Bruno Andrioletti

Rational investigations in the ring opening of cyclic carbonates by amines

Non-isocyanate polyurethanes (NIPUs) constitute a promising alternative for more classical polyurethanes (PUs) as they may display mechanical properties that can match those of PUs and their synthesis does not involve the use of toxic isocyanates. Yet, because of the lower reactivity of carbonates versus isocyanates, the synthesis of NIPUs is not straightforward and generally requires the use of a catalyst. Recently, several groups have reported on the use of different ranges of catalysts for promoting the nucleophilic attack of the amine on the carbonate. However, many of these studies involve the use of highly reactive amine and/or carbonate proscribing a complete panorama of the potentialities of the reaction. Herein, we propose a rational study of the catalyzed aminolysis of four representative cyclic carbonates that reveals that the thiourea organocatalyst 1 outperforms in many aspects, classical inorganic or other organic catalysts.

Anions as Efficient Chain Stoppers for Hydrogen-Bonded Supramolecular Polymers†

The chain length of hydrogen-bonded supramolecular polymers and thus their rheological properties can be controlled by the presence of so-called chain stoppers: these monofunctional monomers are able to interact with the monomers and break the polymer chains. In this letter, we show that the use of anions, strong hydrogen bond competitors, instead of precisely designed complementary units is a very simple approach to tuning the rheology of a bisurea-based hydrogen-bonded supramolecular polymer. All of the anions tested were able to break the supramolecular chains, resulting in a dramatic drop in the viscosity of the solutions and were found to be more efficient than a previously described organic stopper. A careful study of the rheological properties of bisurea solutions in the presence of H2PO4,N(C4H9)4 showed that the presence of this ion does not modify the nature of the bisurea supramolecular assembly. For a molar fraction of stopper of only 10(-5), the viscosity of bisurea solutions decreases by a factor of 10 as a result of the formation of shorter supramolecular assemblies.

Ultrasound and ionic liquid: An efficient combination to tune the mechanism of alkenes epoxidation

In this proof of concept study, the advantageous properties of both H(2)O(2)/NaHCO(3)/imidazole/Mn(TPP)OAc oxidation system and MOPyrroNTf(2) ionic liquid have been combined under ultrasonic irradiation to give an exceptionally favorable environment for Mn(TPP)OAc catalyzed olefin oxidations. The results reveal the crucial role played by the ultrasonic irradiations that influence drastically the oxidation process. In MOPyrroNTf(2) and under ultrasonic irradiation, the mechanism probably involves an oxo-manganyl intermediate at the expense of the classical bicarbonate-activated peroxide route.

A study of cyclic carbonate aminolysis at room temperature: effect of cyclic carbonate structures and solvents on polyhydroxyurethane synthesis

In recent years, intensive research and development have been carried out for the synthesis of isocyanate free polyurethanes from the reaction between five-membered cyclic carbonates and amines to yield polyhydroxyurethanes (PHU). Nevertheless, this reaction presents two main drawbacks: the low reactivity of cyclic carbonate aminolysis and the low molar masses of synthesized PHUs. Firstly, our work intends to propose a wider reactivity study on various C5 and C6 in order to determine the influence of substituents attached to the cyclic carbonate and to compare the reactivity of C5 and C6 with exactly the same substituents. Moreover, we completed this study with new structures with promising reactivity such as C5 and C6 with ethyl-ester or trimethylhexanoate substituents that have never been studied in the literature. Hence, a range of cyclic carbonate models with different structures, 5-, 6-membered cyclic carbonate (C5, C6) or 5-membered-dithio-cyclic carbonate (Cs), were synthesized. Secondly, this kinetic study has brought to light a partial conversion of precursors during the aminolysis reaction that can be responsible for the low molar masses of PHUs. This partial conversion is caused mainly by the formation of hydrogen bonding inter- and intra-chains limiting the diffusivity of species during the polymerization. A model study showed that the use of protic solvents improves the reactivity of cyclic carbonates and increases the conversion during their aminolysis reaction. Therefore, this protic solvent gives its mobility back to the precursors by limiting the creation of hydrogen bonding inter- and intra-chains. Finally, the efficiency of protic solvents on the synthesis of PHU polymers was evaluated.

A highly sustainable route to pyrrolidone derivatives – direct access to biosourced solvents

Access to a series of 5-methylpyrrolidone derivatives is described directly using the biosourced levulinic acid in the absence of any additive, catalyst or solvent. The highly selective reaction proceeds with an E-factor as low as 0.2. Products are recovered in very good yields after a simple distillation.

Conformational plasticity of hydrogen bonded bis-urea supramolecular polymers.

We report a detailed structural investigation of supramolecular polymers formed by hydrogen bonded self-assembly of bis-urea monomers. The careful exploration of the energy landscape by molecular mechanics/molecular dynamics (MM/MD) simulations has allowed us to identify three distinct self-assembled structures of similar stabilities. These structures have been compared to X-ray crystal data. We observe that a slight change in the molecular structure can favor a particular structure over the others. Detailed analysis shows that hydrogen bonds stabilize all three structures to a similar extent. Therefore, it is the interactions among the lateral substituents, and with the filament environment, that are the decisive factors in the competition between the possible self-assembled structures. This study constitutes a clear reminder that the conformation of a supramolecular polymer is a sensitive function of the molecular structure and may significantly differ from the solid-state conformation of a model compound.

Dipyrrinphenol-Mn(III) complex: synthesis, electrochemistry, spectroscopic characterisation and reactivity.

Herein, we report the manganese complex with a novel trianionic ligand, the pentafluorophenyldipyrrinphenol ligand DPPH(3). The X-ray crystal structure reveals that the Mn(III) complex exists in a dimeric form in the solid state. Electrochemical studies indicate two quasi-reversible one electron oxidation processes. EPR data on the one electron oxidised species in solution support the formation of a monuclear Mn complex with an S = 3/2 spin system. Preliminary studies towards epoxidation reactions were tested in the presence of iodosylbenzene (PhIO) and are in favour of an oxygen-atom-transfer (OAT) reaction catalyzed by the Mn(III) complex.

Urea- and Thiourea-Catalyzed Aminolysis of Carbonates.

The aminolysis of (poly)carbonates by (poly)amines provides access to non-isocyanate polyurethanes (NIPUs) that are toxic-reagent-free analogues of polyurethanes (PUs). Owing to their low reactivity, the ring opening of cyclic carbonates requires the use of a catalyst. Herein, we report that the more available and cheaper ureas could advantageously be used for catalyzing the formation of NIPUs at the expense of the thiourea analogues. In addition, we demonstrate a medium-range pKa of the (thio)urea and an unqeual substitution pattern is critical for controlling the efficiency of the carbonate opening.

Chain stopper engineering for hydrogen bonded supramolecular polymers

Summary Supramolecular polymers are linear chains of low molar mass monomers held together by reversible and directional non-covalent interactions, which can form gels or highly viscous solutions if the self-assembled chains are sufficiently long and rigid. The viscosity of these solutions can be controlled by adding monofunctional compounds, which interact with the chain extremities: chain stoppers. We have synthesized new substituted ureas and thioureas and tested them as chain stoppers for a bis-urea based supramolecular polymer. In particular, the bis-thiourea analogue of the bis-urea monomer is shown not to form a supramolecular polymer, but a good chain stopper, because it is a strong hydrogen bond donor and a weak acceptor. Moreover, all substituted ureas tested reduce the viscosity of the supramolecular polymer solutions, but the best chain stopper is obtained when two hydrogen bond acceptors are placed in the same relative position as for the monomer and when no hydrogen bond donor is present.

Experimental and Theoretical Investigations of the Stereoselective Synthesis of P‐Stereogenic Phosphine Oxides

An efficient enantioselective strategy for the synthesis of variously substituted phosphine oxides has been developed, incorporating the use of (1S,2S)-2-aminocyclohexanol as the chiral auxiliary. The method relies on three key steps: 1)u2005Highly diastereoselective formation of P(V) oxazaphospholidine, rationalized by a theoretical study; 2)u2005highly diastereoselective ring-opening of the oxazaphospholidine oxide with organometallic reagents that takes place with inversion of configuration at the P atom; 3)u2005enantioselective synthesis of phosphine oxides by cleavage of the remaining P-O bond. Interestingly, the use of a P(III) phosphine precursor afforded a P-epimer oxazaphospholidine. Hence, the two enantiomeric phosphine oxides can be synthesized starting from either a P(V) or a P(III) phosphine precursor, which constitutes a clear advantage for the stereoselective synthesis of sterically hindered phosphine oxides.