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A series of 12 Ru(II) complexes of the type [Ru(tpy)(L)(CH3CN)]n+, 1–12, containing the tridentate tpy ligand (tpy = 2,2′:6′,2″-terpyridine) and various bidentate ancillary ligands, L, were synthesized and evaluated for their ability to photodissociate CH3CN, a model for nitrile-containing drugs. Although the bidentate ligands chosen display a similar degree of steric bulk around the metal center in the ground state, the photosubstitution efficiencies of 1–12 vary by approximately an order of magnitude. The complexes containing the most electron-donating bidentate ligands, 8–11, exhibit the larger quantum yield values for ligand exchange in water. Complexes 8–11 also possess the smallest energy gap between the ground state and the lowest energy triplet metal-to-ligand charge transfer (3MLCT) excited state. In addition, density functional theory calculations indicate that a large degree of ligand character is present in their highest occupied molecular orbitals (HOMOs) and in their 3MLCT excited states. Th...

We describe the design, preparation and assembly of chair-shaped molecules, comprising a tris-bicyclo[2.2.1]heptane hub that extends into three phthalimides carrying amino acids or short peptides. In water, molecular chairs stack in an antiparallel manner to give hexavalent dendritic structures, in spite of holding equal charges. The here described strategy for increasing the multivalency of peptides is easy to implement in practice, therefore holding potential for creating novel soft materials and therapeutics.

The blue emission of M2biQ can be tuned to specific wavelengths throughout the visible region by changing the identity of the cation it interacts with. These optical properties are observed in MeCN solution and the solid state. White light is obtained in MeCN by using either the proper ratio of zinc ions or acid. Thus, M2biQ acts as a nearly universal emitter (λem = 468-690 nm) with large Stokes shifts (116-306 nm, Δν = 7,042-11,823 cm-1). Full spectral profiles as well as quantum yields, lifetimes, and the crystal structures of key RGB and yellow emitters are reported. Emission wavelengths correlate with cationic radius, and TD-DFT calculations show that, for 1:1 complexes, the smaller the ion, the shorter the N-cation bond, and the greater the bathochromic emission shift.

1,3-Dienes are ubiquitous and easily synthesized starting materials for organic synthesis and alkyl acrylates are among the most abundant and cheap feedstock carbon sources. A practical, highly enantioselective union of these two readily available precursors giving valuable, enantio-pure skipped 1,4-diene esters (with two configurationally defined double bonds) is reported. The process uses commercially available cobalt salts and chiral ligands. As illustrated by the use of 20 different substrates including 17 prochiral 1,3-dienes and 3 different acrylates, this heterodimerization reaction is tolerant of a number of common organic functional groups (e.g., aromatic substituents, halides, isolated mono- and di-substituted double bonds, esters, silyl ethers and silyl enol ethers). The novel results including ligand, counter ion and solvent effects uncovered during the course of these investigations show a unique role of a possible cationic Co(I) intermediate in these reactions. The rational evolution of a mechanism-based strategy that led to the eventual successful outcome and the attendant support studies may have further implications for the expanding use of low-valent group 9 metal complexes in organic synthesis.

The interligand charge dynamics of the lowest singlet metal-to-ligand charge-transfer states (1MLCT S1 states) of a series of quadruply bonded trans-Mo2(NN)2(O2C–X)2 paddlewheel compounds are investigated, where NN is a π-accepting phenylpropiolamidinate ligand and O2C–X (X = Me, tBu, TiPB, or CF3) is an auxiliary carboxylate ligand. The compounds show strong light absorption in the visible region due to MLCT transitions from the Mo2 center to the NN ligands. The transferred electron density was followed by femtosecond time-resolved infrared (fs-TRIR) spectroscopy with vibrational reporters such as the ethynyl groups on the NN ligands. The observed fs-TRIR spectra show that these compounds have asymmetric 1MLCT S1 excited states where the transferred electron mainly resides on a single NN ligand. The presence of interligand electron transfer (ILET) is suggested to explain the shape of the ν(C≡C) bands and the influence of auxiliary ligands and solvents on the interligand electronic coupling. The ILET in t...

Four photophysically interesting dimolybdenum paddlewheel compounds are synthesized and characterized: I and II contain amide ligand (N,3-diphenyl-2-propynamide), and III and IV contain thioamide ligand (N,3-diphenyl-2-propynethioamide). I and III are trans-Mo2L2(O2C-TiPB)2-type compounds, and II and IV are Mo2L4-type compounds, where O2C-TiPB is 2,4,6-triisopropylbenzoate. I–IV display strong light absorption due to metal to ligand charge transfer (MLCT) transitions from molybdenum to the amide/thioamide ligands. Charge transfer dynamics in the MLCT excited states of I–IV have been examined using femtosecond transient absorption (fs-TA) spectroscopy and femtosecond time-resolved infrared (fs-TRIR) spectroscopy. The asymmetric amide/thioamide ligands show two forms of regioarrangements in the paddlewheel compounds. Analyses of the ν(C≡C) bands in the fs-TRIR spectra of I and II show similar electron density distribution over ligands in their 1MLCT S1 states where only two amide ligands are involved and th...

Directing the outcome of electrophilic addition reactions of norbornenes could be a challenging task. We have found that the ionic addition of bromine to dichloro-norbornene 2 is accompanied with the formation of a bromonium cation followed by anchimeric assistance of juxtaposed chlorine to give five-membered chloronium cation, which upon reacting with bromide gives norbornane 4 in >90% yield. At higher temperatures, however, the radical addition of Br2 dominates so that dibromo compound 3 appears as the principal reaction product (72%). Stereo- and regioselective rearrangements of norbornenes, reported herein, could be of interest for the syntheses of complex haloalkanes.

Four new metabolites, 4-epi-citreoviridin (1), auransterol (3), and two analogues (2 and 4) of paxisterol (6), together with two known metabolites (15R*,20S*)-dihydroxyepisterol (5) and (6), were isolated from cultures of the fungal associate, Penicillium aurantiacobrunneum of the lichen, Niebla homalea, endemic to California and Baja California. The structures of all compounds were determined by comprehensive spectroscopic and spectrometric methods, including single-crystal X-ray diffraction for the determination of the absolute configuration of 3. Compound 1 showed selective cytotoxicity towards MCF-7 breast and A2780 ovarian cells with IC(50) values of 4.2 and 5.7 μM respectively.

Much of the recent work on catalytic hydroboration of alkenes has focused on simple alkenes and styrene derivatives with few examples of reactions of 1,3- dienes, which have been reported to undergo mostly 1,4- additions to give allylic boronates. We find that reduced cobalt catalysts generated from 1,n-bis- diphenylphosphinoalkane complexes [Ph(2)P-(CH(2))(n)- PPh(2)]CoX(2); n = 1~5) or from (2- oxazolinyl)phenyldiarylphosphine complexes [(G- PHOX)CoX(2)] effect selective 1,2-, 1,4-, or 4,3-additions of pinacolborane (HBPin) to a variety of 1,3-dienes depending on the ligands chosen. Conditions have been found to optimize the 1,2-additions. The reactive catalysts can be generated from the cobalt (II)-complexes using trimethylaluminum, methyl aluminoxane or activated zinc in the presence of sodium tetrakis[(3,5-trifluoromethyl)phenyl]borate (NaBARF). The complex, (dppp)CoCl(2), gives the best results (ratio of 1,2- to 1,4-addition >95:5) for a variety of linear terminal 1,3-dienes and 2-substituted 1,3-dienes. The [(PHOX)CoX(2)] (X = Cl, Br) complexes give mostly 1,4-addition with linear unsubstituted 1,3-dienes, but, surprisingly selective 1,2-additions with 2-substituted or 2,3-disubstituted 1,3-dienes. Isolated and fully characterized (X-ray crystallography) Co(I)-complexes, (dppp)(3)Co(2)Cl(2) and [(S,S)-BDPP](3)Co(2)Cl(2), do not catalyze the reaction unless activated by a Lewis acid or NaBARF, suggesting a key role for a cationic Co(I) species in the catalytic cycle. Regio-and enantioselective 1,2-hydroborations of 2- substituted 1,3-dienes are best accomplished using a catalyst prepared via activation of a chiral phosphinooxazoline-cobalt(II) complex with zinc and NaBARF. A number of common functional groups, among them, -OBn, -OTBS, - OTs, N-phthalimido- groups, are tolerated and er’s >95:5 are obtained for several dienes including 1- alkenylcycloalk-1-enes. This operationally simple reaction expands the realm of asymmetric hydroboration to provide direct access to a number of nearly enantiopure homoallylic boronates, which are not readily accessible by current methods. The resulting boronates have been converted into the corresponding alcohols, potassium trifluroroborate salts, N-BOC amines and aryl derivatives by C-BPin to C-aryl transformation.

In this work, we report a mechanism by which stereoisomeric and twisted capsules P/M-1 direct their dynamic chirality in the presence of haloalkane guests. The capsule comprises a static, but twisted, cage that is linked to a dynamic tris(2-pyridylmethyl)amine (TPA) lid at its top. From the results of experimental (NMR spectroscopy and X-ray crystallography) and computational (DFT) studies, the TPA lid was shown to assume clockwise (+) and counterclockwise (-) folds with diastereomeric (but racemic) capsules M-1(+) and M-1(-) interconverting at a rapid rate (Delta G(189K)(not equal)=9.1 kcal mol(-1)). The relative stability of the capsules was found to be a function of guest(s) residing in their interior (243/262 angstrom(3)) with small CH2Cl2 (61 angstrom(3)) yielding roughly equal population of diastereomeric inclusion complexes. Larger guests, such as CCl4 (89 angstrom(3)) and CBr4 (108 angstrom(3)), however, formed M-1(-)subset of CX4 at the expense of M-1(+)subset of CX4 in circa 3:1 ratio. To account for the observation, theory (DFT:M06-2X/6-31+G*) and experiments (H-1 NMR spectroscopy) were used to deduce that CX4 guests become localized inside the twisted cage of the capsule by forming a C-X...pi halogen bond [N-c=d/(r(H)+r(X))=0.91-0.92] with the benzene floor while encountering electrostatic repulsions with closer naphthalimide boundaries. At last, the TPA lid used its central methylene hydrogens to establish, within the M-1(-)subset of CX4, three stabilizing C-H...X-C interactions with the guest. The same C-H...X-C interactions, however, became weaker (or possibly vanished) after the conformational reorganization of the lid and the formation of less stable M-1(+)subset of CX4 complex. On individual basis, C-H...X-C intermolecular contacts are weak and hardly detectable in the solution phase. In the case of capsule P/M-1, however, these contacts were multivalent and altogether strong enough to direct the host's dynamic chirality., National Science Foundation [CHE-1606404]; Scientific and Technological Research Council of Turkey (TUBITAK), This work was financially supported with funds obtained from the National Science Foundation under CHE-1606404. We are grateful for the postdoctoral fellowship (to M.G.) received from the Scientific and Technological Research Council of Turkey (TUBITAK). We thank the Ohio Supercomputer Center for generous allocations of computational resources.

Single-chromophore single-molecule photocatalysts for the conversion and storage of solar energy into chemical bonds are rare, inefficient and do not use significant portions of the visible spectrum. Here we show a new, air-stable bimetallic scaffold that acts as a single-chromophore photocatalyst for hydrogen-gas generation and operates with irradiation wavelengths that span the ultraviolet to the red/near-infrared. Irradiation in acidic solutions that contain an electron donor results in the catalytic production of hydrogen with 170 ± 5 turnovers in 24 hours and an initial rate of 28 turnovers per hour. The catalysis proceeds through two stepwise excited-state redox events—atypical of the currently known homogeneous photocatalysis—and features the storage of multiple redox equivalents on a dirhodium catalyst enabled by low-energy light. Homogeneous photocatalysts for the conversion and storage of solar energy typically feature separate sensitizer–catalyst assemblies, whereas previous examples of single-chromophore single-molecule photocatalysts are inefficient and do not use significant portions of the visible spectrum. Now a dirhodium single-chromophore single-molecule catalyst has been developed that generates hydrogen using low-energy light through a previously unobserved mechanism.

Hydrogen is expected to be important for future sustainable energy applications. Recent interest in adsorbing water splitting catalysts on a semiconductor surface for electrocatalytic hydrogen production warrants careful study of electrocatalysts with functional groups capable of binding to a surface. The monomeric complex Fe2(μ-S2(CH2)3)(CO)5PPh2C6H4CO2H (S2(CH2)3 = 1,3-propanedithiolate, pdt) and the dimeric complexes [{Fe2(μ-pdt)(CO)5}2(μ,κ1,κ1-Ph2PCH2N(Ar)CH2PPh2)] (Ar = p-CO2H-Ph, 3,5-CO2HPh, p-CH2CO2HPh, m-CO2H-Ph) bearing carboxylic acid functional groups have been prepared. The first electrochemical study of these dimeric FeFe complexes indicate that the complexes degrade upon reduction to form the species [Fe2(μ-pdt)(CO)4(κ2-Ph2PCH2N(Ar)CH2PPh2)]. A route is proposed for the formation of [Fe2(μ-pdt)(CO)4(κ2-Ph2PCH2N(Ar)CH2PPh2)] from [{Fe2(μ-pdt)(CO)5}2(μ,κ1,κ1-Ph2PCH2N(Ar)CH2PPh2)] and a crystal structure of an intermediate in the proposed electrochemical degradation pathway is presented. The electrochemical study presented herein provides valuable insight into degradation pathways of FeFe hydrogenase mimics bearing carboxylic acids amenable to surface immobilization.

A series of Novel Bacterial Topoisomerase Inhibitors (NBTIs) employing a linker derived from isomannide were synthesized and evaluated. Reduced hERG inhibition was observed compared to structure-matched analogues with different linkers, and compound 6 showed minimal proarrhythmic potential using an in vitro panel of cardiac ion channels. Compound 6 also displayed excellent activity against fluoroquinolone-resistant MRSA (MIC90 = 2 μg/mL) and other Gram-positive pathogens.

A series of three dirhodium complexes cis-[Rh2(DPhB)2(bncn)2](BF4)2 (1, DPhB = diphenylbenzamidine; bncn = benzocinnoline), cis-[Rh2(DPhTA)2(bncn)2](BF4)2 (2, DPhTA = diphenyltriazenide), and cis-[Rh2(DPhF)2(bncn)2](BF4)2 (3, DPhF = N,N′-diphenylformamidinate) shown to act as single-molecule photocatalysts for H2 production was evaluated. Complexes 1–3 are able to generate H2 in the absence of any other catalyst in homogenous acidic solution upon irradiation with red light in the presence of the sacrificial electron donor BNAH (1-benzyl-1,4-dihydronicotinamide). The excited state of each complex is reductively quenched by BNAH, producing the corresponding one-electron reduced complex. The latter is also able to absorb a photon and oxidize another BNAH molecule, producing the doubly-reduced, activated form of the catalyst that is able to generate H2. The present work shows the effect of substitution on the bridging ligands on the driving force for reductive quenching and hydricity of the proposed active intermediate, both of which affect the efficiency of hydrogen production. Complexes 1–3 operate following a double reductive quenching mechanism and, importantly, are active with red light. This work lays the foundation for the design of single-molecule photocatalysts that operate from the ultraviolet to the near-infrared, such that solar photons throughout this entire range are harnessed and utilized for solar energy conversion., Three dirhodium complexes cis-[Rh2(DPhB)2(bncn)2](BF4)2, cis-[Rh2(DPhTA)2(bncn)2](BF4)2 and cis-[Rh2(DPhF)2(bncn)2](BF4)2 are shown to act as single-molecule photocatalysts for H2 production.

In this study, we report the preparation, conformational dynamics, and recognition characteristics of novel molecular capsule 1 comprising a bowl-shaped framework conjugated to a tris(2-pyridylmethyl)amine (TPA) lid. With the assistance of experiment (1H NMR spectroscopy) and theory (MM and DFT) we found that C3 symmetric 1 is poorly preorganized with three pyridines at the rim adopting a propeller-like orientation and undergoing P-to- M (or vice versa) stereoisomerization (Δ G⧧ < 8 kcal/mol, VT 1H NMR). Capsule 1 binds CH4, CH3Cl, CH2Cl2, CHCl3, and CCl4 with Ka < 7 M-1. Protonation of 1 with HCl, however, gives [1·H]-Cl, with the solid-state structure showing the TPA lid being "flattened" and the +N-H---Cl hydrogen-bonded group residing outside. Importantly, the P-to- M stereoisomerization would for [1·H]-Cl occur with Δ G⧧ = 11 kcal/mol (VT 1H NMR). Less dynamic and more preorganized [1·H]-Cl binds CH4, CH3Cl, CH2Cl2, CHCl3, and CCl4 guests with a greater affinity ( Ka = 100-400 M-1) than 1. The results of our studies suggest that the complexation of increasingly larger guests takes place in an induced-fit fashion, with [1·H]-Cl (a) elongating along its vertical axis and concurrently potentially (b) twisting pyridines from P into M (and vice versa) orientation. The addition of Et3N to [1·H]-Cl⊂CH2Cl2 causes deprotonation of the capsule and the release of CH2Cl2 with the process being fully reversed after the addition of HCl. Allosteric capsule 1 with unique structural and dynamic characteristics is expected to, in the future, assist the construction of complex molecular machines and smart functional materials.

The molecular structures of three parthenolide analogues, (–)-goyazensolide (1), (–)-15-deoxygoyazensolide (2), and (–)-ereglomerulide (3), isolated from the leaves of Piptocoma rufescens in a previous study, were determined by X-ray analysis, and the absolute configuration of (–)-goyazensolide (1) was confirmed crystallographically using Cu Kα radiation at low temperature. Compounds 1–3, (+)-rufesolide A (4), and commercial parthenolide were found to be growth inhibitory toward MOLM-13 and EOL-1 human acute myeloid leukemia cells using PKC412 (midostaurin) as the positive control, with 1–3 being more active than parthenolide. Also, compounds 1–4 exhibited synergistic effects, when tested with PKC412, but parthenolide did not show this type of activity. At a concentration lower than 2.0 μM, both 1 and 2 induced approximately 50% of the cells to become apoptotic at a late-stage of the cell cycle, but no similar apoptotic effects were observed for 3, 4, or parthenolide. Leukemia cell apoptosis was induced by these compounds through the activation of caspase-3 and the inhibition of NF-κB, as indicated by immunoblotting analysis, and compounds 1 and 2 seem to be promising leads for development as potential antileukemic agents.

A green and efficient method for the synthesis of newer 2-imino-4-oxothiazolidin-5-ylidene acetate derivatives under catalyst-free conditions by simply stirring symmetrical and unsymmetrical 1,3-diarylthioureas with dialkyl acetylenedicarboxylates in ethanol at room temperature has been developed. Interestingly, the regioselective synthesis affords the 2-imino-4-oxothiazolidin-5-ylidene acetate derivatives: the amine nitrogen bonded to an electron-withdrawing substituent becomes part of the imino component, and the amine nitrogen bonded to an electron-donating substituent becomes the heterocyclic nitrogen. This is the first report wherein the impact of substituents in directing the regiocyclization has been explained and the structure conflict resolved by single-crystal X-ray analysis.

We prepared dual-cavity basket 1 to carry six (S)-alanine residues at the entrance of its two juxtaposed cavities (289 Å(3)). With the assistance of (1)H NMR spectroscopy and calorimetry, we found that 1 could trap a single molecule of 4 (K1 = 1.45 ± 0.40 × 10(4) M(-1), ITC), akin in size (241 Å(3)) and polar characteristics to nerve agent VX (289 Å(3)). The results of density functional theory calculations (DFT, M06-2X/6-31G*) and experiments ((1)H NMR spectroscopy) suggest that the negative homotropic allosterism arises from the guest forming C-H···π contacts with all three of the aromatic walls of the occupied basket's cavity. In response, the other cavity increases its size and turns rigid to prevent the formation of the ternary complex. A smaller guest 6 (180 Å(3)), akin in size and polar characteristics to soman (186 Å(3)), was also found to bind to dual-cavity 1, although giving both binary [1⊂6] and ternary [1⊂62] complexes (K1 = 7910 M(-1) and K2 = 2374 M(-1), (1)H NMR spectroscopy). In this case, the computational and experimental ((1)H NMR spectroscopy) results suggest that only two aromatic walls of the occupied basket's cavity form C-H···π contacts with the guest to render the singly occupied host flexible enough to undergo additional structural changes necessary for receiving another guest molecule. The structural adaptivity of dual-cavity baskets of type 1 is unique and important for designing multivalent hosts capable of effectively sequestering targeted guests in an allosteric manner to give stable supramolecular polymers.

A new chemosensor (Z)-ethyl 2-((Z)-2-(benzo[d]thiazol-2-ylimino)-4-oxo-3-phenylthiazolidin-5-ylidene)acetate (receptor 1) was designed and synthesized under catalyst-free conditions. Receptor 1 was characterized by various spectroscopic techniques and its structure was solved by single-crystal X-ray diffraction. Receptor 1 was shown to be based on an internal charge transfer mechanism with the benzothiazole unit. These results were complemented by density functional theory calculations. The fluorescent emission of receptor 1 in CH3OH/H2O (50:50 v/v) was significantly quenched in the presence of Cu2+ and Hg2+, but not in the presence of other tested metal ions. Receptor 1 formed complexes in a 1:1 stoichiometry with Cu2+ and Hg2+ and the detection limits were 0.36 and 2.49 μM, respectively. In addition to the sensing study, the nature of the interactions of 1 with aldose reductase inhibitor was investigated using molecular docking studies.

Enantiopure silanediols derived from BINOL are an innovative family of stereoselective hydrogen-bond donor (HBD) catalysts. Silanediols incorporated into a BINOL framework are attractive catalysts, as they are readily accessible and highly customizable. Structural modifications of the BINOL backbone affect the reactivity and selectivity of the silanediol catalysts in the additions of silyl ketene acetals to N-acyl isoquinolinium ions. The best results were obtained when the silanediol scaffold was substituted at the 4,4′- and 6,6′-positions. This report includes details regarding the properties of selected BINOL-based silanediol catalysts, including their acidities, binding constants, and X-ray crystal structures.

The new heteroleptic paddlewheel complexes cis-[Rh

The interligand charge dynamics of the lowest singlet metal-to-ligand charge-transfer states (

Over the past half a century, the structure and configuration of the rotenoids, a group of natural products showing multiple promising bioactivities, have been established by interpretation of their NMR and electronic circular dichroism spectra and confirmed by analysis of single-crystal X-ray diffraction data. The chemical shift of the H-6′ 1H NMR resonance has been found to be an indicator of either a cis or trans C/D ring system. In the present study, four structures representing the central rings of a cis-, a trans-, a dehydro-, and an oxadehydro-rotenoid have been plotted using the Mercury program based on X-ray crystal structures reported previously, with the conformations of the C/D ring system, the local bond lengths or interatomic distances, hydrogen bond angles, and the H-6′ chemical shift of these compounds presented. It is shown for the first time that a trans-fused C/D ring system of rotenoids is preferred for the formation of a potential intramolecular C6′–H6′•••O=C4 H-bond, and that such H-bonding results in the 1H NMR resonance for H-6′ being shifted downfield.

Four photophysically interesting dimolybdenum paddlewheel compounds are synthesized and characterized: I and II contain amide ligand (N,3-diphenyl-2-propynamide), and III and IV contain thioamide ligand (N,3-diphenyl-2-propynethioamide). I and III are trans-Mo

Structural studies of the N-(2,4-dinitrophenyl) derivative of a DielsAlder-cyclized 1,2-dihydropyridine both unequivocally established the polycyclic framework and revealed interesting distortions of aromatic structure and unique dimeric clustering of the aromatic entities in the solid state.

Two new (1 and 2) and four known arylnaphthalene lignan lactones (3–6) were isolated from different plant parts of Phyllanthus poilanei collected in Vietnam, with two further known analogues (7 and 8) being prepared from phyllanthusmin C (4). The structures of the new compounds were determined by interpretation of their spectroscopic data and by chemical methods, and the structure of phyllanthusmin D (1) was confirmed by single-crystal X-ray diffraction analysis. Several of these arylnaphthalene lignan lactones were cytotoxic toward HT-29 human colon cancer cells, with compounds 1 and 7-O-[(2,3,4-tri-O-acetyl)-α-l-arabinopyranosyl)]diphyllin (7) found to be the most potent, exhibiting IC50 values of 170 and 110 nM, respectively. Compound 1 showed activity when tested in an in vivo hollow fiber assay using HT-29 cells implanted in immunodeficient NCr nu/nu mice. Mechanistic studies showed that this compound mediated its cytotoxic effects by inducing tumor cell apoptosis through activation of caspase-3, but it did not inhibit DNA topoisomerase IIα activity.

Caeruleanone A (1), a novel rotenoid with an unprecedented arrangement of the D-ring, was isolated with another two new analogues, caeruleanones B (2) and C (3), together with 11 known rotenoids from the fruits of Millettia caerulea. The structures of the new compounds were determined by spectroscopic data analysis, with that of 1 being confirmed by single-crystal X-ray diffraction. Compounds 2 and 3 displayed potent mitochondrial transmembrane potential inhibitory and quinone reductase induction activities.

Bimetallic yttrium- and lanthanide-salen complexes, readily prepared from commercially available metal isopropoxides, 2-dimethylaminoethanol, 1,1′-binaphthyl-2,2′-diamine and 2-hydroxy-3-methoxybenzaldehyde (3 steps) catalyze highly enantioselective ring opening (∼90–99% ee) reactions of meso-N-4-nitrobenzoyl aziridines by TMSCN and TMSN3. The TMSN3-mediated reactions give the highest enantioselectivities reported to date for several prototypical aziridines. Selectivity in a related ring opening by silyl isothiocyanates depends on the substituents on silicon, larger tBuPh2SiNCS giving the best selectivities, especially when an yttrium or ytterbium complex is used as the catalyst. The bimetallic yttrium complex also effects unprecedented regiodivergent parallel kinetic resolution of racemic monosubstitued aziridines upon reaction with TMSN3. In these reactions, each of the enantiomers undergoes nucleophilic addition of azide at different carbons giving two products in nearly enantiomerically pure form. To explain the dramatic differences in the selectivities between the mono- and bimetallic catalysts in these reactions, a mechanism that involves activation of both the electrophile (aziridine) and the nucleophile (azide or cyanide) at two different metals of the bimetallic complex is proposed. Molecular weight determination by vapor pressure osmometry, diffusion ordered NMR spectroscopy (DOSY) and kinetic studies, which suggest first order dependence on the concentration of the catalyst, provide strong support for this proposal.

Previous theoretical studies have predicted structural differences between the tris(cyclopentadienyl) zirconium and hafnium complexes Cp3MX (Cp = C5H5; M = Zr, Hf). Cp3ZrCl can be isolated via the stoichiometric reaction of Cp2ZrCl2 and NaCp, but forming the analogous Hf complex is complicated by ligand redistribution. Partial crystallographic analysis of these two complexes indicates likely structural differences wherein the Zr complex has three η5 Cp ligands (“3-5” structure) while the Hf complex has two η5 Cp ligands and one η1 Cp ligand (“2-5,1-1” structure). The use of C5H4CH3 (MeCp) simplifies both the syntheses and the procurement of suitable crystals. The preparation of a number of MeCp complexes of Zr and Hf is reported along with crystallographic characterization of (MeCp)3HfCl, which has a 2-5,1-1 structure and (MeCp)4Zr, which has a 3-5,1-1 structure.

The complex cis-[Ru(phpy)(phen)(CH3CN)2]+ (phpy = 2-phenylpyridine, phen = 1,10–phenanthroline) was investigated as a potential photodynamic therapy (PDT) agent. This complex presents desirable photochemical characteristics including a low energy absorption tail extending into the PDT window (600–850 nm) and photoinduced exchange of the CH3CN ligands, generating a species analogous to the chemotherapy drug cisplatin. Furthermore, photochemical reactivity can be controlled through selective irradiation into the Ru-phen singlet metal-to-ligand charge transfer (1MLCT) band (λirr = 500 nm) of [Ru(phpy)(phen)(CH3CN)2]+ in the presence of excess t-butylammonium chloride (TBACl) resulting in efficient photoinduced production of [Ru(phpy)(phen)(CH3CN)Cl] (Φ = 0.25). This lower energy irradiation resulted in greater quantum yield of photosubstitution when compared to direct irradiation into the Ru-phpy 1MLCT peak (λirr = 450 nm; Φ = 0.08) in CH2Cl2. It was found that the lower quantum yield observed for irradiation into the Ru→phpy− 1MLCT band results from significant orbital mixing of the phpy− ligand with the t2g-type filled set in the metal, giving this state significant ligand-centered character. Lastly, this complex produced a decrease in the mobility of linearized ds-DNA when irradiated with λirr ≥ 420 nm, indicative of covalent binding by the transition metal complex similar to that observed for cisplatin. No change in mobility was found for the same samples kept in the dark indicating, unlike cisplatin, DNA binding of cis-[Ru(phpy)(phen)(CH3CN)2]+ only occurs with the activation of light. These observations support the use of cis-[Ru(phpy)(phen)(CH3CN)2]+ as a potential PDT agent by the photoinduced generation of a cisplatin analog.

New convenient procedures for the preparation of ammonia monochloroborane (NH(3)BH(2)Cl) and cyclotriborazane [(BH(2)NH(2))(3)] are described. Crystal structures have been determined by single-crystal X-ray diffraction. Strong H···Cl···H bifurcated hydrogen bonding and weak N-H···H dihydrogen bonding are observed in the crystal structure of ammonia monochloroborane. When heated at 50 °C or under vacuum, ammonia monochloroborane decomposes to (NH(2)BHCl)(x), which was characterized by NMR, elemental analysis, and powder X-ray diffraction. Redetermination of the crystal structure of cyclotriborazane at low temperature by single-crystal X-ray diffraction analysis provides accurate hydrogen positions. Similar to ammonia borane, cyclotriborazane shows extensive dihydrogen bonding of N-H···H and B-H···H bonds with H(δ+)···H(δ-) interactions in the range of 2.00-2.34 Å.

In a one-pot process without isolation of intermediates, (but-3-en-1-yl)pyridine (13) is treated sequentially with dicyclohexylborane, trimethylaluminium, and ethyl carbonochloridate yielding ethyl 1,4-dihydro-4,4-(tetramethylene)pyridine-1-carboxylate (=ethyl 8-azaspiro[4.5]deca-6,9-diene-8-carboxylate; 2) in 46% yield based on starting alkenylpyridine 13 (Scheme 5).

Two new dirhodium complexes, the head-to-tail (H,T) and head-to-head (H,H) isomers of cis-[Rh(2)(HNOCCH(3))(2)(CH(3)CN)(6)](2+), were synthesized, separated, and characterized following the reaction of Rh(2)(HNOCCH(3))(4) with trimethyloxonium tetrafluoroborate in CH(3)CN. The products were characterized by (1)H NMR spectroscopy, mass spectrometry, elemental analysis, and single crystal X-ray diffraction. Each bis-amidato isomer has a total of six CH(3)CN ligands, two along the internuclear Rh-Rh axis, CH(3)CN(ax), two in equatorial positions trans to the oxygen atoms of the bridging amidato groups, CH(3)CN(eq)(O), and two in equatorial positions trans to the amidato nitrogen atoms, CH(3)CN(eq)(N). When aqueous solutions of the complexes are irradiated with low energy light (λ(irr) ≥ 495 nm, 60 min), both types of CH(3)CN(eq) ligands undergo efficient ligand exchange with solvent H(2)O molecules to form monoaqua, followed by bis-aqua, adducts, releasing two CH(3)CN(eq) ligands in the process. The quantum yields, Φ(400nm), for the H,T and H,H isomers to form monoaqua adducts are 0.43 and 0.38, respectively, which are substantially greater than the 0.13 yield observed for cis-[Rh(2)(O(2)CCH(3))(2)(CH(3)CN)(6)](2+); importantly, no ligand exchange is observed when the complexes are kept in the dark. Finally, low energy excitation (λ(irr) ≥ 610 nm, 30 min) of the H,T isomer was shown to generate photoproducts that covalently bind to linearized DNA, making 2 a potential agent for photochemotherapy that does not require the formation of (1)O(2), as is typical of organic photodynamic therapy (PDT) agents.

Six new (1-6) and eight known germacranolide-type sesquiterpene lactones, along with several known phenylpropanol coumarates and methylated flavonoids, were isolated from the leaves of Piptocoma rufescens, collected in the Dominican Republic. The new compounds were identified by analysis of their spectroscopic data, with the molecular structure of 3 being established by single-crystal X-ray diffraction. The absolute configurations of the sesquiterpene lactones isolated were determined from their CD and NOESY NMR spectra, together with the analysis of Mosher ester reactions. Bioassay screening results showed the majority of the sesquiterpene lactones isolated (1-13) to be highly cytotoxic toward the HT-29 human colon cancer cell line, with the most potent compound being 15-deoxygoyazensolide (10, IC(50), 0.26 µM). In addition, several of the sesquiterpene lactones exhibited NF-κB (p65) inhibitory activity.

From the reactions between M(2)(T(i)PB)(4), where T(i)PB = 2,4,6-triisopropylbenzoate and two equivalents each of 2-furan carboxylic acid, FuCO(2)H, and 2-selenophene carboxylic acid, SpCO(2)H in toluene, the new compounds trans-M(2)(T(i)PB)(2)(O(2)CFu)(2) (1a M = Mo, 2a M = W) and trans-M(2)(T(i)PB)(2)(O(2)CSp)(2) (1b M = Mo, 2b M = W) were formed. These new compounds have been characterized by (1)H NMR, steady-state UV-Vis-NIR absorption and emission spectroscopy, cyclic and differential pulse voltammetry, and fs and ns transient absorption spectroscopy. The compound Mo(2)(T(i)PB)(2)(O(2)CSp)(2) (1b) has been characterized by single crystal X-ray crystallography. These data are compared with those previously reported for related 2-thiophene carboxylate derivatives: M(2)(T(i)PB)(2)(O(2)CTh)(2). The physico-chemical data correlate well with electronic structure calculations performed on model compounds. All compounds have detectible S(1) photoexcited states with lifetimes that vary from ∼5 ps to < 1 ps. The molybdenum compounds have T(1) states with microsecond lifetimes that are assigned as MMδδ* whereas the T(1) states for tungsten are (3)MLCT with lifetimes on the order of nanoseconds. In all cases, shorter lifetimes were seen in complexes containing heavier atoms.

The synthesis and initial biological evaluation of 3-carboranylthymidine analogues (3CTAs) that are (radio)halogenated at the closo-carborane cluster are described. Radiohalogenated 3CTAs have the potential to be used in the radiotherapy and imaging of cancer because they may be selectively entrapped in tumor cells through monophosphorylation by human thymidine kinase 1 (hTK1). Two strategies for the synthesis of a (127)I-labeled form of a specific 3CTA, previously designated as N5, are described: (1) direct iodination of N5 with iodine monochloride and aluminum chloride to obtain N5-(127)I and (2) initial monoiodination of o-carborane to 9-iodo-o-carborane followed by its functionalization to N5-(127)I. The former strategy produced N5-(127)I in low yields along with di-, tri-, and tetraiodinated N5 as well as decomposition products, whereas the latter method produced only N5-(127)I in high yields. N5-(127)I was subjected to nucleophilic halogen- and isotope-exchange reactions using Na(79/81)Br and Na(125)I, respectively, in the presence of Herrmann's catalyst to obtain N5-(79/81)Br and N5-(125)I, respectively. Two intermediate products formed using the second strategy, 1-(tert-butyldimethylsilyl)-9-iodo-o-carborane and 1-(tert-butyldimethylsilyl)-12-iodo-o-carborane, were subjected to X-ray diffraction studies to confirm that substitution at a single carbon atom of 9-iodo-o-carborane resulted in the formation of two structural isomers. To the best of our knowledge, this is the first report of halogen- and isotope-exchange reactions of B-halocarboranes that have been conjugated to a complex biomolecule. Human TK1 phosphorylation rates of N5, N5-(127)I, and N5-(79/81)Br ranged from 38.0% to 29.6% relative to that of thymidine, the endogenous hTK1 substrate. The in vitro uptake of N5, N5-(127)I, and N5-(79/81)Br in L929 TK1(+) cells was 2.0, 1.8, and 1.4 times greater than that in L929 TK1(-) cells.

The synthesis of an iridium complex bearing the unusual di-tert-butylheptanoylphosphine ligand is described. In exploring the chemistry of this complex, it was found that the acylphosphine ligand u...

The singlet S 1 and triplet T 1 photoexcited states of the compounds containing MM quadruple bonds trans -M 2 (T i PB) 2 (O 2 CC 6 H 4 -4-CN) 2 , where T i PB = 2,4,6-triisopropylbenzoate and M = Mo ( I ) or M = W ( I ′ ), and trans -M 2 (O 2 CMe) 2 ((N[ i Pr ]) 2 CC ≡ CC 6 H 5 ) 2 , where M = Mo ( II ) and M = W ( II ′ ), have been investigated by a variety of spectroscopic techniques including femtosecond time-resolved infrared spectroscopy. The singlet states are shown to be delocalized metal-to-ligand charge transfer (MLCT) states for I and I ′ but localized for II and II ′ involving the cyanobenzoate or amidinate ligands, respectively. The triplet states are MoMo δδ * for both I and II but delocalized 3 MLCT for I ′ and localized 3 MLCT for II ′ . These differences arise from consideration of the relative orbital energies of the M 2 δ or M 2 δ * and the ligand π ∗ as well as the magnitudes of orbital overlap.

The reaction between W(2)(T(i)PB)(4), where T(i)PB = 2,4,6-triisopropylbenzoate, and 2 equiv of 4-isonicotinic acid (nicH) yields the compound W(2)(T(i)PB)(2)(nic)(2), 2, and T(i)PBH. Compound 2 is related to the previously reported molybdenum analog, Mo(2)(T(i)PB)(2)(nic)(2), 1. Compounds 1 and 2 react with 2 equiv of B(C(6)F(5))(3) in THF to form the adducts M(2)(T(i)PB)(2)(nic-B(C(6)F(5))(3))(2), 1B (M = Mo) and 2B (M = W), which have been crystallographically characterized as solvates M(2)(T(i)PB)(2)(nic-B(C(6)F(5))(3))(2)·2THF n-hexane. Compounds 1 and 2 are intensely colored due to M(2) δ to π* MLCT transitions, and upon complexation with B(C(5)F(5))(3) to give 1B and 2B, these bands shift to lower energy and gain in intensity. Each compound shows two one-electron ligand-based reductions with a ΔE(1/2) = 120 (1), 300 (1B), 440 (2), and 650 mV (2B). The larger ΔE(1/2) values for the tungsten compounds reflect the greater orbital mixing of the metal 5d-based M(2) δ and the nic π* LUMO. Reduction of solutions of 1B and 2B with (C(5)Me(5))(2)Co leads to the anions 1B(-) and 2B(-), which have been characterized spectroscopically by electron paramagnetic resonance (EPR) and UV-vis-NIR absorption. The EPR spectra of 1B(-) and 2B(-) are consistent with ligand-based (i.e., organic) radicals. The electronic spectra contain low-energy narrow charge resonance (IVCT) bands at 3800 (1B(-)) and 4500 cm(-1) (2B(-)), consistent with fully delocalized mixed valence radical anions. The results are compared with electronic structure calculations and with the spectral features of the metal-centered delocalized mixed valence radical cations [(Bu(t)CO(2))(3)M(2)](2)-μ(2)-(O(2)C-CO(2))(+), to which they are remarkably similar, as well as with other organic-based mixed valence systems.

Two new Ru(II) complexes, [Ru(bpy) 2 (1-COO-iqu)] + ( 2 ; bpy = 2,2′-bipyridine, 1-COO-iqu − = isoquinoline-1-carboxylate) and [Ru(bpy) 2 (3-COO-iqu)] + ( 3 ; 3-COO-iqu − = isoquinoline-3-carboxylate), were prepared and their crystal structures solved. The ground and excited state properties of 2 and 3 were characterized and compared to those of [Ru(bpy) 3 ] 2+ ( 1 ). The presence of the oxygen atom in the Ru(II) coordination sphere makes 2 and 3 easier to oxidize than 1 . The Ru → bpy MLCT absorption and emission of 2 and 3 are red-shifted relative to that of 1 in CH 2 Cl 2 , and the E 00 energies were estimated to be 1.89 eV and 1.95 eV from the low temperature emission of 2 and 3 , resulting in excited state oxidation potentials of −1.03 V and −1.10 V vs SCE, respectively. In addition to the short-lived emissive 3 MLCT state, a long-lived species is observed in the transient absorption of 3 in DMSO ( τ = 49 μs) and pyridine ( τ = 44 μs), assigned to a solvent-coordinated complex. This intermediate is not observed for 3 in non-polar solvents or for 2 . The absence of the solvent coordinated intermediate in 2 is explained by the stronger Ru–O bond afforded by the lower conjugation in that extends onto the carboxylic acid in the 1-COO-iquo − ligand, compared to that in the 3-COO-iqu − ligand in 3 . Transient absorption experiments also show that the 3 MLCT excited state of 3 is able to reduce methyl viologen.

The single-crystal structure, paramagnetic, and oxygen-sensing characteristics of a new tetragonal polymorph of lithium octa-n-butoxynaphthalocyanine, LiNc-BuO (Tg), is reported. The compound was synthesized as fine, diamond-shaped, neutral radicalcrystalsby reacting octa-n-butoxynaphthalocyanine (Nc-BuO) with lithium metal in n-butanol. Single-crystal X-ray diffraction analysis revealed a saddle-shaped conformation of the molecule with a crystallographic 2-fold rotation axis in a tetragonal unit cell. This represents the first single-crystal, structurally characterized, lithium naphthalocyanine complex. Unlike the triclinic polymorph of LiNc-BuO (Pandian, et al. J. Mater. Chem.2006,16,3609),the tetragonal(Tg)formof LiNc-BuOdid notshowthepresence oflargeopen channels in the crystalline packing. The magnetic susceptibility and EPR spectroscopic properties were in agreement with the X-ray crystal structure showing the existence of a high degree of spin exchange in the crystalline system. The effective magnetic moment calculated for the LiNc-BuO (Tg) was 1.56 μB per formula unit, which was smaller than the expected value of 1.73 μB for a spin system with S = 1/2. The crystals showed a single, sharp EPR spectrum with an unusually low line width of 20(5mGunderanoxicconditions.TheEPRlinewidthwaslinearlydependentonpartialpressureof oxygen(pO2)intherange0-760mmHg,withasensitivityof4.54(0.50mG/mmHg.TheLiNc-BuO (Tg) crystals possess several desirable properties for use as a probe for EPR oximetry.

Facile CuI-mediated N-arylation of diketopiperazine using the Fukuyama modification of the Ullmann-Goldberg reaction can be exploited in new approaches to enantio-pure polycyclic diketopiperazines from easily assembled dipeptides or functionalized Schollkopf reagents.