Alexandre Martinez

Azaphosphatranes as Structurally Tunable Organocatalysts for Carbonate Synthesis from CO2 and Epoxides

Three azaphosphatranes were used as organocatalysts for the synthesis of cyclic carbonates from CO2 and epoxides. They proved to be efficient single-component, metal-free catalysts for the reaction of simple or activated epoxides (styrene oxide, epichlorohydrin, glycidyl methyl ether) with CO2 under mild reaction conditions, displaying high stability and productivity over several days of reaction. Substitution patterns on the catalyst were shown to affect activity and stability. Kinetic analysis allowed investigation of the reaction mechanism.

Combined Cation–π and Anion–π Interactions for Zwitterion Recognition

Brothers and enemies: Anion-π and cation-π interactions act in a synergistic way when gathered in the molecular cavity of a hemicryptophane host, affording an efficient contribution (-170 kJ mol(-1)) in zwitterion recognition. NMR titration experiments and calculations reveal the positioning of the guest in the cavity of the heteroditopic receptor. This study emphasizes the importance of anion-π bonds in host-guest chemistry.

Reversible, solvent-induced chirality switch in atrane structure: control of the unidirectional motion of the molecular propeller.

Here we demonstrate that atrane-hemicryptophane molecular cages exhibit a reversible change in chirality uniquely controlled by the solvent, thus establishing the feasibility of a new mode of stimulation for atrane-based molecular switches. The oxidovanadium(V) complexes of hemicryptophane molecules exist as diastereomeric mixtures because of the P or M handedness of the cyclotriveratrylene unit and the chiral ether groups with the S configuration. The Δ/Λ propeller-like arrangement of the atrane moiety introduces a new local dissymmetry because of the conformationally restricted helical structure. (1)H NMR experiments provided significant data for the Δ ⇆ Λ interconversion process, where the solvent profoundly influences the chirality sense of the propeller motion, making control of the chirality by the choice of solvent possible. The reversible chirality inversion process is induced by alternating changes of solvent from CDCl(3) to C(6)D(6). The ratio of the rates of the clockwise and anticlockwise tilting motions of the atrane structure shows that the solvent directs the rotational motion of the vanatrane moiety, so the propeller sense of the motion can be considered as unidirectional.

Oxidation of cycloalkanes by H2O2 using a copper–hemicryptophane complex as a catalyst

Efficient alkane C-H bond oxidation was achieved using a newly designed Cu(II)-hemicryptophane complex. Protection of the copper site in the inner cavity of the host leads to enhanced yields and allows discriminating cyclohexane from cyclooctane or adamantane in competitive experiments.

The cooperative effect in ion-pair recognition by a ditopic hemicryptophane host.

The heteroditopic hemicryptophane 1, which bears a tripodal anion binding site and a cation recognition site in the molecular cavity, proved to be an efficient ion-pair receptor. The hemicryptophane host binds anions selectively depending on shape and hydrogen-bond-accepting ability. It forms an inclusion complex with the Me(4)N(+) ion, which can simultaneously bind anionic species to provide anion@[1⋅Me(4)N(+)] complexes. The increased affinity of [1⋅Me(4)N(+)] for anionic species is attributed to a strong cooperative effect that arises from the properly positioned binding sites in the hemicryptophane cavity, thus allowing the formation of the contact ion pair. Density functional theory calculations were performed to analyze the Coulomb interactions of the ion pairs, which compete with the ion-dipole ones, that originate in the ion-hemicryptophane contacts.

Encaging the Verkade’s Superbases: Thermodynamic and Kinetic Consequences

Proazaphosphatranes, also known as Verkades superbases, are nonionic species, which exhibit catalytic properties for a wide range of reactions. The properly designed host molecule 3 and its protonated counterpart [3·H](+)Cl(-) were synthesized to study how confinement can modify the stability and the reactivity of a Verkades superbase. The results show that the encapsulation does not alter the strong basicity of the proazaphosphatrane, but dramatically decreases the rate of proton transfer.

Controlling Helical Chirality in Atrane Structures: Solvent‐Dependent Chirality Sense in Hemicryptophane‐Oxidovanadium(V) Complexes

The diastereomeric hemicryptophane oxidovanadium(V) complexes (P)-(S,S,S)-3 and (M)-(S,S,S)-4 have been synthesized. (1)H and (51)V NMR spectra in solution are consistent with the formation of Lambda and Delta forms of the propeller-like vanatrane moiety, leading to two diastereomeric conformers for each complex: that is, (P)-(S,S,S-Lambda)-3/(P)-(S,S,S-Delta)-3 and (M)-(S,S,S-Lambda)-4/(M)-(S,S,S-Delta)-4. The Lambda/Delta ratio is rather temperature-insensitive but strongly dependent on the solvent (the de of (M)-(S,S,S)-4 changes from 0 in benzene to 92 % in DMSO). The solvent therefore controls the preferential clockwise or anticlockwise orientation of the propeller-like atrane unit. The energy barriers for the Lambdaright arrow over left arrowDelta equilibrium were determined by NMR experiments, and the highest DeltaG( not equal) value (103.7 kJ mol(-1)) was obtained for (P)-(S,S,S)-3, much higher than those reported for other atrane derivatives. This is attributed to the constraints arising from the cage structure. Determination of the activation parameters provides evidence for a concerted, rather than a stepwise, interconversion mechanism with entropies (DeltaS( not equal)) of -243 and -272 J mol(-1) K(-1) for (P)-(S,S,S)-3 and (M)-(S,S,S)-4, respectively. The molecular structure of the (P)-(S,S,S-Lambda)-3 isomer was solved by X-ray diffraction and shows a distorted structure with one of the linkers located in the CTV cavity. Complementary quantum chemical calculations were carried out to obtain the energy-minimized structures of (P)-(S,S,S)-3 and (M)-(S,S,S)-4. Our density functional theory calculations suggest that the (P)-(S,S,S-Lambda)-3 is favored, in agreement with experimental data. For the M series, a similar strategy was used to extract molecular structures and relative energies. As in the case of the P diastereomer, the Lambda form dominates over the Delta one.

A New Class of C3-Symmetrical Hemicryptophane Hosts: Triamide- and Tren-hemicryptophanes

The first hemicryptophanes derived from tris(N-alkyl-carbamoylmethyl)amine and tris(2-aminoethyl)amine (tren) have been synthesized following a single synthetic pathway that allows the subsequent formation of the two heteroditopic hosts 3 and 4. X-ray crystal structures show a well-defined cavity encapsulating a solvent guest for both compounds emphasizing their complexation properties.

Azaphosphatrane Organocatalysts in Confined Space: Cage Effect in CO 2 Conversion

The endohedral functionalization of a molecular cage by an azaphosphatrane unit has allowed for the creation of highly engineered catalytic cavities for efficient conversion of CO2 into cyclic carbonates. Strong structure/activity/stability correlations have been demonstrated by careful adjustment of the size, shape, and electronic properties of the hemicryptophane host.

Recent advances in H2PO4− fluorescent sensors

Dihydrogen phosphate (H2PO4−) plays an essential role in a number of chemical and biological processes. The sensitive and selective detection of H2PO4− is of great interest to many scientific fields, ranging from supramolecular chemistry to life sciences. For the detection of H2PO4−, fluorescent methods have plenty of distinct advantages, for example they are simplistic and allow low levels of determination. Therefore, this review will focus on the current progress in the development of H2PO4− fluorescent sensors based on organic scaffolds, for sensing in both organic and aqueous solutions. Three main types of fluorescent probes will be categorized in this review: (i) intensity-based “turn-off” fluorescent sensors; (ii) intensity-based “turn-on” fluorescent sensors; and (iii) ratiometric fluorescent sensors that involve a ratio of two emission outputs. This review should provide a comprehensive description of this research area to date and be instructive for the design and synthesis of new fluorescent sensors for H2PO4−. In addition, the principles and mechanisms employed in the design of H2PO4− sensors will be thoroughly described.