-yl)borate donation by varying the extent of phenyl substituent fluorination.

The importance of electron deficient Tp ligands motivates the introduction of electron-withdrawing substituents into the scorpionate framework. Since perfluorophenyltris(pyrazol-1-yl)borate affects significant anodic shifts in half-cell potentials in their metal complexes relative those of phenyltris(pyrazol-1-yl)borate analogues, the tuning opportunities achieved using 3,4,5-trifluorophenyl- and 3,5-bis(trifluoromethyl)phenyl(pyrazol-1-yl)borates were explored. Bis(amino)boranes ((3,4,5-F)CH)B(NMe) and ((3,5-CF)CH)B(NMe) are precursors to fluorinated tris(pyrazol-1-yl)phenylborates.

Photophysical Behavior of Self-Organizing Derivatives of 10- and 12-Vertex p-Carboranes, and their Bicyclo[2.2.2]octane and Benzene Analogues.

Four series of isostructural derivatives of 3-ring liquid crystalline derivatives containing p-carboranes (12-vertex A, and 10-vertex B), bicyclo[2.2.2]octane (C), or benzene (D) as the variable structural element were investigated for their mesogenic behavior and electronic interactions.

One-electron bonds in copper-aluminum and copper-gallium complexes.

Odd-electron bonds have unique electronic structures and are often encountered as transiently stable, homonuclear species. In this study, a pair of copper complexes supported by Group 13 metalloligands, M[N((-CH)NCHPPr)] (M = Al or Ga), featuring two-center/one-electron (2c/1e) σ-bonds were synthesized by one-electron reduction of the corresponding Cu(i) ⇢ M(III) counterparts. The copper bimetallic complexes were investigated by X-ray diffraction, cyclic voltammetry, electron paramagnetic spectroscopy, and density functional theory calculations.

Syntheses and crystal structures of new naphthalene- and anthracene-vanadate salts and an unprecedented dimetallabis(anthracene) sandwich complex: [Na(tetrahydrofuran)][V(anthracene)].

Reduction of bis(naphthalene)vanadium(0) by potassium naphthalene (KNp) in tetrahydrofuran (THF) provides a highly reactive, thermolabile, and so far unisolable brown substance, which affords the first reported derivatives of bis(naphthalene)vanadates. From these solutions, thermally stable (298 K) and structurally characterized compounds have been obtained, including dark-red rods of catena-poly[bis(μ-η:η:η-naphthalene)tetrakis(tetrahydrofuran)dipotassiumvanadium], [KV(CHO)(CH)] or [K(THF)][V(CH)] (3), and red plates of (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.

Effect of Spin-Orbit Coupling on Phonon-Mediated Magnetic Relaxation in a Series of Zero-Valent Vanadium, Niobium, and Tantalum Isocyanide Complexes.

Spin-vibronic coupling leads to spin relaxation in paramagnetic molecules, and an understanding of factors that contribute to this phenomenon is essential for designing next-generation spintronics technology, including single-molecule magnets and spin-based qubits, wherein long-lifetime magnetic ground states are desired. We report spectroscopic and magnetic characterization of the isoelectronic and isostructural series of homoleptic zerovalent transition metal triad M(CNDipp) (M = V, Nb, Ta; CNDipp = 2,6-diisopropylphenyl isocyanide) and show experimentally the significant increase in spin relaxation rate upon going from V to Nb to Ta. Correlated electronic calculations and first principle spin-phonon computations support the role of spin-orbit coupling in modulating spin-phonon relaxation.

Unmasking Steps in Intramolecular Aromatic Hydroxylation by a Synthetic Nonheme Oxoiron(IV) Complex.

In this study, a methyl group on the classic tetramethylcyclam (TMC) ligand framework is replaced with a benzylic group to form the metastable [Fe (O )(Bn3MC)] (2-syn; Bn3MC=1-benzyl-4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane) species at -40 °C. The decay of 2-syn with time at 25 °C allows the unprecedented monitoring of the steps involved in the intramolecular hydroxylation of the ligand phenyl ring to form the major Fe -OAr product 3. At the same time, the Fe (Bn3MC) (1) precursor to 2-syn is re-generated in a 1:2 molar ratio relative to 3, accounting for the first time for all the electrons involved and all the Fe species derived from 2-syn as shown in the following balanced equation: 3 [Fe (O)(L )] (2-syn)→2 [Fe (L )] (3)+[Fe (L )] (1)+H O.

Partial Dehydration of Levothyroxine Sodium Pentahydrate in a Drug Product Environment: Structural Insights into Stability.

Levothyroxine sodium pentahydrate (LSP; CHINNaO·5HO) gradually loses one molecule of water of crystallization as the water vapor pressure is decreased from 90% to 15% RH (40 °C), a behavior characteristic of nonstoichiometric hydrates. LSP loses four molecules of water of crystallization to form levothyroxine sodium monohydrate (LSM; CHINNaO·HO) under realistic storage conditions (40 °C/0% RH for 3 h). The crystal structure of LSP was determined following which the specimen was partially dehydrated to form LSM.

Ring-Fused 1,4-Dihydro[1,2,4]triazin-4-yls through Photocyclization.

Halogen lamp irradiation of benzo[][1,2,4]triazines in CHCl solutions leads to planar ring-fused 1,4-dihydro[1,2,4]triazin-4-yl radicals through a novel, potentially general, cyclization mechanism. The scope and efficiency of the method were established for unsubstituted and -substituted (X = NH, Br, NO) phenoxy, naphthyloxy, and quinolinoxy derivatives . The regioselectivity of photocyclization was rationalized with DFT computational methods.

Seventeen-electron chromium(i)tricarbonyltris(phosphine) complexes supported by tris(phosphinomethyl)phenylborates.

The inaugural crystallographic characterization of chromium(i)tricarbonyltris(phosphine) radicals has been achieved. Oxidation of [PPN][Cr(CO)(PhBP)] (PhBP = [PhB(CHPPh)]) and analogous Cr(0) complexes featuring 3,5-dimethylphenyl and 3,5-bis(trifluoromethyl)phenyl borate substituents affords charge-neutral Cr(CO)(PhBP) zwitterions, containing the first fully characterized [Cr(CO)P] units. The stabilization affected by the intramolecular charge separation established by PhBP ligands dramatically increases the robustness of these seventeen-electron Cr(i) complexes.

A Highly Stabilized Phosphonium Ylide that Forms Supramolecular Dimers in Solution and the Solid State.

This work describes the unexpected formation of an unusual phosphonium ylide when attempting the synthesis of bisphosphonium pyromellitic diimides. Spectroscopic and crystallographic characterization reveals that a combination of π-π and CH⋅⋅⋅O interactions leads to supramolecular homodimerization of the ylide both in solution and in the solid-state. Only strong acids are able to protonate the ylide, which is otherwise inert to Wittig and alkylation reactivity.

Thermodynamic and kinetic studies of H and N binding to bimetallic nickel-group 13 complexes and neutron structure of a Ni(η-H) adduct.

Understanding H binding and activation is important in the context of designing transition metal catalysts for many processes, including hydrogenation and the interconversion of H with protons and electrons. This work reports the first thermodynamic and kinetic H binding studies for an isostructural series of first-row metal complexes: NiML, where M = Al (), Ga (), and In (), and L = [N(-(NCHPPr)CH)]. Thermodynamic free energies (Δ°) and free energies of activation (Δ ) for binding equilibria were obtained variable-temperature P NMR studies and lineshape analysis.

Niobium isocyanide complexes, Nb(CNAr), with Ar = 2,6-dimethylphenyl (Xyl), a diamagnetic dimer containing four reductively coupled isocyanides, and Ar = 2,6-diisopropylphenyl (Dipp), a paramagnetic monomer analogous to the highly unstable hexacarbonylniobium(0).

Treatment of bis(mesitylene)niobium(0) with 6-7 equivalents of 2,6-dimethylphenyl isocyanide (CNXyl) affords two products with the empirical formula Nb(CNXyl) (n = 7 or 6), which have been shown to be the diamagnetic dimers bis[μ-N,N',N'',N'''-tetrakis(2,6-dimethylphenyl)squaramidinato(2-)]bis[pentakis(2,6-dimethylphenyl isocyanide)niobium(I)], [Nb(CHN)(CHN)] or [Nb(CNXyl)][μ-C(NXyl)]·xSolvent, 1, and bis[μ-N,N',N'',N'''-tetrakis(2,6-dimethylphenyl)squaramidinato(2-)]bis[tetrakis(2,6-dimethylphenyl isocyanide)niobium(I)] tetrahydrofuran trisolvate, [Nb(CHN)(CHN)]·3CHO or [Nb(CNXyl)][μ-C(NXyl)]·3THF (THF = tetrahydrofuran), 2. Each contains Nb bound to either five or four terminal isocyanides, respectively, and to an unprecedented bridging tetraarylsquaramidinate(2-) unit, coordinated as a bidentate ligand to each niobium center, symmetrically due to the crystallographic inversion center that coincides with the centroid of the central C unit. Thus, in the presence of CNXyl, the bis(mesitylene)niobium(0) is oxidized to niobium(I), resulting in the facile loss of both mesitylene groups and the reductive coupling of two CNXyl groups per niobium to provide the first examples of tetraarylsquaramidinate(2-) ligands, [cyclo-CNAr], coordinated to metals.

Crystal structures and spectroscopic characterization of MBr(CNXyl) (M = Fe and Co, n = 4; M = Ni, n = 2; Xyl = 2,6-dimethylphenyl), and of formally zero-valent iron as a cocrystal of Fe(CNXyl) and Fe(CNXyl).

Structures and spectroscopic characterization of the divalent complexes cis-dibromidotetrakis(2,6-dimethylphenyl isocyanide)iron(II) dichloromethane 0.771-solvate, [FeBr(CHN)]·0.771CHCl or cis-FeBr(CNXyl)·0.

Crystal Structures of DOTMA Chelates from Ce to Yb : Evidence for a Continuum of Metal Ion Hydration States.

The crystal structures of chelates formed between each stable paramagnetic lanthanide ion and the octadentate polyamino carboxylate ligand DOTMA are described. A total of 23 individual chelates structures were obtained; in each chelate the coordination geometry around the metal ion is best described as a twisted square antiprism (torsion angle -25.0°--31.

Tantalum isocyanide complexes: TaI(CNDipp) (Dipp is 2,6-diisopropylphenyl) and ionic [Ta(CNDipp)][Ta(CNDipp)], a formal disproportionation product of the 17-electron Ta metalloradical Ta(CNDipp).

Treatment of tetraethylammonium hexacarbonyltantalate, [EtN][Ta(CO)], with 1.1 equivalents of molecular iodine (I) in tetrahydrofuran (THF) at 200 K, followed by the addition of 6.0 equivalents of 2,6-diisopropylphenyl isocyanide (CNDipp) and slow warming to 293 K over a 24 h period gave the tantalum(I) iodide derivative hexakis(2,6-diisopropylphenyl isocyanide-κC)iodidotantalum(I), [TaI(CHN)] or TaI(CNDipp), 1.

Investigation of ( S)-(-)-Acidomycin: A Selective Antimycobacterial Natural Product That Inhibits Biotin Synthase.

The synthesis, absolute stereochemical configuration, complete biological characterization, mechanism of action and resistance, and pharmacokinetic properties of ( S)-(-)-acidomycin are described. Acidomycin possesses promising antitubercular activity against a series of contemporary drug susceptible and drug-resistant M. tuberculosis strains (minimum inhibitory concentrations (MICs) = 0.

Syntheses of PDE3A inhibitor ORG9935 and determination of the absolute stereochemistries of its enantiomers by X-ray crystallography.

Two synthetic methods were developed for the synthesis of PDE3A inhibitor ORG9935. The first one proceeds in six steps and 34% overall yield and the second one in five steps and an overall yield of 69% starting from commercially available starting material 5,6-dimethoxybenzo[]thiophene-2-carboxylic acid (). The enantiomers of ORG9935 were separated by chiral column chromatography and the absolute stereochemistry of the (+)-enantiomer, ORG20865 was determined by X-ray crystallography to possess the (-configuration.

The crystal structure of bis-{3,5-di-fluoro-2-[4-(2,4,6-tri-methyl-phen-yl)pyridin-2-yl]phen-yl}(picolinato)iridium(III) and its 4--butyl-pyridin-2-yl analogue.

The crystal structures of bis-{3,5-di-fluoro-2-[4-(2,4,6-tri-methyl-phen-yl)pyridin-2-yl]phenyl-κ , }(picolinato-κ ,)iridium(III), [Ir(CHFN)(CHNO)], , and bis-[2-(4--butyl-pyridin-2-yl)-3,5-di-fluoro-phenyl-κ , ](picolinato-κ ,)iridium(III), [Ir(CHFN)(CHNO)], , are presented herein. These phospho-rescent cyclo-metallated iridium(III) compounds have been structurally investigated in order to better understand the nature of their blue-shifted emssions while maintaining high quantum yields. Compound exhibits substantial twisting of the mesitylene rings out of the plane of the attached pyridine ring, with dihedral angles of 67.

Crystallographic Evidence for a Sterically Induced Ferryl Tilt in a Non-Heme Oxoiron(IV) Complex that Makes it a Better Oxidant.

Oxoiron(IV) units are often implicated as intermediates in the catalytic cycles of non-heme iron oxygenases and oxidases. The most reactive synthetic analogues of these intermediates are supported by tetradentate tripodal ligands with N-methylbenzimidazole or quinoline donors, but their instability precludes structural characterization. Herein we report crystal structures of two [Fe (O)(L)] complexes supported by pentadentate ligands incorporating these heterocycles, which show longer average Fe-N distances than the complex with only pyridine donors.

Formal Nickelate(-I) Complexes Supported by Group 13 Ions.

Formal nickelate(-I) complexes bearing Group 13 metalloligands (M=Al and Ga) were isolated. These 17 e complexes were synthesized by one-electron reduction of the corresponding Ni →M precursors, and were investigated by single-crystal X-ray diffraction, EPR spectroscopy, and quantum chemical calculations. Collectively, the experimental and computational data support: 1) the strengthening of the Ni-M bond upon one-electron reduction, and 2) the delocalization of the unpaired spin across the Ni and M atoms.

Inductive modulation of tris(phosphinomethyl)phenylborate donation at group VI metals via borate phenyl substituent modification.

A series of zerovalent group VI metal complexes of tris(diisopropylphosphinomethyl)phenylborate ([PhB(CH2PiPr2)3]-, PhBPiPr3), including [PPN][M(CO)3(PhBPiPr3)] (M = Cr, Mo, W) and the first bimetallics in which PhBPiPr3 serves as a bridging ligand via binding M(CO)3 units at the three phosphorus atoms and the borate phenyl substituent, have been synthesized and fully characterized. Two new tris(phosphinomethyl)borates featuring 3,5-dimethylphenyl and 3,5-bis(trifluoromethyl)phenyl borate substituents were prepared as crystallographically characterized thallium salts, and metallated giving their inaugural transition metal complexes [PPN][M(CO)3(((3,5-Me)C6H3)BPPh3)] and [PPN][M(CO)3(((3,5-CF3)C6H3)BPPh3)]. A comparative ν(CO) infrared spectroscopic analysis and examination of half wave potentials assessed by cyclic voltammetry supports a ligand donor ranking of Tp > PhBPiPr3 ≥ Cp > PhBPPh3 > triphos.