Non-Linear Effects in Asymmetric Catalysis:Impact of Catalyst Precipitation

International audienceNon-linear effects between the enantiomeric excesses of both the ligand and the product are ubiquitous phenomena in asymmetric catalysis, allowing asymmetric amplification (or depletion) and are widely used tools for mechanistic investigations. Non-linear effects are caused by catalyst aggregation; however, the effect of catalyst precipitation on NLEs has not been systematically investigated to date, except in special cases such as ternary phase systems. In this article, we show through simulations and with several literature cases at hand how precipitation affects shape and amplitude of NLE curves. The limit of solubility of the homo- or heterochiral dimeric species causes broken-shaped NLE curves or very pronounced NLEs even though the equilibria between the different species in solution are not favorable, at first sight. Peculiar features such as horizontal segments, inverse S-shaped curves and a strong effect of total catalyst concentration are also observed. Overall, this study allows to get a better understanding of chiral catalytic systems and gives an outlook at other types of phase separation leading to NLEs

Catalyst-free hydrophosphination of alkenes in presence of 2-methyltetrahydrofuran: a green and easy access to a wide range of tertiary phosphines

International audienceA hydrophosphination reaction that is free of base, acid and catalyst, using only 2-methyltetrahydrofuran as additive has been performed. A new family of mono-, di,-tri-and tetra-phosphines compounds are obtained in good to excellent yields by adding diphenylphosphine to alkenes, mono-and polyfunctional acrylics (based on acrylate and methacrylate motifs) and acrylamide substrates. Addition of four equivalent of bio-mass derived 2-MeTHF into the reaction media improves both conversion and time of the reaction and reduces the sensitivity of the reactants over oxidation. This simple, straightforward and atom-economy method respects the principles of Green Chemistry. Furthermore, in each case this transformation shows an exclusive regioselectivity towards the anti-Markovnikov products

Synthesis and structural characterization of benzyl-functionalized N-heterocyclic carbene platinum complexes: Dramatic substituent effect on anti-cancer activity

International audienceA series of platinum (II) complexes bearing N-heterocyclic carbene NHC ligands functionalized by various benzyl moieties were synthesized and characterized. The molecular structure of two complexes has been confirmed by X-ray diffraction studies on single crystals. Investigation of in vitro cytotoxic activities against various cancer cell lines revealed a strong substituent effect: IC50 as low as 0.005 μM were obtained depending on the substituent on the benzyl moiety

Synthesis of alternating metallocopolymers by chiral recognition

International audienceWe report the synthesis of chiral enantiopure polytopic bridging ligands, which may lead to the formation of metallosupramolecular polymers with zinc (II) as metal linker. We show that chiral C2‐symmetric bisoxazoline ligands are useful moieties to efficiently generate heterochiral complexes and thus polymeric entities. The corresponding metallopolymers were further characterized by powder X‐ray diffraction (PXRD) to obtain information on the level of crystallinity of our different metallopolymers

Easy ruthenium-catalysed oxidation of primary amines to nitriles under oxidant free conditions

International audienceA dehydrogenation of primary amine to give the corresponding nitrile under oxidant-and base-free conditions catalysed by simple [Ru(p-cym)Cl2]2 with no extra ligand is reported. The system is highly selective for alkyl amine whereas benzylamine derivatives gave the nitrile product together with the imine in ratio ranging from 14:1 to 4:1 depending on the substrate. Preliminary mechanistic investigations have been performed to identify the key factors that govern the selectivity

N-Heterocyclic Carbene-Platinum Complexes Featuring an Anthracenyl Moiety: Anti-Cancer Activity and DNA Interaction

International audienceA platinum (II) complex stabilized by a pyridine and an N-heterocyclic carbene ligand featuring an anthracenyl moiety was prepared. The compound was fully characterized and its molecular structure was determined by single-crystal X-ray diffraction. The compound demonstrated high in vitro antiproliferative activities against cancer cell lines with IC50 ranging from 10 to 80 nM. The presence of the anthracenyl moiety on the N-heterocyclic carbene (NHC) Pt complex was used as a luminescent tag to probe the metal interaction with the nucleobases of the DNA through a pyridine-nucleobase ligand exchange. Such interaction of the platinum complex with DNA was corroborated by optical tweezers techniques and liquid phase atomic force microscopy (AFM). The results revealed a two-state interaction between the platinum complex and the DNA strands. This two-state behavior was quantified from the different experiments due to contour length variations. At 24 h incubation, the stretching curves revealed multiple structural breakages, and AFM imaging revealed a highly compact and dense structure of platinum complexes bridging the DNA strands

MINIREVIEW N-heterocyclic carbene platinum complexes: a big step forward for effective anti-tumor compounds

International audienceThe discovery of cisplatin is an important milestone in the history of successful anti-cancer drugs. This is also a notable example of the translational scientific achievement that remains a driving force in multidisciplinary research. The clinical success of cisplatin has led chemists to vary the ligands around the platinum metal to improve cisplatin's effectiveness while reducing its side effects. While there have been more failures than successes, key developments in the elucidation of mechanisms of the tumor-resistance properties have been accomplished. N-Heterocyclic carbene as ligand for organometallic chemistry is a relatively young area that offers new opportunities in many fields including bio-inorganic chemistry. These ligands fit the prerequisites for metal drug development and recent achievements have demonstrated the great potential of these compounds. The properties of these metal NHC complexes also allow for easy post-functionalization, thus enabling molecular diversity for efficient drug design. Overall, N-heterocyclic carbene ligands reveal new opportunities for Pt drug development

Recent progress in developing thioether-containing ligands for catalysis applications.

International audienceThe ligand that stabilizes the metal center is crucial to its catalytic activity. Historically dominated by phosphorus and nitrogen, sulfur has long been little considered as a hetero element for stabilizing a potentially active metal center. However, this situation is changing and we are seeing more and more examples that incorporate this element. This review provides an overview of recent transition metal-catalyzed reactions with ligands containing neutral sulfur groups, i.e. thioethers. A selection of examples published over the last decade illustrates the diversity of applications of thioether-containing ligands and shows that sulfur should be more widely used in the development of homogeneous catalysis