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The structure of acetatodimethylthallium 2 has been used as a model in an attempt to predict and ‘engineer’ a phase of dimethyl(propynoato)thallium 3 which would be reactive in the solid state. Upon irradiation with X-rays or 60Co γ-rays, 3 is indeed converted to the corresponding deep-brown polypropynoate. The crystal structure of 3 contains, as expected, an infinite set of short contacts (3.454 A) between acetylene moieties; the presence of such a chain is a requirement for a propynoate material to be sensitive to ionizing radiation. However, the crystal structures of 2 and 3 are quite different owing to subtle changes in CH⋯O hydrogen bonding, Crystals of 3, (CH3)2Rl(O2CC≡CH), belong to the orthorhombic system, space group Pnma, a = 7.316(4), b = 11.268(6), c = 9.033(5) A ; Z = 4 . Full-matrix least-squares refinement of positional and displacement parameters for all nonhydrogen atoms, using 338 data for which |Fo| > 3.92σ(|Fo|), led to R = 0.059 and Rw = 0.068.

A tris(phosphino)amide-ligated Zr–Co heterobimetallic complex has been shown to activate N–H bonds of hydrazine derivatives via a proton-coupled electron transfer process. Such reactivity is highly unusual for an early metal such as Zr, but is promoted by the adjacent redox active Co atom.

We have examined the reaction of N-(benzyloxycarbonyl)-L-alanyl-L-glycyl-L-phenylalanyl chloromethyl ketone (ZAGFCMK) with chymotrypsin (Cht) and have found that, in addition to irreversible alkylation of the enzyme, some of the corresponding hydroxymethyl ketone is produced. For each molecule of hydroxy ketone formed, 3.6 molecules of chymotrypsin are inactivated. Chloroketone hydrolysis is also observed with chymotrypsin methylated at N-3 of the active site histidine (MeCht). The hydrolysis proceeds slowly (k = 0.14 min-1). Alkylation of the modified enzyme was not observed. An initial burst of free chloride is detected during the MeCht-catalyzed hydrolysis. The magnitude of the chloride burst is proportional to the enzyme concentration in an approximate 1:1 stoichiometry and indicates a relatively rapid chloride-releasing step which gives rise to an intermediate which is more slowly converted to hydroxy ketone. We have also investigated both the solution and MeCht-mediated hydrolysis of the S isomer of N-acetyl-L-alanyl-L-phenylalanyl chloroethyl ketone (S-AcAFCEK). We have concluded that the nonenzymatic hydrolysis proceeds with inversion of configuration at the stereocenter, while the enzymatic process occurs with retention of configuration. The two nucleophilic displacements attending the MeCht-mediated hydrolysis of S-AcAFCEK imply the formation of an intermediate, possibly of an epoxy ether, formed by internal displacement of the chloride by the oxyanion of the initially generated enzyme-chloroketone hemiketal adduct.

X-ray structure determinations of HBTU and HATU, well-known reagents for peptide bond formation, show that the solid-state structures of these compounds differ markedly from those commonly presented in the literature. The solid-state structures are isomers of the N,N,N',N'-tetramethyluronium salt formulation commonly written for HBTU and HATU. HBTU and HATU, obtained either directly from synthesis or from CH3CN solution, crystallize as the guanidinium N-oxide isomers. Both compounds crystallize in nearly identical conformations, despite marked differences in crystal packing.

Mixing 2-butynoic acid and 2-aminopyridine in acctone produces the salt 2-aminopyridinium 2-butynoate (4) in high yield. An X-ray structure determination of 4 (Space Group P21/n, Z = 4) shows it to contain short acetylene-acetylene contacts as well as short contacts between the pyridine N atom and the β-carbon atom of the butynoate moiety. The contacts are between centrosymmetrically-rclated “dimer pairs” of the cocrystalline salt, and are not part of an infinite array. The material is stable to heating or exposure to 60Co γ-rays.

The diarylamido/bis(phosphine) PNP pincer ligand (2-(i)Pr(2)P-4-MeC(6)H(3))(2)N has been evaluated as a scaffold for supporting a BF(2) fragment. Compound (PNP)BF(2) (6) was prepared by simple metathesis of (PNP)Li (5) with Me(2)SBF(3). NMR spectra of 6 in solution are of apparent C(2) symmetry, suggestive of a symmetric environment about boron. However, a combination of X-ray structural studies, low-temperature NMR investigations, and DFT calculations consistently establish that the ground state of this molecule contains a classical four-coordinate boron with a PNBF(2) coordination environment, with one phosphine donor in PNP remaining "free". Fortuitous formation of a single crystal of (PNP)BF(2)·HBF(4) (7), in which the "free" phosphine is protonated, furnished another structure containing the same PNBF(2) environment about boron for comparison and the two PNBF(2) environments in 6 and 7 are virtually identical. DFT studies on several other diarylamido/bis(phosphine) pincer (PNP)BF(2) systems were carried out and all displayed a similar four coordinate PNBF(2) environment in the ground state structures. The symmetric appearance of the room-temperature NMR spectra is explained by the rapid interconversion between two degenerate four-coordinate, C(1)-symmetric ground-state forms. Lineshape analysis of the (1)H and (19)F NMR spectra over a temperature range of 180-243 K yielded the activation parameters ΔH(‡) = 8.1(3) kcal mol(-1) and ΔS(‡) = -6.0(15) eu, which are broadly consistent with the calculated values. Calculations indicate that the exchange of phosphine donors at the boron center proceeds by an intrinsically dissociative mechanism.

At room temperature, the early/late heterobimetallic complex Co((i)Pr(2)PNMes)(3)Zr(THF) has been shown to oxidatively add CO(2), generating (OC)Co((i)Pr(2)PNMes)(2)(μ-O)Zr((i)Pr(2)PNMes). This compound can be further reduced under varying conditions to generate either the Zr oxoanion (THF)(3)Na-O-Zr(MesNP(i)Pr(2))(3)Co(CO) or the Zr carbonate complex (THF)(4)Na(2)(CO(3))-Zr(MesNP(i)Pr(2))(3)Co(CO). Additionally, reactivity of the CO(2)-derived product has been observed with PhSiH(3) to generate the Co-hydride/Zr-siloxide product (OC)(H)Co((i)Pr(2)PNMes)(3)ZrOSiH(2)Ph.

The Pd(I)-Pd(I) dimer [((F)PNP)Pd-](2) reacts with O(2) upon exposure to light to produce either the superoxide ((F)PNP)PdO(2) or the peroxide [((F)PNP)PdO-](2), which exist in equilibrium with free O(2). Both complexes contain square-planar Pd(II) centers. The unpaired electron density in ((F)PNP)PdO(2) is localized on the superoxide ligand.

The synthesis of a new pincer ligand containing a central cationic N-heterocyclic phosphenium donor is described. The electrophilic nature of this cationic ligand renders it non-innocent, and coordination of this ligand to a PtCl(2) fragment leads to chloride migration from Pt to the cationic phosphorus center.

Mn(III)-based oxidative free-radical cyclization of phenylmenthyl ester 1e afforded 90% of 13 with 86% de. Cyclization of 31b provided 56% of (+)-podocarpic acid precursor 32e with 82% de. The direction of de was opposite in these two cases. Oxidative cyclization of α-methyl β-keto ester 44b gave a 1:1.6 mixture of 46b and 47b while α-propyl β-keto ester and produced a >10:1 mature of46d and 47d indicating that the extent and direction of de is dependent on the size of the α-substituent. The reaction proceeds through transition states 12 and 56 with large α-substituents and through transition states 19 and 57 with small α-substituents. The de depends on the double-bond substitution pattern

Allylic cyclobutanols 1, 10, 21, 27, 32, 39, 51, and 58 are oxidatively fragmented by Mn(OAc) 3 -2H 2 O in EtOH to give tertiary radicals as shown in eq 1. These tertiary radicals undergo both 6-endo-cyclization to the α,β-unsaturated ketone to afford α-keto radicals and 5-exo-cyclization to provide β-keto cyclopentylmethyl radicals. The α-keto radicals produced by 6-endo-cyclization are reduced to ketones or dimerize. The β-keto radicals formed by 5-exo-cyclization are oxidized by Cu(OAc) 2 to yield methylenecyclopentanones and rearrange to give 3-oxocyclohexyl radicals that are oxidized by Cu(OAc) 2 to afford cyclohexenones. Acetylenic cyclobutanols 47, 49, and 65 are oxidatively fragmented by Mn(OAc) 3 .2H 2 O in EtOH to provide tertiary radicals that cyclize to give α-keto vinyl radicals, which abstract a hydrogen atom to yield methylenecyclopentanones. Pentenylcyclobutanol 75 is oxidatively fragmented by Mn(OAc) 3 .2H 2 O to afford tertiary radical 74, which cyclizes to furnish cyclopentylmethyl radicals 77 and 78, which are oxidized by Cu(OAc) 2 to methylenecyclopentanes 76 and 79

The reaction of cyclopentadienylcopper dimethyl sulfide with 1,8-diiodonaphthalene provides a method for coupling cyclopentadienyl groups to the naphthalene nucleus. The product formed by coupling of two such groups in peri positions on the naphthalene ring is the Diels-Alder adduct 3. Deuterium labeling experiments have been carried out which show that this product is formed through conversion of the initial 1-iodo-8-(5-cyclopentadienyl)naphthalene (9) to 1,8-di(5-cyclopentadienyl)-naphthalene (10). This, in turn, undergoes a single sigmatropic [1.5] hydrogen shift to give 1-(1-cyclopentadienyl)-8-(5-cyclopentadienyl)naphthalene (11), which collapses to the Diels-Alder adduct 3

A new chiral catalyst, based on the alkaloid-derived thiourea and a carboxylic acid, is applied in the reaction of the variety of aromatic, heteroaromatic and aliphatic aldehydes with silyloxy furan (I) and substituted derivatives [cf.

The kinetic products derived from addition of phthalimide, N-methyltoluenesulfonamide, or benzenethiol to homochiral Fp(dioxene)BF 4 salts [Fp=CpFe(CO) 2 ] undergo unimolecular dyotropic rearrangement, resulting in inversion of the two initially formed asymmetric centers

In summary, we have shown that the models used by Reusch and Valenta to predict the regioselectivity of Lewis acid catalyzed Diels-Alder reactions of quinones are too simple to be applied to our case. The nature of the complexes formed in solution is dependent on the substitution of the quinone, the reactivity of the diene, and the nature of the Lewis acid used. Variations of these conditions can lead to a competing acid catalysed dimerization of the quinone

The reaction of cyclopentadienylcopper dimethyl sulfide with 1,8-diiodonaphthalene provides a method for coupling cyclopentadienyl groups to the naphthalene nucleus. The product formed by coupling of two such groups in peri positions on the naphthalene ring is the Diels-Alder adduct 3. Deuterium labeling experiments have been carried out which show that this product is formed through conversion of the initial 1-iodo-8-(5-cyclopentadienyl)naphthalene (9) to 1,8-di(5-cyclopentadienyl)-naphthalene (10). This, in turn, undergoes a single sigmatropic [1.5] hydrogen shift to give 1-(1-cyclopentadienyl)-8-(5-cyclopentadienyl)naphthalene (11), which collapses to the Diels-Alder adduct 3

An asymmetric synthesis of the naturally occurring antipode of the tetrahydrofuran lignan sesaminone ((−)-1) has been achieved. An X-ray crystal structure of the synthetic material validated the structure proposed in the literature for this lignan. Additionally, the absolute configuration of the natural product was established by correlation of the synthetic tetrahydrofuran with the known absolute configuration of l-Phe. The opening of the synthesis was a diastereoselective Evans aldol reaction between N-4-pentenoyloxazolidinone 6 and piperonal. Reduction of the major diastereomer of the aldol product provided enantiomerically pure diol 4. The primary and secondary hydroxyl groups of 4 were protected in tandem to generate silyl ether-MOM ether 9. The vinyl group contained in 9 was then elaborated, via a series of four steps, to aryl ketone 10. This aryl ketone was transformed to a mixture of silyl enol ether stereoisomers (11a,b); TiCl4-mediated activation of the MOM ethers contained in this mixture of en...

Enamides 3a-c and 6 crystallize in α-packing modes with short intermolecular distances of 3.7–4.0 A between alkene carbon atoms of adjacent molecules related by a center of symmetry. Irradiation at 350 nm of these crystalline tertiary phenylethenyl enamides affords head-to-tail dimers 8a-c and 9, respectively, in 87–92% yield, in marked contrast to the E to Z isomerization that is the exclusive reaction upon solution irradiation of enamides 3a and 6.

Tetraene 1 was prepared in nine steps from the known propargylic alcohol 7 in 17% overall yield or as a 2:1 E/Z mixture in only five steps in 7% overall yield. Oxidative cyclization of 1 with 2 equiv of Mn(OAc)3·2H2O and 1 equiv of Cu(OAc)2 in MeOH at 25 °C provided 35% of tetracycle 2. Further elaboration provided (±)-isosteviol (3) in six steps in 51% yield and (±)-beyer-15-ene-3β,19-diol in four steps in 17% yield.

The tricyclic triamine core27 of martinellic acid (2) has been prepared stereospecifically in eight steps from 2-hydroxymethylaniline in 11% overall yield. The key steps are the addition of 2-hydroxymethylaniline to vinylcyclopropane14 to prepare cycloaddition precursor19 in only two steps and an intramolecular [3+2] azomethine ylide cycloaddition reaction to produce tetracycle20 with>9:1 diastereoselectivity. Download : Download full-size image

The first synthesis of (±)-anchinopeptolide D (4) has been accomplished in seven steps in 10% overall yield from octopamine hydrochloride (17), N-(Boc)glycine (16), and 5-amino-2-hydroxypentanoic acid (22). The key step is the aldol dimerization and hemiaminal formation of α-keto amide 26, which gives primarily protected anchinopeptolide D 27 under kinetically controlled conditions. Cycloanchinopeptolide D (31) has been prepared by the unprecedented head-to-head photodimerization of the two hydroxystyrylamides of 4 using the hydrophobic effect in water to force the two side chains into close proximity so that [2 + 2] cycloaddition is faster than trans to cis double bond isomerization. Coupling of amine 21 with pyroglutamic acid affords the naturally occurring tripeptide 35, which had been assigned glutamic acid structure 34.

Syntheses of several Mn complexes supported by a monoanionic amido/bis(phosphino) PNP ligand (PNP = [2-P(CHMe(2))(2)-4-MeC(6)H(3)](2)N) from anhydrous MnCl(2) are reported. Treatment of (PNP)Li (2) with MnCl(2) in tetrahydrofuran (THF) led to isolation of either (PNP)Mn(mu-Cl)(2)Li(THF)(2) (5) or (PNP)MnCl (6), depending on the workup. Reaction of 6 with 2 equiv of MeLi resulted in isolation of (PNP)Mn(mu-Me)(2)Li(THF)(2) (7) that is structurally similar to 5. Reduction of 6 in the presence of pyridine produced material analytically consistent with (PNP)Mn(py)(3) (8), whereas reduction in the presence of 2,2'-bipyridine gave fully characterized (PNP)Mn(bipy) (9). Compounds 5 and 7 display magnetic moments indicative of high-spin Mn(II) (S = 5/2). The magnetic moment of 9 (S = 2) was interpreted as an antiferromagnetic combination of a high-spin Mn(II) center and a singly reduced bipyridine ligand. Addition of a single CO ligand to 9 generated diamagnetic, low-spin (PNP)Mn(bipy)(CO) (10). Solid-state structures of 5, 7, 9, and 10 were determined by X-ray diffraction methods and used in conjunction with density functional theory studies to analyze the electronic nature of the (PNP)Mn complexes under study.

Trialkylsilylium cation equivalents partnered with halogenated carborane anions (such as Et(3)Si[HCB(11)H(5)Cl(6)]) function as efficient and long-lived catalysts for hydrodehalogenation of C-F, C-Cl, and C-Br bonds with trialkylsilanes as stoichiometric reagents. Only C(sp(3))-halogen bonds undergo this reaction. The range of C-F bond-containing substrates that participate in this reaction is quite broad and includes simple alkyl fluorides, benzotrifluorides, and compounds with perfluoroalkyl groups attached to an aliphatic chain. However, CF(4) has proven immune to this reaction. Hydrodechlorination was carried out with a series of alkyl chlorides and benzotrichlorides, and hydrodebromination was studied only with primary alkyl bromide substrates. Competitive experiments established a pronounced kinetic preference of the catalytic system for activation of a carbon-halogen bond of a lighter halide in primary alkyl halides. On the contrary, hydrodechlorination of C(6)F(5)CCl(3) proceeded much faster than hydrodefluorination of C(6)F(5)CF(3) in one-pot experiments. A solid-state structure of Et(3)Si[HCB(11)H(5)Cl(6)] was determined by X-ray diffraction methods.

The three-dimensional structure of a protein is the assembly of different secondary structural elements, such as alpha-helices, beta-pleated sheets, and beta-turns. Although the conformation of hundreds of proteins has been elaborated in the solid state, only a vague understanding of the mechanism of their conformational folding is known. One facet of this topic is the conformational interconversion of one or more beta-turns to a helical structure (and vice versa), which may also be related to the formation of helix-turn-helix motifs often observed in globular proteins. Based on a comprehensive structural analysis of proteins, Sundaralingam and Sekharudu [Sundaralingam, M. & Sekharudu, Y. C. (1989) Science 244, 1333-1337] previously suggested that "structure-water" molecules in proteins may mediate such a conformational change. An x-ray crystal structure determination of t-butoxycarbonyl (Boc)-Val-Ser-NHCH3 reveals (i) an ideal type I beta-turn backbone conformation and (ii) a hydrogen-bond network more typical of an alpha-helix than a beta-turn conformation. The molecular packing of this simple beta-turn model reported here provides a plausible and simple alternative of how a beta-turn-like conformation may serve as a conformational template for helical-structure formation (and vice versa) during the folding procedure.

The molecular structure of a homologous series of palladium(II) porphyrin, chlorin, and isobacteriochlorin complexes were determined by X-ray diffraction. The porphyrin compound (2,3,7,8,12,13,17,18-octaethylporhyrinato)palladium(II), Pd(OEP), crystallizes in the triclinic space group PI (Z=1) with unit cell dimensions a=7.809 (5) A, b=9.934 (4) A, c=10.429 (3) A, α=91.05 (2) o , β=98.07 (4) o , γ=111.05 (4) o , and V=745.4 (5) A 3

White Beam Synchrotron X-ray Topography has been used to characterize defects in solution-grown p-terphenyl single crystals. Defects observed include growth dislocations, mechanically introduced dislocations, macroscopic twins, twin lamellae, and dislocations emitted from twin boundaries. Line direction and Burgers Vector analysis of the growth and mechanically introduced dislocations, using projective geometry calculations and g. b analysis, respectively, are presented, along with complete analysis of the twin operation, obtained from a combination of analysis of optical micrographs and of orientation contrast on synchrotron topographs. The relationship between the Burgers vector of the dislocations generated at the twin boundary and the strain associated with the twins is discussed. Interesting interactions between mechanically introduced dislocations and twin boundaries are presented. Defect analyses are discussed in the context of results obtained previously using transmission electron micros...

Mixing propynoic acid and 4-(l-pyrrolidino)-pyridine in ethanol produces the salt 4-(l-pyrrolidino)-pyridinium propynoate (1) in high yield. An X-ray structure determination of 1 (Space Group P2I , Z=4) shows it to contain two independent cation-anion sets. Each set is interconnected by N-H-0 and C-H-O hydrogen bonds; there are no hydrogen bonds formed between the two sets. Each set contains an infinite array of short acetylene-acetylene contacts (3.57 and 3.74 A, respectively); despite this characteristic, the material does not polymerize upon exposure to 60Co γ-rays. Heating 1 at 125 °C for 23 hours converts it, in high yield, to a 19:1 mixture of (E and Z)-4-(l-pyrrolidino)-pyridinium-l-acrylate. To the best of our knowledge, this is the first example of the addition of a pyridine moiety to an acetylene in the solid state.

Reduction of Zr/Co heterobimetallic complexes ICo(MesNP(i)Pr(2))(3)ZrCl (1) and ICo((i)PrNP(i)Pr(2))(3)ZrCl (2) with excess Na/Hg under N(2), followed by subsequent benzene extraction to remove coordinated Na halide salts, leads to neutral two-electron reduced, dinitrogen-bound complexes (THF)Zr(MesNP(i)Pr(2))(3)Co-N(2) (4) and Zr((i)PrNP(i)Pr(2))(3)Co-N(2) (5). Upon halide loss, a THF solvent molecule coordinates to the axial site of the Zr center in 4, while this axial site remains unoccupied in 5. X-ray crystallography reveals short Co-Zr distances in 4 and 5, indicative of metal-metal multiple bonding, and an unprecedented trigonal monopyramidal geometry about the Zr center in 5. Reduction of 4 under an Ar atmosphere (in the absence of N(2)) results in another unusual structure type: an unoccupied axial Co coordination site and a trigonal monopyramidal Co center in (THF)Zr(MesNP(i)Pr(2))(3)Co (6). X-ray crystallography reveals that, in the absence of coordinated N(2), the Co-Zr bond can attain full triple bond character with a Co-Zr distance of 2.14 A, the shortest M-M distance in an early/late heterobimetallic complex reported to date. To further assess the electronic structure and bonding in 4, 5, and 6, calculations were performed on these molecules using DFT and the results of these theoretical investigations will be discussed.

The syntheses of meridionally ligated tricarbonyl complexes (PNP)Mn(CO)(3) and (PNP)Re(CO)(3) are described (PNP = [2-P(CHMe(2))(2)-4-MeC(6)H(3)](2)N(-)). Cyclic voltammograms show reversible one-electron redox couples for both parent compounds (-0.34 V vs Cp(2)Fe(0/+) for (PNP)Mn(CO)(3), -0.25 V vs Cp(2)Fe(0/+) for (PNP)Re(CO)(3)), and chemical oxidation with AgOTf results in formation of the corresponding paramagnetic triflate salts [(PNP)Mn(CO)(3)]OTf and [(PNP)Re(CO)(3)]OTf. Electron paramagnetic resonance spectra and computational results indicate that this event is primarily ligand centered; allylation of the organic ligand moiety of [(PNP)Mn(CO)(3)]OTf with allyltributylstannane is consistent with this assignment. The oxidation (PNP)Mn(CO)(3) to [(PNP)Mn(CO)(3)]OTf results in a shift in average CO stretching frequency of 30 cm(-1); protonation of (PNP)Mn(CO)(3) with TfOH to form [(PNHP)Mn(CO)(3)]OTf results in a similar magnitude shift.

The main molecule of the title compound, C(37)H(36)·CDCl(3), is a hydro-carbon with two naphthalene segments attached to opposite ends of a rigid norbornylogous spacer with an overall structure that is approximately C-shaped. The dihedral angle between the naphthalene ring planes is 9.27 (7)°. The cleft that exists between the naphthalene rings is large enough that the compound crystallizes with a solvent mol-ecule (CDCl(3)) in the cleft. The CDCl(3) solvent mol-ecule is present in two disordered orientations in a 3:2 ratio, each involving C-D⋯π to C(6) ring centers.

Interaction of the amido/bis(phosphine)-supported (PNP)Ir fragment with a series of linear and cyclic ethers is shown to afford, depending on substrate, products of α,α-dehydrogenation (carbenes), α,β-dehydrogenation (vinyl ethers), or decarbonylation. While carbenes are exclusively obtained from tert-amyl methyl ether, sec-butyl methyl ether (SBME), n-butyl methyl ether (NBME), and tetrahydrofuran (THF), vinyl ethers or their adducts are observed upon reaction with diethyl ether and 1,4-dioxane. Decarbonylation occurs upon interaction of (PNP)Ir with benzyl methyl ether, and a mechanism is proposed for this unusual transformation, which occurs via a series of C−H, C−O, and C−C bond cleavage events. The intermediates characterized for several of these reactions as well as the α,α-dehydrogenation of tert-butyl methyl ether (MTBE) are used to outline a reaction pathway for the generation of PNP-supported iridium(I) carbene complexes, and it is shown that the long-lived, observable intermediates are substrate-dependent and differ for the related cases of MTBE and THF. Taken together, these findings highlight the variety of pathways utilized by the electron-rich, unsaturated (PNP)Ir fragment to stabilize itself by transferring electron density to ethereal substrates through oxidative addition and/or the formation of π-acidic ligands.

Motivated by the Haldane conjecture, the powder susceptibilities of two nickel complexes (1: NiCl2L2, with LP(CH2CH2CN)3; 2: bis(propiolato)tetraaquonickel(II)) have been investigated as part of a search for new S=1 antiferromagnetic linear chains. The effective moments of both complexes correspond to high-spin S=1 Ni(II) ions at room temperature but decrease rapidly below 20 K. Analysis of the data showed the decreases to correspond to the effects of single-ion anisotropy and not magnetic exchange. The susceptibilities of 1 and 2 can be described as resulting from single-ion anisotropy parameters D/k=7 and 8.5 K, respectively, with the ms=0 single state low for both complexes. Neither 1 nor 2 can be considered a magnetic linear chain.

The crystal and molecular structure of a fragment of a face-to-face metallocene polymer, the [2,3]-oligomer( 2a , n = 2) of 1,8-diferrocenylnaphthalene( 1a ), has been determined in order to better define the structural features of the polymer. The molecular structure of this compound shows the same form and magnitude of molecular distortions as those found in the monomeric unit 1a . An unusual feature of the oligomer is the cis arrangement of the two naphthalene nuclei, which brings several of the carbon centers on each naphthalene ring in close proximity. These structural aspects are discussed in the context of possible structures for the related polymer.

These results demonstrate that β-keto sulfoxides and β-keto sulfones can be used as substrates for Mn(III)- and Cu(II)-based oxidative free-radical cyclizations. The sulfoxide chiral center completely controls the stereochemistry of the cyclization so that these reactions can be used for the efficient preparation of optically active bicyclo [3.2.1] octanones. Cyclizations of α-sulfinyl radicals may prove to be a general procedure for controlling absolute stereochemistry in radical cyclizations

Filtered beam synchrotron white radiation topography has been used to investigate the role of defects in the x-ray induced, single crystal to amorphous, solid state polymerization reaction of bis(propiolato)tetraaquozinc(II). Images of growth dislocations, which were well defined prior to reaction, were observed to become more and more diffuse as cumulative x-ray exposure increased. This behavior is consistent with existing models for the nucleation of single crystal to amorphous reactions at dislocations, whereby the stress field of the dislocations is relaxed during reaction.

The reactions of 2-pyrones with electron-deficient dienophiles constitute a synthetically useful class of Diels−Alder reaction. By exploring cinchona alkaloid-derived organic molecules as acid−base bifunctional catalysts, we successfully developed the first highly enantioselective and diastereoselective catalytic Diels−Alder reaction with 2-pyrones. Furthermore, we demonstrated the possibility of using such catalysts to control the endo/exo selectivity in a Diels−Alder reaction.