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Is 1JC-H coupling constant for protonated carbene a relevant measure of its s-donation ability? This paper investigates this assertion by comparing the calculated 1JC-H values for N-heterocyclic carbenes and their derivatives to other approaches such as HEP and ETS-NOCV methods. The obtained correlations are significantly better for similar compounds.

The acid-catalyzed rearrangement of organic peroxides is generally associated to C-C-bond cleavages (Hock and Criegee rearrangements), with the concommittent formation of an oxocarbenium intermediate. This article describes the tandem process between a Hock or Criegee oxidative cleavage and a nucleophilic addition onto the oxocarbenium species (in particular a Sakurai-Hosomi-type allylation), under InCl3 catalysis. It was applied to the synthesis of 2-substituted benzoxacycles (chromanes, benzoxepanes), including a synthesis of the 2-(aminomethyl)chromane part of sarizotan, and a total synthesis of erythrococcamide B.

The Hock rearrangement is an acid catalyzed reaction involving organic hydroperoxides and resulting in an oxidative cleavage of adjacent C–C bonds. It has significant industrial applications, like the production of phenol (cumene process), but it remains scarcely used in organic synthesis. In addition, its detailed mechanism has never been studied. Thus, we report herein a theoretical study of the Hock rearrangement, using InCl3 as a Lewis acid catalyst. The aim of this work was to fully understand the mechanism of this fundamental reaction, and to rationalize the influence of the substrate electronic properties on the reaction outcome. Furthermore, the structure of the active indium(III) catalyst interacting with the per-oxide substrate was investigated, showing the superiority of a coordinated monomeric form of the Lewis acid as the active catalytic species, compared to dimeric species. However, we show that In2Cl6 species coordinated to the substrate are cen-tral in this catalytic cycle, serving as a reservoir of active monomeric species.

The enantioselective tandem cycloisomerization / addition reactions of 2-alkynyl enones with 1- and 2-naphthols have been investigated using gold(I) catalysts featuring hybrid phosphine-phosphoric acid ligands, according to the Tethered Counteri-on-Directed Catalysis strategy. The reactions occur at low catalytic loading (0.2-1 mol%), without silver additives, and the naphthols act as both O- and C-nucleophiles, leading to the corresponding addition products in high yields and enantioselec-tivities. Monitoring of the reaction course highlights both conversion of O-addition into C-addition products and racemiza-tion processes that can affect the enantiomeric excess of the final products. Examples of solvent-dependent enantiodiver-gence, as well as further conversion of the C-addition products into highly enantioenriched heteropolycycles are shown.

The TCDC approach enables tandem cycloisomerization/nucleophilic addition reactions of 2-alkynyl enones with naphthols, with good to excellent control of the regioselectivity and ees up to 99%, under optimized reaction conditions.

Total syntheses of (+)-cinereain and (-)-janoxepin, two fungal cyclotripeptides featuring a complex heterocyclic core and interesting phytotoxic and antimalarial activities, have been achieved in a convergent manner. A key step in this synthesis is a one-pot cascade initiated by the cyclocondensation of two fragments-a hindered 2-vinylcyclopropane-1-acyl fluoride and an electron-deficient cyclic amidine-to release a reactive spiro[2-vinylcyclopropane-1,5'-pyrimidine-4',6'-dione]. This intermediate underwent a spontaneous retro-Claisen rearrangement that was rationalized by DFT calculations. The cascade directly afforded a 2,5-dihydrooxepin-fused heterotricyclic product, and the challenging oxepin ring was finally forged by the palladium-catalyzed β-hydride elimination of an allylic fluoride intermediate.

International audience; These last decades, it has been widely assumed that 18-crown-6-ether (CE) plays a spectator role during the chemical processes occurring in isolated host-guest complexes between peptides or proteins and CE, after activation in mass spectrometers. Our present experimental and theoretical results challenge this hypothesis by showing that CE can abstract a proton or a protonated molecule from protonated peptides after activation by collisions in argon or electron capture/transfer. Furthermore, thanks to comparison between experimental and calculated values of collision cross-sections, we demonstrate that CE can change binding site after electron transfer. We also propose detailed mechanisms for these processes.

The Tethered Counterion-Directed Catalysis (TCDC) approach has been applied to the enantioselective Au(I) catalyzed dearomatizations of 1-naphthols with allenamides. Stereocontrol is ensured by the intramolecular ion-pairing between the chiral gold-tethered phosphate and an iminium unit, that provides a rigid, well-defined chiral environment to the key electrophilic intermediate.

The association of a mycotoxin-ochratoxin A (OTA)-with a high-affinity DNA aptamer (anti-OTA) immobilized on a functionalized surface has been investigated at the molecular level. Anti-OTA aptamers are coupled by aminolysis in several steps on an acid-terminated alkyl monolayer grafted on a silicon substrate, and Fourier transform infrared spectroscopy in attenuated total reflection geometry is used to assess the immobilization of anti-OTA (in its unfolded single-strand form) and determine its areal density (ca. 1.4/nm2). IR spectra further demonstrate that the OTA/anti-OTA association is efficient and selective and that several association/dissociation cycles may be conducted on the same surface. The areal density of OTA measured after association on the surface (IR spectroscopy) and after dissociation from the surface (UV-vis spectroscopy) falls in the range 0.16-0.3/nm2 which is close to the areal density of a closed-packed monolayer of anti-OTA aptamers folded to form their G-quadruplex structure. The interactions between OTA and its aptamer at the surface are discussed with the help of density functional theory calculations-to identify the complex IR vibrational modes of OTA in solution-and UV-vis spectroscopy-to determine the protonation state of the adsorbing species (i.e., OTA dissolved in the buffer solution).

Quantum chemical calculations using DFT and NBO, ETS-NOCV, QTAIM and ELF interpretative approaches have been carried out on X-BH2+ borenium complexes for 39 divalent C-donor ligands X including various N-heterocyclic carbenes and carbones. The C-B bond length and the barrier of rotation around the C-B bond were calculated and compared with various descriptors of the C-B pi-bond strength obtained from the orbital localization, energy partitioning or topological methods. Two families of descriptors emerged: intrinsic indicators, which measure the intensity of the pi-bond in the investigated molecule, and relative indicators, among them the rotational barrier, which compare the studied molecule with its conformer in which the pi-interaction is prevented. Relative indicators are influenced by other interactions in addition to purely pi-interactions. For both families of descriptors, excellent correlations are obtained, showing that the interpretative methods, despite their conceptual differences, describe the same chemical properties. These results also reveal noticeable shortcomings in these methods, and some precautions that need to be taken to interpret their results adequately.

International audience; Platinum(IV) complexes are extensively studied for their activity against cancer cells as potential substitutes for the widely used platinum(II) drugs. PtIV complexes are kinetically inert and need to be reduced to PtII species to play their pharmacological action, thus acting as prodrugs. The mechanism of the reduction step inside the cell is however still largely unknown. Gas-phase activation of deprotonated platinum(IV) prodrugs was found to generate products in which platinum has a formal +3 oxidation state. IR multiple photon dissociation spectroscopy is thus used to obtain structural information helping to define the nature of both the platinum atom and the ligands. In particular, comparison of calculations at DFT, MP2 and CCSD levels with experimental results demonstrates that the localization of the radical is about equally shared between the dxz orbital of platinum and the pz of nitrogen on the amino group, the latter acting as a non-innocent ligand.

Quantum chemical calculations using DFT and NBO, ETS-NOCV, QTAIM and ELF interpretative approaches have been carried out on X-BH2+ borenium complexes for 39 divalent C-donor ligands X including various N-heterocyclic carbenes and carbones. The C-B bond length and the barrier of rotation around the C-B bond were calculated and compared with various descriptors of the C-B pi-bond strength obtained from the orbital localization, energy partitioning or topological methods. Two families of descriptors emerged: intrinsic indicators, which measure the intensity of the pi-bond in the investigated molecule, and relative indicators, among them the rotational barrier, which compare the studied molecule with its conformer in which the pi-interaction is prevented. Relative indicators are influenced by other interactions in addition to purely pi-interactions. For both families of descriptors, excellent correlations are obtained, showing that the interpretative methods, despite their conceptual differences, describe the same chemical properties. These results also reveal noticeable shortcomings in these methods, and some precautions that need to be taken to interpret their results adequately.

International audience; Tethering a metal complex to its phosphate counterion via a phosphine ligand enables a new strategy in Asymmetric Counteranion-Directed Catalysis (ACDC). A straightforward, scalable synthetic route gives access to the gold(I) complex of a chiral phosphine displaying a phos-phoric acid function. The complex generates a catalytically active species with an unprecedented intramolecular relationship between the cati-onic Au(I) center and the phosphate counterion. The benefits of tethering the two functions of the catalyst is demonstrated here in a tandem cycloisomerization/nucleophilic addition reaction, by attaining high enantioselectivity levels (up to 97% ee) at a remarkable low 0.2 mol% catalyst loading. Remarkably the method is also compatible with a silver-free protocol.

International audience; The complexes (Cy2PC3H6PCy2)Ni(η2-arene) (arene = toluene (3), naphthalene (4)) have been synthesized and studied in detail. Displacement reactions of the toluene ligand afford the complexes (Cy2PC3H6PCy2)Ni(η2-styrene) (5), (Cy2PC3H6PCy2)Ni(PhCN) (6), (Cy2PC3H6PCy2)Ni(CO)2 (7), (Cy2PC3H6PCy2)Ni(PPh3) (8), (Cy2PC3H6PCy2)Ni(PCy3) (9), {(Cy2PC3H6PCy2)Ni}2(μ-H)2 (10), (Cy2PC3H6PCy2)Ni(η2-CO2) (11), and [(Cy2PC3H6PCy2)Ni]2(μ,η2-1,5-COD) (12). The relative rates of ArCl oxidative addition at Ni complexes 3, 4, 6, 8, and 12 have been evaluated experimentally, and the mechanism has been calculated by DFT. Complexes 3 and 4 are efficient catalysts for the Suzuki–Miyaura reaction between chloroarenes and Ar′B(OH)2.

International audience; Metallotropism of the M[N(SiMe3)2]2 metal fragment in the tautomeric system IAR⇌ACR involving imidazolium salts/N‐heterocyclic carbenes with remote aminide/amine substituents, respectively, is manifested by its CNHC carbophilicity (R=tBu, M=Co, Fe) or NRaminido nitrogenophilicity (R=Cy, M=Co, Fe; R=Mes, M=Fe) and has been rationalized on the basis of steric and electronic effects. The thermolysis products of the [M{N(SiMe3)2}2]/ IAR⇌ACR system are also substituent‐dependent, leading to a rearranged aminide‐functionalized aNHC Co2 complex of an unprecedented type or to ring‐opened metallaketenimines; they are postulated to originate from different metalloisomers. The results are interpreted on the basis of the X‐ray diffraction analysis of 11 new compounds.

The linear, two-coordinate and isostructural heteroleptic [M(IPr){N(SiMe3)2}] (IPr = 1,3-bis(diisopropylphenyl)-imidazol-2-ylidene), formally MI complexes (M = Co, 3; Fe, 4) were obtained by the reduction of [M(IPr)Cl{N(SiMe3)2}] with KC8, or [Co(IPr){N(SiMe3)2}2] with mes*PH2, mes* = 2,4,6-tBu3C6H2. The magnetism of 3 and 4 implies CoII and FeII centres coupled to one ligand-delocalized electron, in line with XPS and XANES data; the ac susceptibility of 4 detected a pronounced frequency dependence due to slow magnetization relaxation. Reduction of [Fe(IPr)Cl{N(SiMe3)2}] with excess KC8 in toluene gave the heteronuclear ‘inverse-sandwich’ Fe–K complex 7, featuring η6-toluene sandwiched between one Fe0 and one K+ centre.

International audience; The role of Hartree-Fock exchange in describing the structural changes occurring upon reduction of bipyridine-based ligands and their complexes is investigated within the framework of density functional theory calculations. A set of 4 free ligands in their neutral and radical anionic forms, and 2 of their zinc complexes in their dicationic and monocationic radical forms, is used to compare a large panel of pure, conventional, and long-range corrected hybrid DFT functionals; coupled cluster single and double calculations are used alongside experimental results as benchmarks. Particular attention has been devoted to the magnitude of the change, upon reduction, of the D-parameter, which measures the difference between the Cpy-Cpy and the C-N bond lengths in bipyridine ligand and is known to experimentally correlate with the charge of the ligands. Our results indicate that the structural changes significantly depend on the amount of exact exchange included in the functional. A progressive evolution is observed for the free ligands, whereas two distinct sets of results are obtained for the complexes. Functionals with a small degree of HF exchange, e.g., B3LYP, do not adequately describe geometric changes for the considered species and, quite surprisingly, the same holds for the CC2 method. The best agreement to experimental and CCSD values is obtained with functionals that include a significant but not excessive part of exact exchange, e.g., CAM-B3LYP, M06-2X, and wB97X-D. The calculated localisation of the added electron after reduction, which depends on the self-interaction error, is used to rationalize these outcomes. Static correlation is also shown to play a role in the accurate description of electronic structure.

International audience; A one-pot methodology to synthesize metastable bicyclic 2,5-dihydrooxepines from cyclic 1,3-diketones and 1,4-dibromo-2-butenes is reported, through the retro-Claisen rearrangement of syn-2-vinylcyclopropyl diketone intermediates. High-level quantum chemical calculations were performed to understand the reaction selectivity and mechanisms towards [1,3] or [3,3]-sigmatropic rearrangements, highlighting the crucial influence of temperature in close relation to experimental results. The reaction was successfully applied to a short protecting group-free total synthesis of radulanin A, a natural 2,5-dihydrobenzoxepine, featuring an unprecedented aromatization strategy of the transient bicyclic 2,5-dihydrooxepine. We demonstrate for the first time the strong herbicidal potential of this natural product.

International audience; Double deprotonation of 2,6-bis-(di-tert-butylphosphinomethyl)-pyridine (tBuPNtBuP), with KCH2C6H5 afforded K2(tBuP*NatBuP*), Na = anionic amido N, tBuP* = di-tert-butyl vinylic P donor. The analogous [Li2(tBuP*NatBuP*)]2 (1) was reacted with [CrCl2(THF)2] and [ZrCl4(THT)2] to give the helical [Cr{Cr(tBuP*NatBuP*)Cl}2] (2) and [Zr(tBuP*NatBuP*)Cl2] (3), respectively. DFT calculations support dearomatisation of P*NaP* and its high donor ability.

International audience; We report an intramolecular Diels-Alder reaction efficiently accelerated by Schreiner's thiourea, to build a functionalized cytochalasin scaffold (periconiasin series) amenable to biological purpose. DFT calculation highlighted a unique multidentate cooperative hydrogen bonding in this catalysis. The deprotection end-game afforded a collection of diverse structures and showed the peculiar reactivity of the Diels-Alder cycloadducts upon functionalization. Biological studies revealed strong cytotoxicity of a few compounds on breast cancer cell lines, while preserving actin polymerization.

International audience; The two first steps of the Strecker synthesis of glycine, namely (a) addition of ammonia to formaldehyde to give aminomethanol and (b) its dehydration leading to methaneimine, is studied using high level quantum chemistry computations (G3B3). Water solvation is modeled by considering the effect of adding a discrete number of active or passive molecules of water (up to four) and by immersing the identified water-solute complexes in a conductor-like polarizable continuum solvent model. Activation of the reactants by protonation is also examined. Exhaustive search of microhydrated neutral and protonated aminomethanol has been performed using a combination of hierarchical and genealogical approaches. Critical energies associated with all the elementary reaction steps were estimated using the accurate G3B3 composite method thus providing benchmarks to discuss the possible occurrence of Strecker synthesis in prebiotic chemistry.

International audience; The enantioselective H-transfer hydrogenation of quinoline by Hantzsch ester is a relevant example of Brønsted acid catalyzed cascade reactions, with phosphoric acid being a privileged catalyst. The generally accepted mechanism points out the hydride transfer step as the rate- and stereodetermining step, however computations based on these models do not totally fit with experimental observations. We hereby present a computational study that enlightens the stereochemical outcome and quantitatively reproduces the experimental enantiomeric excesses in a series of H-transfer hydrogenations. Our calculations suggest that the high stereocontrol usually attained with BINOL-derived phosphoric acids results mostly from the steric constraints generated by an aryl substituent of the catalyst, which hinders the access of the Hantzsch ester to the catalytic site and enforces approach through a specific way. It relies on a new model involving the preferential assembly of one of the stereomeric complexes formed by the chiral phosphoric acid and the two reaction partners. The stereodetermining step thus occurs prior to the H-transfer step.

A novel, sequential, palladium-catalyzed, cross-coupling reaction using N-tosylhydrazone and bromonitrobenzene derivatives followed by reductive cyclization has been developed. This transformation providing an efficient route to unexpected N-arylindole derivatives involves, in a one-pot reaction, the formation of one Csp

International audience; Extensive exploration of the potential energy surfaces of protonated Nα-acetylhistidine hydrated by 0–3 molecules of water was performed. The methodology combined hierarchical and genealogical (Darwin family tree) approaches using polarizable AMOEBA force field and M06 functional. It is demonstrated that this mixed approach allows recovering a larger number of conformers than the number recovered by using any one of the two methods alone. Hydration enthalpies of protonated Nα-acetylhistidine and of model compounds have been computed using higher theoretical methods, up to the G4MP2 procedure. Excellent agreement with experiment is observed for successive hydration of methylamonium and imidazolium cations using MP2/6-311++G(2d,2p)//M06/6-311++G(d,p) and G4MP2 methods, thereby validating the theory levels used for hydrated protonated Nα-acetylhistidine. It is found that the first hydration enthalpy of protonated Nα-acetylhistidine is ca. 10 kJ mol–1 lower than that of imidazolium, a result explained by the local environment of the positively charged imidazolium moiety.

A novel, sequential, palladium-catalyzed, cross-coupling reaction using N-tosylhydrazone and bromonitrobenzene derivatives followed by reductive cyclization has been developed. This transformation providing an efficient route to unexpected N-arylindole derivatives involves, in a one-pot reaction, the formation of one Csp2–Csp2 bond and two Csp2–N bonds together with the cleavage of one Csp2–heteroatom bond. Evaluation of the biological activity led to the identification of compound 5a, which displays potent activity at nanomolar concentrations against human colon carcinoma cell line.

International audience; This work aims to improve the computation of infrared spectra of gas-phase cations using DFT methods. Experimental IRMPD spectra for ten Zn and Ru organometallic complexes have been used to provide reference data for 64 vibrational modes in the 900-2000 cm-1 range. The accuracy of the IR vibrational frequencies predicted for these bands has been assessed over five DFT functionals and three basis sets. The functionals include the popular B3LYP and M06-2X hydrids and the range-separated hybrids (RSH) CAM-B3LYP, LC-BLYP and B97X-D. B3LYP gives the best mean absolute error (MAE) and root-mean-square error (RMSE) values of 7.1 and 9.6 cm-1 , whilst the best RSH functional, B97X-D, gives 12.8 and 16.6 cm-1 respectively. Using linear correlations instead of scaling factors improves the prediction accuracy significantly for all functionals. Experimental and computed spectra for a single complex can show significant differences even when the molecular structure is calculated correctly, and a means of defining confidence limits for any given computed structure is also provided.

International audience; We assess the pros and cons of a large panel of DFT exchange-correlation functionals for the prediction of the electronic structure of hydrogen-rich peptide radicals formed after electron attachment on a protonated peptide. Indeed, despite its importance in the understanding of the chemical changes associated with the reduction step, the question of the attachment site of an electron, and more generally of the reduced species formed in the gas phase through electron induced dissociation (ExD) processes in mass spectrometry, is still a matter of debate. For hydrogen-rich peptide radicals in which several positive groups and low lying π* orbitals can capture the incoming electron in ExD, inclusion of full Hartree-Fock exchange at long-range interelectronic distance is a prerequisite for an accurate description of the electronic states, excluding therefore several popular exchange-correlation functionals, e.g., B3LYP, M06-2X or CAM-B3LYP. However, we show that this condition is not sufficient by comparing the results obtained with asymptotically correct range separated hybrids (M11, LC-BLYP, LC-BPW91, ωB97, ωB97X and ωB97X-D) and with reference CASSCF-MRCI and EOM-CCSD calculations. The attenuation parameter ω significantly tunes the spin density distribution and the excited states vertical energies. The investigated model structures, ranging from methylammonium to hexapeptide, allow us to obtain a description of the nature and energy of the electronic states depending on: (i) the presence of hydrogen bond(s) around the cationic site(s); (ii) the presence of π* MOs; and (iii) the selected DFT approach. It turns out that, in the present framework, LC-BLYP and ωB97 yields the most accurate results.

The cystamine-based hybrid perovskite, α-[NH3(CH2)2S-S(CH2)2NH3]PbI4 (1a), can be transformed into its polymorph, β-[NH3(CH2)2S-S(CH2)2NH3]PbI4 (1b), by heat activation (T = 150 °C). The crystal structures have been characterised by single-crystal X-ray diffraction, whereas the phase transition was followed by both solid-state 1H,13C cross-polarisation magic-angle spinning (CPMAS) NMR spectroscopy and thermodiffractometry techniques. At 150 °C, compound 1a is transformed into 1b, and, remarkably, the β phase (1b) can be nearly retained down to room temperature, which means that both polymorphs 1a and 1b can coexist over a large temperature range. The structure of 1b has been solved, and it was found that cystamine molecules are disordered over two positions: the two related components with opposite helical conformations. Solid-state 1H,13C CPMAS NMR spectroscopic measurements show a significant broadening of the NMR spectroscopic line associated with two disordered carbon atoms when cooling 1b from 160 to 50 °C, thereby revealing the presence of exchange between these related atoms, and this favours a molecular dynamical disorder. Disulfide bridges of cystamine molecules are engaged in weak interactions with neighbours, either another cystamine molecule in 1a (SS***SS interactions), or iodine atoms in 1b (SS***I interactions). To evaluate the donating and accepting abilities of the disulfide bridge, and their impact on such weak interactions, a detailed partition of the interaction energy of ten dimer models has been calculated and revealed that the main contribution to the intermolecular bonding comes from the dispersion forces.

International audience; Aromatic enynes can be transformed into arylnaphthalenes or benzofulvenes depending on the reaction conditions. Under gold(I) catalysis, exclusive or major 6-endo-dig cyclization took place leading to arylnaphthalenes. However, a catalytic system based on palladium iodide/1,3-Bis(diphenylphosphino)propane, in the presence of cesium carbonate as a base was necessary to furnish exclusively 5-exo-dig cyclization pattern, regardless to the electronic effects of the substituents. In the latter transformation, a mechanistic study (Kinetic Isotopic Effect, Density Functional Theory) involving a C-H activation is suggested for the exclusive benzofulvenes formation.

International audience; There is high prospect that derivatives of pentazole can lead to high energy density materials. However these molecules are potentially hazardous because of their high formation enthalpies and weak N-N bonds. In order to devise efficient protocols, possible schemes for the synthesis of nitro and azido derivatives of pentazole, and their mono- and di-oxides, have been explored using quantum chemical methods. Reaction pathways have been investigated in detail, with particular emphasis on locating transition states and on obtaining a reliable treatment of solvent effects. Oxidation by ozone is found to be a favorable process, leading to some regioselectivity in favor of b-mono-oxides. Nitration by NO2+BF4- is also predicted to be favorable. In contrast the electrochemical azidation of N5- and its oxidized derivatives is found to be energetically inaccessible. Combination of the individual addition and oxidation steps leads to recommendations for future synthetic work. Finally the kinetic stability of products with respect to N2 and N2O elimination is assessed.

The new tetradentate ligand 1,4-bis(5 H-dibenzo[a,d]cyclohepten-5-yl)-1,4-diazabuta-1,3-diene ((H)tropdad) allows the syntheses of the 16-electron cationic rhodium complexes [M((H)tropdad)](O(3)SCF(3)) (M=Rh, Ir). The structure of the rhodium complex was determined by X-ray analysis and points to a description of these as [M(+1)((H)tropdad)(0)] with short Cd-N bonds (av 1.285 A) and a long C-C bond (1.46 A) in the diazabutadiene (dad) moiety, that is the M-->dad charge-transfer is negligible. Both [Rh((H)tropdad)](+) and [Ir((H)tropdad)](+) are reduced at very low potentials (E(1) (1/2)= -0.56 V and E(1) (1/2)=-0.35 V, respectively) which allowed the quantitative synthesis of the neutral paramagnetic complexes [M((H)tropdad)](0) (M=Rh, Ir) by reacting the cationic precursor complexes simply with zinc powder. The [M((H)tropdad)](0) complexes are stable against protic reagents in organic solvents. Continuous wave and pulse EPR spectroscopy was used to characterize the paramagnetic species and the hyperfine coupling constants were determined: [Rh((H)tropdad)](0): A(iso)((14)N)=11.9 MHz, A(iso)((1)H)=14.3 MHz, A(iso)((103)Rh)= -5.3 MHz; [Ir((H)tropdad)](0): A(iso)((14)N)=11.9 MHz, A(iso)((1)H)=14.3 MHz. In combination with DFT calculations, the experimentally determined g and hyperfine matrices could be orientated within the molecular frame and the dominant spin density contributions were determined. These results clearly show that the complexes [M((H)tropdad)](0) are best described as [M(+1)((H)tropdad)(.-)] with a [16+1] electron configuration.

International audience; Electron capture and electron transfer dissociations are bioanalytical methods for fragmenting cations after reduction by an electron. Previous computational studies based on conventional DFT schemes have concluded that the first step of these processes, the attachment of the electron, leads to extensive delocalization of the spin density in the intermediate radical cation. Here, we show that most DFT methods produce unphysical results when studying single electron reduction of a dicationic peptide. This is not the case for post-HF methods and long-range corrected functionals which show satisfying electron affinities, intermolecular interaction energies and spin density trends. Our results suggest that the charged group with the highest electron affinity on the precursor cation is also the site of spin density in the electronic ground state after electron attachment. These findings have important implications for the interpretation of experimental data from electron-based processes in biomolecules and may guide the development of new functionals.

International audience; A new synthetic approach to hexahydroisoindol-4-ones is reported, based on the formal [3+2] cyclization reaction between N-arylsulfonylimines and cyclic conjugated dienes, under phosphine catalysis. Key substrates are 3-vinylcyclohex-2-enones with electron-withdrawing substituents (ester, amido, cyano, phosphoryl and keto groups) on the exocyclic double bond, which afford the three atom synthons for the construction of the pyrroline ring. Total syn stereoselectivity is observed in these annulations. The scope of the reaction has been demonstrated and mechanistic issues are considered, based on deuteration experiments and DFT calculations.

International audience; Square-planar platinum(II) complexes that combine chiral diphosphines and NHC ligands have been obtained in high yields from (NHC)Pt(0)(dvtms) complexes, via an oxidative addition/ligand exchange sequence. The use of suitable carbene−diphosphine pairs allows axially chiral, configurationally stable platinum complexes to be isolated. The Pt(II) complexes have been evaluated as precatalysts for the cycloisomerization reaction of an allyl propargylamine derivative. Their catalytic properties have been examined as a function of structural variations on both the diphosphine and the NHC units. For axially chiral species possible epimerization pathways have been envisioned and the inversion barriers have been estimated through computational studies

International audience; Alkylation of zinc-bound thiolates occurs in both catalytic and structural zinc sites of enzymes. Recent biomimetic studies have led to a controversy as to which mechanism is operative in thiolate alkylation. Building on one of these biomimetic complexes, we have devised a series of models that allow for an appraisal of the roles of charge, ligand nature, and hydrogen bonding to sulfur on reactivity. The reactions of these complexes with methyl iodide, leading to thioethers and zinc iodide complexes, have been examined by density functional theory calculations, in the gas phase as well as in an aqueous solution. In all cases, a S(N)2 reaction is favored over sigma-bond metathesis. Both the net electronic charge and the hydrogen bond play a significant role in the nucleophilicity of the thiolate. We find that the mechanistic diversity observed experimentally can be explained by the difference in the net charge of the complexes. A dianionic complex follows a dissociative pathway, whereas an associative one is preferred for a neutral system.

Electron capture dissociation (ECD) was studied with doubly charged dipeptide ions that were tagged with fixed-charge tris-(2,4,6-trimethoxyphenyl)phosphonium-methylenecarboxamido (TMPP-ac) groups. Dipeptides GK, KG, AK, KA, and GR were each selectively tagged with one TMPP-ac group at the N-terminal amino group while the other charge was introduced by protonation at the lysine or arginine side-chain groups to give (TMPP-ac-peptide + H)(2+) ions by electrospray ionization. Doubly tagged peptide derivatives were also prepared from GK, KG, AK, and KA in which the fixed-charge TMPP-ac groups were attached to the N-terminal and lysine side-chain amino groups to give (TMPP-ac-peptide-ac-TMPP)(2+) dications by electrospray. ECD of (TMPP-ac-peptide + H)(2+) resulted in 72% to 84% conversion to singly charged dissociation products while no intact charge-reduced (TMPP-ac-dipeptide + H)(+) ions were detected. The dissociations involved loss of H, formation of (TMPP + H)(+), and N-C(alpha) bond cleavages giving TMPP-CH(2)CONH(2)(+) (c(0)) and c(1) fragments. In contrast, ECD of (TMPP-ac-peptide-ac-TMPP)(2+) resulted in 31% to 40% conversion to dissociation products due to loss of neutral TMPP molecules and 2,4,6-trimethoxyphenyl radicals. No peptide backbone cleavages were observed for the doubly tagged peptide ions. Ab initio and density functional theory calculations for (Ph(3)P-ac-GK + H)(2+) and (H(3)P-ac-GK + H)(2+) analogs indicated that the doubly charged ions contained the lysine side-chain NH(3)(+) group internally solvated by the COOH group. The distance between the charge-carrying phosphonium and ammonium atoms was calculated to be 13.1-13.2 A in the most stable dication conformers. The intrinsic recombination energies of the TMPP(+)-ac and (GK + H)(+) moieties, 2.7 and 3.15 eV, respectively, indicated that upon electron capture the ground electronic states of the (TMPP-ac-peptide + H)(+*) ions retained the charge in the TMPP group. Ground electronic state (TMPP-ac-GK + H)(+*) ions were calculated to spontaneously isomerize by lysine H-atom transfer to the COOH group to form dihydroxycarbinyl radical intermediates with the retention of the charged TMPP group. These can trigger cleavages of the adjacent N-C(alpha) bonds to give rise to the c(1) fragment ions. However, the calculated transition-state energies for GK and GGK models suggested that the ground-state potential energy surface was not favorable for the formation of the abundant c(0) fragment ions. This pointed to the involvement of excited electronic states according to the Utah-Washington mechanism of ECD.

International audience; Unexpected and unprecedented directed remote lateral lithiation at one CH(CH3)2 of the 3-(2,6-di-isopropylphenyl) wingtip took place upon the reaction of functionalised N-heterocyclic carbene-type molecules with excess of LiCH2SiMe3, leading to dilithiated dianionic 4-amido-N-heterocyclic carbenes. DFT calculations show that the nature of the isolated species are under thermodynamic control.

International audience; Hydrogen-atom loss and intramolecular hydrogen-atom migration in peptide radical and cation radical were investigated by quantum chemical calculations for models that include zero to three hydrogen bonds with the ammonium groups. Five different DFT functionals have been checked to study the geometry relaxation and fragmentation processes after electron attachment to peptide cations. The structural changes associated with the geometry relaxation are shown to be dependent on the level of calculation. Furthermore, comparison with CCSD(T) calculations indicates that an adequate description of the electronic state of the reduced protonated peptide is not a sufficient prerequisite to provide accurate energy barrier. Calculating fragmentation reactions of hydrogen-rich peptide cation radicals is pointed out to be a challenging task as none of the DFT functionals are fully effective to describe the whole process. M06-2X is an adequate choice if it provides the correct ground state, otherwise LC-BLYP should be chosen.The electron attachment site and the electron affinity value are highly sensitive to the number of hydrogen bonds with the ammonium group. An ammonium cation with zero, one, and, to a smaller extent, two hydrogen bonds easily captures an incoming electron and subsequently undergoes an H-atom loss process rather than a proton coupled electron transfer. This suggests an explanation for the low amount of c and z fragments observed upon ECD for small protonated peptides, where the ammonium groups cannot be highly intramolecularly “solvated”.

International audience; Combining electron capture dissociation mass spectrometry and infrared multiple photon dissociation action spectroscopy allows the formation, selection and characterisation of reduced metal complexes containing non-innocent ligands. Zinc complexes containing diazafluorenone ligands have been studied and the localisation of the single electron on the metal atom in the mono-ligated complex has been demonstrated.

This work expands on the recent synthesis and reactivity of the two-coordinate P(III)-containing dication [((Ph3P)2C)P(NiPr2)]2+ (3a2+). Two additional dications of general formula [((RPh2P)2C)P(NR′2)]2+ (3b2+, R = 1/2 (CH2)3, R′ = iPr; 3c2+, R = Ph, R′ = Cy) have been prepared. Solution and solid-state 31P NMR isotropic shifts for this dication class were observed around 360 ppm. Except for [3a][SbF6]2, the 31P CP/MAS NMR spectra reveal a high degree of structural disorder around the dicationic site in the solid state. Surprisingly, the synthesis of dication 3a2+ was only possible in the presence of AlCl4–, SbF6–, and substituted tetraarylborates, while the use of ClO4–, OTf–, BF4–, PF6–, and BPh4– resulted in complex product mixtures. Single-crystal X-ray analysis of dications 3a2+ and 3c2+ suggested a 4π allyl-like structure for the central CPN fragment, and this has been supported through detailed theoretical investigations. Initial reactivity studies between dications 3a2+/3c2+ and PMe3 show an equilibrium between the free dication and the target adduct. Furthermore, 3a2+ has been shown to be capable of O–H bond activation using water and methanol and polymerizes THF when it is dissolved in this solvent ASTAR (Agency for Sci., Tech. and Research, S’pore) Accepted version

International audience; In this work, the tuneability of the π acceptor or donor properties of a set of N-heterocyclic carbenes (NHCs) with a wide spectrum of electronic characteristics is established by means of density functional theory and energy decomposition analysis (EDA) tools. Even though the main orbital interaction contribution to the NHC coordination is the σ donation, a significant contribution of the π interactions to the bond is observed. By means of carefully selected coordination sites, different contributions to the π interactions could be identified and isolated. It includes not only the well known back donation and donation interactions, but also the intrafragment polarization, which has not been considered in previous studies. This can be obtained through the use of the extended transition state method for EDA combined with the natural orbitals for chemical valence and the constrained space orbital variation analysis. The contributions vary with the position of the heteroatoms and the presence of exocyclic substituents; the donation/backdonation π interactions between NHC and the coordination site can range between 2 and 61% of the total π orbital interactions, while the rest is owed to intrafragment polarization. Our results do not only contribute to the understanding of the electronic structure of NHC-based complexes, giving ways to improve their catalytic properties, but also provide comprehension on the modelization methods used to study their donor–acceptor interactions.

International audience; Phosphoric acids with planar chiral paracyclophane scaffolds have been prepared in optically pure form starting from 1,8-dibromobiphenylene, by means of a chiral phosphorodiamidate as the phosphorylating agent. Structural characterization and configurational assignment have been performed by X-ray diffraction studies. The acids promote the organocatalytic enantioselective H-transfer reduction of α-arylquinolines with up to 90% enantiomeric excess.

A new family of planar chiral phosphoric acids containing a ferrocene unit is prepared with the shown derivative (FPC) giving the best results for the asymmetric transfer hydrogenation of quinolines.