Anne-Christine Chamayou

A chiral C3-symmetric hexanuclear triangular-prismatic copper(II) cluster derived from a highly modular dipeptidic N,N′-terephthaloyl-bis(S-aminocarboxylato) ligand

The enantiomeric dipeptidic ligand N,N′-terephthaloyl-bis(L-phenylalaninato) (TBPhe2–) reacts with copper(II) acetate in ethanol under the formation of the hexanuclear double-layered triangular-prismatic cluster [Cu2(μ4-TBPhe-κO : κO′ : κO″ : κO′″)2(EtOH)(H2O)]3·∼28(H2O/0.33EtOH) with C3-symmetry, homochiral conformer assembly in the crystal and strong antiferromagnetic coupling within the Cu2(O2CR)4 paddle-wheel unit (J = −214 K).

Hydrophilic interior between hydrophobic regions in inverse bilayer structures of cation–1,1′-binaphthalene-2,2′-diyl phosphate salts

A series of 1,1′-binaphthalene-2,2′-diyl phosphate (BNPPA−) salts have been synthesized. Their crystal packings show a separation of the hydrophobic naphthyl and hydrophilic (RO)2PO2− phosphate/cation/solvate regions. Hydrogen bonding in the latter is the driving force for “inverse bilayer” formation, with a hydrophilic interior exposing the hydrophobic binaphthyl groups to the exterior. Stacking of the inverse bilayers occurs less through π–π and more through CH⋯π interactions between the naphthyl groups, which correlates with the formation of thin crystal plates along the stacking direction. Cations used with R- or rac-BNPPA− are protonated isonicotin-1-ium amide (1), isonicotin-1-ium acid (2), guanidinium (3), the metal complexes trans-tetraammine-dimethanol-copper(II) (4), trans-diaqua-tetramethanol-copper(II) (5) and cis-diaqua-bis(ethylene diamine)-nickel(II) (6). Crystallization occurs with inclusion of water and methanol solvent molecules, except in 2. Starting from R-BNPPA, inversion takes place with calcium acetate to give 1 as the racemate. 2 is crystallized as the R-BNPPA salt. The inversion-symmetrical complex trans-[Cu(H2O)2(CH3OH)4]2+ in 5 has Cu–OH2 bond lengths of 1.937(4) A, and Cu–O(methanol) of 2.112(4) and 2.167(4) A, corresponding to a compressed tetragonal geometry.

Chirality and Diastereoselection of Δ/Λ-Configured Tetrahedral Zinc Complexes through Enantiopure Schiff Base Complexes: Combined Vibrational Circular Dichroism, Density Functional Theory, 1H NMR, and X-ray Structural Studies

The metal-centered Δ/Λ-chirality of four-coordinated, nonplanar Zn(A(^)B)(2) complexes is correlated to the chirality of the bidentate enantiopure (R)-A(^)B or (S)-A(^)B Schiff base building blocks [A(^)B = (R)- or (S)-N-(1-(4-X-phenyl)ethyl)salicylaldiminato-κ(2)N,O with X = OCH(3), Cl, Br]. In the solid-state the (R) ligand chirality induces a Λ-M configuration and the (S) ligand chirality quantitatively gives the Δ-M configuration upon crystallization as deduced from X-ray single crystal studies. The diastereoselections of the pseudotetrahedral zinc-Schiff base complexes in CDCl(3) solution were investigated by (1)H NMR and by vibrational circular dichroism (VCD) spectroscopy. The appearance of two signals for the Schiff-base -CH═N- imine proton in (1)H NMR indicates an equilibrium of both Δ- and Λ-diastereomers with a diastereomeric ratio of roughly 20:80% for all three ligands. VCD proved to be very sensitive to the metal-centered Δ/Λ-chirality because of a characteristic band representing coupled vibrations of the two ligands C═N stretch modes. The absolute configuration was assigned on the basis of agreement in sign with theoretical VCD spectra from Density Functional Theory calculations.

Structure–solid-state CPMAS 13C NMR correlation in palladacycle solvates (pseudo-polymorphs) with a transformation from Z′ = 1 to Z′ = 2

The dinuclear µ-acetato-µ-benzophenone iminato palladium complex [{(C∧N)Pd}2(µ-OAc)(µ-NCPh2)] (1) [C∧N = N,N-dimethylbenzylamine-κN,κC)] is prepared by reaction of [{(C∧N)Pd(µ-OAc)}2] with benzophenone imine and [NBu4]OH in ethanol. The dinuclear palladacycle 1 can crystallize with different solvents molecules as 1·1.5C6H5CH3, 1·0.25C6H5CH3 (Z′ = 2), 1·1.5C6H6 and 1·C6H14 (n-hexane) upon hexane diffusion into a toluene, benzene or CH2Cl2 solution, respectively. The structure of 1·0.25C6H5CH3 with two palladacycle molecules and two partly occupied toluene molecules in the asymmetric unit (Z′ = 2) is a consequence of partial toluene solvent loss from 1·1.5C6H5CH3 (Z′ = 1) as was followed by solid-state CPMAS 13C NMR. The transformation from Z′ = 1 to Z′ = 2 (crystal “on the way”?) toluene solvate can proceed in a solid-state single-crystal-to-crystal transition as evidenced from multiple single-crystal X-ray diffraction studies, also when the crystals are still in their mother liquor. During this transformation the remaining toluene crystal solvent becomes “locked in” (immobile from static 2H (D) NMR, only lost above 80° from TGA) and the crystals of 1·0.25C6H5CH3 (Z′ = 2) remain crystalline in air in the absence of mother liquor or toluene, different from the other solvates. A rotational disorder of one of the benzene molecules in 1·1.5C6H6 (Z′ = 1) around its pseudo-six-fold axis is supported by the line-shape analysis of the static 2H (D) spectrum.

Solvation-Induced Helicity Inversion of Pseudotetrahedral Chiral Copper(II) Complexes

The helicity of four-coordinated nonplanar complexes is strongly correlated to the chirality of the ligand. However, the stereochemical induction of either the Δ- or the Λ-configuration at the metal ion is also modulated by environmental factors that change the conformational distribution of ligand rotamers. Calculation of the potential energy surface of bis{(R)-N-(1-(4-X-phenyl)ethyl)salicylaldiminato-κ(2)N,O}copper(II) with X = Cl at the density functional theory level showed a clear dependence of the helicity-determining angle θ between the two coordination planes on the relative population of different ligand conformers. The influence of different substituents (X = H, Cl, Br, and OCH3) on complex helicity was studied by determination of the absolute configuration at the metal ion in complexes with either (R)- or (S)-configured ligands. X-ray single-crystal analysis showed that (R)-configured ligands with H, Cl, Br induce Δ, while OCH3-substituted (R)-configured ligands induce Λ in the solid state. According to vibrational circular dichroism and electronic circular dichroism studies in solution, however, all tested complexes with (R)-ligands exhibited a propensity for Δ, with high diastereomeric ratio for X = Cl and X = Br and moderate diastereomeric ratio for X = H and X = OCH3 substituted ligands. Therefore, solvation of copper complexes with X = OCH3 goes along with helicity inversion. This solid-state versus solution study demonstrates that it is not sufficient to determine the chiral-at-metal configuration of a compound by X-ray crystallography alone, because the solution structure can be different. This is particularly important for the use of chiral-at-metal complexes as catalysts in stereoselective synthesis.

Syntheses, Spectroscopy And Crystal Structures Of (R)-N-(1-Aryl-Ethyl)Salicylaldimines And [Rh{(R)-N-(1-Aryl-Ethyl)Salicylaldiminato}(η4-Cod)] Complexes

Condensation of salicylaldehyde with enantiopure (R)-(1-aryl-ethyl)amines yields the enantiopure Schiff bases (R)-N-(1-aryl-ethyl)salicylaldimine (HSB*; aryl = phenyl, 2-methoxyphenyl, 3- methoxyphenyl, 4-methoxyphenyl (4), 4-bromophenyl (5), 2-naphthyl). These Schiff bases readily react with dinuclear (acetato)(η4-cycloocta-1,5-diene)rhodium(I), [Rh(μ-O2CMe)(η4-cod)]2, to afford the mononuclear complexes, cyclooctadiene-((R)-N-(1-aryl-ethyl)salicylaldiminato-κ2N,O)- rhodium(I), [Rh(SB∗)(η4-cod)] (SB* = deprotonated chiral Schiff base = salicylaldiminate; aryl = phenyl (7), 2-methoxyphenyl, 4-methoxyphenyl, 4-bromophenyl, 2-naphthyl). The complexes have been characterized by IR, UV/vis, 1H/13C NMR and mass spectrometry, optical rotation as well as by single-crystal X-ray structure determination for 4, 5 and 7. The structure of 5 shows C-Br· · ·π contacts. Compound 7 is only the second example of a Rh(η4-cod) complex with a six-membered Rh-N,O-chelate ring

Can a small amount of crystal solvent be overlooked or have no structural effect? Isomorphous non-stoichiometric hydrates (pseudo-polymorphs): the case of salicylaldehyde thiosemicarbazone†

Compound (E)-2-(2-hydroxybenzylidene)hydrazinecarbothioamide (salicylaldehyde thiosemicarbazone) (1) is discussed as an isomorphous non-stoichiometric hydrate, that is, while the relative amount of the water guest molecules varies all the crystal structures are “nearly the same” and all the molecular structures of 1 are “the same”. Compound 1 can crystallize isomorphous with no and different non-stoichiometric small amounts of crystal water (0.095, 0.17 and 0.20H2O per formula unit were found). Unit cell dimensions and the crystal packing of the molecules with their hydrogen bonding are virtually unaffected by the presence or absence of the crystal water.

Tris(2,2′‐bipyridine‐κ2N,N′)copper(II) bis(tetrafluoridoborate)

The title compound, [Cu(C 10 H 8 N 2 ) 3 ](BF 4 ) 2 , shows the expected Jahn-Teller distortion at the pseudo-octa¬hedrally coordinated Cu II atom. Each Cu II complex cation is surrounded by six BF 4 - anions and each anion by three cations with weak C-H F hydrogen bonds between them. One of the two BF 4 - anions exhibits a rotational disorder (0.6:0.4) around one of the B-F bonds.

Broad-Range Spectral Analysis for Chiral Metal Coordination Compounds: (Chiro)optical Superspectrum of Cobalt(II) Complexes

Chiroptical broad-range spectral analysis extending from UV to mid-IR was employed to study a family of Co(II) N-(1-(aryl)ethyl)salicylaldiminato Schiff base complexes with pseudotetrahedral geometry associated with chirality-at-metal of the Δ/Λ type. While common chiral organic compounds have well-separated absorption and circular dichroism spectra (CD) in the UV/vis and IR regions, chiral Co(II) complexes feature an almost unique continuum of absorption and CD bands, which cover in sequence the UV, visible, near-IR (NIR), and IR regions of the electromagnetic spectrum. They can be collected in a single (chiro)optical superspectrum ranging from the UV (230 nm, 5.4 eV) to the mid-IR (1000 cm-1, 0.12 eV), which offers a fingerprint of the structure and stereochemistry of the metal complexes. Each region of the superspectrum contributes to one piece of information: the NIR-CD region, in combination with TDDFT calculations, allows a reliable assignment of the metal-centered chirality; the UV-CD region facilitates the analysis of the Δ/Λ diastereomeric equilibrium in solution; and the IR-VCD region contains a combination of low-lying metal-centered electronic states (LLES) and ligand-centered vibrations and displays characteristically enhanced and monosignate VCD bands. Circular dichroism in the NIR and IR regions is crucial to reveal the presence of d-d transitions of the Co(II) core which, due to the electric-dipole forbidden character, would be otherwise overlooked in the corresponding absorption spectra.