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International audience; Two types of bicyclic N-cyclopropyl glycine ester derivatives have been prepared and put under scrutiny as possible precursors of azomethine ylides. The results demonstrate that they can indeed participate in 1,3-dipolar cycloaddition reactions with dipolarophiles, as illustrated in the cases of phenyl vinyl sulfone, N-phenylmaleimide, diethyl fumarate and diethyl maleate. The relative configurations of the major diastereoisomers produced are consistent with the predicted generation of azomethine ylide species, reacting in concerted cycloaddition processes. This unprecedented way of generating such 1,3-dipoles provides access to functionalised pyrrolizidine and pyrrolidine derivatives, that would be difficult to make directly by more classic methods. It was also found that using phenyl vinyl sulfone or N-phenylmaleimide as the dipolarophile reactant, a domino nucleophilic conjugate addition/1,3-dipolar cycloaddition process may operate competitively.

A structure−activity relationship (SAR) study was performed principally at the N1 position of N1-arylsulfonyl-N2-[1-(1-naphthyl)ethyl]-trans-1,2-diaminocyclohexanes, a new family of calcilytics acting at the calcium sensing receptor (CaSR). The most active compound in this series was the 4-(trifluoromethoxy)benzenesulfonyl derivative 7e, which displayed an IC50 of 5.4 ± 0.5 μM with respect to the inhibition of calcium-induced tritiated inositol phosphate ([3H]IP) accumulation in Chinese hamster ovarian (CHO) cells expressing the CaSR. Replacement of the sulfonamide linkage of this compound by a carboxamide led to a 6-fold increase in activity (7m, IC50 = 0.9 ± 0.2 μM). Among the carboxamides synthesized, one of the most active compounds was the 4-chlorophenylcarboxamide (1S,2S,1‘R)-7n (Calhex 231, IC50 = 0.33 ± 0.02 μM). The absolute configuration of (1S,2S,1‘R)-7n was deduced from an X-ray crystallographic study of one of the diastereomers of compound 7d. The stereochemical preference for the (1S,2S,1‘R)...

Molecules bearing a 4,4-difluoro-8-(aryl)-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (bodipy) core and 1-pyrenyl-1-phenyl-4-(1-ethynylpyrene), or 1-phenyl-4-[1-ethynyl-(6-ethynylpyrene)pyrene] units were constructed in a step-by-step procedure based on palladium(0)-promoted cross-coupling reactions with the required preconstructed modules. X-ray structures of single crystals reveal a twisted arrangement of the two chromophores. In one case, an almost perfect orthogonal arrangement is found. These dyes are strongly luminescent in solution and display rich electrochemistry in which all redox processes of the bodipy and pyrene fragments are clearly resolved. The absorption spectra indicate that the bodipy and pyrene chromophores are spectrally isolated, thereby inducing a large "virtual" Stokes shift. The latter is realised by efficient transfer of intramolecular excitation energy by the Förster dipole-dipole mechanism. The rate of energy transfer depends on the structure of the dual-dye system and decreases as the centre-to-centre separation increases. The energy transfer efficiency, however, exceeds 90 % in all cases. The linkage of two pyrene residues by an ethyne group leads to a decrease in the energy-transfer efficiency, with the two polycycles acting as a single chromophore. The directly linked bodipy-pyrene dual dye binds to DNA and operates as an efficient solar concentrator when dispersed in plastic.

Two new dithiazolylethenes, 1a {1,2-bis[5′-methyl-2′-(2′′-pyridyl)thiazolyl]perfluorocyclopentene} and 2a {1,2-bis[4′-methyl-2′-(2′′-pyridyl)thiazolyl]perfluorocyclopentene}, have been synthesized. Their photochromic behavior has been fully investigated in solution as well as in the crystalline phase. They display both fatigue-resistant and thermally irreversible photochromic reactions, with more than 80% of the closed-ring forms (1b and 2b, respectively) in the photo-stationary state. Upon UV irradiation, a colorless solution of 1a turns purple while the yellow color of a 2a solution becomes more intense. Such marked differences in their electronic absorption spectra are reproduced by DFT calculations. Finally, although structurally closely related, only 1a shows photochromism in the crystalline phase whereas 2a displays reversible photo-modulation of fluorescence in solution.

A novel family of highly functionalized molecules consisting of a central 4-methyl-3,5-diacylaminobenzene platform linked in close proximity to the methyl group by two lateral aromatic rings each equipped with two long alkoxy chains has been rationally designed. The presence of amide tethers and a chelating phenanthroline fragment connected via an ester dipole formed a new class of gelating reagents and mesomorphic materials. A few of these compounds have the tendency to form macromolecule-like aggregates through noncovalent interactions in hydrocarbon solvents and were found to exhibit thermotropic cubic mesophases. In light of the X-ray molecular structure of the methoxy ligand, an infinite network maintained by intermolecular hydrogen bonds as well as by pi-pi stacking of the phenyl subunits was evidenced. FT-IR studies confirm that the common driving force for aggregation in the organogels and microsegregation in the mesophase is the occurrence of a tight intermolecular H-bonded network that does not persist in diluted solution. This situation is switched when the ligands are interlocked by a copper(I) cation. A strong intramolecular H-bond confirmed by X-ray diffraction of a single crystal for the methoxy case provides very stable complexes but inhibits the gelation of the solvents. Heating the complexes bearing long paraffin chains (n = 12 and 16) in the dried state leads to a self-organization into a columnar liquid-crystalline phase in which the columns are arranged along a 2D oblique symmetry as deduced from powder XRD experiments. In this case, the complexes with the appended counteranions self-assemble in a specific way to form columns. A striking observation is that the intramolecular hydrogen bond persists in the mesophase as it does in solution without any evidence of an extended network. As far as we are aware, these ligands and complexes are rare examples in which organogelation and thermotropic mesomorphic behavior could be observed in parallel with molecules bearing a chelating platform. Due to the synthetic availability of the 4-methyl-3,5-diacylaminobenzene core and the simplicity by which the chelating platforms can be graphed, this methodology represents a practical alternative to the production of functionalized organogelators and mesomorphic materials.

The synthesis of stable and highly organized phenanthroline, terpyridine, and pyridino-oxazoline ligands bearing one or two 4-methyl-3,5-diacylaminophenyl modules equipped with two lateral dialkoxyphenyl groups has been performed using EDC.HCl and DMAP reagents in the final coupling reaction. Evidently, in the final ligands and in the solid state intermolecular hydrogen bonding maintains the coherence of the tridimensional structure as clearly evidenced by FT-IR and X-ray diffraction spectroscopy in the cases of the methoxy ligands. The supramolecular packing is also maintained by additional pi-pi stacking interactions.

The g-tensors and hyperfine tensors of the S = (1)/(2) ground state of the mixed valence [LMn(IIImu-O)(2)Mn(IV)L](3+) complex (L = N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine) was deter-mined in the solid-state and frozen acetonitrile solution by high-field EPR. Both samples exhibited complex anisotropic temperature behaviors that precluded the use of routine spectrum simulation procedures to extract the spin parameters. To circumvent this problem, the parameters were measured directly by using multifrequency techniques. In the case of the frozen solution, this approach yielded seven of the nine spin parameters with varying uncertainty, the two extreme principal g-values, the four hyperfine couplings associated with each of these two g-values, and the middle g-value. This latter parameter was obtained from a first moment analysis. Unlike simulations, the statistical errors associated with each value could be assigned in a straightforward and rigorous manner. The directly measured g-values were different in frozen solution and polycrystalline powder. The temperature dependence of the high-field EPR spectra of the polycrystalline powder revealed a spin-spin interaction between the neighboring binuclear complexes.

A new ligand based on a p-tert-butylcalix[4]arene functionalised with three 6-carboxylato-2,2′-bipyridine arms reacted with lanthanide(III) cations to form 2:2 complexes in the solid state, whereas in solution, a concentration-dependent equilibrium is observed between 2:2 and 1:1 species, as evidenced by ES-MS and metal luminescence measurements. In the X-ray molecular structure of the terbium complex two branched calixarene platforms share one pendant arm in order to provide a neutral dimeric structure which is held together by a strong hydrogen bonded network together with efficient π–π stacking of two pyridine rings belonging to each ligand.

Very stable copper(I) complexes were engineered from pyridine ligands bearing on one side an iminophenyl fragment and on the other a pivotal methyl group. The phenyl group was substituted in the para position either by a methoxy group or by a phenyl ester group grafted with three paraffin chains (n = 8, 12, 16). The methoxy complex in the crystalline state was characterized by X-ray diffraction. Its molecular structure was found to correspond to a distorted tetrahedral arrangement round the copper(I) metal centre. The long-chain complexes near room temperature were found to produce columnar liquid crystals of hexagonal symmetry. The columns were found to result from the aggregation of the wedge-shaped molecules round the columnar axis with the metal-containing iminopicoline ligands crowded together in the centre and the alkyl chains pointing outwards with a disordered conformation. The degree of molecular aggregation, around 7, was found to decrease significantly on heating.

The catalytic asymmetric synthesis of an axially chiral biaryl, potentially useful intermediate in the synthesis of dibenzocyclooctadiene lignans, has been performed. The key step consisted of a diastereoselective Suzuki coupling between a chiral benzylic alcohol and a sterically hindered boronic ester. The 1,3-induction from the benzylic stereocenter to the biaryl axis proceeded with very good diastereoselectivity.

The palladium-catalyzed, two-step, one-pot borylation/Suzuki coupling (BSC) reaction was developed to synthesize sterically hindered 2,2'-disubstituted biphenyl and phenyl-indole compounds in a short, simple, and efficient manner from two easily accessible aryl halides. High yields can be obtained by choosing properly both components according to their rough electronic properties. The illustration of the utility of this method was provided by the solution and solid-phase synthesis of seven- or eight-membered biphenyl lactams 5a-e, as well as paullone 3a. These compounds exhibit moderate albeit significant cytotoxicities and may serve as structural models for future medicinal chemistry developments.

The crystal structure of a dimeric bis(µ‐carboxylato)MnIIMnII complex (2) with a tetradentate N‐centered tripodal ligand, N,N‐bis[(1‐methylimidazol‐2‐yl)methyl]glycinate, is presented. The carboxylates are bridging monodentate. This complex shows some striking differences to the previously published parent compound 1 obtained with the closely related ligand N‐[(1‐methylimidazol‐2‐yl)methyl]‐N‐(2‐pyridylmethyl)glycinate. The carboxylato bridges in both structures are shown to be disrupted in solution. The reactivities in solution of compounds 1 and 2 toward superoxide were studied. In anhydrous DMSO solutions, a pathway involving a bis(µ‐oxo)MnIIIMnIV complex was identified. In water solutions, IC50 values were measured by the Fridovich test (1.7 ± 0.2 µM for 2 and 2.0 ± 0.2 µM for 1), which showed these complexes to be good superoxide scavengers. Association constants for the complexes were estimated by means of a method based on IC50 measurements of the complexes under several conditions (alone and in the presence of excess ligand). They were found to be consistent with literature data.

Ligand L, containing two 6-methyl-6′-methyl-yl-2,2′-bipyridine moieties linked by a “PhPO” spacer, has been prepared. Subsequent complexation with [Cu(CH3CN)4](BF4) led to a unique complex of formula [CuL](BF4). The molecular structure has been determined by X-ray crystallography in the solid state and NMR studies in solution. The complex displays an intense absorption band in the visible wavelength range with maxima at 418 and 509 nm, and is oxidised reversibly at +0.66 V (ΔEp = 80 mV) to the corresponding Cu(II) species, while two successive reductions of the coordinated bipyridine fragments occur at −1.60 (ΔEp = 66) and −1.84 V (ΔEp = 70 mV) s. SCE. Direct spectrophotometric titrations with global analysis allowed us to elicit stability constants for the emergent complex and to highlight the formation of a dinuclear complex in the presence of excess copper.

The tripodal heptadentate ligand TPAA (TPAA=tris[N-(2-pyridylmethyl)-2-aminoethyl]amine) is found to undergo an iron(II)-assisted oxidative dehydrogenation with its three amine functions oxidized into three imine groups, giving the tripodal potentially heptadentate ligand (py)3tren ((py)3tren=tris[N-(2-pyridylmethyl)-2-iminoethyl]amine). This oxidative process induces structural changes and spin conversion in the three identified iron(II) complexes, Fe–TPAA complex (1), Fe–py3tren complexes (2) and (3). X-ray crystallographic studies revealed differences in the coordination geometry of the bridging nitrogen atom and shifts in the coordination number from seven to six. Complex 1 is seven-coordinate and is characterized by a pyramidal environment of the tripodal centered nitrogen and a short NtripodalFe distance equal to 2.504 A. Complex 3 is hexa-coordinate with a planar environment of the centered nitrogen located at 3.435 A from iron(II) and therefore not bound to the iron. Complex 2 which is an isomeric form of complex 3 is found to be a structural intermediate between complexes 2 and 3 with a pseudo-coordination of six as shown by the NtripodalFe distance equal to 2.754 A. Electronic changes were recognized from NMR studies in solution and EPR and SQUID measurements of susceptibilities in solid state. Complex 1 is high-spin with the S=2 state characterized by a g factor equal to 2.25. Complex 3 is low-spin but its isomer, the intermediate complex 2 exhibits a temperature-dependent spin conversion from the S=2 high-spin form at room temperature to a lower spin that we provisionally identify as a S=1 intermediate spin form. DFT Becke3LYP calculations were carried out on the two isomeric complexes 2 and 3. The planar complex was found to be 3.2 kcal mol−1 more stable than the pyramidal isomer, in agreement with the experiment.

The crystal structure of an infinite inorganic chain consisting of MnII and an N-centered tripodal ligand N,N-(2-pyridylmethyl)[(1-methylimidazol-2-yl)-methyl]glycinate is presented. It exhibits a chiral helical structure with a pitch of two monomeric units (each monomeric unit containing one Mn atom). Each manganese is connected to its neighbor through a carboxylate bridge in a syn-anti geometry. Around each manganese center, two carboxylates bind in a cis geometry. This peculiar bridging geometry (syn-anticis) provides a broken-line chain, running in a zig-zag manner along the b axis of the P21 space group. The magnetic properties have been investigated. They show a pseudo-2D magnetic structure, with one major pathway along the chain and an inter-chain minor one. The intrachain coupling is a weak antiferromagnetic interaction (J/k = -0.25). This low value is entirely consistent with the geometry of the bridge. The interchain coupling is a weaker antiferromagnetic coupling (J'/k = -0.11) and could be mediated through π-π interactions between pyridine and imidazole from two adjacent helixes.

The water soluble acyclic 1 and macrocyclic 2 receptor molecules, based on acridine units, form 1:1 complexes with the cis- or trans-2,2′ and 3,3′-azobenzene dicarboxylate substrates. The stability constants of these complexes, determined by 1H NMR spectroscopy, cover a wide range from 30 to 105M–1, thus displaying very pronounced structure selectivity with respect to both substitution pattern and cis, transconfiguration. The complexes of the cyclo-bis-intercaland receptor 2 are two or three orders of magnitude more stable than those of 1. The inclusion complex of cyclo-bis-intercaland 2 with trans-3,3′- azobenzene dicarboxylate has been isolated and its structure has been determined by X-ray crystallography using synchrotron radiation, confirming the intercalation of the substrate between the acridine residues in the species formed.

The new tripodal potentially heptadentate ligand N(CH2CH2NCHR)3 (L) with R = 1-triphenylmethyl-4-imidazolyl containing three 4-substitutes imidazole functions, where Nτ nitrogen atoms are protected with highly aromatic triphenylmethyl (trityl) groups, was synthesized. The corresponding iron(II) complex [Fe(L)](PF6)2 was prepared and characterized. Its molecular structure was determined by X-ray crystallography (monoclinic space group P2 1 n with a = 21.148(9), b = 23.484(9), c = 14.668(6) A , β = 97.44(4)°, Z = 4), and R = 0.0787). The Fe(II) ions is hexa-coordinated from three imine and three imidazole nitrogens. The tripodal bridging N atom is not bonded to the iron (3.1 A). The complex is high spin as shown by NMR and electron paramagnetic resonance studies. UV-Vis and electrochemical properties are also reported. The reactivity of the complex with superoxide was investigated. A new species was discovered as ultimate product of the reaction with potassium superoxide in DMSO solution, which confirms effective superoxide scavenging by the complex despite the steric hindrance of the ligand.

The complex [L(H2O)Fe(μ-O)Fe(OH)L](ClO4)3·H2O, where L = N,N‘-dimethyl-N,N‘-bis(2-pyridylmethyl)ethane-1,2-diamine, was synthesized. It crystallizes in the orthorhombic space group P212121 with a = 13.283(5) A, b = 16.050(9) A, c = 20.050(9) A, V = 4476(6) A3, and Z = 4. It presents the hydrogen-bonded [(H2O)Fe(μ-O)Fe(OH)]3+ core unit characterized by an Fe−O−Fe angle of 137.5(2)° and an Fe−Fe distance of 3.396(1) A. The measurement of the magnetic susceptibility as a function of the temperature indicated an antiferromagnetic coupling between the two high-spin Fe(III) ions J = −184 cm-1 (H = −JS1·S2). In the solid state the symmetric stretching vibration was observed at 438 cm-1. Upon dissolution in dry acetonitrile, this vibration was no longer detected and an intense band was observed at 600 cm-1. This frequency can be correlated with an Fe−O−Fe angle of 111°. This value suggests that the species which exists in these conditions is the protonated diamond core [Fe(μ-O)(μ-OH)Fe]3+, analogous to that ident...

The species LFe III Cl ( 1 ) was synthesized where L 2− is the dianion N , N ′-bis(4-methyl-6-tert-butyl-2-methyl-phenolato)- N , N ′-bismethyl1,2-diaminoethane. It crystallizes in the triclinic space group P -1 with a = 14.704(6), b = 17.421(7), c = 17.328(8) A , α = 89.45(8) , β = 129.76(9), γ = 102.71(9)°, V = 3277(2) A 3 and Z = 2 . The molecule has approximately a square pyramidal structure. In the presence of DBCH 2 (3,5-di-tert-butylcatechol), this complex gives LFe III (DBSQ) ( 2 ), a stable Fe(III)-semiquinonato complex (DBSQ − stands for the 3,5-di-tert-butyl- o -benzosemiquinone monoanion). It crystallizes in the monoclinic space group C 2/ c with a = 36.24(2), b = 10.438(5), c = 23.928(12) A , β = 115.31(5)°, V = 8183(7) A 3 and Z = 8 . This X-ray study allows the structure of the DBSQ − monoanion complexed to Fe(III) to be compared with that of the DBC 2− dianion complexed to Fe(III) as found in several complexes already described (see for instance H.G. Jang, D.D. Cox and L. Que, Jr., J. Am. Chem. Soc., 113 (1991) 9200–9204). A clear alternation is found in CC bond lengths in the DBSQ − monoanion. Magnetic coupling between the S Fe = 5 2 electronic spin on Fe(III) and the S R = 1 2 electronic spin on the DBSQ − anion radical has been deduced from the behavior of the magnetic susceptibility as a function of temperature. It has been found antiferromagnetic with J = −206 cm −1 (with the notation H = − JS Fc S R ). This is a weaker coupling than that found in other analogous complexes. Mossbauer spectroscopy confirms the S = 2 nature of the ground state. Analysis of the 57 Fe hyperfine coupling parameters prove that the earlier description of the electronic structure of 2 is correct. It is possible to reduce 2 to get [LFe III (DBC)] − ( E 0 = −0.3 V/SCE in AcN). This species has UV-Vis and EPR properties typical of this type of complex. In the absence of protons, [LFe III (DBC)] − is stable under pure O 2 but the addition of protons results in its oxidation to form 2 . The insensitivity of [LFe III (DBC)] − to O 2 is compatible with the idea that the system has to go through an Fe(II) (DBSQ) form by internal electron transfer to allow the attack of the aromatic ring by O 2 (see L. Que and R.Y.N. Ho, Chem. Rev., 96 (1996) 2607–2624, for a review). Observation of the lowest energy LMCT band in [LFe III (DBC)] − at 620 nm (2.00 eV, AcN) suggests that the Fe(II) (DBSQ) form is indeed at high energy ( ΔG 0 ) above the catechol form. This contributes from Marcus theory to a high activation energy. In intradiol dioxygenases the decoordination of one of the tyrosine ligands (D.H. Ohlendorf, A.M. Orville and J.D. Lipscomb, J. Mol. Biol., 244 (1994) 586–608) is certainly important for the deprotonation of the catechol substrate but could also accelerate the formation of the postulated Fe(II)-semiquinonato intermediate. The stability of 2 under O 2 also demonstrates the importance of the Fe(II) oxidation state in order to lead to a peroxo form of the oxygen adduct. The insensitivity of [LFe III (DBC)] − to O 2 argues against the view of the dioxygenase activity as the result of an electrophilic attack of the catecholato by O 2 in model complexes.

The dinuclear species [(trispicMeen)(ClFeOFeCl)-O-III-Cl-III(trispicMeen)]Cl(OH)(H2O)(7) (1) (trispicMeen = N,N,N'-tris-(2-pyridylmethyl)-N'-methylethane- 1,2-diamine) was synthesized. It crystallizes in the monoclinic space group C2/c with a = 33.87(2) Angstrom, b = 17.42(2) Angstrom, c = 23.41(5) Angstrom, beta = 132.88(5)degrees, V = 10 121(25) Angstrom(3), and Z = 8. It contains an almost linear unit (Fe-O-Fe angle = 177.4(7)degrees). The potentially pentadentate Ligand is in fact only tetracoordinated with one pyridine not bound to the metal ion. The octahedral coordination of Fe(Ln) is completed by one chloride ion. The structure of [(bispicMeen)ClFeOFeCl(bispicMeen)]Cl-2 . CH3COCH3 . 2H(2)O (2) (bispicMeen = N,N'-bis(2-pyridylmethyl)-N'-methylethane-1,2-diamine) was also determined. It crystallizes in the monoclinic space group C2/c with a 11.124(4) Angstrom, b = 22.769(9) Angstrom, c = 15.874(6) Angstrom, beta = 97.79(4)degrees, V = 3984(3) Angstrom(3), and Z = 4. The main difference from 1 is that, in 2, the Fe-O-Fe unit is bent with an FeOFe angle 152.3(3)degrees. In cyclic voltammetry, 1 exhibits two reduction peaks at -0.230 and -0.960 V/SCE. They correspond respectively to the reduction to the (FeFeIII)-Fe-II and (FeFeIII)-Fe-II states. Cyclic voltammetry shows that the mixed-valent form [(trispicMeen)(ClFeOFeCl)-O-II-Cl-III(trispicMeen)](+) (E degrees = -0.175 V/SCE) is in equilibrium with another species (E degrees = +0.065 V/SCE) proposed to be [(trispicMeen)(FeOFeCl)-O-II-Cl-III(trispicMeen)](2+) in which a chloride ion has been displaced by the originally unbound pyridine. The equilibrium constant was estimated to be 90 M(-1), and the rate of the recombination of chloride to the [(trispicMeen)(FeOFeCl)-O-III-Cl-III(trispicMeen)](3+) complex was found equal to 3 x 10(5) M(-1) s(-1). Controlled potential electrolysis of an acetonitrile solution of 1 allowed the preparation of the mixed-valent Fe(II)-O-Fe(III) form which gives an almost isotropic EPR signal similar to that already observed with ore-bridged model compounds (Holt, et al. Inorg. Chem. 1993, 32, 5844. Hartman, et al. J. Am. Chem. Sec. 1987, 109, 7387) but different from the rhombic one observed in the mixed valent form of MMO. The mixed-valent forms slowly disproportionate to a mixture of (FeFeIII)-Fe-III and Fe(II) forms. The mixed-valent forms could be generated by radiolysis at 77 K, and an EPR study of the mixed-valent forms obtained by this procedure demonstrated that these species could not be protonated. Radiolysis of 1 at 77 K afforded the EPR spectrum of [(trispicMeen)(ClFeOFeCl)-O-II-Cl-III(trispicMeen)](+); upon annealing at 200 K, the solution gave an EPR spectrum very similar to that observed on the electrochemically reduced solution. This is in agreement with the observation of substitution of a chloride ligand. The mixed-valent form was not detected with the analogous complexes of the bispicen family: [(bispicMeen)ClFeOFeCl(bispicMeen)]Cl-2 . CH3COCH3 . 2H(2)O (2) and [(bispicMe(2)en)ClFeOFeCl(bispicMe(2)en)]Cl-2 (3). Upon reduction, these complexes quickly (at CV time scale) decompose to mononuclear species.

The crystal structures of [Fe(oep)L 2 ][O 3 SCF 3 ] and [Co(oep)L 2 ][ClO 4 ] [H 2 oep = 2,3,7,8,12,13,17,18-octaethylporphyrin, L = [Fe(C 5 H 5 )(C 4 H 4 N)] have been determined. The azaferrocene ligands L in both compounds are seen to be parallel. The axial M–N (azaferrocene) bonds are longer than those found in analogous imidazole and pyridine complexes. Rhombic EPR spectra for bis(azaferrocene) complexes of iron(III) porphyrins are postulated to be a result of steric interactions of the azaferrocene H2,5 atoms splitting the degeneracy of the d xz and d yz orbitals. The Mossbauer spectra of these iron complexes were recorded and interpreted as evidence for σ bonding of the azaferrocene nitrogen atom to the porphyrin iron core with little or no π back bonding from the porphyrinic iron to the N atom. This is in agreement with the long bond lengths found in the structures. The rhombic EPR spectra observed are in keeping with a parallel arrangement of the ligand planes, as are the magnitudes of the Mossbauer quadrupole splittings. It is shown that the large g z values of the complexes are not unusual and must relate to long axial bonds and to steric effects splitting the d xz and d yz orbitals.

Three macrobicyclic octamines 1–3 and the macrotricyclic hexadecamine 14 have been synthesized. The octamines 1–3 bind anionic substrates when protonated. The stability constants of the complexes between the protonated forms of the macrobicyclic polyamines and halide anions have been determined by pH-metric measurements. The stability constants in H2O are very high; 1 in its hexaprotonated form binds F− with high selectivity (selectivity F−/Cl− > 108), while 3 exhibits strong stability constants for both F− and Cl−. Three X-ray structures have been obtained, one where F− is held inside the cavity of 1 · 6H+, one where Cl− is included in 3 · 6H+, and 3 · 6H+ where the cavity is empty.

The new biomimetic ligand (bis((1-methylimidazol-2-yl)methyl)amino)acetic acid (LH) has been synthesized, which increases the growing family of tripodal tetradentate ligands. Reaction of LH with FeCl3·6H2O allowed us to obtain the corresponding iron(III) complex [Fe(L)Cl2]. The crystal structure reveals mononuclear neutral molecules with four chiral molecules per asymmetric unit (crystal data: monoclinic, P21, a = 12.564(5) A, b = 25.960(10) A, c = 9.875(4) A, α = 90.00°, β = 60.494(4)°, γ = 90.00°, V = 3221(2) A3, Z = 8, R = 0.0601 for 2433 unique reflections with Fo > 4σ(F) and 452 variable parameters). The iron(III) center is located in a distorted octahedral environment consisting of four donor atoms from the ligand L, two imidazole nitrogens, an amine nitrogen, and one oxygen of the carboxylate group, with the 6-fold coordination being completed by two chloride anions. UV−vis and EPR spectra are solvent dependent due to the two labile chloride positions. Cyclic voltammograms run under an argon atmos...

A new manganese(II) complex, Mn(II)−tris[2-[N-(2-pyridylmethyl)amino]ethyl]bishexafluorophosphate (Mn−TPAA), has been synthesized, its X-ray crystal structure resolved, and its superoxide stoichiometric scavenging activity established. The complex has been formed with the tripodal potentially heptadentate ligand TPAA which turns out to be the single ligand coordinated to the metal ion and therefore achieves the seven coordination. The complex crystallizes in the space group P212121, a = 19.654(9) A, b = 15.416(5) A, c = 10.425(4) A, with four formula units per unit cell. The manganese is bonded to three pyridine nitrogen atoms, to three amine groups, and to the tripodal bridging nitrogen N. The reactivity toward superoxide has been investigated using the indirect xanthine−xanthine oxidase−cytochrome c method, the electrochemical reaction of in-situ generated superoxide, and γ and pulse radiolysis measurements. From the cytochrome c assay, it has been found that the IC50 value is equal to 4.4 μM. From elec...

The compound [Mn2III,IVO2(bisimMe2en)2](ClO4)3·H2O (bisimMe2en = N,N‘-dimethyl-N,N‘-bis(imidazol-4-ylmethyl)ethane-1,2-diamine) was synthesized. It crystallizes in the monoclinic space group C2/c with a = 18.139(8) A, b = 12.694(5) A, c = 17.694(8) A, β = 107.5(6)°, V = 3885(6) A3, and Z = 4. The cation [Mn2III,IVO2(bisimMe2en)2]3+ contains a di-manganese di-μ-oxo unit. The Mn−Mn axis is a C2 axis. The Mn−imidazole distances for MnIII or MnIV are distinct: respectively, 2.208(9) and 2.004(8) A. The ground state is a |SA2,SB3/2,S1/2〉 state separated by 420 cm-1 from the S = 3/2 state. The EPR spectrum has been simulated with |A1x,y| = 160.10-4 cm-1, |A1z| = 136.10-4 cm-1, |A2x,y| = 72.10-4 cm-1, |A2z| = 71.10-4 cm-1, gxy = 1.997, gz = 1.993. The ESEEM spectrum is reported. The 2H nuclei corresponding to the exchangeable hydrogen atoms of imidazole groups in D2O have been detected at 2.4 MHz at 3480 G. In cyclic voltammetry, [Mn2III,IVO2(bisimMe2en)2]3+ presents in oxidation two reversible waves at 1.04 an...

The water-soluble tetra- and hexasulfonated calix[4] and calix[6]arenes bind very strongly the neurotransmitter acetylcholine and other quaternary ammonium cations with association constants Ks up to 4×105 M−1 for NEt4 +. The high affinities for choline and acetylcholine (Ks=5×104 to 8×104 M−1) are comparable to those of the biological recognition sites. The crystal structure of the [choline-tetrasulfonated calix[4]arene] complex was determined. Two complexes A and B were observed in the asymmetric unit. In each one, the choline inserts its N-terminal inside the cavity of the receptor. The calix[4]arene adopts a single cone conformation but the choline substrate is in an extended conformation in complex A and adopts two other folded conformations in complex B (75 % –25 %). The very high association constants and the crystal structure provide important information about the nature of the binding in this biologically most relevant complex.

The chiral bicyclic bis-lactam 1 has been resolved and the crystal structures of the racemate (±)-1 and of enantiomerically pure (−)-1 have been determined. They show that the chiral nature of the substance determines the supramolecular architecture generated by hydrogen bonding self-assembly, giving an infinite zig-zag chain for the racemate and a cyclic tetramer for the enantiomer.

Two new diterpenoids have been detected in Calceolaria purpurea and identified as 2α-malonyloxy- abieta-11 (12)-ene-9α,13α-endoperoxide, and 2α-malonyloxy-abieta-11(12)-ene-9β,13β-endoperoxide. The structure of the first terpenoid was determined by a combination of spectroscopic and single crystal X-ray diffraction analysis. The proposed structure of the second terpenoid was established by spectroscopic means and by comparison with the first terpenoid.

The expected [1:2] complex between a tetraprotonated tetraazapara-cyclophane and squaric acid is not formed and the ligand undergoes drastic deformation. The peculiar features of this structure is the coexistence, in the same crystal cell, of 2 types of crystal lattice inclusions, corresponding to 2 different dissociation modes of squaric acid.

The water-soluble macrobicyclic cyclophane molecule 16– has been crystallized in two very different shapes that display the operation of medium, especially hydrophobic effects: an inflated cage structure building up cylinders disposed in an hexagonal array; a flattened structure stacked in molecular layers separated by aqueous layers in a lamellar arrangement.

The palladium-catalyzed, two-step, one-pot borylation/Suzuki coupling (BSC) reaction was developed to synthesize sterically hindered 2,2'-disubstituted biphenyl and phenyl-indole compounds in a short, simple, and efficient manner from two easily accessible aryl halides. High yields can be obtained by choosing properly both components according to their rough electronic properties. The illustration of the utility of this method was provided by the solution and solid-phase synthesis of seven- or eight-membered biphenyl lactams 5a-e, as well as paullone 3a. These compounds exhibit moderate albeit significant cytotoxicities and may serve as structural models for future medicinal chemistry developments.

The synthesis of the title compound 8c is described. The inhibitor of Angiotensin Converting Enzyme (ACE) contains aza-2 bicyclo [2, 2, 2] octane-carboxylic acid, a bulky cyclic amino acid replacing the proline moiety present in most ACE inhibitors described in the literature. Structural analysis of 8c supports the hypothesis of preferred conformations for this type of pseudo peptidic molecule, in solution (1H, 13C NMR) and in the solid state (X- Ray).

The crystal structures of the LiBr complexes of two macrobicyclic ligands, [py.py.bpy]1 and [py.biqi.biqi] 2, have been determined. They confirm the cryptate nature of these species. In 3, the Li+ cation is bound in the shallow cavity of a ligand of flattened shape, whereas in 4, it is buried inside the macrobicycle and surrounded by its three bridges.

Two new molecular dyads, comprising pyrromethene (bodipy) and 2,2‘:6‘,2‘ ‘-terpyridine (terpy) subunits, have been synthesized and fully characterized. Absorption and fluorescence spectral profiles are dominated by contributions from the bodipy unit. Zinc(II) cations bind to the vacant terpy ligand to form both 1:1 and 1:2 (cation:ligand) complexes, as evidenced by X-ray structural data, NMR and spectrophotometric titrations. Attachment of the cations is accompanied by a substantial decrease in fluorescence from the bodipy chromophore due to intramolecular electron transfer across the orthogonal structure. At low temperature, nuclear tunneling occurs and the rate of electron transfer is essentially activationless. However, activated electron transfer is seen at higher temperatures and allows calculation of the corresponding reorganization energy and electronic coupling matrix element. In both cases, charge recombination is faster than charge separation.

Under aqueous conditions, 4-azidouracil/tetrazolo[1,5-c]pyrimidin-5(6H)-one nucleosides undergo a very efficient photochemical nitrogen elimination and ring expansion to 1,3,5-triazepin-2,4-dione nucleosides whose structure has been confirmed by X-ray crystallography. In contrast, when the photolysis was attempted under anhydrous conditions in the presence of a nucleophile, a ring contraction reaction occurred, affording 2-oxoimidazolone nucleosides. A mechanism to account for the formation of ring expansion and contraction reactions and involving a carbodiimide intermediate is proposed which is reminiscent of the known photochemical behavior of 2-azidopyridines/tetrazolo[1,5-a]pyridines.

Two Mn(II) complexes are isolated and X-ray characterized, namely, cis-[(L(2))Mn(II)(Cl)(2)] (1) and [(L(3))Mn(II)Cl(OH(2))](ClO(4)) (2(ClO(4))), where L(2) and L(3) are the well-known tetradentate N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine and N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)propane-1,3-diamine ligands, respectively. The crystal structure reveals that whereas the ligand L(2) is in the cis-alpha conformation in complex 1, the ligand L(3) is in the more unusual cis-beta conformation in 2. EPR spectra are recorded on frozen solutions for both complexes and are characteristic of Mn(II) species. Electrochemical behaviors are investigated on acetonitrile solution for both complexes and show that cation 2 exists as closely related Mn(II) species in equilibrium. For both complexes exhaustive bulk electrolyses of acetonitrile solution are performed at oxidative potential in various experimental conditions. In the presence of 2,6-lutidine and after elimination of chloride ligands, the formation of the di-mu-oxo mixed-valent complexes [(L(2))Mn(III)(mu-O)(2)Mn(IV)(L(2))](3+) (3a) and [(L(3))Mn(III)(mu-O)(2)Mn(IV)(L(3))](3+) (4) is confirmed by UV-vis and EPR spectroscopies and cyclic voltammetry. In addition crystals of 4(ClO(4))(3) were isolated, and the X-ray structure reveals the cis-alphaconformation of L(3). In the absence of 2,6-lutidine and without elimination of the exogenous chloride ions, the electrochemical oxidation of 1 leads to the formation of the mononuclear Mn(III) complex, namely, [(L(2))Mn(III)(Cl)(2)](+) (5), as confirmed by UV-vis as well as parallel mode EPR spectroscopy and cyclic voltammetry. In the same conditions, the electrochemical oxidation of complex 2 is more intricate, and a thorough analysis of EPR spectra establishes the formation of the binuclear mono-mu-oxo mixed-valent [(L(3))ClMn(III)(mu-O)Mn(IV)Cl(L(3))](3+) (6) complexes. Electrochemical conversion of Mn(II) complexes into mixed-valent Mn(2)(III,IV) oxo-bridged complexes in the presence of 2,6-lutidine is discussed. The role of the chloride ligands as well as that of L(3) in the building of oxo bridges is discussed. Differences in behavior between L(2) and L(3) are commented on.

A variety of mono-oxidized pyridine, bipyridine, terpyridine, and pyridine/pyridazine are readily prepared under mild conditions using Pyrolusite MnO2. This phase has been characterized by means of X-ray powder diffraction and scanning electron microscopy. The oxidative activity is in keeping with the nature, morphology, and surface area of the MnO2 reagent.

The diastereoselective synthesis of hydrazinocyclopentenes 6 or 7 can be achieved in a straightforward manner from Diels-Alder adduct 4 using an acid-catalyzed rearrangement or a palladium-catalyzed allylic substitution reaction. In the latter case, enantioenriched compounds with ee values up to 58% can be obtained when an appropriate chiral ligand is used. [reaction: see text]

X-ray structures for six Fe(II) and Fe(III) complexes from two closely heptadentate N-tripodal ligands, L1H(3) = tris[(imidazol-4-yl)-3-aza-3-butenyl]amine and L2H(3) = tris[(imidazol-2-yl)-3-aza-3-butenyl]amine, are described: three complexes in the L1 series (namely, [Fe(II)(L1H(3))](2+) and [Fe(III)(L1H(3))](3+) at low pH and [Fe(III)(L1)](0) at high pH) and three complexes in the L2 series (namely, [Fe(II)(L2H(3))](2+) at low pH and [Fe(II)(L2H)](0) and [Fe(III)(L2)](0) at high pH). Most of these complexes are stable in both Fe(II) and Fe(III) redox states and with the ligand in various protonation states. In the solid state, hydrogen bonds networks were obtained. Structural differences induced by 2- or 4-imidazole substitution are described and discussed. In solution, interconversions between different forms, with regard to oxidation and protonation states, were investigated by UV-visible spectroscopy, cyclic voltammetry, and potentiometry. The deprotonation pattern of these polyimidazole iron(II) and iron(III) complexes is described in detail. pK(a)s of the imidazolate/imidazole moieties in MeOH/H(2)O are reported. Two new species, namely, [Fe(II)(L1)](-) and [Fe(II)(L2)](-), were shown to be obtained in DMSO upon strong base addition and characterized by UV-vis spectroscopy and cyclic voltammetry. Half-wave potentials of Fe(III)/Fe(II) complexes with ligand moieties in several protonation states are reported, both in DMSO and in MeOH/H(2)O. Because of the presence of free imidazole groups coordinated to the iron, the potential of the iron(III)/iron(II) couples can be tuned by pH. A shift of DeltaE = E(deprot) - E(prot) ranging from -270 to -320 mV per exchanged proton in DMSO was measured. This study shows moreover that interconversions (with regard to both redox and protonation states) can be reversed several times. As the complexes have been isolated in order to be tested as superoxide dismutase mimics, preliminary reactions with dioxygen and with superoxide, considered as oxidant and reducer of biological importance, are reported. In these two series, O(2)(-) behaves either as a base or as a reducer and no adducts have been observed.

A new class of highly luminescent dyes is reported. The characteristic feature of these compounds is that a terpyridine fragment is closely appended to a boradiazaindacene moiety in such a way that cation binding to the vacant terpyridine causes strong perturbations of the photophysical properties of the boradiazaindacene unit. In particular, these sensors are especially applicable to the fluorescence detection of trace quantities of zinc(II) ions in solution. The mechanism of the cation-induced quenching process has been investigated by a combination of electrochemistry, UV/Vis absorption, emission, and NMR spectroscopy. Highly luminescent arrays can be formed by doping transparent polymers with low concentrations of these new dyes. In such materials, the change in photophysical properties upon cation binding is so marked that "cation writing" becomes feasible under routine conditions.

There has been considerable interest in metal complexes of binucleating ligands as models for the coordination environment of the active sites in binucleating metalloenzymes. Numerous synthetic systems, like di-copper or di-cobalt complexes, have been demonstrated to function as catalysts for the transformation (oxidation, hydrolysis) of organic substrates other than the ligand itself. The catalytic efficiency and the selectivity depends critically on the distance between the metallic centers, the conformation of the spacer and the stability of the complex.

Molecular recognition of flat substrates requires the design of receptor molecules containing complementary flat units. If two such units are incorporated into a macrocyclic framework, a face to face inclusion of a planar substrate may take place, leading to an intercalative supramolecular structure.

A new example of a site-selective metal-assisted oxidative cleavage of a C-N bond is reported. This phenomenon occurs in the nitrogen-centered tetradentate tripodal BPG ligand (BPG = (bis(2-pyridylmethyl)amino)acetate), which combines one carboxylate and two pyridines as pendant groups, when coordinated to iron(III). The corresponding iron(III) [Fe(BPG)Cl(2)] complex (1) is transformed to the iron(III) [Fe(BPA)Cl(3)] complex (2) with the tridentate BPA ligand (BPA = bis(2-pyridylmethyl)amine) retaining only two pyridine pendant groups, while the initial BPG carboxylate group is transformed to glyoxylic acid. The [Fe(BPA)Cl(3)] complex (2) has been fully characterized as well as another, [Fe(BPE)Cl(3)] (3), formed with the tridentate BPE ligand (BPE = methyl (bis(2-pyridylmethyl)amino)acetate) which, in addition to two pyridines, presents an ester group. The crystal structures of these two complexes have been resolved. The asymmetric unit of complex 2 has been characterized by two mononuclear neutral molecules linked by two hydrogen bonds. (Crystal data for 2: orthorhombic, Pna2(1), a = 15.603(8) Å, b = 8.485(4) Å, c = 22.752(11) Å, alpha = beta = gamma = 90 degrees, V = 3012(3) Å(3), Z = 8, R = 0.0582 [2813 reflections with I2sigma(I)], and R(w) = 0.1430.) Complex 3 is symmetric with the iron center, the amine nitrogen, one choride and the three atoms of the carboxylate group in special positions in the mirror plane. (Crystal data for 3: orthorhombic, Pmn2(1), a = 10.418(4) Å, b = 12.952(5) Å, c = 7.353(3) Å, alpha = beta = gamma = 90 degrees, V = 992.2(7) Å(3), Z = 2, R = 0.0500 [513 reflections with I2sigma(I)], and R(w) = 0.1231.) Redox potentials corroborate the structural features (E degrees = -38 mV for 1, -19 mV for 2, and +145 mV for 3 vs SCE in acetonitrile). Preliminary studies of the [Fe(BPG)Cl(2)] complex have shown that it reacts in its reduced form with dioxygen.

International audience; Studies of the properties of a series of amphiphilic calixarenes show that they can form stable monolayers, Langmuir-Blodgett layers and solid lipid nanoparticles, the mesostructures were investigated by atomic force microscopy and the crystal structure of one compound shows a partially interdigitated tilted bilayer structure.Studies of the properties of a series of amphiphilic calixarenes show that they can form stable monolayers, Langmuir-Blodgett layers and solid lipid nanoparticles, the mesostructures were investigated by atomic force microscopy and the crystal structure of one compound shows a partially interdigitated tilted bilayer structure.

A newly-synthesized 4′-[bis(diphenylphosphino)methane]–2,2′∶6′,2 ″-terpyridine-based (dppm–terpy) ligand forms complexes by selective complexation of the terpy or diphos segment, respectively, with Fe(II) or Pd(II) salts; in the latter case, an X-ray structural analysis reveals the formation of a neutral square-planar complex assembled from the deprotonated ligands.