Search

N-Butyl-2,3-bis(dicyclohexylamino)cyclopropenimine (1) crystallizes from benzene and hexanes in the presence of HCl as a monobenzene solvate of the hydrochloride salt, [1H]Cl⋅C6H6 or C31H54N3 +⋅Cl⋅C6H6, in the P21/n space group. The protonation of 1 results in the generation of an aromatic structure based upon the delocalization of the cyclopropene double bond around the cyclopropene ring, giving three intermediate C--C bond lengths of 1.41 A °, and the delocalization of the imine-type C--N double bond, giving three intermediate C--N bond lengths of 1.32 A °. Ion-ion and ion-benzene packing interactions are described and illustrated. [ABSTRACT FROM AUTHOR]

The properties of catenated nitrogen molecules, molecules containing internal chains of bonded nitrogen atoms, is of fundamental scientific interest in chemical structure and bonding, as nitrogen is uniquely situated in the periodic table to form kinetically stable compounds often with chemically stable N-N bonds but which are thermodynamically unstable in that the formation of stable multiply bonded N2 is usually thermodynamically preferable. This unique placement in the periodic table makes catenated nitrogen compounds of interest for development of high-energy-density materials, including explosives for defense and construction purposes, as well as propellants for missile propulsion and for space exploration. This review, designed for a chemical audience, describes foundational subjects, methods, and metrics relevant to the energetic materials community and provides an overview of important classes of catenated nitrogen compounds ranging from theoretical investigation of hypothetical molecules to the practical application of real-world energetic materials. The review is intended to provide detailed chemical insight into the synthesis and decomposition of such materials as well as foundational knowledge of energetic science new to most chemists. [ABSTRACT FROM AUTHOR]

Tolnaftate, a classic antifungal compound, has been found to crystallize from 1:1 (v/v) acetone-water as large flat colorless needles in the centrosymmetric monoclinic space group P21/c. These crystals contain a 50:50 mixture of the (+ap,-sp,+ac,-ac) and (-ap,+sp,-ac,+ac) conformers. The bond lengths in the central CNOS unit are 1.3444 (19), 1.3556 (18) and 1.6567 (15) A À for C--N, C--O and C--S, respectively, and the CNOS and C3N moieties are flat and nearly coplanar with each other, consistent with the C--N bond possessing partial double-bond character. Tolnaftate and the four most closely related N,N-disubstituted thiocarbamates in the Cambridge Structural Database (CSD) all exist as E-conformational isomers in the solid state. Among these five compounds, tolnaftate is the only one in which the N-tolyl moiety is positioned trans to the S atom, i.e. the N-aryl substituent in each of the other compounds is positioned cis to their respective S atom. Notably, and more importantly, our experimental X-ray structure is unlike all prior theoretical models available for tolnaftate. The implication, either directly or indirectly, is that some of those theoretical models used in earlier studies to explain the spectroscopic properties of tolnaftate and to suggest which protein-ligand interactions are responsible for the binding of tolnaftate to squalene epoxidase are either inappropriate or structurally unreasonable, i.e. the results and conclusions from those prior studies are in need of critical reassessment. [ABSTRACT FROM AUTHOR]

New regimes of energy density in energetic materials may be achieved by replacement of oxidizing nitro groups with stronger oxidants such as oxychlorine species. We report the energetic material 1,3-di- tert-butyltetrazolium-5-imidoperchloratomanganese(II) 2, which crystallizes as an oligomeric cubane cluster. Bomb calorimetry on the amorphous, solvent-free phase gives an energy density of at least 40±3 MJ L−, higher than hydrocarbon combustion in air, more than twice that of traditional energetic nitramines, and ≈70 % higher than that of the unmetalated tetrazolium perchlorate salt without metal linkage. The effects of solid-state structure, charge, and lattice energy on the energy of 2 are discussed. [ABSTRACT FROM AUTHOR]

Polynuclear metal clusters frequently feature geometric structural features not common in traditional coordination chemistry. These structures are of particular interest to bioinorganic chemists studying metallocluster enzymes, which frequently possess remarkably unusual inorganic structures. The structure of the manganese cluster μ5-oxido-di-μ3-phenoxido-hexa-μ-phenoxido-hexakis(pyridine-κ N)hexamanganese(II) pyridine monosolvate, [Mn5(C6H5O)8O(C5H5N)6]·C5H5N or MnII5(μ-OPh)6(μ3-OPh)2(μ5-O)(Py)6·Py, containing an unusual trigonal bipyramidal central oxide, is described. The compound was isolated from a reaction mixture containing bis(trimethylsilylamido)manganese(II) and phenol. The central O atom is presumed to have originated as adventitious water. The molecule crystalizes in a primitive monoclinic crystal system and is presented in the centrosymetric P2/ n space group. The molecule possesses crystallographically imposed twofold symmetry, with the central O atom centred on the twofold axis and surrounded by a distorted trigonal bipyramidal arrangement of Mn atoms, which are further bridged by phenoxide ligands, and terminally ligated by pyridine. A pyridine solvent molecule resides nearby, also situated on a crystallographic twofold axis. The cluster is compared to three closely related previously reported structures. [ABSTRACT FROM AUTHOR]

A rhodium(II) dibenzotetramethylaza[l4]-annulene dimer ([(tmtaa)Rh]2) (l) reacts with CO and H2 in toluene and pyridine to form equilibrium distributions with hydride and formyl complexes ((tmtaa)-Rh-H (2); (tmtaa)Rh-C(0)H (3)). The rhodium formyl complex ((tmtaa)Rh-C(O)H) was isolated under a CO/H2 atmosphere, and the molecular structure was determined by X-ray diffraction. Equilibrium constants were evaluated for reactions of (tmtaa)Rh-H with CO to produce formyl complexes in toluene (K2(298 K)(tol) = 10.8 (1.0) × 103) and pyridine (K2(298 K)(py) = 2.2 (0.2) × 103). Reactions of 1 and 2 in toluene and pyridine are discussed in the context of alternative radical and ionic pathways. The five-coordinate 18-electron Rh(l) complex ([(py)-(tmtaa)Rh1]-) is proposed to function as a nucleophile toward CO to give a two-electron activated bent Rh-CO unit. Results from DFT calculations on the (tmtaa)Rh system correlate well with experimental observations. Reactions of 1 with CO and H2 suggest metal catalyst design features to reduce the activation barriers for homogeneous CO hydrogenation. [ABSTRACT FROM AUTHOR]

The article focuses on the trans-Bis(hinokitiolato)copper(II) trans-bis(hinokitiolato)palladium(II) cocyrstals with (5/1) and (3/2) formulations which contain molecules possessing crystallographic inversion symmetry. Hinokitiol has antitumor, antibacterial and antifungal properties. Metal complexes of the hinokitolate anion show antiviral and antimicrobial properties. The bis(hinokitiolato)copper(II) exists in at least three crystalline modifications including polymorphic that has four crystalline forms.

The reaction of Fe(N{SiMe3}2)2 (1) with 1 equiv of arylthiol (ArSH) results in material of notional composition Fe(SAr)(N{SiMe3}2) (2), from which crystalline Fe2(μ-SAr)2(N{SiMe3}2)2(THF)2 (Ar = Mes) can be isolated from tetrahydrofuran (THF) solvent. Treatment of 2 with 0.5 equiv of 1,2-diarylhydrazine (Ar′NH-NHAr′, Ar′ = Ph, p-Tol) yields ferric-imide-thiolate cubanes Fe4(μ3-NAr′)4(SAr)4 (3). The site-differentiated, 1-electron reduced iron-imide cubane derivative [Fe(THF)6][Fe4(μ3-N-p-Tol)4(SDMP)3(N{SiMe3}2)]2 ([Fe(THF)6][4]2; DMP = 2,6-dimethylphenyl) can be isolated by adjusting the reaction stoichiometry of 1/ArSH/Ar′NHNHAr′ to 9:6:5. The isolated compounds were characterized by a combination of structural (X-ray diffraction), spectroscopic (NMR, UV-vis, Mössbauer, EPR), and magnetochemical methods. Reactions with a range of hydrazines reveal complex chemical behavior that includes not only N-N bond reduction for 1,2-di- and trisubstituted arylhydrazines, but also catalytic disproportionation for 1,2-diarylhydrazines, N-C bond cleavage for 1,2-diisopropylhydrazine, and no reaction for hindered and tetrasubstituted hydrazines. [ABSTRACT FROM AUTHOR]

Three iron-5,10,1 5,20-tetraarylporphyrins (Fe(Por-Ar[sub4]), Ar = 2,3,5,6-tetrafluro-N,N,N-trimethylafliliniUm (1), N,N,N- trimethylanilinium (2), and p-sulfonatophenyl (3)) have been investigated as catalysts for the dismutation of chlorite (CIO[sub2][sup—]). Degradation of CIO[sub2][sup—] by these catalysts occurs by two concurrent pathways. One leads to formation of chlorate (CIO[sub3][sup—]) and chloride (Cl[sup—]), which is determined to be catalyzed by O=Fe[supIV](Por) (Compound II) based on stopped-flow absorption spectroscopy, competition with 2,2'-Azino-bis(3-ethylbenzothiazoline-6-Sulfoflicacid), [sup18]O- labeling studies, and kinetics. The second pathway is a concerted dismutation of chlorite to dioxygen (O[sub2]) and chloride. On the basis of isotope labeling studies using a residual gas analyzer, the mechanism is determined to be formation of O=Fe[supIV](Por) ∙ [sup+] (Compound I) from oxygen atom transfer, and subsequent rebound with the resulting hypochiorite ion (CIO[sup—]) to give dioxygen and chloride. While the chlorate production pathway is dominant for catalysts 2 and 3, the O[sub2]-producing pathway is significant for catalyst 1. In addition to chlorite dismutation, complex 1 catalyzes hypochiorite disproportionation to chloride and dioxygen quantitatively. [ABSTRACT FROM AUTHOR]

The sterically hindered Fe(ll) thiolate dimer Fe2(¼-STriph)2(STriph)2 (1; [STriph]- = 2,4,6-triphenylbenzenethiolate) reacts with primary amines ('BuNH2, aniline) and N2H4 to form the structurally characterized addition complexes Fe(STriph)2(NH2'Bu)2, Fe2(μ-STriph)2(STriph)2(NH2Ph)2, and Fe2(μ-η1:η1-N2H4)4(STriph)4 in high yield. Chemical and NMR spectroscopic evidence indicate that the binding of these nitrogen donors is labile in solution and multispecies equilibria are likely. With arylhydrazines, 1 catalytically disproportionates 1,2-diphenylhydrazine to aniline and azobenzene, and it rearranges 1-methyl-1,2-diarylhydrazines to give, after treatment with alumina, mononuclear, trigonal bipyramidal Fe(lll) complexes of composition Fe(ISQ)2(STriph), where [ISQ]- denotes an appropriately substituted bidentate o-diiminobenzosemiquinonate ligand. Complex 1 shows no reaction with hindered 1,2-dialkyihydrazines (isopropyl or tert-butyl) or tetrasubstituted 1 ,2-dimethyl-i ,2-diphenylhydrazine. [ABSTRACT FROM AUTHOR]

Hydrogen atom transfer (HAT) reactions from dihydroanthracene to ArINTs (Ar = 2-tert-butylsulfonyl)benzene and Ts = p-toluenesulfonyl) is catalyzed by Mn(tpfc) (tpfc = 5,1O,15-tris(pentafluorophenyl)corrole). Kinetics of HAT was monitored by gas chromatography. Conversion to the major products anthracene, TsNH2, and An is too fast to be explained by direct HAT from the terminal imido complex T5N=Mn(tpfc), which forms from the reaction of Mn(tpfc) with ArINTs. Steady-state kinetics, isotope effects, and variation of the initial catalyst form (Mnlll(tpfc) vs TsN=Mnv(tpfc)) support a mechanism in which the active catalytic species is an adduct of manganese(lll) with the oxidant, (ArINTs)Mnlll(tpfc). This species was detected by rapid-scan stopped-flow absorption spectroscopy. Kinetic simulations demonstrated the viability of this mechanism in contrast to other proposals. [ABSTRACT FROM AUTHOR]

Hydrogen atom transfer (HAT) reactions of (tpfc)MnNTs have been investigated (tpfc = 5,10,-15-tris(pentafluorophenyl)corrole and Ts = p-toluenesulfonate). 9,10-Dihydroanthracene and 1,4-dihydrobenzene reduce (tpfc)MnNTs via HAT with second-order rate constants 0.16 ± 0.03 and 0.17 ± 0.01 M-1 s-1, respectively, at 22 °C. The products are the respective arenes, TsNH2 and (tpfc)MnIII. Conversion of (tpfc)MnNTs to (tpfc)Mn by reaction with dihydroanthracene exhibits isosbestic behavior, and formation of 9,9′,10,10′-tetrahydrobianthracene is not observed, suggesting that the intermediate anthracene radical rebounds in a second fast step without accumulation of a MnIV intermediate. The imido complex (tpfc)-MnVNTs abstracts a hydrogen atom from phenols as well. For example, 2,6-di-tert-butyl phenol is oxidized to the corresponding phenoxyl radical with a second-order rate constant of 0.32 ± 0.02 M-1 s-1 at 22 °C. The other products from imido manganese(V) are TsNH2 and the trivalent manganese corrole. Unlike reaction with dihydroarenes, when phenols are used isosbestic behavior is not observed, and formation of (tpfc)-MnIV(NHTs) is confirmed by EPA spectroscopy. A Hammett plot for various p-substituted 2,6-di-tert-butyl phenols yields a V-shaped dependence on σ, with electron-donating substituents exhibiting the expected negative ρ while electron-withdrawing substituents fall above the linear fit (i.e., positive ρ). Similarly, a bond dissociation enthalpy (BDE) correlation places electron-withdrawing substituents above the well-defined negative slope found for the electron-donating substituents. Thus two mechanisms are established for HAT reactions in this system, namely, concerted proton-electron transfer and proton-gated electron transfer in which proton transfer is followed by electron transfer. [ABSTRACT FROM AUTHOR]

The protolysis of mononuclear ferric amide precursors FeCI[N(SiMe3)2]2(THF) (1) or [FeCl2{N(SiMe3)2}2]- (2) by primary amines provides, under suitable conditions, an effective route to dinuclear weak-field ferric-imide clusters with [Fe2(μ-NR)2]2+ cores. In the synthesis of known arylimide clusters [Fe2(μ-NAr)2Cl4]2- (Ar = Ph, p-Tol, Mes) from 2, the counterion has a major effect on selectivity and yield, and the use of quaternary ammonium salts affords a substantial improvement over earlier, Li+-based chemistry. The new tert-butylimide core is obtained by protolysis of 1 with excess iBuNH2 to give crystalline cis-Fe2(μ-NtBu)2Cl2(NH2tBu)2 (9). Complex 9 can be transformed to other dinuclear species through substitution of the terminal amines by pyridines, PEt3, or chloride, or through protolysis of bridging alkylimides by arylamines, allowing isolation of trans-Fe2(μ-NtBu)2Cl2(DMAP)2 (DMAP = 4-dimethylaminopyridine), cis-Fe2(μ-NtBu)2Cl2(PEt3)2, [Fe2(μ-NtBu)2Cl4]-, and trans-Fe2(μ-NPh)2Cl2(NH2tBu)2. The susceptibility of alkyl substituents to β-elimination appears to limit the general applicability of protolytic cluster assembly using alkylamines. The dinuclear clusters have been characterized by X-ray, spectroscopic, and electrochemical analyses. [ABSTRACT FROM AUTHOR]

The reaction of ArI=NTs (Ar = 2-(tert-butylsulfonyl)benzene and Ts = p-toluenesulfonyl) and (tpfc)Mn (tpfc = 5,10,15-tris(pentafluorophenyl)corrole), 1, affords the high-valent (tpfc)Mnv=NTs, 2, on stopped-flow time scale. The reaction proceeds via the adduct [(tpfc)Mn"P(ArlNTs)], 3, with formation constant K3 = (10 ± 2) × 103 L mo1-1. Subsequently, 3 undergoes unimolecular group transfer to give complex 2 with the rate constant k4 = 0.26 ± 0.07 s-1 at 24.0 °C. The complex (tpfc)Mn catalyzes [NTs] group transfer from ArlNTs to styrene substrates with low catalyst loading and without requirement of excess olefin. The catalytic aziridination reaction is most efficient in benzene because solvents such as toluene undergo a competing hydrogen atom transfer (HAT) reaction resulting in H2NTs and lowered aziridine yields. The high-valent manganese imido complex (tpfc)Mn=NTs does not transfer its [NTs] group to styrene. Double-labeling experiments with ArlNTs and ArlNTs1Bu (Ts1Bu = (p-tert-butylphenyl)sulfonyl) establish the source of [NR] transfer as a ‘third oxidant’, which is an adduct of Mn(V) imido, [(tpfc)Mn(NTs1Bu)(ArlNTs)] (4). Formation of this oxidant is rate limiting in catalysis. [ABSTRACT FROM AUTHOR]

Catalytic deoxygenation of epoxides and diols is underdeveloped. This reaction is appealing in the context of making value-added organics from biomass. Methyltrioxorhenium (MTO) catalyzes the conversion of epoxides and vicinaf diols to olef ins with dihydrogen (H2) as the reduclant under reasonably mild conditions (150 °C and 80-300 psi). The only reaction byproduct is water. The reaction is selective for cis cyclic diols, signaling a mechanism of alkene extrusion from a coordinated epoxide via a metallaoxetane intermediate. [ABSTRACT FROM AUTHOR]

The solid-state structures of the Na+, Li+, and NH4+ salts of the 4,5-dihydroxybenzene-1,3-disulfonate (tiron) dianion are reported, namely disodium 4,5-dihydroxybenzene-1,3-disulfonate, 2Na+·C6H4O8S22-,·-4,5-dihydroxybenzene-1,3-disulfonato-bis[aqualithium(I)] hemihydrate, [Li2(C6H4O8S2)(H2O)2]·0.5H2O, and diammonium 4,5-dihydroxybenzene-1,3-disulfonate monohydrate, 2NH4+·C6H4O8S22-·H2O. Intermolecular interactions vary with the size of the cation, and the asymmetric unit cell, and the macromolecular features are also affected. The sodium in Na2(tiron) is coordinated in a distorted octahedral environment through the sulfonate oxygen and hydroxyl oxygen donors on tiron, as well as an interstitial water molecule. Lithium, with its smaller ionic radius, is coordinated in a distorted tetrahedral environment by sulfonic and phenolic O atoms, as well as water in Li2(tiron). The surrounding tiron anions coordinating to sodium or lithium in Na2(tiron) and Li2(tiron), respectively, result in a three-dimensional network held together by the coordinate bonds to the alkali metal cations. The formation of such a three-dimensional network for tiron salts is relatively rare and has not been observed with monovalent cations. Finally, (NH4)2(tiron) exhibits extensive hydrogen-bonding arrays between NH4+ and the surrounding tiron anions and interstitial water molecules. This series of structures may be valuable for understanding charge transfer in a putative solid-state fuel cell utilizing tiron. [ABSTRACT FROM AUTHOR]

A rhodium(II) dibenzotetramethylaza[14]annulene dimer ([(tmtaa)Rh]2) undergoes metathesis reactions with [CpCr(CO)3]2, [CpMo(CO)3]2, [CpFe(CO)2]2, [Co(CO)4]2, and [Mn(CO)5]2 to form (tmtaa)Rh-M complexes (M = CrCp(CO)3, MoCp(CO)3, FeCp(CO)2, Co(CO)4, or Mn(CO)5). Molecular structures were determined for (tmtaa)Rh-FeCp(CO)2, (tmtaa)Rh-Co(μ-CO)(CO)3, and (tmtaa)Rh-Mn(CO)5 by X-ray diffraction. Equilibrium constants measured for the metathesis reactions permit the estimation of several (tmtaa)Rh-M bond dissociation enthalpies (Rh--Cr = 19 kcal mol-1, Rh--Mo = 25 kcal mol-1, and Rh--Fe = 27 kcal mol-1). Reactivities of the bimetallic complexes with synthesis gas to form (tmtaa)Rh-C(O)H and M-H are surveyed. [ABSTRACT FROM AUTHOR]

Low-valent molybdenum dicarbonyl complexes with a diazabutadiene [mesDABR; [ArN=C(R)C(R)=NAr]; Ar = 2,4,6-trimethylphenyl (mes), R = H or CH3] ligand liave been syntiiesized and fully characterized. The tide complexes exhibit elongated DAB C--N and shortened C--C bond lengths over the free ligand and other zerovalent molybdenum complexes of DAB. Compared to known examples theoretically described as iminato π-radicals (L·-), the oxidation state assignment fits a molybdenum-(II) description. However, Mo K-edge X-ray absorption spectros-copy indicates that the complexes are best described as molybdenum(O). This example demonstrates that caution should be exercised in assigning the oxidation state based on structural parameters alone. Cyclic voltammetry studies reveal an electrochemical--chemical process that has been identified by in situ Fourier transform infrared spectroelectrochemistry as cis-to-transisomerization. [ABSTRACT FROM AUTHOR]

Chlorite dismutase (Cld) is a heme b-dependent. O-O bond forming enzyme that transforms toxic chlorite (ClO[sub2][sup-]) into innocuous chloride and molecular oxygen. The mechanism and specificity of the reaction with chlorite and alternate oxidants were investigated. Chlorite is the sole source of dioxygen as determined by oxygen-18 labeling studies. Based on ion chromatography and mass spectrometry results, Cld is highly specific for the dismutation of chlorite to chloride and dioxygen with no other side products. Cld does not use chlorite as an oxidant for oxygen atom transfer and halogenation reactions (using cosubstrates guaiacol, thioanisole. and monochlorodimedone, respectively). When peracetic acid or H[sub2]O[sub2] was used as an alternative oxidant, oxidation and oxygen atom transfer but not halogenation reactions occurred. Monitoring the reaction of Cld with peracetic acid by rapid-mixing UV-visible spectroscopy, the formation of the high valent compound I intermediate, [(Por[sup•+])Fe[supIV] = O], was observed [k[sub1] = (1.28 ± 0.04) x 10[sup6] M[sup-1] s[sup-1]]. Compound I readily decayed to form compound II in a manner that is independent of peracetic acid concentration (k[sub2] = 170 ± 20 s[sup-1]). Both compound I and a compound Il-associated tryptophanyl radical that resembles cytochrome c peroxidase (Ccp) compound I were observed by EPR under freeze-quench conditions. The data collectively suggest an O-O bond-forming mechanism involving generation of a compound I intermediate via oxygen atom transfer from chlorite, and subsequent recombination of the resulting hypochiorite and compound I. [ABSTRACT FROM AUTHOR]

• Review of the history of heterocubane clusters. • Connections between biological and synthetic systems. • Connections between bioinorganic cubanes and older synthetic systems or other synthetic systems not previously connected to biology. • Discussion of electronic structure, spectroscopic, and computational aspects. The heterocubane (commonly referred to as the cubane cluster, a molecular species comprising a cube-shaped core with different atom types at opposite corners) is a conserved general structure found in some of nature's most crucial enzymes. Nature owes some of its most important reactions—like catalytic water splitting, nitrogen fixation, and the citric acid cycle—to the reactive versatility of the cubane structure. Few reviews have comprehensively highlighted the importance of this naturally occurring structure outside of (and prior to) the biological context, or have explicitly focused on the role of the cluster's global coordination environment on reactivity and electronic structure across multiple core metal and core ligand identities. In this review we summarize the scope of existing synthetic chemistry in context of coordination environment and geometry. Connections are drawn between these systems and the natural systems to offer insights into the properties of heterocubane clusters and their relation to biology. With biological uses ranging from simple one-electron transfer to some of the most challenging chemistries such as water oxidation and nitrogen fixation, the cubane cluster is ubiquitous and requires a more general elaboration than has been previously provided; thus, we aim to provide a summary of the history and the current research climate regarding heterocubanes, hoping that it will inspire future endeavors and discoveries. [ABSTRACT FROM AUTHOR]

A series of Ca–Mn clusters with the ligand 2-pyridinemethoxide (Py-CH2O) have been prepared with varying degrees of topological similarity to the biological oxygen-evolving complex. These clusters activate water as a substrate in the oxidative degradation of propylene carbonate, with activity correlated with topological similarity to the OEC, lowering the onset potential of the oxidation by as much as 700 mV. [ABSTRACT FROM AUTHOR]

The discovery of solid‐phase, inexpensive transition‐metal‐based water oxidation catalysts is a central goal for renewable energy, and has led to a general consensus that a partially populated metal eg d‐electronic state is desirable, leading to favorable catalysis for certain elements in specific oxidation states. In manganese systems, the key species is manganese(III), whose high‐spin d4 electronic configuration places an unpaired electron in the eg orbital, which is postulated to contribute to electronic and structural features that support catalysis. Based on density functional theory calculations, it is predicted that electron transfer would be facilitated by a catalyst with alternating low‐ and high‐MnIII‐content sheets, which positions neighboring band edges in closer energetic proximity. The preparation of such catalysts is demonstrated for the first time and it is shown that the catalytic activity is maximized in these systems over more uniform, but more MnIII‐rich systems. The best catalyst possesses alternating high‐and low‐average oxidation state sheets with interlayer Cs+ ions, and has an overpotential of 450 mV at 10 mA, which represents an improvement of 250 mV over the best unmodified synthetic potassium birnessites. Using scanning tunneling spectroscopy, bandgap modulations consistent with the theoretically predicted band edge shifts are detected. [ABSTRACT FROM AUTHOR]

Mn4(μ-NHPh)4(μ-PhNNPh-κ²N,N')2(py)4 (3) is synthesized via self assembly from dimeric Mn2(μ-NHPh)2(NR2)2 and PhNHNHPh (R = SiMe3). This cluster represents the N-N cleaved version of the previouslyreported Mn4(μ-NHPh)2(μ3-PhNNPh-κ³N,N')2(μ-PhNNPh-κ²N,N')(py)4 ''pinned butterfly'' cluster (2), formally reduced by two hydrogen atoms. Cluster 2 may be converted to 3 by addition of N,N'-diphenylhydrazine as a two-electron reductant. [ABSTRACT FROM AUTHOR]

High-valent, four-coordinate manganese imido- and nitrido-bridged heterodicubane clusters have been prepared and characterized by single-crystal X-ray diffraction and spectroscopic techniques. The title compound, a corner-nitride-fused dicubane with the chemical formula [Mn5Li3(μ6-N)(N)(μ3-NtBu)6(μ-NtBu)3(NtBu)] (1), has been prepared as an adduct with a nearly isostructural tetramanganese cluster with one Mn atom replaced by Li. An important feature of the reported chemistry is the formation of nitride from tert-butylamide, indicative of N-C bond cleavage facilitated by manganese. [ABSTRACT FROM AUTHOR]

A metastable Mn(iv) tris(N,N′)diphenylhydrazide complex, Li2Mn(κ2-N2Ph2)3(1) has been prepared, and characterized by X-ray diffraction analysis and spectroscopic techniques. Mn precursors are reacted with LiNHtBu to form an intermediate manganese-imido mixture, which reacts with N,N′-diphenylhydrazine, oxidizing the metal, and forming 1. Despite ease of formation, 1is poised for reactivity, as loss of ether ligand triggers reductive elimination of azobenzene. [ABSTRACT FROM AUTHOR]

Selective reaction of 2,6-isophthaloyl chloride at the methine positions of two dibenzotetramethyltetraaza[14]annulene (tmtaa) units results in tethering of the macrocycles by either one or two 2,6-isophthaloyl bridging groups. The single tethered dibenzotetramethyltetraaza[14]annulene derivative (SIT-tmtaa) was isolated and characterized by X-ray crystallography, ESI-MS, 1H and 13C NMR. The syn conformation of the two tmtaa units observed in the crystal structure, has tetraaza[14]annulene macrocycles that are more distorted from planarity than in the structure of the parent tmtaa. The di-nickel(ii) complex was prepared and characterized by ESI-HRMS, 1H and 13C NMR. DFT computations place the LUMO on the 2,6-isophthaloyl bridge rather than on the tethered tmtaa units and suggest that the 2,6-isophthaloyl tether provides a level of flexibility in the inter tmtaa distances that is comparable to the Pacman Effect observed for tethered porphyrins. [ABSTRACT FROM AUTHOR]

The crystal structures of two closely related compounds, 1-cyclo­hexyl-2-(2-nitro­phen­yl)-1,3-thia­zolidin-4-one, C15H18N2O3S, (1) and 1-cyclo­hexyl-2-(2-nitro­phen­yl)-1,3-thia­zolidin-4-one 1,1-dioxide, C15H18N2O5S, (2), are presented. These compounds are comprised of three types of rings: thia­zolidinone, nitrophenyl and cyclo­hexyl. In both structures, the rings are close to mutually perpendicular, with inter­planar dihedral angles greater than 80° in each case. The thia­zol­idinone rings in both structures exhibit envelope puckering with the S atom as flap and the cyclo­hexyl rings are in their expected chair conformations. The two structures superpose fairly well, except for the orientation of the nitro groups with respect to their host phenyl ring, with a difference of about 10° between 1 and 2. The extended structure of 1 has two kinds of weak C—H. . .O inter­actions, giving rise to a closed ring formation involving three symmetry-related molecules. Structure 2 has four C—H. . .O inter­actions, two of which are exclusively between symmetry-related thia­zolidinone dioxide moieties and have a parallel `give-and-take-fashion' counterpart. In the other two inter­actions, the nitrophenyl ring and the cyclo­hexane ring each offer an H atom to the two O atoms on the sulfone group. Additionally, a C—H. . .π inter­action between a C—H group of the cyclo­hexane ring and the nitrophenyl ring of an adjacent mol­ecule helps to consolidate the structure. [ABSTRACT FROM AUTHOR]

Abstract: Two lead complexes, Tetrakis(μ3‐(4‐methyl‐3‐nitrophenyl imido lead (II))) 1, and Bis(2‐nitrodiphenyl amido lead(II)) 2, were prepared by protolysis of bis(bis(trimethylsilyl)amido)lead(II) with two compounds relevant to double‐base propellant stabilizers: 2‐nitrodiphenylamine (NDPA) and 4‐methyl‐3‐nitroaniline. Crystal structures were determined as tetrahydrofuran solvates, and exhibit a number of unusual geometric features, including low lead coordination number. Heats of combustion and formation were determined using bomb calorimetry and converted to energy density using crystallographic densities. Compound 1 has an energy density of 30 MJ/L, whereas 2 was 38.2 MJ/L. [ABSTRACT FROM AUTHOR]

Birnessite, a layered-structure MnO2, is an earth-abundant functional material with potential for various energy and environmental applications, such as water oxidation. An important feature of birnessite is the existence of Mn(III) within the MnO2 layers, accompanied by interlayer charge-neutralizing cations. Using first-principles calculations, we reveal the nature of Mn(III) in birnessite with the concept of the small polaron, a special kind of point defect. Further taking into account the effect of the spatial distribution of Mn(III), we propose a theoretical model to explain the structure-performance dependence of birnessite as an oxygen evolution catalyst. We find an internal potential step which leads to the easy switching of the oxidation state between Mn(III) and Mn(IV) that is critical for enhancing the catalytic activity of birnessite. Finally, we conduct a series of comparative experiments which support our model. [ABSTRACT FROM AUTHOR]

We investigated the dependence of the electrocatalytic activity for the oxygen evolution reaction (OER) on the interlayer distance of five compositionally distinct layered manganese oxide nanostructures. Each individual electrocatalyst was assembled with a different alkali metal intercalated between two nanosheets (NS) of manganese oxide to form a bilayer structure. Manganese oxide NS were synthesized via the exfoliation of a layered material, birnessite. Atomic force microscopy was used to determine the heights of the bilayer catalysts. The interlayer spacing of the supported bilayers positively correlates with the size of the alkali cation: NS/Cs+/NS > NS/Rb+/NS > NS/K+/NS > NS/Na+/NS > NS/Li+/NS. The thermodynamic origins of these bilayer heights were investigated using molecular dynamics simulations. The overpotential (η) for the OER correlates with the interlayer spacing; NS/Cs+/NS has the lowest η (0.45 V), while NS/Li+/NS exhibits the highest η (0.68 V) for OER at a current density of 1 mA/cm2. Kinetic parameters (η and Tafel slope) associated with NS/Cs+/NS for the OER were superior to that of the bulk birnessite phase, highlighting the structural uniqueness of these nanoscale assemblies. [ABSTRACT FROM AUTHOR]

The molecular mechanism of the Oxygen Evolving Center of photosystem II has been under debate for decades. One frequently cited proposal is the nucleophilic attack by water hydroxide on a pendant Mn═O moiety, though no chemical example of this reactivity at a manganese cubane cluster has been reported. We describe here the preparation, characterization, and a reactivity study of a synthetic manganese cubane cluster with a pendant manganese-oxo moiety. Reaction of this cluster with alkenes results in oxygen and hydrogen atom transfer reactions to form alcohol- and ketone-based oxygen-containing products. Nitrene transfer from core imides is negligible. The inorganic product is a cluster identical to the precursor, but with the pendant Mn═O moiety replaced by a hydrogen abstracted from the organic substrate, and is isolated in quantitative yield. 18O and 2H isotopic labeling studies confirm the transfer of atoms between the cluster and the organic substrate. The results suggest that the core cubane structure of this model compound remains intact, and that the pendant Mn═O moiety is preferentially reactive. [ABSTRACT FROM AUTHOR]

Due to the flammability of liquid electrolytes used in lithium ion batteries, solid lithium ion conductors are of interest to reduce danger and increase safety. The two dominating general classes of electrolytes under exploration as alternatives are ceramic and polymer electrolytes. Our group has been exploring the preparation of molecular solvates of lithium salts as alternatives. Dissolution of LiCl or LiPF6 in pyridine (py) or vinylpyridine (VnPy) and slow vapor diffusion with diethyl ether gives solvates of the lithium salts coordinated by pyridine ligands. For LiPF6, the solvates formed in pyridine and vinylpyridine, namely tetrakis(pyridine-κ N)lithium(I) hexafluorophosphate, [Li(C5H5N)4]PF6, and tetrakis(4-ethenylpyridine-κ N)lithium(I) hexafluorophosphate, [Li(C7H7N)4]PF6, exhibit analogous structures involving tetracoordinated lithium ions with neighboring PF6− anions in the I and Aea2 space groups, respectively. For LiCl solvates, two very different structures form. catena-Poly[[(pyridine-κ N)lithium]-μ3-chlorido], [LiCl(C5H5N)] n, crystalizes in the P212121 space group and contains channels of edge-fused LiCl rhombs templated by rows of π-stacked pyridine ligands, while the structure of the LiCl-VnPy solvate, namely di-μ-chlorido-bis[bis(4-ethenylpyridine-κ N)lithium], [Li2Cl2(C7H7N)4], is described in the P21/ n space group as dinuclear (VnPy)2Li(μ-Cl)2Li(VnPy)2 units packed with neighbors via a dense array of π-π interactions. [ABSTRACT FROM AUTHOR]

We investigated the dependence of the electrocatalytic activity for the oxygen evolution reaction (OER) on the interlayer distance of five compositionally distinct layered manganese oxide nanostructures. Each individual electrocatalyst was assembled with a different alkali metal intercalated between two nanosheets (NS) of manganese oxide to form a bilayer structure. Manganese oxide NS were synthesized via the exfoliation of a layered material, birnessite. Atomic force microscopy was used to determine the heights of the bilayer catalysts. The interlayer spacing of the supported bilayers positively correlates with the size of the alkali cation: NS/Cs+/NS > NS/Rb+/NS > NS/K+/NS > NS/Na+/NS > NS/Li+/NS. The thermodynamic origins of these bilayer heights were investigated using molecular dynamics simulations. The overpotential (η) for the OER correlates with the interlayer spacing; NS/Cs+/NS has the lowest η (0.45 V), while NS/Li+/NS exhibits the highest η (0.68 V) for OER at a current density of 1 mA/cm². Kinetic parameters (η and Tafel slope) associated with NS/Cs+/NS for the OER were superior to that of the bulk birnessite phase, highlighting the structural uniqueness of these nanoscale assemblies. [ABSTRACT FROM AUTHOR]

The preparation and characterization of the cocrystalline solid-organic sodium ion electrolyte NaClO4(DMF)3 (DMF=dimethylformamide) is described. The crystal structure of NaClO4(DMF)3 reveals parallel channels of Na+ and ClO4− ions. Pressed pellets of microcrystalline NaClO4(DMF)3 exhibit a conductivity of 3×10−4 S cm−1 at room temperature with a low activation barrier to conduction of 25 kJ mol−1. SEM revealed thin liquid interfacial contacts between crystalline grains, which promote conductivity. The material melts gradually between 55-65 °C, but does not decompose, and upon cooling, it resolidifies as solid NaClO4(DMF)3, permitting melt casting of the electrolyte into thin films and the fabrication of cells in the liquid state and ensuring penetration of the electrolyte between the electrode active particles. [ABSTRACT FROM AUTHOR]

The preparation and characterization of the cocrystalline solid-organic sodium ion electrolyte NaClO4(DMF)3 (DMF=dimethylformamide) is described. The crystal structure of NaClO4(DMF)3 reveals parallel channels of Na+ and ClO4− ions. Pressed pellets of microcrystalline NaClO4(DMF)3 exhibit a conductivity of 3×10−4 S cm−1 at room temperature with a low activation barrier to conduction of 25 kJ mol−1. SEM revealed thin liquid interfacial contacts between crystalline grains, which promote conductivity. The material melts gradually between 55-65 °C, but does not decompose, and upon cooling, it resolidifies as solid NaClO4(DMF)3, permitting melt casting of the electrolyte into thin films and the fabrication of cells in the liquid state and ensuring penetration of the electrolyte between the electrode active particles. [ABSTRACT FROM AUTHOR]

We have developed a sequential one-pot Mitsunobu/intramolecular aza-Baylis–Hillman reaction to construct the ABCE tetracyclic core of the Strychnos alkaloids and applied this method to the total synthesis of (−)-melotenine A ( 1 ), a novel rearranged Aspidosperma alkaloid with potent cytotoxic activity. Additional key steps in the synthesis included (1) a Piers annulation of a vinyl iodide and a methyl ketone to prepare the D ring and (2) a site-selective intermolecular vinylogous aldol reaction to functionalize the E ring. [ABSTRACT FROM AUTHOR]

We report a synthetic method to enhance the electrocatalytic activity of birnessite for the oxygen evolution reaction (OER) by intercalating Ni2+ ions into the interlayer region. Electrocatalytic studies showed that nickel (7.7 atomic %)-intercalated birnessite exhibits an overpotential ( η) of 400 mV for OER at an anodic current of 10 mA cm−2. This η is significantly lower than the η values for birnessite ( η≈700 mV) and the active OER catalyst β-Ni(OH)2 ( η≈550 mV). Molecular dynamics simulations suggest that a competition among the interactions between the nickel cation, water, and birnessite promote redox chemistry in the spatially confined interlayer region. [ABSTRACT FROM AUTHOR]

We report a synthetic method to enhance the electrocatalytic activity of birnessite for the oxygen evolution reaction (OER) by intercalating Ni2+ ions into the interlayer region. Electrocatalytic studies showed that nickel (7.7 atomic %)-intercalated birnessite exhibits an overpotential ( η) of 400 mV for OER at an anodic current of 10 mA cm−2. This η is significantly lower than the η values for birnessite ( η≈700 mV) and the active OER catalyst β-Ni(OH)2 ( η≈550 mV). Molecular dynamics simulations suggest that a competition among the interactions between the nickel cation, water, and birnessite promote redox chemistry in the spatially confined interlayer region. [ABSTRACT FROM AUTHOR]

The first chemical syntheses of complex, bis- Strychnos alkaloids (−)-sungucine ( 1), (−)-isosungucine ( 2), and (−)-strychnogucine B ( 3) from (−)-strychnine ( 4) is reported. Key steps included (1) the Polonovski-Potier activation of strychnine N-oxide; (2) a biomimetic Mannich coupling to forge the signature C23−C5′ bond that joins two monoterpene indole monomers; and (3) a sequential HBr/NaBH3CN-mediated reduction to fashion the ethylidene moieties in 1- 3. DFT calculations were employed to rationalize the regiochemical course of reactions involving strychnine congeners. [ABSTRACT FROM AUTHOR]

The first synthetic manganese tetrazene complexes are described as a redox pair comprising anionic [Mn(N4Ad2)2]− ( 1) and neutral Mn(N4Ad2)2 ( 2) complexes (N4Ad2=[Ad-N−N=N−N-Ad]2−). Compound 1 is obtained in two forms as lithium salts, one as a cationic Li2Mn cluster, and one as a Mn-Li 1D ionic polymer. Compound 1 is electronically described as a MnIII center with two [N4Ad2]2− ligands. The one-electron oxidized 2 is crystalized in two morphologies, one as pure 2 and one as an acetonitrile adduct. Despite similar composition, the behavior of 2 differs in the two morphologies. Compound 2- MeCN is relatively air and temperature stable. Crystalline 2, on the other hand, exhibits a compositional, dynamic disorder wherein the tetrazene metallacycle ring-opens into a metal imide/azide complex detectable by X-ray crystallography and FTIR spectroscopy. Electronic structure of 2 was examined by EPR and XPS spectroscopies and DFT calculations, which indicate 2 is best described as a MnIII ion with an anion radical delocalized across the two ligands through spin-polarization effects. [ABSTRACT FROM AUTHOR]

Concise biomimetic syntheses of the Strychnos-Strychnos-type bis-indole alkaloids (−)-leucoridine A ( 1) and C ( 2) were accomplished through the biomimetic dimerization of (−)-dihydrovalparicine ( 3). En route to 3, the known alkaloids (+)-geissoschizoline ( 8) and (−)-dehydrogeissoschizoline ( 10) were also prepared. DFT calculations were employed to elucidate the mechanism, which favors a stepwise aza-Michael/spirocyclization sequence over the alternate hetero-Diels-Alder cycloaddition reaction. [ABSTRACT FROM AUTHOR]

Concise biomimetic syntheses of the Strychnos-Strychnos-type bis-indole alkaloids (−)-leucoridine A ( 1) and C ( 2) were accomplished through the biomimetic dimerization of (−)-dihydrovalparicine ( 3). En route to 3, the known alkaloids (+)-geissoschizoline ( 8) and (−)-dehydrogeissoschizoline ( 10) were also prepared. DFT calculations were employed to elucidate the mechanism, which favors a stepwise aza-Michael/spirocyclization sequence over the alternate hetero-Diels-Alder cycloaddition reaction. [ABSTRACT FROM AUTHOR]

The role of the manganese average oxidation state (AOS) in water oxidation catalysis by birnessite was investigated. Low AOS samples were most active, generating O2 immediately. Samples with a relatively high AOS showed an initial induction period and decreased turnover. Mn(ii- and iii)-enriched samples gave a 10–50 fold enhancement in turnover number. [ABSTRACT FROM AUTHOR]

A mechanistic pathway for the formation of the structurally characterized manganese-amide-hydrazide pinned butterfly complex, Mn4(μ3-PhN-NPh-γ³N,N')2(μ-PhN-NPh-γ³-N,N')(μ-NHPh)2L4 (L = THF, py), is proposed and supported by the use of labeling studies, kinetic measurements, kinetic competition experiments, kinetic isotope effects, and hydrogen atom transfer reagent substitution, and via the isolation and characterization of intermediates using X-ray diffraction and electron paramagnetic resonance spectroscopy. The data support a formation mechanism whereby bis[bis-(trimethylsilyl)amido]manganese(II) (Mn(NR2)2, where R = SiMe3) reacts with N,N'-diphenylhydrazine (PhNHNHPh) via initial proton transfer, followed by reductive N--N bond cleavage to form a long-lived Mnlv imido multinuclear complex. Coordinating solvents activate this cluster for abstraction of hydrogen atoms from an additional equivalent of PhNHNHPh resulting in a Mn(II)phenylamido dimer, Mn2(μ-NHPh)2-(NR2)2L2. This dimeric complex further assembles in fast steps with two additional equivalents of PhNHNHPh replacing the terminal silylamido ligands with η¹-hydrazine ligands to give a dimeric Mn20-NHPh)2 (PhN-NHPh)2L4 intermediate, and finally, the addition of two additional equivalents of Mn(NR2)2 and PhNHNHPh gives the pinned butterfly cluster. [ABSTRACT FROM AUTHOR]

Solvent-free single crystals of 1,3,5,7,9,11,13,15-octaphenylpentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane (abbreviated as octaphenyl-POSS), C48H40O12Si8, were obtained by dehydration/condensation of the tetrol Si4O4(Ph)4(OH)4. The powder pattern generated from the single-crystal data matches well with the experimentally measured powder pattern of commercial octaphenyl-POSS. The geometry of the centrosymmetric molecule in the crystal was compared with that in the gas phase, and had shorter Si-O bond lengths and a broader range of Si-O-Si bond angles. The average Si-O bond length [1.621 (3) Å], and Si-O-Si and O-Si-O bond angles [149 (5) and 109 (1)°, respectively] were within the same range measured previously for octaphenyl-POSS solvates. [ABSTRACT FROM AUTHOR]

A series of hydrogen-bonding catalysts have been designed for the aromatic Claisen rearrangement of a 1,1-dimethylallyl coumarin. These catalysts were designed as mimics of the two-point hydrogen-bonding interaction present in ketosteroid isomerase that has been proposed to stabilize a developing negative charge on the ether oxygen in the migration of the double bond.¹ Two hydrogen bond donating groups, a phenol alcohol and a carboxylic acid, were grafted onto a conformationally restrained spirocyclic scaffold, and together they enhance the rate of the Claisen rearrangement by a factor of 58 over the background reaction. Theoretical calculations correctly predict the most active catalyst and suggest that both preorganization and favorable interactions with the transition state of the reaction are responsible for the observed rate enhancement. [ABSTRACT FROM AUTHOR]

The first structurally, spectroscopically, and electronically characterized metal-spiroligomer complexes are reported. The binuclear [M2L2]4+ ions (M = Mn, Zn) are macrocyclic "squares" and are characterized by X-ray diffraction, 1H and 13C NMR, electronic absorption, emission, and mass spectroscopies. The manganese complex contains two spin-independent MnII ions and is additionally characterized using EPR and CD spectroscopies and CV. [ABSTRACT FROM AUTHOR]

Palladium and platinum metal complexes of 2,5-bis(ɑ-pyridyl)-pyrrolate (PDP) are reported and characterized by spectroscopic methods, single-crystal X-ray diffraction, and elemental analysis. The single-crystal X-ray structures of these complexes exhibit structural features indicative of significant π-backbonding. To illustrate the effect, bond lengths are statistically compared to unmetalated PDP and to a previously reported Zn(II) complex that exhibits no backbonding. Density functional theory calculations are used to aid understanding of the electronic structural basis of the observed phenomena. [ABSTRACT FROM AUTHOR]