Synthesis of conformationally constrained diaminodicarboxylic acid derivatives.

Functionally protected forms of three conformationally constrained diaminodicarboxylic acids were synthesized and characterized. 2,2'-Diaminospiro[3.3]heptane-2,2'-dicarboxylic acid, an analogue of diaminopimelic acid, was prepared in racemic form and the structure established by X-ray crystallographic analysis of the methyl ester hydrochloride. trans-1,4-Diaminocyclohexane-1,4-dicarboxylic acid was prepared and its structure established by X-ray crystallographic analysis of the corresponding Cbz-protected ethyl ester. cis- and trans-2,6-diamino-1,2,3,5,6,7-hexahydro-s-indacene-2,6-dicarboxylic acids were synthesized and the structures assigned by X-ray crystallographic analysis of the corresponding Boc-protected ethyl ester and Cbz-protected ethyl ester, respectively.

(S,S)-4''-Cyano-7,7''-dimethoxy-3',6'-dioxodispiro[indane-2,2'-piperazine-5',2''-indane]-4-carboxamide methanol solvate: interrupting the amide-to-amide hydrogen-bonded tape.

The title methanol solvate, C(24)H(22)N(4)O(5).CH(3)OH, forms an extended three-dimensional hydrogen-bonded structure, assisted by the presence of several good donor and acceptor sites. It shows none of the crystal packing features typically expected of piperazinediones, such as amide-to-amide R(2)(2)(8) hydrogen bonding. In this structure the methanol solvent appears to play only a space-filling role; it is not involved in any hydrogen bonding and instead is disordered over several sites. This study reports, to the best of our knowledge, the first crystal structure of an indane-containing piperazinedione compound which exhibits a three-dimensional hydrogen-bonded structure formed by classical (N-H...O and N-H...N) hydrogen-bonding interactions.

Models of the cytochromes: crystal structures and EPR spectral characterization of low-spin bis-imidazole complexes of (OETPP)Fe(III) having intermediate ligand plane dihedral angles.

The preparation, EPR spectra, and crystal structures of octaethyltetraphenylporphyrinatoiron(III) having two imidazole, N-benzylimidazole, and N-methylimidazole axial ligands are reported, [(OETPP)Fe(HIm)2]Cl, [(OETPP)Fe(N-BzIm)2]Cl, and [(OETPP)Fe(N-MeIm)2]Cl. Despite large variation in axial ligand size, the unit cell parameters for all complexes are very similar; each structure has the same basic motif, with large voids formed by the extended porphyrin framework (filled by ordered or disordered axial ligands and disordered solvent), which allows differently sized ligands to fit within the same cell dimensions. Each porphyrin core adopts a saddled conformation with absolute value(deltaC(beta)) = 1.13-1.15 A. The dihedral angles between axial ligand planes, delta phi, are far from being either ideal parallel or perpendicular: 30.1 degrees, 57.2 degrees for [(OETPP)Fe(HIm)2]Cl (molecules 1 and 2), 56.8 degrees for [(OETPP)Fe(N-BzIm)(2)]Cl, and 16.0 degrees, 44.6 degrees, 59.6 degrees, and 88.1 degrees for [(OETPP)Fe(N-MeIm)2]Cl, which has disordered axial ligands. Among the complexes of this study, an axial ligand delta phi of 56.8 degrees is found to be the largest "parallel" angle (as defined by the observation of a normal rhombic or Type II EPR signal (N-BzIm, g = 3.08, 2.19, 1.31)), while 57.2 degrees is found to be the smallest "perpendicular" delta phi (as defined by the observation of a "large gmax" or Type I EPR signal (HIm, gmax = 3.24)). From the results of this study, it is clear that the size of the largest g for Types I and II complexes varies continuously, with no break between the two. While the switch in EPR signal type, from Type II to Type I, appears to be very sharp in this study, this may be somewhat artificial based upon limited numbers of examples and the required saddle distortion of the (OETPP)Fe(III) complexes. However, in comparison to several proteins with dihedral angles near 60 degrees and Type II EPR spectra, we may conclude that the switch in EPR signal type occurs near 57 degrees +/- 3-5 degrees.

(1R,2S)-Benzyl N-[3-(diisopropylaminocarbonyl)-2-phenylprop-3-enyl]carbamate.

The title compound, C(25)H(32)N(2)O(3), was synthesized as part of a series of related compounds using a modified Eschenmoser-Claisen rearrangement reaction. The compound is racemic and the structure features a centrosymmetric hydrogen-bonded dimerization along with some aromatic stacking stabilization.

4-{N-[2-(1,3-Dioxo-1,3-dihydroisoindol-2-yl)-3-phenylpropionyl]anilino}-1-phenethylpiperidinium chloride methanol disolvate.

The structure of the title compound, a fentanyl derivative with formula C(36)H(36)N(3)O(3) (+)·Cl(-)·2CH(3)OH, crystallizes as a racemic mixture. The organic cation has an extended conformation and the structure displays O-H⋯O, O-H⋯Cl and N-H⋯Cl hydrogen bonding.

[N-({(R)-2-[(N-Benzylprolyl)amino]phenyl}-phenylmethylene)-2(S)-(pent-4-enyl)-glycinato]nickel(II).

The title compound, [Ni(C(32)H(33)N(3)O(3))], crystallized as a minor product during the purification of its 2(R)-pent-4-enyl diastereomer. Mixtures of the title compound and its enantiomer self-resolve.

Synthesis of 1,10-dimethylbicyclo[8.8.8]hexacosane and 1,10-dihydroxybicyclo[8.8.8]hexacosane.

[structure: see text] 1,10-Dimethylbicyclo[8.8.8]hexacosane (1) and 1,10-dihydroxybicyclo[8.8.8]hexacosane (2) were prepared in 4% yield over seven steps and in 18% yield over three steps, respectively, starting from 1,10-cyclooctadecanedione. The identities and out,out conformations of these compounds were established by single-crystal X-ray analysis.

"Matched/mismatched" diastereomeric dirhodium(II) carboxamidate catalyst pairs. Structure-selectivity correlations in diazo decomposition and hetero-Diels-Alder reactions.

Homo-ligated dirhodium(II) carboxamidates provide well-defined structural frameworks with which to investigate catalyst-controlled multiple asymmetric induction ("match/mismatch" effects). Diastereomeric pairs of methyl 2-oxoimidazolidine-4(S)-carboxylate ligands containing 2-phenylcyclopropane (4S,2'S,3'S-HMCPIM and 4S,2'R,3'R-HMCPIM) and N-benzenesulfonylproline (4S,2'S-HBSPIM and 4S,2'R-HBSPIM) attachments at the 1-N-acyl site have been prepared; the resulting (cis-2,2)-Rh(2)L(4) compounds have been produced in good yields, and the X-ray crystal structure of each dirhodium(II) compound has been obtained. The incorporation of additional stereocenters into the dirhodium(II) ligands leads to recognizable levels of double asymmetric induction for C-H insertion, cyclopropanation, and hetero-Diels-Alder cycloaddition applications. The configurationally "matched" cases provide modest increases in enantioselectivity for intramolecular C-H insertion reactions relative to the model catalyst Rh(2)(MPPIM)(4), but applications of the configurationally mismatched catalysts result in significant lowering of enantioselectivity. The Rh(2)(BSPIM)(4) catalysts show the highest degree of differential selectivity. Hetero-Diels-Alder reactions show inverse behavior from the configurationally matched and mismatched Rh(2)L(4) catalysts to that found in the metal carbene transformations.

Determination of the g-tensors and their orientations for cis,trans-(L-N2S2)Mo(V)OX (X = Cl, SCH2Ph) by single-crystal EPR spectroscopy and molecular orbital calculations.

A single-crystal study of cis,trans-(L-N2S2)MoVOCl (1) doped into cis,trans-(N2S2)MoVIO2 (3) has enabled the g-tensor of 1 and its orientation with respect to the molecular structure to be determined. The EPR parameters (g1, 2.004; g2, 1.960; g3, 1.946; A1, 71.7 x 10(-4) cm(-1); A2, 11.7 x 10(-4) cm(-1); A3, 32.0 x 10(-4) cm(-1)) of cis,trans-(L-N2S2)MoVOCl [L-N2S2H2 = N,N'-dimethyl-N,N'-bis(mercaptophenyl)ethylenediamine] mimic those of the low-pH form of sulfite oxidase and the "very rapid" species of xanthine oxidase. The principal axis that corresponds to g1 is rotated approximately 10 degrees from the Mo[triple bond]O vector, while the principal axis that corresponds to g3 is located in the equatorial plane and approximately 38 degrees from the Mo-Cl vector. Independent theoretical calculations of the g-tensor of 1 were performed using two types of techniques: (1) the spectroscopically parametrized intermediate neglect of differential overlap technique (INDO/S) combined with single-excitation configuration interaction (CIS); (2) a scalar relativistic DFT (BP86 and B3LYP functionals) treatment using the zeroth order regular approximation to relativistic effects (ZORA) in combination with recently developed accurate multicenter mean field spin-orbit operators (RI-SOMF) and the estimation of solvent effects using dielectric continuum theory at the conductor-like screening model (COSMO) level. The excellent agreement between experiment and theory, as well as the high consistency between the INDO/S and BP86/ZORA results, provides a sound basis for analysis of the calculated orientation of the g-tensor for cis,trans-(L-N2S2)MoVO(SCH2Ph) (2), for which single-crystal EPR data are not available but which contains three equatorial sulfur donor atoms, as occurs in sulfite oxidase and xanthine oxidase. The implications of these results for the EPR spectra of the Mo(V) centers of enzymes are discussed.

(4R,4aR,6S,7S,7aS)-6-Hydroxy-7-hydroxymethyl-4-methylperhydrocyclopenta[c]pyran-1-one chloroform solvate from Valeriana laxiflora.

The structure of an iridolactone isolated from Valeriana laxiflora was established as (4R,4aR,6S,7S,7aS)-6-hydroxy-7-hydroxymethyl-4-methylperhydrocyclopenta[c]pyran-1-one chloroform solvate, C(10)H(16)O(4).CHCl(3). The two rings are cis-fused. The delta-lactone ring adopts a slightly twisted half-chair conformation with approximate planarity of the lactone group and the cyclopentane ring adopts an envelope conformation. The hydroxy group, the hydroxymethyl group and the methyl group all have beta orientations. The absolute configuration was determined using anomalous dispersion data enhanced by the adventitious inclusion of a chloroform solvent molecule. Hydrogen bonding, crystal packing and ring conformations are discussed in detail.

LB films of rodlike phthalocyanine aggregates: specular X-ray reflectivity studies of the effect of interface modification on coherence and microstructure.

We present here X-ray specular reflectivity (XRR) characterization of the ordering of Langmuir-Blodgett films of the liquid crystalline phthalocyanine (Pc) 2,3,9,10,16,17,23,34-octakis(2-benzyloxyethoxy)copper(II) phthalocyanine, 1, on Si(100) wafers with a native oxide layer and these same substrates modified with monolayers of varying percentages of methyl- and phenyl-terminated silanes. The central copper atom in these Pc's provides for high contrast in X-ray reflectivity for single-bilayer films of 1. The XRR data are modeled as arising from multiple layers of organic material, above and below the rows of copper atoms in the aligned Pc cores; variations in the total thickness of these films, and the spacing between the rows of copper atoms, are attributed to changes in the interaction with the substrate, and changes in the Pc orientation and side chain packing. The most pronounced effect on these parameters comes from variations in the ratio of the phenyl-silane versus methyl-silane content of the substrate modifiers and annealing of these films past their crystalline (K) --> liquid crystalline (LC) mesophase transition temperature. Transfer of multiple bilayers of this Pc leads to additional changes in the thickness of each layer, eventually forming a hexagonal close-packed array, reminiscent of bulk fibers of this material, as revealed by X-ray diffraction (XRD).

Low-spin ferriheme models of the cytochromes: correlation of molecular structure with EPR spectral type.

The preparation and characterization of the following bis-imidazole and bis-pyridine complexes of octamethyltetraphenylporphyrinatoiron(III), Fe(III)OMTPP, octaethyltetraphenylporphyrinatoiron(III), Fe(III)OETPP, and tetra-beta,beta'-tetramethylenetetraphenylporphyrinatoiron(III), Fe(III)TC(6)TPP, are reported: paral-[FeOMTPP(1-MeIm)(2)]Cl, perp-[FeOMTPP(1-MeIm)(2)]Cl, [FeOETPP(1-MeIm)(2)]Cl, [FeTC(6)TPP(1-MeIm)(2)]Cl, [FeOMTPP(4-Me(2)NPy)(2)]Cl, and [FeOMTPP(2-MeHIm)(2)]Cl. Crystal structure analysis shows that paral-[FeOMTPP(1-MeIm)(2)]Cl has its axial ligands in close to parallel orientation (the actual dihedral angle between the planes of the imidazole ligands is 19.5 degrees ), while perp-[FeOMTPP(1-MeIm)(2)]Cl has the axial imidazole ligand planes oriented at 90 degrees to each other and 29 degrees away from the closest N(P)-Fe-N(P) axis. [FeOETPP(1-MeIm)(2)]Cl has its axial ligands close to perpendicular orientation (the actual dihedral angle between the planes of the imidazole ligands is 73.1 degrees ). In all three cases the porphyrin core adopts relatively purely saddled geometry. The [FeTC(6)TPP(1-MeIm)(2)]Cl complex is the most planar and has the highest contribution of a ruffled component in the overall saddled structure compared to all other complexes in this study. The estimated numerical contribution of saddled and ruffled components is 0.68:0.32, respectively. Axial ligand planes are perpendicular to each other and 15.3 degrees away from the closest N(P)-Fe-N(P) axis. The Fe-N(P) bond is the longest in the series of octaalkyltetraphenylporphyrinatoiron(III) complexes due to [FeTC(6)TPP(1-MeIm)(2)]Cl having the least distorted porphyrin core. In addition to these three complexes, two crystalline forms each of [FeOMTPP(4-Me(2)NPy)(2)]Cl and [FeOMTPP(2-MeHIm)(2)]Cl were obtained. In all four of these cases the axial planes are in nearly perpendicular planes in spite of quite different geometries of the porphyrin cores (from purely saddled to saddled with 30% ruffling). The EPR spectral type correlates with the geometry of the OMTPP, OETPP and TC(6)TPP complexes. For the paral-[FeOMTPP(1-MeIm)(2)]Cl, a rhombic signal with g(1) = 1.54, g(2) = 2.51, and g(3) = 2.71 is consistent with nearly parallel axial ligand orientation. For all other complexes of this study, "large g(max)" signals are observed (g(max) = 3.61 - 3.27), as are observed for nearly perpendicular ligand plane arrangement. On the basis of this and previous work, the change from "large g(max)" to normal rhombic EPR signal occurs between axial ligand plane dihedral angles of 70 degrees and 30 degrees.

Crystal engineering of a liquid crystalline piperazinedione.

[structure: see text] A molecule designed to self-assemble via hydrogen bonding, arene-arene, and van der Waals interactions and expected to possess thermotropic liquid crystalline properties has been synthesized and characterized. Results support the validity of an assembly paradigm based on incorporation of chemically orthogonal and spatially independent recognition elements in the molecular building blocks.

Hydrogen-bonded extended arrays of the [Re6(mu3-Se)8]2+ core-containing clusters.

Site-differentiated solvated clusters of the general formula [Re(6)(mu(3)-Se)(8)(PEt(3))(n)(MeCN)(6)(-)(n)](SbF(6))(2) (n = 4, cis and trans; n = 5) undergo ligand substitution reaction with isonicotinamide to afford the corresponding amide derivatives, [Re(6)(mu(3)-Se)(8)(PEt(3))(n)(isonicotinamide)(6)(-)(n)](2+) [1 (n = 5); 2 (n = 4, trans); 3 (n = 4, cis)]. Retention of stereochemistry in each case was confirmed by (1)H and (31)P NMR. The solid-state structures of all three compounds were established crystallographically, which revealed self-complementary hydrogen-bonding interactions between adjacent cluster units. While complex 1 exists as hydrogen-bonded dimers in the solid state, compounds 2 and 3 form one-dimensional chains of clusters bridged by paired hydrogen bonds. It is the rigid stereochemistry of the cluster, combined with the classic crystal engineering motif of complementary N-H.O amide hydrogen bonding, that affords the predictable solid-state structures and dimensionality.

Asymmetric halo aldol reaction (AHA).

[reaction: see text] The asymmetric halo aldol reaction (AHA) using Evans oxazolidinones as chiral auxiliaries has been established for tandem I-C/C-C bond formations. The new asymmetric reaction provides a practical approach to a variety of halo aldols of a non-Evans type that cannot be easily synthesized by other methods. Excellent diastereoselectivity (>95%) and yields (80-93%) have been obtained for eight examples.

New oxovanadium bis(1,2-dithiolate) compounds that mimic the hydrogen-bonding interactions at the active sites of mononuclear molybdenum enzymes.

Reaction of VO(acac)(2) with 1,2-dithiols in the presence of triethylamine gives pentacoordinate oxovanadium complexes [HNEt(3)](2)[VO(bdt)(2)] (1), [HNEt(3)](2)[VO(tdt)(2)] (2), and [HNEt(3)](2)[VO(bdtCl(2))(2)] (3) (where H(2)bdt = 1,2-benzenedithiol, H(2)tdt = 3,4-toluenedithiol, and H(2)bdtCl(2) = 3,6-dichloro-1,2-benzenedithiol). Compounds 1-3 have been characterized by IR, UV/visible, EPR, and mass spectroscopies. The X-ray crystal stuctures of 1 and 2 show hydrogen-bonding interactions between the terminal oxo atom and triethylammonium counterions and between ligand sulfur atoms and the counterions. These interactions are comparable with those found at the active sites of mononuclear molybdenum enzymes.

Novel concentration-driven structural interconversion in shape-specific solids supported by the octahedral [Re(6)(mu3-Se)8]2+ cluster core.

A complex containing the face-capped octahedral [Re(6)(mu(3)-Se)(8)](2+) cluster core, cis-[Re(6)(mu(3)-Se)(8)(PPh(3))(4)(4,4'-dipyridyl)(2)](SbF(6))(2) (1), is used as a ditopic ligand with an enforced right angle between the two 4,4'-dipyridyl moieties for the coordination of Cd(2+) ion. Two coordination polymers, [[Re(6)(mu(3)-Se)(8)(PPh(3))(4)(4,4'-dipyridyl)(2)](2)[Cd(NO(3))(2)]](SbF(6))(4).21C(4)H(10)O.21CH(2)Cl(2) (2) and [[Re(6)(mu(3)-Se)(8)(PPh(3))(4)(4,4'-dipyridyl)(2)][Cd(NO(3))(3)]](NO(3)).2C(4)H(10)O.CH(2)Cl(2) (3), are obtained. The relative concentration of Cd(2+) determines which species is isolated, and the conversion of the first structure into the second is demonstrated experimentally.

Built to order: molecular tinkertoys from the [Re(6)(mu(3)-Se)(8)](2+) clusters.

Ligand substitution of [Re(6)(mu(3)-Se)(8)(PEt(3))(5)(CH(3)CN)](SbF(6))(2) (1) with pyridyl-based ligands, 2,4,6-tri-4-pyridyl-1,3,5-triazine (L1) and 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (L2), produced respectively the star-shaped tricluster (T1) and tetracluster (T2) arrays, wherein three (T1) and four (T2) units of the [Re(6)(mu(3)-Se)(8)](2+) core-containing clusters are interconnected by the corresponding bridging ligands. These novel supramolecular assemblies were characterized by a combination of NMR ((1)H and (31)P) spectroscopy, ESI-MS, and microanalysis. The molecular and solid-state structures of T1 have also been established by single-crystal X-ray diffraction.

A triboluminescent europium(III) complex.

The crystal structure of (4,4'-dimethyl-2,2'-bipyridyl)tris[3,3,3-trifluoro-1-(2-thenoyl)propan-2-onato]europium(III), or more commonly (4,4'-dimethyl-2,2'-bipyridyl)tris(2-thenoyltrifluoroacetonato)europium(III), [Eu(C8H4F3O2S)3(C12H12N2)], has been determined. Crystals of the complex emit vivid red light when scratched or fractured. This triboluminescent activity seems to correlate with the non-centrosymmetric crystal structure and disorder of the thienyl rings and CF3 groups which is present here and in similar compounds. While modeling the thienyl-ring disorder, it was noted that the bond angle at the C atom replaced by S is a sensitive sign of even small rotational ring disorder. The coordination geometry of the Eu(III) ion can be described as square antiprismatic, with coordination by the six O atoms of the three chelating beta-diketonate ligands and the two N atoms of the neutral bipyridyl ligand.

Halide-templated assembly of polynuclear lanthanide-hydroxo complexes.

A series of pentadecanuclear lanthanide-hydroxo complexes possessing a common core of the formula [Ln(15)(mu(3)-OH)(20)(mu(5)-X)](24+)(1, Ln = Eu, X = Cl(-); 2, Ln = Nd, X = Cl(-); 3, Ln = Gd, X = Cl(-); 4, Ln = Pr, X = Br(-); 5, Ln = Eu, X = Br(-)) were prepared by L-tyrosine-controlled hydrolysis of corresponding lanthanide perchlorates in the presence of added Cl(-) or Br(-). The cationic cluster core comprises five vertex-sharing cubane-like [Ln(4)(mu(3)-OH)(4)](8+) units centered on the halide template. In the case of templating I(-), dodecanuclear complexes were isolated instead. The core component, [Ln(12)(mu(3)-OH)(16)(I)(2)](18+) (6, Ln = Dy; 7, Ln = Er), consists of four vertex-sharing cubane-like [Ln(4)(mu(3)-OH)(4)](8+) units and exists as a square-shaped cyclic structure with one I(-) located on each side of the square plane. An analogous hydrolytic reaction involving Er(NO(3))(3), L-tyrosine, and NaOH affords the known hexanuclear complex [Er(6)(mu(6)-O)(mu(3)-OH)(8)(NO(3))(6)(H(2)O)(12)](NO(3))(2) whose core component is a face-capped octahedral [Er(6)(mu(6)-O)(mu(3)-OH)(8)](8+) cluster with an interstitial mu(6)-oxo group (Wang, R.; Carducci, M. D.; Zheng, Z. Inorg. Chem. 2000, 39, 1836-1837.). The efficient self-assembly of halide-encapsulating multicubane complexes (1-7) and the inability to produce an analogous nitrate-containing complex demonstrate the superior templating roles played by the halide ion(s). Further credence for the halide template effects was provided by the isolation of the cationic pentadecanuclear complex 3 as the sole product when tyrosine-supported hydrolysis of Gd(NO(3))(3) was carried out in the presence of competitive Cl(-). Magnetic moments of complexes 1-7 measured at room temperature by using Evans' method are in excellent agreement with those calculated by the Van Vleck equation, assuming magnetically noninteractive lanthanide ions.