Gilles Frapper

Catalyst-free aqueous multicomponent domino reactions from formaldehyde and 1,3-dicarbonyl derivatives

Here we report a catalyst-free aqueous multicomponent domino reaction (MCR) capable of affording a wide range of valuable dihydropyran derivatives from simple, cheap and readily available reactants such as formaldehyde, 1,3-dicarbonyl derivatives, styrene, indole and aniline derivatives. Within the framework of green chemistry, these MCRs gather many advantages such as (i) utilization of water as a solvent, (ii) creation of up to six bonds in one sequence, (iii) 100% of carbon economy and (iv) water as a sole waste. These MCRs exhibit a broad substrate scope and open access to valuable chemicals traditionally produced through multistep processes involving catalysts or organic solvents. More generally, this work opens a new way for creating molecular complexity with maximum simplicity.

Phase stability, chemical bonding and mechanical properties of titanium nitrides: a first-principles study

We have performed first-principles evolutionary searches for stable Ti-N compounds and have found, in addition to the well-known rock-salt TiN, new ground states Ti3N2, Ti4N3, Ti6N5 at atmospheric pressure, and Ti2N and TiN2 at higher pressures. The latter nitrogen-rich structure contains encapsulated N2 dumbbells with a N-N distance of 1.348 Å at 60 GPa. TiN2 is predicted to be mechanically stable and quenchable. Our calculations on the mechanical properties (bulk modulus, shear modulus, Youngs modulus, Poissons ratio, and hardness) are in excellent agreement with the available experimental data. Further analyses of the electronic density of states, crystal orbital Hamilton population and the electron localization function reveal that the hardness is enhanced by strengthening directional covalent bonds and disappearance of Ti-Ti metallic bonding.

Selective synthesis of gem-chlorofluorinated nitrogen-containing derivatives after superelectrophilic activation in superacid HF/SbF5.

The first direct selective synthesis of novel gem-chlorofluorinated nitrogen-containing building blocks in superacid is reported. The dramatic role of the chlorine atom on the reaction is shown by in situ NMR experiments and allows the involvement of a novel original superelectrophilic activation process in superacid HF/SbF(5) to be postulated.

Anti-Markovnikov additions to N-allylic derivatives involving ammonium–carbenium superelectrophiles

Anti-Markovnikov additions to non-conjugated unsaturated amines in superacid are reported. In situ NMR studies, DFT calculations and labelled substrates reactions support the involvement of new ammonium-carbenium superelectrophiles in this original process.

Pressure-driven formation and stabilization of superconductive chromium hydrides

Chromium hydride is a prototype stoichiometric transition metal hydride. The phase diagram of Cr-H system at high pressures remains largely unexplored due to the challenges in dealing with the high activation barriers and complications in handing hydrogen under pressure. We have performed an extensive structural study on Cr-H system at pressure range 0 ∼ 300 GPa using an unbiased structure prediction method based on evolutionary algorithm. Upon compression, a number of hydrides are predicted to become stable in the excess hydrogen environment and these have compositions of Cr2Hn (n = 2–4, 6, 8, 16). Cr2H3, CrH2 and Cr2H5 structures are versions of the perfect anti-NiAs-type CrH with ordered tetrahedral interstitial sites filled by H atoms. CrH3 and CrH4 exhibit host-guest structural characteristics. In CrH8, H2 units are also identified. Our study unravels that CrH is a superconductor at atmospheric pressure with an estimated transition temperature (T c) of 10.6 K, and superconductivity in CrH3 is enhanced by the metallic hydrogen sublattice with T c of 37.1 K at 81 GPa, very similar to the extensively studied MgB2.

Exploration of stable compounds, crystal structures, and superconductivity in the Be-H system

Using first-principles variable-composition evolutionary methodology, we explored the high-pressure structures of beryllium hydrides between 0 and 400 GPa. We found that BeH2 remains the only stable compound in this pressure range. The pressure-induced transformations are predicted as Ibam→P3m1→R3m→Cmcm→P4/nmm, which occur at 24, 139, 204 and 349 GPa, respectively. P3m1 and R3m structures are layered polytypes based on close packings of H atoms with Be atoms filling all octahedral voids in alternating layers. Cmcm and P4/nmm contain two-dimensional triangular networks with each layer forming a kinked slab in the ab-plane. P3m1 and R3m are semiconductors while Cmcm and P4/nmm are metallic. We have explored superconductivity of both metal phases, and found large electron-phonon coupling parameters of λ = 0.63 for Cmcm with a Tc of 32.1-44.1 K at 250 GPa and λ = 0.65 for P4/nmm with a Tc of 46.1-62.4 K at 400 GPa. The dependence of Tc on pressure indicates that Tc initially increases to a maximum of 45...

First-principles study of Zr–N crystalline phases: phase stability, electronic and mechanical properties

Using a variable-composition ab initio evolutionary algorithm, we investigate stability of various Zr–N compounds. Besides the known ZrN and Zr3N4, new candidate structures with Zr : N ratios of 2 : 1, 4 : 3, 6 : 5, 8 : 7, 15 : 16, 7 : 8 and 4 : 5 are found to be ground-state configurations, while Zr3N2 has a very slightly higher energy. Besides Zr2N, the newly discovered ZrxNy compounds adopt rocksalt structures with ordered nitrogen or zirconium vacancies. The electronic and mechanical properties of the zirconium nitrides are further studied in order to understand their composition–structure–property relationships. Our results show that bulk and shear moduli monotonically increase with decreasing vacancy content. The mechanical enhancement can be attributed to the occurrence of more Zr–N covalent bonds and weakening of the ductile Zr–Zr metallic bonds. These simulations could provide additional insight into the vacancy-ordered rocksalt phases that are not readily apparent from experiments.

Can carbon monoxide polymerize? A theoretical investigation of polyketone

State of the art ab initio calculations on R(CO)nR (R = H, Me; n = 1–11) indicate that the hypothetical polymer of carbon monoxide, poly-CO, would be energetically less stable than the molecular form only by a few kcal mol–1, making it a plausible stable allotropic form of CO.

Elucidation of the role of betaine hydrochloride in glycerol esterification: towards bio-based ionic building blocks

The mechanism of bio-based betaine hydrochloride esterification with glycerol has been studied through DFT modelling and experimental approaches. Interestingly, our proposed mechanism differs from the classical Watson and Ingold ones. In particular, we found that the glycine betaine hydrochloride cluster contains a non-dissociated HCl molecule in its structure. This trapped HCl acted as a proton relay to favor the formation of unconstrained six-membered ring transition state structures both in nucleophilic addition (C–O bond coupling) and H2O elimination pathways. These findings led us to optimize this reaction. In particular, glyceryl betaine esters were produced in a yield up to 90% and with a space time yield up to 670 kg m−3 h−1 unreported to date. The absence of an external catalyst and solvent, as well as the use of a stoichiometric mixture of acidified glycine betaine and glycerol, two co-products of the sugar beet and vegetable oil industries, respectively, represent notable advantages within the framework of sustainable chemistry. This work opens a straightforward route to bio-based and valuable ionic building blocks which are of high interest for the synthesis of ionic surfactants or liquids. Furthermore, the results reported in this work also rationalize the high catalytic performances of glycine betaine hydrochloride recently reported in acid-catalyzed reactions.

Synthesis of Fe4(CO)8(µ-PPh2)2(µ4-η1,η1,η2,η2-C2Ph)2via coupling of acetylides at a binuclear centre: a molecule with through-the-cluster carbon–carbon bonding?

Thermolysis of Fe2(CO)6(µ-PPh2)(µ-η1,η2-C2Ph) affordsthe rectangular cluster Fe4(CO)8(µ-PPh2)2(µ4-η1,η1,η2,η2-C2Ph)2 with two face-capping acetylides linked through the Fe4 face by a short carbon–carbon contact: reaction with CO leads to Fe3(CO)8{µ-Ph2PC(CPh)C(CPh)PPh2} as a result of C–C and C–P bond-forming processes.