Nathalie Saffon

Copper(I) complexes derived from mono- and diphosphino-boranes: Cu-->B interactions supported by arene coordination.

The monophosphino-boranes o-iPr(2)P(C(6)H(4))BR(2) (1: R = Ph and 3: R = Cy) and diphosphino-boranes [o-R(2)P(C(6)H(4))](2)BPh (5: R = Ph and 6: R = iPr) readily react with CuCl to afford the corresponding complexes {[o-iPr(2)P(C(6)H(4))BPh(2)]Cu(mu-Cl)}(2) 2, {[o-iPr(2)P(C(6)H(4))BCy(2)]Cu(mu-Cl)}(2) 4, {[o-Ph(2)P(C(6)H(4))](2)BPh}CuCl 7, and {[o-iPr(2)P(C(6)H(4))](2)BPh}CuCl 8. The presence of Cu-->B interactions supported by arene coordination within complexes 2, 7, and 8 has been unambiguously evidenced by NMR spectroscopy and X-ray diffraction studies. The unique eta(2)-BC coordination mode adopted by complexes 7 and 8 has been thoroughly analyzed by density-functional theory (DFT) calculations.

Gold(I) Complexes of Phosphanyl Gallanes: From Interconverting to Separable Coordination Isomers†

Gallant exchange: Upon coordination of phosphanyl gallane ligands to AuCl, both neutral and zwitterionic complexes coexist. NMR spectroscopy provides direct evidence for the transfer of the chloride between gold and gallium in diphosphanyl gallane. The introduction of a third phosphanyl buttress allows the separation and structural characterization of the two coordination isomers (see picture; Au yellow, P red, Cl green, Ga blue).

Design, Synthesis, and Biological Evaluation of New Cinnamic Derivatives as Antituberculosis Agents

Tuberculosis, HIV coinfection with TB, emergence of multidrug-resistant TB, and extensively drug-resistant TB are the major causes of death from infectious diseases worldwide. Because no new drug has been introduced in the last several decades, new classes of molecules as anti-TB drugs are urgently needed. Herein, we report the synthesis and structure-activity relationships of a series of thioester, amide, hydrazide, and triazolophthalazine derivatives of 4-alkoxy cinnamic acid. Many compounds exhibited submicromolar minimum inhibitory concentrations against Mycobacterium tuberculosis strain (H(37)Rv). Interestingly, compound 13e, a 4-isopentenyloxycinnamyl triazolophthalazine derivative, was found to be 100-1800 times more active than isoniazid (INH) when tested for its ability to inhibit the growth of INH-resistant M. tuberculosis strains. The results also revealed that 13e does not interfere with mycolic acid biosynthesis, thereby pointing to a different mode of action and representing an attractive lead compound for the development of new anti-TB agents.

Organo-catalyzed ring opening polymerization of a 1,4-dioxane-2,5-dione deriving from glutamic acid.

The (3S)-[(benzyloxycarbonyl)ethyl]-1,4-dioxan-2,5-dione (BED) was prepared in four steps starting from glutamic acid and bromoacetyl bromide. According to X-ray diffraction analysis, the pendant functional group is located in equatorial position and points away from the six-membered ring. The organo-catalyzed ring-opening polymerization of BED was promoted with 4-dimethylaminopyridine (DMAP) and the combination of thiourea TU(Cy) and (-)-sparteine. PolyBED samples of number-average molar mass M(n) up to 36000 and narrow polydispersity (M(w)/M(n) < 1.25) were thereby prepared in a controlled manner under mild conditions (dichloromethane solution, 30 degrees C), as substantiated by size-exclusion chromatography, matrix-assisted laser desorption ionization time-of-flight-mass spectrometry (MALDI-TOF-MS) and nuclear magnetic resonance (NMR) spectroscopy. The pendant functional group does not interfere with the polymerization and BED was even found to be slightly more reactive than lactide. Despite the strongly dissymmetric substitution pattern of the 1,4-dioxan-2,5-dione core, the ensuing polyBED polymers present a random distribution of glycolic-[(benzyloxycarbonyl)ethyl]glycolic (gly glu) units, as supported by a (1)H-(13)C HMBC 2D NMR experiment. The preparation of 1:1 adducts with n-pentanol confirmed that ring-opening of BED occurs almost indifferently on either of the endocyclic ester groups. Poly(alpha-hydroxyacids) featuring pendant carboxylic acids were finally obtained by acetylation of the terminal OH groups followed by hydrogenolysis.

Reaction of Singlet Dioxygen with Phosphine–Borane Derivatives: From Transient Phosphine Peroxides to Crystalline Peroxoboronates†

The last two decades has witnessed a spectacular renaissance in main group chemistry. Of particular interest are ambiphilic compounds that result from the combination of donor and acceptor moieties, typically involving Group 13 and 15 elements. Most strikingly, the groups of D. W. Stephan and G. Erker have shown that phosphine–boranes R2P-spacerB(C6F5)2 (R = tBu or Mes (2,4,6-Me3C6H2); spacer = p-C6H4 or CH2CH2) reversibly activate dihydrogen under mild conditions, opening new avenues in metal-free catalytic hydrogenation. Recently, reversible binding of carbon dioxide has also been reported. Moreover, our group has evidenced versatile coordination properties for monoand polyphosphine–boranes featuring o-C6H4 linkers, which provide a better understanding of unusual interactions between transition metals and Lewis acids. The borane moiety ortho to phosphorus was also exploited to stabilize highly reactive adducts of phosphines. Accordingly, the reaction of R2P(o-C6H4)BMes2 with phenyl azide was shown to give a phosphazide that is dramatically stabilized by intramolecular a N!B interaction that undergoes an unusual photoisomerization process. Furthermore, treatment of the o-phenylene phosphine–borane system with diethyl azodicarboxylate and phenyl isocyanate afforded stable versions of the zwitterionic intermediates involved in the Mitsunobu reaction and cyclooligomerization of isocyanates, respectively. Our continued interest in phosphine–borane compounds prompted us to investigate their behavior toward singlet dioxygen. 9] Very little is known about peroxidic adducts between phosphines and O2. Indeed, the phosphadioxirane deriving from the tris(o-methoxyphenyl)phosphine is the only such adduct that has been characterized to date, thanks to low-temperature NMR techniques. Herein we report that the presence of a Lewis acid in close proximity to the phosphorus center dramatically influences the fate of the reaction. In particular, phosphine–boronates are shown to readily split O2. The initially formed phosphine peroxides are stabilized by intramolecular O!B interactions, but spontaneously rearrange by B!O migration to give stable peroxoboronates. We began to investigate the behavior of phosphine– borane compounds towards dioxygen with the previously described phosphine–borane 1. No sign of oxidation was observed after several hours when a toluene solution of 1 was subjected to air bubbling at room temperature. In marked contrast, compound 1 rapidly reacted with O2 (generated by irradiation of O2 in the presence of tetraphenylporphyrin as photosensitizer) to afford a new compound 2 (Scheme 1). The

A new insight into ortho-(dimesitylboryl)diphenylphosphines: applications in Pd-catalyzed Suzuki-Miyaura couplings and evidence for secondary π-interaction.

ortho-(Dimesitylboryl)phenylphosphines 1 and 2 were applied in Pd-catalyzed Suzuki-Miyaura C-C couplings. Coordination studies were performed in order to rationalize the relationship between structure and reactivity. Full characterization of a Pd(0) complex derived from 1 has evidenced a new coordination mode for phosphine-arylboranes involving secondary π-interaction between one of the mesityl groups at boron and the metal centre.

2-Indenylidene pincer complexes of zirconium and palladium.

[IndH(2)(Ph(2)P=X)(2)] derivatives (1, X = NMes; 4, X = S) react with [Zr(NMe(2))(4)] and [PdCl(2)(cod)] to afford the complexes {[Ind(Ph(2)PNMes)(2)]Zr(NMe(2))(2)} (3), {[Ind(Ph(2)PS)(2)]Zr(NMe(2))(2)} (5), and {[Ind(Ph(2)PS)(2)]Pd(HNc-Hex(2))} (7). The ability of the phosphazene and thiophosphinoyl side arms to support the coordination of the indenyl ring as 2-indenylidene was evidenced by NMR spectroscopy and X-ray diffraction studies. Analysis of the bonding situation by density functional theory calculations revealed a strong sigma interaction but a negligible (if any) pi interaction between C2 and the metal.

Aggregation-induced emission enhancement in organic ion pairs.

We present here a new example of aggregation-induced emission enhancement (AIEE), which involves an original mechanism based on the formation of organic ion pairs. The phenol 4-hydroxy-7-nitrobenzoxadiazole (NBDOH) is dissociated in water at pH 5.0 to give the corresponding phenolate, which is poorly fluorescent in this medium. We bring evidence that fluorescence quenching is due to an interaction with water molecules. In the presence of a relatively bulky ammonium salt, specifically tetrabutylammonium bromide (TBAB), NBDOH forms a hydrophobic salt, TBA(+)NBDO(-). This has no influence on the fluorescence of the anion as long as the salt is dissolved. However, the salt readily crystallizes in the medium and transition to the solid state is accompanied by a strong increase in fluorescence intensity. This effect can be explained by two reasons. The anions are protected from water molecules, and above all, the presence of the bulky cations prevents parallel-stacking of the anions, thus leading to an original molecular arrangement that is favorable to fluorescence. As the nature of the organic cation may be easily changed, the versatility of the system is very interesting for the design of new organic micro- and nanoparticles that must be fluorescent in the solid state, possibly in an aqueous environment.

Bis(amidinato)germylenerhodium complexes: synthesis, structure, and density functional theory calculations.

The first monogermylenerhodium complexes stabilized by bulky amidinato ligands on the divalent germanium center have been synthesized and characterized by NMR spectroscopy and X-ray crystallography. Their stability strongly depends on the steric hindrance of the amidinato ligand. With trimethysilyl groups on the nitrogen atoms of the amidinato ligand, only the germylene oxide rhodium complex could be obtained; by contrast, with t-Bu groups, the germylenerhodium complex was isolated. In both cases, the formation of amidinatorhodium complexes was observed. The donating ability of the germylene ligand has been assessed from the CO stretching frequency of the corresponding dicarbonylrhodium complex and was confirmed by density functional theory calculations.

1,3-Bis(thiophosphinoyl)indene: a unique and versatile scaffold for original polymetallic complexes.

The coordination of tridentate ligands featuring lateral coordination sites prone to acting as bridging ligands was explored with the aim of obtaining original polymetallic species in a straightforward and controlled manner. Accordingly, the 2-indenylidene chloropalladate [{Ind(Ph(2)P═S)(2)}PdCl](-) was found to behave as a κ(2)-C,S bidentate ligand toward metal fragments, giving access to homo- and heteropolymetallic complexes. X-ray diffraction analyses reveal the presence of short metal-metal contacts in all of these complexes. Density functional theory calculations unambiguously substantiate that the metals engage in unusual d(8)···d(8) interactions with a quasi-perpendicular arrangement of their coordination planes.