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Mononuclear amino triphenolate iron(III) complexes have been synthesized and characterized (UV/Vis spectroscopy, cyclic voltammetry, ESI-MS, 1H NMR spectroscopy, X-ray diffraction). These complexes act as biomimetic catalysts promoting the aerobic auto-oxidation of 3,5-di-tert-butylcatechol to the corresponding o-benzoquinone at room temperature and displaying catalase activity for the hydrogen peroxide dismutation with remarkable activity (TON up to 4000).

Lipophilic linear semirigid side arms containing two or three successive phenyl rings separated by carboxylate spacers have been connected to the 5 or 6 positions of bent aromatic terdentate 2,6-bis(benzimidazol-2-yl)pyridine binding units to give extended V-shaped (L11) and I-shaped receptors (L12, L12b, and L13). The carboxylate spacers limit the flexibility of the side arms and provide crossed arrangements of the successive aromatic rings in the crystal structure of L12b (C63H61N5O10; triclinic, P1̄, Z = 2) in agreement with semiempirical calculations performed on optimized gas-phase geometries. Moreover, the carboxylate spacers in L11−L13 prevent efficient electronic delocalization between the connected aromatic rings and act as weak π acceptors producing a slight increase of the energy of the 1ππ* and 3ππ* levels centered on the terdentate binding unit. Intermolecular π-stacking interactions observed in the crystal of L12b are invoked to rationalize (i) the peculiar excimer emission of L11 in the solid state and (ii) the rich and varied calamitic (I-shaped L12, L12b, and L13) and columnar (V-shaped L11) mesomorphism observed at high temperature. The ColR mesophase detected for L11 demonstrates that V-shaped bent terdentate binding units are compatible with liquid-crystalline behavior. Complexation of L11 with lanthanide(III) produces I-shaped complexes [Ln(L11)(NO3)3] (Ln = La, Eu, Gd, Tb, and Lu) possessing a large axial anisometry as found in the crystal structure of [Lu(L11)(CF3CO2)3(H2O)] (LuC81H87N5O17F9; triclinic, P1̄, Z = 2), which exists in the solid state as H-bonded dimers. No mesomorphism is detected for the complexes as a result of the large perpendicular expansion brought by the metallic coordination site, but the high energy of the ligand-centered 3ππ* prevents Eu(5D0) → L11 back transfer in the Eu(III) complex, which thus exhibits sizable red luminescence at room temperature, a crucial point for the design of luminescent materials.

Well defined, stable, one-point binding ruthenium complexes and selectively bind and activate alpha,beta-unsaturated carbonyl compounds for cycloaddition reactions. These mild Lewis acids catalyze asymmetric 1,4-addition reactions of aryl thiols to enones with product selectivities up to 87% ee. (31)P NMR experiments provide an insight into the intricate equilibria governing the reaction mechanism. The absolute configuration of the major products indicates enones to react in the syn-s-trans orientation. Models based on X-ray structures of the Ru complexes can be used to rationalize selectivity.

Six cyclometalated iridium(III) complexes were investigated to assess their potential as photosensitizers for long-range electron transfer, and two of them were incorporated directly into covalent donor–bridge–acceptor molecules. The influence of ligand substitutions on the excited-state properties and the photoredox behavior of the iridium complexes was explored by optical absorption, steady-state and time-resolved luminescence spectroscopy, as well as by electrochemical methods. Bimolecular electron transfer between the photoexcited complexes and 10-methylphenothiazine and methylviologen was found to be only weakly dependent on the ligand substitutions. Intramolecular long-range electron transfer from phenothiazine to photoexcited iridium(III) in the dyads is slow due to the occurrence of a Coulomb barrier. Consequently, an electron-transfer photoproduct is only observable in the transient absorption spectrum of a donor–bridge–acceptor molecule with a fluorinated photosensitizer that exhibits a very long excited-state lifetime. A flash-quench technique is necessary for detection of an electron-transfer product in the dyad with a non-fluorinated photosensitizer. The occurrence of a Coulomb barrier associated with intramolecular (excited-state) long-range electron transfer in the dyads with cyclometalated iridium(III) photosensitizers represents an important difference to previously investigated similar donor–bridge–acceptor molecules with photosensitizers based on d6 metal diimine complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The europium complex with pyridine-2,6-dicarboxylic acid forms three-dimensional polymers in the solid state. The crystal structure of this assembly shows that europium cation is nine-coordinated and the first coordination sphere contains four water molecules. Mono(dipicolinate) structural units are interconnected by bridging carboxylate oxygens to provide a compact supramolecular structure with a high density.

Chiral framework: Chiral amines with pyrrolidine frameworks catalyze the enantioselective conjugate addition of a wide range of aldehydes to various vinyl sulfones and vinyl phosphonates in high yields and with enantioselectivities up to99 % ee (see scheme). The high versatility of the Michael adducts is exemplified by various functionalizations with conservation of the optical purity.Chiral amines with a pyrrolidine framework catalyze the enantioselective conjugate addition of a broad range of aldehydes to various vinyl sulfones and vinyl phosphonates in high yields and with enantioselectivities up to99 % ee. This novel process provides synthetically useful chiral gamma-gem-sulfonyl or phosphonyl aldehydes which can be widely functionalized with retention of the enantiomeric excess. Mechanistic insights including DFT calculations are explored in detail.

The highly tuned, one-point binding cationic cyclopentadienyl-iron and -ruthenium complexes 1 and 2 that incorporate chiral bidentate pentafluoroaryl-phosphinite ligands selectively coordinate and activate alpha,beta-unsaturated carbonyl compounds towards asymmetric catalytic cycloaddition reactions with diaryl nitrones. The reaction gives isoxazolidine products in good yields, with complete endo selectivity and high enantioselectivity. The products are obtained as a mixture of regioisomers in ratios varying from 96:4 to 15:85. The regioselectivity correlates directly with the electronic properties of the nitrone. This is shown by the experimental and computational data.

We report on the preparation of discrete 3D tetrametallic edifices containing trivalent lanthanides (Eu-Lu). Their formation is thermodynamically controlled through self-assembly with a new tripodal ligand L possessing short binding strands. X-ray crystallography shows that four nine-coordinate cations adopt a regular tetrahedral arrangement in the solid state. These remarkable, highly charged structures are maintained in solution, as demonstrated by NMR spectroscopy, ESI-MS and spectrophotometry. © Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Recently we have demonstrated a series of systems in which complex structures were created from simple amine and aldehyde subcomponents by copper(I)-templated imine bond formation. We describe herein the extension of this "subcomponent self-assembly" concept to the generation of structures based upon the iminoboronate ester motif. Equimolar amounts of diol, amine, and 2-formylphenylboronic acid reacted by reversible B-O and C=N bond formation to generate iminoboronate esters, as has recently been reported by James et al. (Org. Lett. 2006, 8, 609-612). The extent of ester formation was shown to depend upon a number of factors. The exploration of these factors allowed rules and predictions to be formulated governing the self-assembly process. These rules allowed the construction of more complex structures containing multiple boron atoms, including a trigonal cage containing six boron centers, as well as pointing the way to the construction of yet more intricate architectures. The lability of the B-O and C=N bonds also allowed different diol and amine subcomponents to be substituted within these structures. Selection rules were also determined for these substitution reactions, allowing the products to be predicted based upon the electronic properties of the diols and diamines employed. These results thus demonstrate the generality of the subcomponent self-assembly methodology through its application to a new dynamic covalent system.

Mannose-derived hexacoordinated phosphate anions, prepared in as few as two steps from methyl-alpha-D-mannopyranoside and tris(dimethylamino)phosphine, are chiral anionic auxiliaries with broad asymmetric efficiency. These chemically robust anions are effective NMR chiral solvating agents and efficient asymmetry-inducers, able to control the configuration of conformationally labile C2-symmetric monomethinium cations (organic, helical, charge 1+, P or M enantiomers) and D3-symmetric iron(II) trisdiimine complexes (metallo-organic, octahedral, charge 2+, Delta or Lambda enantiomers). Diastereomeric control with often unmatched selective levels was achieved with the help of mannopyranoside backbone of the anions and the substituents on the [1,3]dioxane ring that play a key role in the recognition process, something not obvious at first sight.

Bring on the big cats: New, C2-symmetric bulky N-heterocyclic carbene ligands bring major improvements in the palladium-catalyzed asymmetric intramolecular α-arylation of amides to give oxindoles (see picture, dba=trans,trans-dibenzylideneacetone), which are formed in high yield and excellent enantiomeric purity.

The incorporation of enantiopure 1-amino-2,3-propanediol as a subcomponent into a dicopper double helicate resulted in perfect chiral induction of the helicate's twist. DFT calculations allowed the determination of the helicity of the complex in solution. The same helical induction, in which S amines induced a Lambda helical twist, was observed in the solid state by X-ray crystallography. Electronic structure calculations also revealed that the unusual deep green color of this class of complexes was due to a metal-to-ligand charge transfer excitation, in which the excited state possesses a valence delocalized Cu2(3+) core. The use of a racemic amine subcomponent resulted in the formation of a dynamic library of six diastereomeric pairs of enantiomers. Surprisingly, this library converted into a single pair of enantiomers during crystallization. We were able to observe this process reverse upon redissolution, as initial ligand exchange was followed by covalent imine metathesis.

Bis-iminophosphoranes containing various types of linkers between two R3PN moieties were electrochemically oxidized at controlled potential in situ in the electron spin resonance (ESR) cavity. For linkers constituted of phenylenes, conjugated phenylenes or merely a dicyanoethylenic bond, this oxidation led to well-resolved ESR spectra which were characterized by their g values and by their 1H, 14N and 31P isotropic hyperfine constants. These coupling constants agree with those calculated by DFT for the corresponding cation radicals. Experimental and theoretical results clearly indicate that in these species the unpaired electron is mostly delocalized on the bridge and on the nitrogen atoms while the spin density on the phosphorus atoms is particularly small. Cyclic voltammetry and ESR spectra show that the nature of the bridge between the two iminophosphoranes considerably influences the oxidation potential of the compound as well as the stability of the radical cation. Information about the conformation of the precursor containing two Ph3PN moieties separated by a C(CN)C(CN)group was obtained from its crystal structure. Copyright © 2007 John Wiley & Sons, Ltd.

A series of di-copper(I) complexes has been prepared via the reaction of copper(I) tetrafluoroborate, 2,6-diformylpyridine, 8-aminoquinoline, and a series of aliphatic diamines and 4-substituted anilines. To avoid a “valence-frustrated” state, involving a mismatch between the number of ligand donor atoms and the number of metal acceptor sites, the product structures formed selectively: One of the formyl groups of the diformylpyridine reacted specifically with the aminoquinoline, whereas the other formyl group reacted with the diamine or aniline. The observed selectivity was demonstrated to be thermodynamic in nature: When two dicopper complexes that were stable yet “valence-frustrated” were mixed, an imine metathesis reaction was observed to occur spontaneously to generate a “valence-satisfied” structure. In addition to control over the constitution of the ligands, we were able to exercise control over their relative orientations within the complex. Diamines exclusively gave structures in which the ligand exhibited a head-to-head orientation along the copper–copper axis to avoid stretching. Anilines gave predominantly head-to-tail structures, with the proportion of head-to-head isomer decreasing in complexes that incorporate more electron-deficient anilines and disappearing in less polar solvents. We also demonstrated the removal of the metals and the hydrogenation of the imine bonds to generate a molecule containing nonexchanging secondary amines, suggesting potential uses of this technique in the domain of organic synthesis.

The nonadentate podands L7, L8 et L9 have been prepared according to a multi-step strategy using the flexible 3-(2-hydroxy-ethyl)-pentane-1,5-diol, 4-(3-hydroxy-propyl)-heptane-1,7-diol and 3-(2-hydroxy-ethyl)-3-methyl-pentane-1,5-diol covalent tripods, respectively. Minor changes in the structure of the ligands, i.e. the replacement of the apical hydrogen atom with a methyl group, or the introduction of an extra methylene in the caping moiety, induce dramatic effects in the structures of the resulting lanthanide complexes [Ln(Lx)]3+ (x = 7–9). The complexes [Ln(L7)]3+ and [Ln(L9)]3+ exist as mixtures of two endo isomers which do not interconvert on the NMR time scale, whereas [Ln(L8)]3+ exhibits a single exo isomer. To cite this article: S. Koeller et al., C. R. Chimie 9 (2006).

The absolute configuration and enantiomeric excess of chiral cyclic alcohols can be predicted from the 31P NMR spectra of the two diastereoisomers obtained with organophosphorus diamino-derivatizing agents (CDAs) and the chiral secondary alcohol, according to a simplified model taking into account the spatial location of the substituents of the chiral alcohol center and the 31P NMR signals of the two diastereoisomers.

Paramagnetic complexes M(CO)5P(C6H5)2, with M = Cr, Mo, W, have been trapped in irradiated crystals of M(CO)5P(C6H5)3 (M = Cr, Mo, W) and M(CO)5PH(C6H5)2 (M = Cr, W) and studied by EPR. The radiolytic scission of a P-C or a P-H bond, responsible for the formation of M(CO)5P(C6H5)2, is consistent with both the number of EPR sites and the crystal structures. The g and 31P hyperfine tensors measured for M(CO)5P(C6H5)2 present some of the characteristics expected for the diphenylphosphinyl radical. However, compared to Ph2P*, the 31P isotropic coupling is larger, the dipolar coupling is smaller, and for Mo and W compounds, the g-anisotropy is more pronounced. These properties are well predicted by DFT calculations. In the optimized structures of M(CO)5P(C6H5)2 (M = Cr, Mo, W), the unpaired electron is mainly confined in a phosphorus p-orbital, which conjugates with the metal d(xz) orbital. The trapped species can be described as a transition metal-coordinated phosphinyl radical.

Based on the bond-valence sum model the continual transition between the bidentate and monodentate bonding mode of carboxylato group and minimum of Cu–O bond lengths were estimated. The dependence of Cu⋯Cu separation on Cu–N bond length in binuclear Cu(II) carboxylates with caffeine were derived and fitted to the observed data. The crystal structure of [Cu2(2-bromopropanoato)4(caffeine)2] has been determined by X-ray crystallography. The structure consists of centrosymmetric binuclear units where the two Cu atoms are coordinated by four disordered bridging 2-bromopropionates and two caffeine ligands at the apices of a bicapped square prism. Both 2-bromopropionates show disorder of their –Br and –CH3 substituents. Stacking π·π interactions between the adjacent caffeine molecules link the complex units in 1-D networks. The binuclear structure of the studied compound is consistent with magnetic data and EPR spectrum.

The complex [Cu₂(1)₂]²⁺ (1 = 1,3‐bis(1‐methyl‐1H‐benzimidazol‐2‐yl)benzene) undergoes slow oxidation by dioxygen in DMF solution to give the hydroxylated product [Cu₂(2‐H)₂]²⁺ (2 = 2,6‐bis(1‐methyl‐1H‐benzimidazol‐2‐yl)phenol) characterized by an X‐ray crystal‐structure analysis. The oxidation occurs much faster when CuII is mixed with 1 in the presence of H₂O₂, with 80% hydroxylation observed within a few minutes. The mononuclear complex formed with 1‐methyl‐2‐phenyl‐1H‐benzimidazole (3) shows no hydroxylation under these conditions. It is concluded that the hydroxylation requires the presence of a ligand capable of stabilizing a binuclear species, but no special coordinative activation of the copper is required.

The improved synthesis of the chiral phosphoramidite Ia, based on a biphenol backbone and bearing chiral bis(1-phenylethyl)amine group on the phosphorus atom, is described together with its Pd(II) complex. The chiral complex cis-PdCl2L2 (L = Ia) has been characterized by X-ray crystal structure analysis and spectroscopic data. The series of the chiral P-monodentate phosphoramidite and phosphite ligands was tested in Pd-catalyzed enantioselective allylic substitution of different substrates. In the palladium-catalyzed asymmetric allylic alkylation of 1,3-diphenylallyl acetate with dimethylmalonate, up to 79% ee was achieved with [Pd2(dba)3] × CHCl3 as precatalyst.

A full set of centrosymmetric crystal structures published in Inorganica Chimica Acta as being non-centrosymmetric has been examined. Many have origin-free directions in the non-centrosymmetric description. Frequently insufficient data have been measured. Values obtained for the Flack parameter have been analyzed. With sufficient data coverage, a value close to 0.5 is obtained. With insufficient data a value near to zero has been observed and explained. Many of these structures qualify for the ORTEP-of-the-Year prize.

For 25 years it has been known that 1,4-dihydroxynaphthalene and tetrahydronaphthalene-1,4-dione coexist as stable tautomers; however, the dione has now emerged as an interesting starting material for synthesis. Its efficient isolation is reported, and the corresponding [Cr(CO)3] complexes of the two tautomers are prepared, thus leading to efficient desymmetrization using chiral diamine acyl-transfer catalysts

Herein is reported an investigation towards the stereoselective synthesis of inherently chiral pseudorotaxanes. Chiral ammonium threads were readily prepared in five steps from racemic or enantiopure (M or P) salts of di-n-propyl-1,13-dimethoxyquinacridinium cation. Their self-assembly with DB24C8 or disymmetrically oriented DB24C8F6 rings formed pseudorotaxanes as shown by 1H and 19F NMR spectroscopy as well as MS measurements. A determination of the association constants (Ka) was afforded. The crucial role played by the ammonium counter-ion in the threading process was further demonstrated as salts of TRISPHAT (tris(tetrachlorobenzenediolato)phosphate(V)) anion were quite more effective than their PF6- analogues (x 7.3). A general lack of diastereoselectivity (de

The conformational preferences of protonated 2-benzimidazole cations have been modelled. Non-alkylated benzimidazoles show no strong conformational preferences, but methylation at the N1 position leads to high rotational barriers. The crystal structures are reported for five salts of protonated cations where two or three benzimidazoles are linked by ethylene or cyclohexyl spacers and for one copper(I) complex of a bis-benzimidazole ligand. The conformations observed in the solid state agree with the models. Stacking between benzimidazoles is observed in all cases but one where a high symmetry structure involving six edge-to-face interactions is preferred. Hydrogen bonding to anions or solvent molecules is observed for all salts of protonated benzimidazoles. The packing coefficients of the structures show small but significant variations.

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The title compound (±)-1, a recently discovered, valuable, floral-type odorant, has been synthesized by a straightforward procedure (Scheme 1). To determine the properties of the enantiomers of 1, their separation by preparative HPLC and the determination of their absolute configuration by X-ray crystallography were carried out (Figure). Furthermore, the analogues 2–6 were synthesized, either from differently methylated 2-methylindan-1-ones (Schemes 2 and 3) or, in the case of the 2,4,6-trimethylated homologue 6, by a completely different synthetic approach (Scheme 4). An evaluation of (+)-(S)-1, (−)-(R)-1, and (±)-1 showed only minor differences in terms of odor (Table).

Placing fluorine atoms at selected positions allows enantiopure hexacoordinate phosphate anions to behave as effective chiral solvating and resolving agents for RuII complexes (the structure of one of the anions is shown: F: yellow; O: red; Cl: green; P: purple). The structural features of the asymmetric ion pairing can be determined by NMR spectroscopy owing to the presence of the fluorine atoms. Fluoratome an ausgewählten Positionen machen enantiomerenreine hexakoordinierte Phosphatanionen zu effektiven chiralen solvatisierenden und trennenden Agentien für RuII-Komplexe (die Struktur eines Anions ist gezeigt: F: gelb; O: rot; Cl: grün; P: violett). Die Strukturmerkmale der asymmetrischen Ionenpaarung können wegen der Fluoratome NMR-spektroskopisch bestimmt werden.

The aminal of (benzaldehyde)tricarbonylchromium and en-antiopure bipyrrolidine undergoes diastereoselective ortho-metallation with butyllithium. Quenching with various electrophiles, followed by hydrolysis of the aminal, affords ortho-substituted (benzaldehyde)tricarbonylchromium compounds with high ee (91–99 %). When quenched with Ph2PCl, a new chiral P,N-bidentate ligand is obtained, which shows efficiency in Pd- and Cu-catalysed reactions. The aminal of ferrocenecarbaldehyde could also be formed, but the ortho-deprotonation occurs with only moderate diastereoselectivity (70 %). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Under stoichiometric conditions, the segmental tris-tridentate ligand L9 assembles with two different lanthanide metal ions Ln(1) and Ln(2) (Ln(1), Ln(2)=La, Nd, Sm, Eu, Yb, Lu, Y) to give mixtures of the heterotrimetallic triple-stranded helicates [(Ln(1))(x)(Ln(2))(3-x)(L9)(3)](9+) (x=0-3) in acetonitrile. The combination of qualitative (ESI-MS) and quantitative ((1)H NMR) speciations provides a set of thermodynamic data that were analysed with various statistical chemical models. A satisfying description requires the consideration of different affinities for the terminal N(6)O(3) sites (k(t)(Ln) and for the central N(9) site (k(c)(Ln) for each specific lanthanide. The nontrivial dependence of these parameters on the ionic radius provides size-discriminating effects that favour the formation of heterotrimetallic helicates in which the central site is occupied by the larger metal of the pair. Combining the latter enthalpic driving forces with entropic contributions due to specific stoichiometric conditions allows partial selection (i.e., programming) of a specific heterotrimetallic species in solution, which can be isolated by crystallisation, as demonstrated for [Eu(2.04)La(0.96)(L9)(3)](CF(3)SO(3))(9)(CH(3)NO(2))(9) (1, Eu(2.04)La(0.96)C(207)H(222)N(48)O(51)S(9)F(27), monoclinic, P2(1)/c, Z=4) in which the cation [EuLaEu(L9)(3)](9+) is the major component in the crystal. The scope and limitation of this approach is discussed together with the conditions for explicitly considering intermetallic interaction parameters u(Ln1Ln2) in more sophisticated chemical models.

The unsymmetrical tridentate benzimidazole-pyridine-carboxamide units in ligands L1-L4 react with trivalent lanthanides, Ln(III), to give the nine-co-ordinate triple-helical complexes [Ln(Li)3]3+ (i = 1-4) existing as mixtures of C3-symmetrical facial and C1-symmetrical meridional isomers. Although the beta13 formation constants are 3-4 orders of magnitude smaller for these complexes than those found for the D3-symmetrical analogues [Ln(Li)3]3+ (i = 5-6) with symmetrical ligands, their formation at the millimolar scale is quantitative and the emission quantum yield of [Eu(L2)3]3+ is significantly larger. The fac-[Ln(Li)3]3+--mer-[Ln(Li)3]3+ (i = 1-4) isomerisation process in acetonitrile is slow enough for Ln = Lu(III) to be quantified by 1H NMR below room temperature. The separation of enthalpic and entropic contributions shows that the distribution of the facial and meridional isomers can be tuned by the judicious peripheral substitution of the ligands affecting the interstrand interactions. Molecular mechanics (MM) calculations suggest that one supplementary interstrand pi-stacking interaction stabilises the meridional isomers, while the facial isomers benefit from more favourable electrostatic contributions. As a result of the mixture of facial and meridional isomers in solution, we were unable to obtain single crystals of 1:3 complexes, but the X-ray crystal structures of their nine-co-ordinate precursors [Eu(L1)2(CF3SO3)2(H2O)](CF3SO3)(C3H5N)2(H2O) (6, C45H54EuF9N10O13S3, monoclinic, P2(1)/c, Z = 4) and [Eu(L4)2(CF3SO3)2(H2O)](CF3SO3)(C4H4O)(1.5) (7, C51H66EuF9N8O(15.5)S3, triclinic, P1, Z = 2) provide crucial structural information on the binding mode of the unsymmetrical tridentate ligands.

The crystal structures of three complexes of dicarboxy-2,2'-bipyridyl ligands, 5,5'-dicarboxy-2,2'-bipyridyl (1) and 4,4'-dicarboxy-2,2'-bipyridyl (2) are reported. [Rh(1H)3] shows two interpenetrating, homochiral rhombohedral networks linked by short carboxylate-carboxylic acid hydrogen bonds, in which each complex acts as a node for six hydrogen bonds. [Ru(1H2)(1H)2] forms only four such hydrogen bonds, leading to the formation of heterochiral chains held together by stacking between bipyridyls. [Co(2H)3] can in principle form six hydrogen bonds, but in practice forms only four in a layer structure where stacking interactions are important. This is attributed to differences in molecular shape.

The formal 1,3-cycloaddition of 2-diazocyclohexane-1,3-diones 1a–1d to acyclic and cyclic enol ethers in the presence of RhII-catalysts to afford dihydrofurans has been investigated. Reaction with a cis/trans mixture of 1-ethoxyprop-1-ene (13a) yielded the dihydrofuran 14a with a cis/trans ratio of 85 : 15, while that with (Z)-1-ethoxy-3,3,3-trifluoroprop-1-ene (13b) gave the cis-product 14b exclusively. The stereochemical outcome of the reaction is consistent with a concerted rather than stepwise mechanism for cycloaddition. The asymmetric cycloaddition of 2-diazocyclohexane-1,3-dione (1a) or 2-diazodimedone (=2-diazo-5,5-dimethylcyclohexane-1,3-dione; 1b) to furan and dihydrofuran was investigated with a representative selection of chiral, nonracemic RhII catalysts, but no significant enantioselectivity was observed, and the reported enantioselective cycloadditions of these diazo compounds could not be reproduced. The absence of enantioselectivity in the cycloadditions of 2-diazocyclohexane-1,3-diones is tentatively explained in terms of the Hammond postulate. The transition state for the cycloaddition occurs early on the reaction coordinate owing to the high reactivity of the intermediate metallocarbene. An early transition state is associated with low selectivity. In contrast, the transition state for transfer of stabilized metallocarbenes occurs later, and the reactions exhibit higher selectivity.

The decomposition of cyclohexyl diazo(triethylsilyl)acetate 2a and the t-butyl derivatives 3a,b with [Rh2{(S)-nttl}4] and similar chiral Rh(II)-catalysts proceeds in toluene at room temperature to produce silylated lactones in up to 90% yield. The reaction is highly stereoselective. Enantioselectivities of up to 79% have been observed.

Cyclic voltammetry of Mes*PC(NMe2)2 (1) and Mes*PC(CH3)NMe2 (2) shows that, in solution in DME, these compounds are reversibly oxidized at 395 and 553 mV, respectively. Electrochemical oxidation or reaction of 1 (or 2) with [Cp2Fe]PF6 leads to the formation of the corresponding radical cation, which was characterized by its electron paramagnetic resonance (EPR) spectra. Experimental 31P and 13C isotropic and anisotropic coupling constants agree with density functional theory (DFT) calculations showing that the unpaired electron is strongly localized on the phosphorus atom, in accord with the description Mes*P•−(C(NMe2)2)+. Electrochemical reduction of 1 is essentially irreversible and leads to a radical species largely delocalized on the C(NMe2)2 moiety; this neutral radical results from the protonation of the phosphorus atom and corresponds to Mes*(H)P−•C(NMe2)2. No paramagnetic species is obtained by reduction of 2. The presence of the amino groups, responsible for the inverted electron distribution at the P−C double bond (P-−C+), confers on 1 and 2 redox properties that are in very sharp contrast with those observed for phosphaalkenes with a normal π electron distribution (P+−C-): no detection of the radical anion but easy formation of a rather persistent radical cation. For 1, this radical cation could even be isolated as a powder, 1•+PF6-. As shown by DFT calculations, this behavior is consistent with the decrease of the double bond character of the phosphorus−carbon bond caused by the presence of the amino groups.

The cyclopropanation of olefins with 2-diazodimedone 1a and the corresponding phenyliodonium ylide 1b in the presence of selected chiral Cu(I)- and Rh(II)-catalysts proceeds without significant enantioselectivity. Contrary to previous reports in the literature, the cyclopropanation of styrene with 1a in the presence of [Cu{(+)-facam}2] is not enantioselective. While the transition metal catalyzed 1,3-dipolar cycloaddition of 2-diazodimedone (1a) to furan and dihydrofuran is equally non-selective, the introduction of heteroatoms and/or unsaturation in the carbene precursor results in slightly enhanced enantioselectivity.

The introduction of long semirigid spacers between the capping carbon atom of the tripod and the unsymmetrical tridentate binding units provides the novel, extended covalent podand tris-[2-[2-(6-diethylcarbamoylpyridin-2-yl)-1-ethyl-1H-benzoimidazol-5-yl-methoxy]ethyl]methane (L(15)). Reaction of L(15) with lanthanide(III) in acetonitrile produces stable podates [Ln(L(15))](3+) (Ln=La-Lu) in which three tridentate binding units are facially organized. These wrap around the nine-coordinate pseudo-tricapped trigonal-prismatic metal ions. The crystal structure of [La(L(15))](ClO(4))(3) (18, LaC(67)H(82)N(12)O(18)Cl(3), trigonal, R3c, Z=6) reveals the formation of a C(3)-symmetrical triple-helical podate. Two slightly different arrangements of the flexible ethylenoxy parts of the spacer are observed in the solid state in agreement with the formation of two conformational isomers (M:m) in a 4:1 ratio. A qualitative analysis of the aromatic diamagnetic anisotropies affecting the NMR signals of [Ln(L(15))](3+) (Ln=La, Y, Lu) in solution, combined with the quantitative determination of electron-induced relaxation in the paramagnetic complex [Nd(L(15))](3+), demonstrate that the solid state structure is maintained in solution. This leads to a mixture of two triple-helical conformers of similar stabilities and that do not interconvert on the NMR timescale between 243 and 343 K. Particular attention has been given to the structural programming of extended covalent tripods for facially organizing unsymmetrical tridentate binding units around Ln(III). Photophysical measurements show that L(15) efficiently protects the metallic coordination spheres and sensitizes Eu(III) and Tb(III) upon UV irradiation.

The increase of the curvature of the interface between the rigid mesogenic core and the aliphatic chains in the hexacatenar tridentate ligand L3 overcomes the considerable expansion brought by the complexation of bulky metallic cores, thus leading to organized cubic mesophases for monometallic zincII and lanthanideIII complexes.

The syntheses and coordination chemistry of 5,5′-di(methylene-N-aminoacidyl)-2,2′-bipyridyl ligands, where the amino acid is valine (1) or alanine (2), are presented. Complexes [M(1)3]n+, where M = Co(II), Co(III) and Fe(II), form diastereoselectively when the amine group of the amino acid arm is protonated. At higher pH the diastereoselectivity drops significantly. The solid state structure of [CoIII(1H2)3]Cl2(ClO4)7 was determined by X-ray crystallography. Two chloride ions were found to be encapsulated by the amino acid arms of the complex via electrostatic attractions and hydrogen bonding to the protonated amine groups, as seen previously for the Fe(II) complex. No anion binding was detected in aqueous solution, but complexes [FeII(1H2)2(1H)]7+ and [CoIII(1H2)3]9+ bind chloride ions in CD3OD with binding constants of 60(4) and 24(2) M−1 respectively, as determined by 1H NMR spectroscopy. 1H NMR spectroscopy suggests considerable conformational change of the ligand sidearms upon chloride binding. Complexes [FeII(2)3]2+ and [CoII(2)3]2+ are formed with d.e.'s of 33 and 56% respectively.

The systematic investigation of steric and electronic effects on the formation of lanthanide complexes with the tridentate N,N,N′,N′-tetraalkylpyridine-2,6-dicarboxamide ONO ligands (alkyl = ethyl: L5, isopropyl: L6 and benzyl: L7) shows a reduced affinity with increasing steric demand in the order L5 < L6 < L7. [Ln(Li)]3+ and [Ln(Li)2]3+ are formed with the three ligands, but 1 ∶ 3 complexes are strictly limited to [Ln(L5)3]3+ and [Ln(L6)3]3+ because of the significant steric congestion provided by the twelve benzyl groups located along the three-fold axis in [Ln(L7)3]3+. Comparisons between L6 and L7 in the 1 ∶ 2 complexes evidence superimposable pseudo-monocapped square antiprismatic coordination spheres in the crystal structures of [Ln(Li)2(H2O)2(CF3SO3)](CF3SO3)2 (i = 6, Ln = Eu: 9; i = 7, Ln = Gd: 10). Photophysical properties of [Ln(L6)2]3+ and [Ln(L7)2]3+ (Ln = Eu, Gd, Tb, Lu) are similar except for improved quantum yields for [Ln(L7)2]3+ (Ln = Eu, Tb) which can be assigned to a slightly more efficient L7 → LnIII energy transfer process. The removal of two benzyl groups in the analogous N,N′-dibenzylpyridine-2,6-dicarboxamide ligand (L8) restores the formation of stable triple-helical complexes as demonstrated by the crystal structure of [Tb(L8)3]2(CF3SO3)6 (11). However, the existence of intricate mixtures of isomers in solution which are blocked on the NMR time scale limits their use as building blocks for the design of polymetallic d–f and f–f helicates.

The crystal structures of three salts of diprotonated 1,2-bis(1H-benzimidazol-2-yl)ethane, 1, with tetrahalogenometallates are reported. The crystal lattices are constructed from two types of interactions, the stacking of the protonated benzimidazole groups and N–H⋯Cl hydrogen bonding between the cations and the complex anions. Depending on the conformation of the cation, two- or three-dimensionally stacked structures are formed. A similar packing motif is found with the related cation formed by 1,3-bis(1H-benzimidazol-2-yl)propane, 2, and this suggests that the protonated benzimidazole group may be a useful synthon for crystal engineering.

The ligand 1,2-bis(1H-benzimidazol-2-yl)-1,2-ethanediol, 1, and its methylated derivative 2 are readily synthesized from tartaric acid, and act as chiral, facially coordinating tridentate ligands, forming complexes of composition ML2 with octahedral transition metals. The copper(II) complexes show distorted 4 + 2 coordination with benzimidazoles occupying the equatorial sites and alcohol functions weakly binding in the axial sites. Nickel(II) complexes in three different states of protonation show regular octahedral geometry with the alcohols mutually cis. Deprotonation of the coordinated alcohol produces little structural change but the monodeprotonated complex forms a hydrogen bonded dimer. Magnetic measurements show the hydrogen bonded bridge to offer a pathway for weak antiferromagnetic coupling. UV-Visible spectroscopy shows the ligand to have a field intermediate between water and pyridine. The diastereoselectivity of complexation depends on the geometry: nickel(II) shows a weak preference for the homochiral complex, whereas copper(II) forms almost exclusively homochiral complexes.

Optically active (1S,5R)-(+)-3-azabicyclo[3.2.2]non-6-en-2-one (+)-7 was synthesized via enantioselective intramolecular cyclopropanation of racemic cyclohexen-3-yl diazoacetate 10 in the presence of [Rh2({(2S)-meox}4] catalyst. The cyclopropanation product (−)-9 was converted to the azide 8, which underwent successive Curtius and 3-aza-Cope rearrangements to afford 18, which was reduced to the bicyclic azepinone (+)-7. An analogous sequence based on Cope rearrangement of the SEM-protected enol ether 20 afforded (1S,5R)-bicyclo[3.2.2]nona-3,6-dien-2-one 22.

Dibenzo-18-crown-6 was chosen as ideal ligand for the complexation of a sodium cation in the aim to allow further coordination of iodide and another oxygen donor ligand in order to generate an asymmetric coordination sphere. The crystal structures obtained with NaI with this ligand and second one with a larger cavity are presented, forming molecular units, and featuring interesting physical properties such as optical birefringence dispersion.