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A method has been developed to extract evolved guest molecules from a TGA exhaust stream using solid phase microextraction fibers (SPME). The study was conducted using a known hydrogen bonded framework consisting of Zn(HPDCA)2·(H2O)2 and o-tolidene which has been shown to contain guest molecules. These guests co-crystallize inside the 1-D channels formed during the self-assembly of the hydrogen bonded framework. Single guest as well as mixed-guest-containing host frameworks have been analysed using this method. Guest molecules extracted in this fashion were successfully characterized using gas chromatography and mass spectrometry without the necessity of coupled TGA/GCMS.

Zinc(II) coordination complexes, each having two linearly oriented peripheral carboxylate units, combine with 3,3′-dimethylbenzidene pillars to create channeled structures that host small organic guests. The porous solids reported here are connected solely via strong, charge-assisted hydrogen bonds and contain guests that vary in size, shape, and degree of hydrophobicity. The hydrogen-bonded framework is maintained upon guest loss, under vacuum and up to ∼200 °C. The strength and flexibility of these frameworks make them ideal candidates for molecular storage, separations, guest exchange, and guest transport.

The syntheses and crystal structures of lamellar solids constructed from 3,5-pyrazole dicarboxylic acid and amines are described. While in the past this combination has resulted in one, recurring layer motif, we report here that sterically demanding groups impose different hydrogen-bonding connectivity.

The reaction of (Ph3P)3RuCl2 with 1,1-diphenyl-2-propyn-1-ol was investigated in various solvents. The reaction in thf under reflux is reported to produce the (PPh3)2Cl2Ru(3-phenylindenylidene) complex (3) which has undergone rearrangement of the allenylidene C3-spine. We have improved the reliability of the reported synthesis by adding acetyl chloride which converts the formed water of the reaction and thus increases the acidity of the reaction solution. Without the additive, we observed the exclusive formation of an intermediate of the transformation and identified it as dinuclear (PPh3)2ClRu(μ-Cl)3(PPh3)2Ru C C CPh2 complex (5). The reaction of (Ph3P)3−4RuCl2 with 1,1-diphenyl-2-propyn-1-ol in CH2Cl2 or C2H4Cl2 under reflux in the presence of excess conc. aqueous HCl afforded the new, neutral (PPh3)2Cl3Ru C–CH CPh2 carbyne complex (7), an HCl adduct of previously elusive (PPh3)2Cl2Ru C C CPh2 complex 6 in high yields. In contrast to the formation of complex 3, the reaction in a non-coordinating solvent did not afford the rearrangement of the allenylidene C3-spine. Complex 7 was converted into complex 3 in thf under reflux under loss of a molecule HCl. Complex 7 was converted with triethylamine under loss of HCl to complex 6. Pentacoordinate complex 6 was crystallized in the presence of O-donor ligands (EtOH, MeOH and H2O) to give hexacoordinate (PPh3)2Cl2(ROH)Ru C C CPh2 (R = H, CH3, C2H5) complexes (9)–(11) with the O-donor coordinating in trans-position to the allenylidene moiety. The reaction of complex 7 with 2 equiv. of 4-(N,N-dimethylamino)pyridine (DMAP) gave hexacoordinate (PPh3)2Cl2(DMAP)Ru C C CPh2complex (12) with one molecule DMAP also coordinating in trans-position to the allenylidene group. Methanol and acetic acid in the absence of strong bases afforded the Fischer-carbene complexes (PPh3)2Cl2Ru C(OCH3)–CH CPh2 (14) and (PPh3)2Cl2Ru C(OAc)–CH CPh2 (15) where the nucleophile added to the α-carbon atom. The structures of complexes 5, 7, 9–11, 14, and 15 were solved via X-ray crystallography.

The syntheses of four supramolecular reagents (SRs) based on (N-pyridylmethylene)aminobenzamides are reported. The crystal structure of 4′-(N-4-pyridylmethylene) aminobenzamide is dominated by an amide-py N–H…N hydrogen bond and an amide–carbonyl N–H…O hydrogen bond. The crystal structure of 4′-(N-3-pyridylmethylene)aminobenzamide contains the same N–H…N interaction but this time it is accompanied by an amide-imine N–H…N hydrogen bond. Finally, the crystal structure of 3′-(N-3-pyridylmethylene) aminobenzamide contains a well-known amide-amide ribbon constructed from two inequivalent N–H…O hydrogen bonds. The hydrogen-bond interactions in these three similar compounds are very different which indicates a structural flexibility that may be beneficial for successful co-crystallization reactions.

The di-mixed-valence complex [{(eta(5)-C5H5)Fe(eta(5)-C5H4)}4(eta(4)-C4)Co(eta(5)-C5H5)]2+, 1(2+), has been evaluated as a molecular four-dot cell for the quantum cellular automata paradigm for electronic devices. The cations 1(1+) and 1(2+) are prepared in good yield by selective chemical oxidation of 1(0) and are isolated as pure crystalline materials. The solid-state structures of 1(0) and 1(1+) and the midrange- and near-IR spectra of 1(0), 1(1+), 1(2+), and 1(3+) have been determined. Further, the variable-temperature EPR spectra of 1(1+) and 1(2+), magnetic susceptibility of 1(1+) and 1(2+), Mössbauer spectra of 1(0), 1(1+), and 1(2+), NMR spectra of 1(0), and paramagnetic NMR spectra of 1(1+) and 1(2+) have been measured. The X-ray structure determination reveals four ferrocene "dots" arranged in a square by C-C bonds to the corners of a cyclobutadiene linker. The four ferrocene units project from alternating sides of the cyclobutadiene ring and are twisted to minimize steric interactions both with the Co(eta(5)-C5H5) fragment and with each other. In the solid state 1(2+) is a valence-trapped Robin and Day class II compound on the 10(-12) s infrared time scale, the fastest technique used herein, and unambiguous evidence for two Fe(II) and two Fe(III) sites is observed in both the infrared and Mössbauer spectra. Both EPR and magnetic susceptibility measurements show no measurable spin-spin interaction in the solid state. In solution, the NMR spectra show that free rotation around the C-C bonds connecting the ferrocene units to the cyclobutadiene ring becomes increasingly hindered with decreasing temperature, leading to spectra at the lowest temperature that are consistent with the solid-state structure. Localization of the charges in the cations, which is observed in the paramagnetic NMR spectra as a function of temperature, correlates with the fluxional behavior. Hence, the alignment between the pi systems of the central linker and the ferrocene moieties most likely controls the rate of electron exchange between the dots.

The synthesis of two transition-metal-containing dicarboxylic acids, and their use as starting materials in the supramolecular synthesis of eight different lamellar solids is reported. Ni(II) and Co(II) salts are reacted with 2,4-pyridinedicarboxylic acid (2,4-H2PDCA), in water solution to create the dicarboxylic acid starting materials, which are then allowed to react with a variety of primary amines. A comparison of four resulting crystal structures indicates that the compounds are architecturally consistent; in each case virtually identical layers are separated by a hydrophobic interlayer the nature of which depends on the nature of the organic amine used in the reaction. An analogy is made between lamellar solids created by organic supramolecular reactions (in which dicarboxylic acids and amines are the starting materials) and the reported inorganic−organic hybrid materials (where the dicarboxylic acid is a coordination compound).

The title compound has been prepared through reaction of the corresponding arylimino-triphenylphosphorane with [(n-C4H9)4N]2[Mo6O19] in hot pyridine solution. The single crystal X-ray structure of the title compound has been determined. To cite this article: H. Kwen et al., C. R. Chimie 8 (2005).

The reaction of nido-1,2-(η5-C5Me5Ru)2(μ-H)2B3H7 (1) with the dichloroborane BHCl2·SMe2 results in the formation of three sets of B−Cl inserted metallaborane products: nido-1,2-(η5-C5Me5Ru)2(μ-H)B...

The reaction of [Cp*IrB 4 H 1 0 ] (1) with [{η 6 -(C 6 H 4 )(CH 3 ) 2 }Mo(CO) 3 ] in tetrahydrofuran (THF) leads to [Cp*Ir(CO) 3 (THF)MoB 4 H 8 ] (2), which was characterized by NMR spectroscopy. Intermediate 2 subsequently decomposes to give the tetracarbonyl analogue [Cp*Ir-(CO) 4 MoB 4 H 8 ] (3). In the presence of free CO, the same reaction constitutes a high-yield synthesis of 3. The treatment of 2 (formed in situ) with different Lewis bases led to the replacement of the THF ligand at the molybdenum center and generation of [Cp*Ir(CO) 3 -(L)MoB 4 H 8 ] (L = PPh 3 (4), NCPh (5), CNBu (6), NH 3 (7)). Reaction of the benzonitrile derivative 5 with PPh 3 =CHCO 2 Me afforded the ylide compound [Cp*Ir(CO) 3 (PPh 3 =CHCO 2 -Me)MoB 4 H 8 ] (8). All compounds have been spectroscopically characterized, and 3 and 5-7 have been structurally characterized in the solid state. This work demonstrates that, similarly to metal clusters, metallaboranes with labile metal ligands can serve as versatile synthons.

A ditopic receptor is shown to have an impressive ability to recognize and extract the ion pairs of various alkali halides into organic solution. X-ray diffraction analysis indicates that the salts are bound in the solid state as contact ion pairs. Transport experiments, using a supported liquid membrane and high salt concentration in the source phase, show that the ditopic receptor can transport alkali halide salts up to 10-fold faster than a monotopic cation or anion receptor and 2-fold faster than a binary mixture of cation and anion receptors. All transport systems exhibit the same qualitative order of ion selectivity; that is, for a constant anion, the cation selectivity order is K + > Na + > Li + , and for a constant cation, the anion transport selectivity order is I > Br - > Cl - . The data suggest that with a ditopic receptor, the polarity of the receptor-salt complex can be lowered if the salt is bound as an associated ion pair, which leads to a faster diffusion through the membrane and a higher maximal flux.

Reaction in air of iron(III) salts with tripodal ligands formed from the condensation of tris-(2-aminoethyl)amine (tren) with three equivalents of 2-pyridinecarboxaldehyde (py) or 1-methyl-2-imidazolecarboxaldehyde (NCH3Im) yielded exclusively the iron(II) complexes, [Fetren(py)3]X2 (X=ClO4 − or PF6 −) or [Fetren(NCH3Im)3](ClO4)2. The complexes were characterized by EA, IR, UV, Mossbauer, and mass spectroscopy. The structure of [Fetren(py)3](ClO4)2 was determined at 100 and 290 K. The structures are essentially the same and feature an octahedral iron with facial coordination of pyridine and imine nitrogen atoms with average bond distances of 1.9747 and 1.9523 A, respectively, at 290 K. The short Fe–N bond distances and lack of variation with temperature support a low spin, 1A, assignment for the iron atom. The center nitrogen atom of the tren is essentially planar and is outside of bonding interaction with the iron, 3.45 A. The low spin assignment is supported by Mossbauer spectroscopy, which reveals the presence of two low spin forms that are not in thermal equilibrium. In contrast, the Mossbauer spectrum of [Fetren(NCH3Im)3](ClO4)2 reveals the presence of both high spin, 5T, and low spin, 1A, forms at room temperature, which on cooling to 77 K simplify to the low spin form.

The treatment of [Cp*IrB4H10] (1) and [Cp*IrB3H9] (2) with typical Lewis bases afforded the new substituted iridatetra- and iridatriboranes [Cp*IrB3H7L] (L = PMe3 (3), PMe2Ph (5), PMePh2 (7), PPh3 (10), py (12), NEt3 (14)) and [Cp*IrB2H6L] (L = PMe3 (4), PMe2Ph (6), PMePh2 (8), PPh3 (11), py (13), NEt3 (15)), respectively, plus the adduct BH3L as coproduct. With PPh3, py, and NEt3, the formation of the iridapentaborane [1-Cp*-nido-1-IrB4H8] (9) was also observed. The molecular structure of [Cp*IrB2H6L] was confirmed by X-ray diffraction analysis on compounds 4, 8, and 13. The substituted iridatetraboranes were found to decompose in solution and in the solid state with decomposition pathways that depend on the nature of the L−B bond and the concentration of the free Lewis bases. Two routes involving the apparent disproportionation of iridaborane−base adducts were found to compete with the loss of a {BH} unit. A reaction cycle driven by the Lewis acid/base chemistry of BH3 was constructed from these reactio...

Reaction of iron salts with three tripodal imidazole ligands, H(3)(1), H(3)(2), H(3)(3), formed from the condensation of tris(2-aminoethyl)amine (tren) with 3 equiv of an imidazole carboxaldehyde yielded eight new cationic iron(III) and iron(II), [FeH(3)L](3+or2+), and neutral iron(III), FeL, complexes. All complexes were characterized by EA(CHN), IR, UV, Mössbauer, mass spectral techniques and cyclic voltammetry. Structures of three of the complexes, Fe(2).3H(2)O (C(18)H(27)FeN(10)O(3), a = b = c = 20.2707(5), cubic, I3d, Z = 16), Fe(3).4.5H(2)O (C(18)H(30)FeN(10)O(4.5), a = 20.9986(10), b = 11.7098(5), c = 19.9405(9), beta = 109.141(1), monoclinic, P2(1)/c), Z = 8), and [FeH(3)(3)](ClO(4))(2).H(2)O (C(18)H(26)Cl(2)FeN(10)O(9), a = 9.4848(4), b = 23.2354(9), c = 12.2048(5), beta = 111.147(1) degrees, monoclinic, P2(1)/n, Z = 4) were determined at 100 K. The structures are similar to one another and feature an octahedral iron with facial coordination of imidazoles and imine nitrogen atoms. The iron(III) complexes of the deprotonated ligands, Fe(1), Fe(2), and Fe(3), are low-spin while the protonated iron(III) cationic complexes, [FeH(3)(1)](ClO(4))(3) and [FeH(3)(2)](ClO(4))(3), are high-spin and spin-crossover, respectively. The iron(II) cationic complexes, [FeH(3)(1)]S(4)O(6), [FeH(3)(2)](ClO(4))(2), [FeH(3)(3)](ClO(4))(2), and [FeH(3)(3)][B(C(6)H(5))(4)](2) exhibit spin-crossover behavior. Cyclic voltammetric measurements on the series of complexes show that complete deprotonation of the ligands produces a negative shift in the Fe(III)/Fe(II) reduction potential of 981 mV on average. Deprotonation in air of either cationic iron(II) or iron(III) complexes, [FeH(3)L](3+or2+), yields the neutral iron(III) complex, FeL. The process is reversible for Fe(3), where protonation of Fe(3) yields [FeH(3)(3)](2+).

Reaction of nido-1,2-(Cp*RuH)2B3H7, 1, and methyl acetylene monocarboxylate under kinetic control generates nido-1,2-(Cp*Ru)2(mu-C[[CO2Me]Me])B3H7 (a pair of geometric isomers, 3 and 5) and nido-1,2-(Cp*Ru)2(1,3-mu-C[[CH2CO2Me]H])B3H7, 4, which display the first examples of exo-cluster mu-alkylidene Ru-B bridges generated by hydrometalation of an alkyne on the cluster framework. Both 3 and 5, but not 4, rearrange into arachno-2,8-mu(C)-5-eta1(O)-Me[CO2Me]C-1,2-(Cp*Ru)2B3H7, 2, in which an unprecedented intramolecular coordination of the carbonyl oxygen atom of the alkyne substituent to a boron framework site opens the ruthenaborane skeleton. Compound 2, in turn, is an intermediate in the formation of the ruthenacarborane nido-1,2-(Cp*Ru)2-3-OH-4-OMe-5-Me-4,5-C2B2H5, 12, in which the carbonyl-oxygen double bond has been cleaved as its oxygen atom inserts into a B-H bond and the carbonyl carbon inserts into the metallaborane framework. In a parallel reaction pathway, nido-1,2-(Cp*Ru)2-5-CO2Me-4,5-C2B2H7, 6, nido-1,2-(Cp*Ru)2-4-B(OH)2-5-CO2Me-4,5-C2B2H6, 16, and nido-1,2-(Cp*Ru)2(mu-H)(mu-BH2)-3-(CH2)2CO2Me-CO2Me-4,5-C2B2H4 (a pair of geometric isomers, 7 and 14, which contain an unusual Ru-B borane bridge) are formed. On heating, 7 rearranges to yield nido-1,2-(Cp*Ru)2-3-(CH2)2CO2Me-4-BH2-5-CO2Me-4,5-C2B2H5, 13, whereas 14 converts to nido-1,2-(Cp*Ru)2-3-(CH2)2CO2Me-4-CO2Me-4,5-C2B2H6, 8. Under thermodynamic control, nido-1,2-(Cp*Ru)2-4,5-B[(CH2)2CO2Me]CO(MeO)[C(CH2)CO2Me]-4,5-C2B2H6, 11, is the major product accompanied by lesser amounts of 6 and 1,2-(Cp*Ru)2-4-OMe-5-Me-4,5-C2B2H6, 10. Compound 11 features a five-membered heterocycle containing a boron atom. The structure of 7, which is an intermediate in the formation of 11, provides the basis for an explanation of this complex condensation of three alkynes. A previously unrecognized role for an exo-cluster bridging borene generated from the metallaborane skeleton by addition of the alkyne is also a feature of this chemistry. Reinsertion or loss of this boron fragment accounts for much of the chemistry observed. NMR experiments reveal labile intermediates, and one has been sufficiently characterized to provide mechanistic insight on the early stages of the alkyne-metallaborane addition reaction. All isolated compounds have been spectroscopically characterized, and most have been structurally characterized in the solid state.

Coordination compounds with peripheral hydrogen bonding substituents have been used to assemble infinite frameworks of one, two, and three dimensions. The propagation of 1D, 2D and 3D network depends on the nature of the metal ion, the number of hydrogen bonding substituents used, and the nature and placement of the hydrogen bonding substituents. An overview of coordination complexes connected via simple hydrogen bonding substituents, e.g. carboxylic acids and carboxamides, is given, and analogous organic and inorganic hydrogen bonding networks are discussed. The use of 2D and 3D hydrogen-bonded coordination networks in creating host–guest networks is also discussed.

Reaction of the methylene diphosphonates [(RO)2P(O)]2CH2, where R = iPr or Et, with the metalating reagents NaH, nBuNa or the superbasic mixture tBuONa/nBuLi leads to monodeprotonation, and formation of the complexes [{(iPrO)2P(O)}2CHNa]4 (1) and [{(EtO)2P(O)}2CHNa]6 (2). Single-crystal X-ray diffraction studies revealed that 1 is tetrameric in the solid state, with a central Na4O4 cubane core. Each metal in 1 is rendered pentacoordinate by binding to three μ3-O phosphoryl bridges within the cubane, a chelating phosphoryl unit, and also a single iPrO group. In contrast, the structure of 2 is hexameric, and is composed of an unusual six-rung Na6O6 ladder core. Three distinct sodium environments as well as μ1-, μ2- and μ3-O phosphoryl units are present within the ladder framework. No Na−C interactions are present in either 1 or 2. All of the six-membered NaOPCPO chelate rings display localized P=O double bonds and partial multiple bonding on the P−C−P linkages (mean P−O: 1.49 A, and mean P−C: 1.69 A). Ab initio molecular orbital calculations (HF/6−31G*) on model complexes indicate that the hexameric arrangement found for 2 is thermodynamically more stable than the cubane structure of 1, in the absence of steric effects. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The reactions of [Cp*MH 2 ] 2 , Cp* = η 5 -C 5 Me 5 ; M = Fe, Ru, with BH 3 .THF have been explored. As with [Cp*RuCl 2 ] 2 , [Cp*RuH 2 ] 2 readily reacts with borane to generate nido-1,2-(Cp*RuH) 2 B 3 H 7 . In contrast to the chloride, intermediates are detectible in the hydride reaction and product selectivity is higher. Benefits of the apparently lower reaction barrier appear in the reaction of [Cp*FeH 2 ] 2 with BH 3 .THF. The formation and isolation of the novel hydrogen-rich ferraborane arachno-1-Cp*FeB 4 H 1 1 from the iron hydride contrasts with the production of pentamethylferrocene from a pentamethylcyclopentadienyl iron halide. This metastable ferraborane has been characterized spectroscopically as well as by reaction with Co 2 (CO) 8 to give a good yield of the more stable derivative nido-1-(Cp*Fe)-2-{Co(CO) 3 }B 4 H 8 by metal fragment addition. The latter compound has been spectroscopically characterized in solution as well as in the solid state by a single-crystal X-ray diffraction study as an example of a mixed metal dimetallahexaborane.

Addition of the internal alkyne, 2-butyne, to nido -1,2-(Cp*RuH) 2 B 3 H 7 ( 1 ) at ambient temperature produces nido -1,2-(Cp*Ru) 2 (μ-H)(μ-BH 2 )-4,5-Me 2 -4,5-C 2 B 2 H 4 ( 2 ), nido- 1,2-(Cp*RuH) 2 -4,5-Me 2 -4,5-C 2 B 2 H 4 ( 3 ), and nido- 1,2-(Cp*RuH) 2 -4-Et-4,5-C 2 B 2 H 5 ( 4 ), in parallel paths. On heating, 2 , which contains a novel exo -polyhedral borane ligand, is converted into closo -1,2-(Cp*RuH) 2 -4,5-Me 2 -4,5-C 2 B 3 H 3 ( 5 ) and nido -1,6-(Cp*Ru) 2 -4,5-Me 2 -4,5-C 2 B 2 H 6 ( 6 ) the latter being a framework isomer of 3 . Heating 2 with 2-butyne generates nido- 1,2-(Cp*RuH) 2 -3-{CMeCMeB(CMeCHMe) 2 }-4,5-Me 2 -4,5-C 2 B 2 H 3 ( 7 ) in which the exo -polyhedral borane is triply hydroborated to generate a boron bound CMeCMeB(CMeCHMe) 2 cluster substituent. Along with 3 , 4 , 5 , 6 , and 7 , the reaction of 1 with 2-butyne at 85 °C gives closo -1,7-(Cp*Ru) 2 -2,3,4,5-Me 4 -6-(CHMeCH 2 Me)-2,3,4,5-C 4 B ( 8 ). Reaction of 1 with the terminal alkyne, phenylacetylene, at ambient temperature permits the isolation of nido -1,2-(Cp*Ru) 2 (μ-H)(μ-CHCH 2 Ph)B 3 H 6 ( 9 ) and nido -1,2-(Cp*Ru) 2 (μ-H)(μ-BH 2 )-3-(CH 2 ) 2 Ph-4-Ph-4,5-C 2 B 2 H 4 ( 11 ). The former contains a RuB edge-bridging alkylidene fragment generated by hydrometallation on the cluster framework whereas the latter contains an exo -polyhedral borane like that of 2 . Thermolysis of 11 results in loss of hydrogen and the formation of closo -1,2-(Cp*RuH) 2 -3-(CH 2 ) 2 Ph-4-Ph-4,5-C 2 B 3 H 3 ( 12 ).

The ability of four polymorphic compounds, isonicotinamide (1), 2-amino-3-nitropyridine (2), 4-chlorobenzamide (3), and maleic hydrazide (4), to form molecular cocrystals has been examined in a systematic structural study. Compounds 1−3 participate in a wide variety of binary and ternary (in the case of 1) cocrystals with aromatic or aliphatic compounds substituted with a multitude of functional groups. However, despite considerable efforts, it has not been possible to form any cocrystals with 4. The reason for this may be due to the fact that even though there are three known polymorphs of 4, they all contain the same hydrogen-bonding synthons. In contrast, the polymorphs of 1−3 display considerable synthon flexibility, e.g., different hydrogen bond interactions are present in polymorphs of the same compound. Because 1−3 can form robust synthons in a variety of ways, whereas 4 always engages in the same primary hydrogen bond interactions, it may explain why the former compounds are readily able to accomm...

The X-ray crystal structure determinations of twelve cocrystals involving iso-nicotinamide and a variety of carboxylic acids have revealed a very consistent pattern of hydrogen-bond preferences. The combination of a monocarboxylic acid, an amide, and a pyridine moiety leads, in every case, to discrete "supermolecules" (consisting of two molecules of iso-nicotinamide and two molecules of the relevant carboxylic acid) with well-defined and robust connectivity. The two dominant (regularly occurring) supramolecular synthons in these crystal structures are (1) the heteromeric carboxylic acid.pyridine hydrogen bond and (2) a self-complementary amide.amide hydrogen-bond interaction, both of which prevail in the presence of widely differing chemical functionalities. In four of these cocrystals, a dicarboxylic acid is employed, which alters the structural outcome from discrete entities to infinite assemblies (or to a hexameric complex in a "U-shaped" dicarboxylic acid), which is fully expected since the two primary supramolecular synthons remain intact. This structural study shows that iso-nicotinamide is a supramolecular reagent that can produce well-defined supermolecules (containing carboxylic acids) in very high yields.

Diamide and amide-ester derivatives of imidazole-4,5-dicarboxylic acid form reliable hydrogen-bonding motifs in the solid state. The crystal structures of symmetrically substituted and dissymmetrically substituted diamides as well as amide-ester combinations were analyzed in order to identify the intermolecular hydrogen-bonding patterns. An intramolecular seven-membered hydrogen-bonded conformation forms in all derivatives where the possibility existed due to the functionality present. The motifs observed for the diamides include intermolecular NH···O and NH···N hydrogen-bonded dimers, with the exceptions to these motifs occurring in compounds having benzylamine substituents. The amines with a higher classification (i.e., 3° > 2° > 1°) in the dissymmetrically substituted diamides are the intramolecular hydrogen bond donors in the solid state, consistent with the capacity of the alkyl group to stabilize developing carbocation character resulting from bond polarization. The amide-ester derivatives also form...

The reaction of (Cp*Rh)2B2H6 (1) with BH3THF under mild conditions leads to the intermediate (Cp*Rh)2B3H7, which is shown to exist in the two isomeric forms 1,2-(Cp*Rh)2B3H7 (2a) 1,2-(Cp*Rh)2(μ-H)B3H6 (2b) by a solid-state structure of 2a and low-temperature NMR data of the mixture. 1 slowly decomposes at room temperature to yield a number of products including pileo-(Cp*Rh)3B4H4 (4), which has been characterized by a solid-state structure determination. 2 converts on heating to 2,3-(Cp*Rh)2B3H7 (3), of known structure. 1−3 catalyze the cyclotrimerization of both terminal and internal alkynes with differing activities. The rate of catalysis is inhibited by PPh3 and pyridine and competition experiments show evidence for a multistep mechanism with concentration-dependent selectivity. The pathway proposed suggests the borane fragment acts in an ancillary role by providing a cluster environment for the dimetal fragment. Metal polyhedral edge opening on alkyne (or base) addition is proposed as the novel activa...

Fumaramide derivatives were analyzed in solution by (1)H NMR spectroscopy and in the solid state by X-ray crystallography in order to characterize the formation of CH...O interactions under each condition and to thereby serve as models for these interactions in peptide and protein structure. Solutions of fumaramides at 10 mM in CDCl(3) were titrated with DMSO-d(6), resulting in chemical shifts that moved downfield for the CH groups thought to participate in CH...O=S(CD(3))(2) hydrogen bonds concurrent with NH...O=S(CD(3))(2) hydrogen bonding. In this model, nonparticipating CH groups under the same conditions showed no significant change in chemical shifts between 0.0 and 1.0 M DMSO-d(6) and then moved upfield at higher DMSO-d(6) concentrations. At concentrations above 1.0 M DMSO-d(6), the directed CH...O=S(CD(3))(2) hydrogen bonds provide protection from random DMSO-d(6) contact and prevent the chemical shifts for participating CH groups from moving upfield beyond the original value observed in CDCl(3). X-ray crystal structures identified CH...O=C hydrogen bonds alongside intermolecular NH...O=C hydrogen bonding, a result that supports the solution (1)H NMR spectroscopy results. The solution and solid-state data therefore both provide evidence for the presence of CH...O hydrogen bonds formed concurrent with NH...O hydrogen bonding in these structures. The CH...O=C hydrogen bonds in the X-ray crystal structures are similar to those described for antiparallel beta-sheet structure observed in protein X-ray crystal structures.

The asymmetric synthesis of the conformationally constrained l - and d -lysine derivatives methyl (1S,8S)-1-amino-8-tert-butoxycarbonylamino-1,2,3,4,5,6,7,8-octahydroanthracene-1-carboxylate ( 4 ) and methyl (1R,8S)-1-amino-8-tert-butoxycarbonylamino-1,2,3,4,5,6,7,8-octahydroanthracene-1-carboxylate ( 5 ), respectively are described. Application of the Bucherer hydantoin synthesis to the carbonyl group of 2′,3′,4′,5′,6′,7′-hexahydrospiro[1,3-ethylenedithiole-2,1′-anthracen]-8′-one ( 18 ), which was prepared from 1,8-dichloroanthraquinone ( 14 ) in nine steps and the deprotection of the masked second ketone of 18 yields rac-21. The latter is the precursor for a novel asymmetric reductive amination protocol using (R)-phenylglycinol as a chiral amino auxiliary and NaBH(OAc)3 as a reducing agent. Using this procedure, the asymmetric reductive amination of α-tetralone derivatives and indanone proceeds with >95% de. Lower diastereomeric excesses are observed for benzosuberone (16.7% de) and acetophenone (27.3% de). rac-21 gave (1′S,8′S,1(R)-25a (38% yield) and (1′R,8′S,1(R)-25b (44.5% yield) with greater than 52 and 78% de, respectively. Cleavage of the amino auxiliary of (1′S,8′S,1(R)-25a and of (1′R,8′S,1(R)-25b with lead(IV) tetraacetate and hydrolysis of the hydantoin ring yields the unprotected analogs of 4 and 5 . The latter are transformed into the selectively protected target molecules 4 and 5 through standard protection procedures. The overall yield of the 17- and 18-step synthesis starting from 13 was 0.3% yield for each constrained lysine derivative.

A crown ether-containing macrobicycle was used as the wheel component in a templated synthesis of a [2]rotaxane with an acetal-containing axle. The molecular structures of the macrobicycle and the [2]rotaxane were characterized by NMR spectroscopy and X-ray crystallography. The chloride-binding ability of the macrobicycle, either free in solution or when it is part of a [2]rotaxane, is quite weak as determined by NMR titration experiments. A second analogous [2]rotaxane, with a longer axle, was synthesized, and its solvent-dependent co-conformation was characterized by 2D NMR spectroscopy. The position of the wheel along the axle can be controlled by the solvent polarity, however, attempts to use metal cations such as Na(+), K(+), Ba(2+), and Ag(+) to switch the wheel position in polar solvents were unsuccessful.

The design of complementary hydrogen bonding interactions between molecules is often used in crystal engineering and other molecular recognition research. Herein we report the ability of complement...

The syntheses and crystal structure determinations of three new compounds, bis-[4′-[N-(4-pyridylmethylene)]aminoacetophenone oxime] silver(I) hexafluorophosphate hydrate, bis-[4′-[N-(4-pyridylmethylene)]aminoacetophenone oxime] silver(I) perchlorate hydrate, and bis-[3′-[N-(4-pyridylmethylene)]aminoacetophenone oxime] silver(I) hexafluorophosphate hydrate, demonstrate that the desired primary supramolecular synthon, the oxime⋯oxime dimer, is not disrupted despite extensive ligand modifications (through covalent synthesis) that increase the aromatic content and introduce an additional hydrogen-bond acceptor moiety.

The rhenaborane Cp*ReH3B3H8, which is generated by the reaction of Cp*ReH6 with BH3·THF, has been characterized spectroscopically in solution and by a single-crystal X-ray diffraction study in the solid state as a hydrogen-rich arachno-metallatetraborane.

Three dicarboxylic acids – 3,5-pyrazoledicarboxylic acid, 3,5-pyridinedicarboxylic acid and isophthalic acid – are examined for their ability to participate in lamellar hydrogen-bonded networks upon reaction with alkyl diamines. The use of flexible diamines stems from a desire to mimic the structure and eventually the intercalative abilities of naturally occurring clays. Six structures are reported, with the carbon chain length varying from 3 to 12, and the relative ability of each of the diacids (in combination with flexible diamines) to construct clay-like materials is discussed.

The crystal structures of 5-bromonicotinic acid ethylacetate 1, 5-bromonicotinic acid acetonitrile 2, and 5-bromonicotinic acid methanol 3 (all of which were obtained from single-crystal data) and of 5-bromonicotinic acid 4 (solved from powder diffraction data using a direct-space method based on the Monte Carlo technique) are presented; in 1−3, heteromeric N-H···O/C-H···O hydrogen-bonds lead to infinite polar chains of 5-bromonicotinic acid, whereas in 4, the principal noncovalent connector (head-to-head acid···acid hydrogen bonds) generates centrosymmetric dimers.

A 2,5-diamidopyrrole-capped macrobicycle was synthesized and its chloride salt binding ability evaluated in polar and apolar organic solvents. X-ray crystal structures of the receptor and its sodium chloride complex were obtained and in the latter structure the salt is bound as a contact ion-pair.

Different benzocycloalkane-1-amino-1-carboxylic acids 1a–e have been synthesized via an asymmetric Strecker reaction using (S)-α-methylbenzylamine and (R)-phenylglycinol as chiral auxiliaries. The Zn2+-catalyzed addition of HCN to (S)-α-methylbenzylamine derived ketimines of 1-tetralone (8a) and 1-benzosuberone (8b) yielded mixtures of diastereomeric aminonitriles (1S,1′S)-10a/(1R,1′S)-10a (10:1 ratio) and (1R,1′S)-10b/(1S,1′S)-10b (56:44 ratio), respectively. These aminonitriles are converted to amino acids 1a,b in two steps. The addition of TMSCN to the (R)-phenylglycinol derived ketimines of 8a, 8b, 1-indanone (8c), 7-fluoro-1-tetralone (8d), 7-fluoro-1-benzosuberone (8e) yielded mixtures of diastereomeric trimethylsilylated aminonitriles (1S,1′R)-14a–e/(1R,1′R)-14a–e. The addition proceeded with diastereofacial selectivities ranging from 1:2.9 to 1:25. The selectivity was found to be temperature and solvent dependent. The diastereomeric ratio (dr) of aminonitriles (1S,1′R)-14a/(1R,1′R)-14a increased in different solvents in the order methanol

2-Fluoro substituted benzoyl chlorides undergo cyclocondensation with 2-amino-N-heterocycles to form 4(3H)-quinazolinones. The reaction proceeds in moderate yields with different combinations of benzoyl chlorides and 2-amino-N-heterocycles. The products generally precipitate from the reaction mixture and require no further purification. Two tetrafluoro quinazolinones were found to be moderately active against a number of tumor cell lines.

The syntheses and crystal structures of four new ligands based on “extended” (pyridylmethylene)aminoacetophenone oxime derivatives are reported. The ligands are all prepared in good yields by allowing a suitably substituted pyridine to react with hydroxylamine, followed by Schiff-base condensation with the appropriate pyridinecarboxaldehyde. Their solid-state structures show that the dominating hydrogen bond, a head-to-tail O−H···N interaction between the oxime O−H moiety and the pyridine nitrogen atom, is present in each of the four reported cases despite considerable differences in crystal packing. These structures also contain a multitude of weaker π−π interactions, but they do not display the same consistency and regularity as the O−H···N hydrogen bond, which illustrates the importance of hydrogen bonding as the primary supramolecular synthetic tool.

The syntheses and crystal structures of four cocrystals; 2-pyridone fumaric acid (2/1), 2-pyridone meso -2,3-dibromosuccinic acid (2/1), 5-chloro-2-pyridone adipic acid (2/1) and 6-methyl-2-pyridone ( S )-malic acid (2/1), are reported. The competition between two self- and mutually-complementary hydrogen-bond moieties (carboxylic acid and 2-pyridone) are examined and compared with results obtained from an earlier study of 2-pyridone and unsubstituted aliphatic dicarboxylic acids.

The X-ray structures of cocrystals between 2,2′-dipyridyl- N , N ′-dioxide ( 1 ) with fumaric acid ( 2 ), itaconic acid ( 3 ), succinic acid ( 4 ), and oxalic acid ( 5 ) were solved to determine if concurrent CH···O interactions were capable of orienting the bimolecular association of the two molecules. Cocrystals 1·2 , 1·3 and 1·4 produce cyclic hydrogen bonded motifs employing pair-wise OH···O and CH···O hydrogen bonds, whereas cocrystal 1·5 forms analogous OH···O hydrogen bonds with a different set of intermolecular CH···O hydrogen bonds. Evidence of cocrystal formation was also observed for these complexes by differential scanning calorimetry and FT-IR spectroscopy. The structures of 1·2 , 1·3 and 1·4 demonstrate the potential of the pair-wise OH···O and CH···O hydrogen bonding interactions and serve to illustrate their use as hydrogen bonding isosteres in crystal engineering, molecular recognition, and drug design.

Background: Multidrug resistance (MDR) mediated by expression of MDR1 P-glycoprotein (Pgp) represents one of the best characterized barriers to chemotherapy in cancer patients. Positron emission tomography (PET) agents for analysis of Pgp-mediated drug transport activity in vivo would enable noninvasive assessment of chemotherapeutic regimens and MDR gene therapy. Results: Candidate Schiff-base phenolic gallium(III) complexes were synthesized from their heptadentate precursors and gallium(III)acetylacetonate. Crystal structures demonstrated a hexacoordinated central gallium with overall trans -pseudo-octahedral geometry. Radiolabeled 67 Ga-complexes were obtained in high purity and screened in drug-sensitive (Pgp − ) and MDR (Pgp + ) tumor cells. Compared with control, lead compound 6 demonstrated antagonist-reversible 55-fold lower accumulation in Pgp-expressing MDR cells. Furthermore, compared with wild-type control, quantitative pharmacokinetic analysis showed markedly increased penetration and retention of 6 in brain and liver tissues of mdr1a/b (−/−) gene disrupted mice, correctly mapping Pgp-mediated transport activity at the capillary blood–brain barrier and hepatocellular biliary cannalicular surface in vivo . Conclusions: These results indicate that gallium(III) complex 6 is recognized by MDR1 Pgp as an avid transport substrate, thereby providing a useful scaffold to generate 68 Ga radiopharmaceuticals for molecular imaging of Pgp transport activity in tumors and tissues in vivo using PET.

2,6-Dimethoxyphenylphosphirane is readily converted to its oxide and sulfide whose pyrolysis and (perhaps) photolysis lead to the generation of phosphinidene chalcogenides Ar–P Z (Z=O,S). Trapping experiments were carried out under conditions similar to the kinetic studies of the phosphirane chalcogenide pyrolyses that confirmed the formation of free Ar–P Z. The trapping experiments were in accord with carbene-like character for Ar–P Z, and the activation parameters suggest a non-least motion pathway for the addition of Ar–P Z to olefins. This represents quantitative evidence for the validity of the predictions of frontier-orbital theory for species that undergo reactions with small (or no) enthalpic barriers.

A strategy for the deliberate assembly of lamellar inorganic/organic hybrid materials based on a combination of 1-D coordination polymers and intermolecular hydrogen bonds has been explored. Copper(I) halide coordination polymers provide infinite linear building blocks that are linked into 2-D layers by attaching a pyridine-based ligand to each metal ion. The ligand, which carries a self-complementary hydrogen-bond moiety, provides a selective non-covalent tool for connecting neighboring coordination polymers into a 2-D network. The strategy is illustrated by the crystal structures of [CuCl(6-Me-3-HO2CC5H3N)]∞ and [CuI(6-Me-3-HO2CC5H3N)]∞, both of which display the desired lamellar motifs.

The syntheses and crystal structures of a family of oxime-substituted pyridine ligands [py-C(R)NOH, where R = H, Me, Ph, or NH2] are presented. The compounds are all prepared in good yields by allowing a suitably substituted pyridine to react with hydroxylamine. Their solid-state structures show that the dominating hydrogen bond, a head-to-tail O–H⋯N interaction between the oxime O–H moiety and the pyridine nitrogen atom, is present in each of the seven reported cases. This intermolecular interaction generates infinite chains that are crosslinked into 2D or 3D assemblies by weaker C–H⋯N or C–H⋯O hydrogen bonds.

Tris(triisopropylsilyl)silane (iPr3Si)3SiH has been synthesized and studied by X-ray and neutron diffraction. It possesses an unusual structure in which the four silicon atoms are nearly coplanar, ∠Si−Si−Si = 118.41(5)°. The Si−H distance is found to have a normal value of 1.506(2) A. Thermal and room-temperature photochemical decomposition of (iPr3Si)3SiH leads to the elimination of iPr3SiH and the generation of bis(triisopropylsilyl)silylene, [(iPr3Si)2Si:]. Reactions of (iPr3Si)2Si: include precedented insertions into H−Si bonds and addition to the π-bonds of olefins, alkynes, and dienes. Despite theoretical predictions of a triplet ground state for [(iPr3Si)2Si:], stereospecific addition to cis- and trans-2-butene was observed.

Square-planar and octahedral complexes of NiII and PtII link through head-to-head hydrogen bonds to form porous frameworks with large cavities that are suitable for inclusion of guest molecules. A series of four different complexes with pyridine-based ligands (in the center of the picture) are described, which contain either counterions or small molecules in channels. A=hydrogen-bond acceptor, D=hydrogen-bond donor, M=metal ion.

Quadratisch-planare und oktaedrische Komplexe von Nickel(II) und Platin(II) verknupfen sich uber Kopf-Kopf-Wasserstoffbruckenbindungen unter Bildung poroser Geruste mit grosen Hohlraumen, die Gastmolekule aufnehmen konnen. Vier verschiedene Komplexe mit Liganden auf Pyridinbasis (in der Mitte des Bildes gezeigt) werden vorgestellt, die entweder Gegenionen oder kleine Molekule in Kanalen enthalten. A = H-Brucken-Acceptor, D = H-Brucken-Donor, M = Metallion.

Pyrolysis and photolysis of phosphiranes and their chalcogenides provide routes for the generation of phosphinidenes R-P and their chalcogenides R-P=Z (Z = O,S). Kinetic studies of the pyrolyses allow the elucidation of the mechanisms of the addition reactions of R-P and R-P=Z. Results are in accord with predictions of frontier orbital theory, including alteration of reactivity by manipulation of frontier orbital symmetry.

The syntheses and crystal structures of (6-methylnicotinic acid) (6- methylnicotinato)silver(I), di (6-methylnicotinic acid) silver(I) nitrate, (2-chloro-6-methylnicotinato) silver(I), di (2-chloro-6-methylnicotinic acid) silver(I) nitrate, and (2-methylni-cotinic acid) (2-methylnicotinato) silver(I) are described. These coordination complexes were synthesized under the same conditions and with very similar ligands but their resulting structures are quite different, in part due to the degree of protonation of the nicotinic acid ligand(s). The structures vary from coordination polymers to hydrogen-bonded coordination dimers, to linear structures linked by anion-carboxylic acid hydrogen bonds. This study illustrates some of the difficulties involved in predicting hydrogen-bonded networks in transition-metal systems which contain carboxylic acid moieties and coordinatively unsaturated metal ions.