Convergent Reductive Depolymerization of Wood Lignin to Isolated Phenol Derivatives by Metal-Free Catalytic Hydrosilylation

International audienceThe first examples of reductive depolymerization of lignin are reported under metal-free conditions. Using hydrosilanes as reductants and B(C6F5)3 as a Lewis acid catalyst, wood lignin is efficiently converted to a narrow distribution of phenol derivatives at room temperature. A three-step methodology based on the selection of the wood species and the lignin extraction method followed by a convergent reductive depolymerization enables the production of four structurally defined aromatic compounds. The phenol products were successfully isolated in 7–24 wt% yield from lignin and 0.5–2.4 wt% yield from wood. The strategy is found to be robust and is applied to 15 different wood plants, including gymnosperm and angiosperm species. The efficiency of this novel methodology has been evaluated based on spectroscopic characterization of the lignin preparations and isolated yields of mono-aromatic products

Complexes of the tripodal phosphine ligands PhSi(XPPh2_2)3_3 (X = CH2_2, O): synthesis, structure and catalytic activity in the hydroboration of CO2_2

International audienceThe coordination chemistry of Fe$^{2+}$, Co$^{2+}$ and Cu$^+$ ions was explored with the triphosphine and triphosphinite ligands PhSi{CH$_2$PPh$_2$}$_3$ (1) and PhSi{OPPh$_2$}$_3$ (2), so as to evaluate the impact of the electronic properties of the tripodal phosphorus ligands on the structure and reactivity of the corresponding complexes. The synthesis and characterization of the complexes [Fe(κ$^3$-PhSi{CH$_2$PPh$_2$}$_3$)(MeCN)$_3$][OTf]$_2$ (3) (OTf = O$_3$SCF$_3$), [Fe(κ$^3$-PhSi{OPPh$_2$}$_3$)(MeCN)$_3$][OTf]$_2$ (3’), [Co(κ$^2$-PhSi{CH$_2$PPh$_2$}$_3$)Cl$_2$] (4), [Co(κ$^3$-PhSi {OPPh$_2$}$_3$)Cl$_2$] (4’), [Cu(κ$^3$-PhSi{CH$_2$PPh$_2$}$_3$)Br] (5) and [Cu(κ$^3$-PhSi{OPPh$_2$}$_3$)I] (5’) were carried out. The crystal structures of 3, 3’, 4, 4’, and of the solvates 5·3THF and 5’·THF are reported. Complexes3–5’ were shown to promote the catalytic hydroboration of CO$_2$ with (9-BBN)$_2$ (9-BBN = 9-borabicyclo [3.3.1]nonane). While the iron and cobalt complexes of the triphosphine 1 are more active than the analogous complexes with 2, the opposite trend is observed with the copper catalysts. Overall, the copper catalysts 5 and 5’ are both more reactive and more selective than the Fe and Co catalysts, enabling the formation of the acetal H$_2$C(OBBN)$_2$ with a high molar ratio of H$_2$ C(OBBN)$_2$:CH$_3$OBBN up to 92 : 8

Synthèse et caractérisation de nouveaux polymères du fer(II) à transition de spin

This dissertation deals with the synthesis of new iron(II) coordination polymers, the study of their magnetic and structural properties and the investigation of the factors that can give rise to highly cooperative spin transitions in solid state systems. Several families of spin crossover polymers with bridging ligands such as dicyanamide or bipyridine were obtained by an autoassembly method. The intersite interactions, as well as their influence on the magnetic properties of those systems, were studied through in-depth analysis of their single crystal X-ray diffraction structure. It is observed that the non-covalent interactions that connect the polymeric chains, such as hydrogen bonds and pi-stacking, play a bigger part in enhancing the cooperativity of the spin transition in those systems than the bridging ligands which covalently connect the metal sites together and spread elastic interactions between them.Ce travail présente l'élaboration de polymères de coordination du fer(II) à transition de spin, l'étude de leurs propriétés magnétiques et structurales et la recherche des facteurs conditionnant l'observation de transitions de spin fortement coopératives à l'état solide. La stratégie d'autoassemblage mise en oeuvre a permis l'obtention de plusieurs familles de polymères avec des espaceurs bipyridiniques et dicyanamide. L'analyse approfondie des données structurales concernant ces polymères par diffraction des rayons-X sur monocristal permet d'étudier les interactions inter-sites et leur influence sur les propriétés magnétiques de ces systèmes. On observe ainsi que la coopérativité de la transition de spin est davantage renforcée par les interactions intermoléculaires non-covalentes (liaisons hydrogène, pi-stacking) qui se développent entre les chaînes polymériques que par les interactions élastiques transmises d'un site métallique à l'autre par les ligands pontants plus ou moins rigides

Synthèse et caractérisation de nouveaux polymères du fer(II) à transition de spin

Ce travail présente l'élaboration de polymères de coordination du fer(II) à transition de spin, l'étude de leurs propriétés magnétiques et structurales et la recherche des facteurs conditionnant l'observation de transitions de spin fortement coopératives à l'état solide. La stratégie d'autoassemblage mise en oeuvre a permis l'obtention de plusieurs familles de polymères avec des espaceurs bipyridiniques et dicyanamide. L'analyse approfondie des données structurales concernant ces polymères par diffraction des rayons-X sur monocristal permet d'étudier les interactions inter-sites et leur influence sur les propriétés magnétiques de ces systèmes. On observe ainsi que la coopérativité de la transition de spin est davantage renforcée par les interactions intermoléculaires non-covalentes (liaisons hydrogène, pi-stacking) qui se développent entre les chaînes polymériques que par les interactions élastiques transmises d'un site métallique à l'autre par les ligands pontants plus ou moins rigides.This dissertation deals with the synthesis of new iron(II) coordination polymers, the study of their magnetic and structural properties and the investigation of the factors that can give rise to highly cooperative spin transitions in solid state systems. Several families of spin crossover polymers with bridging ligands such as dicyanamide or bipyridine were obtained by an autoassembly method. The intersite interactions, as well as their influence on the magnetic properties of those systems, were studied through in-depth analysis of their single crystal X-ray diffraction structure. It is observed that the non-covalent interactions that connect the polymeric chains, such as hydrogen bonds and pi-stacking, play a bigger part in enhancing the cooperativity of the spin transition in those systems than the bridging ligands which covalently connect the metal sites together and spread elastic interactions between them.LYON-ENS Sciences (693872304) / SudocSudocFranceF

A spin-crossover iron( ii ) coordination polymer with the 8-aminoquinoline ligand: synthesis, crystal structure and magnetic properties of [Fe(aqin) 2 (4,4′-bpy)](ClO 4 ) 2 ·2EtOH (aqin = 8-aminoquinoline, 4,4′-bpy = 4,4′-bipyridyl)

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Additive-free selective methylation of amines with formic acid over a Pd/In2O3 catalyst

Formic acid is used as the sole carbon and hydrogen source in the methylation of aromatic and aliphatic amines to methylamines. The reaction proceeds via a formylation/transfer hydrogenation pathway over a solid Pd/In2O3 catalyst without the need for any additive

Additive-free selective methylation of secondary amines with formic acid over a Pd/In2_2O3_3 catalyst

International audienceFormic acid is used as the sole carbon and hydrogen source in the methylation of aromatic and aliphatic amines to methylamines. The reaction proceeds via a formylation/transfer hydrogenation pathway over a solid Pd/In$_2$O$_3$ catalyst without the need for any additive

Additive-free selective methylation of amines with formic acid over a Pd/In2_2O3_3 catalyst

Formic acid is used as the sole carbon and hydrogen source in the methylation of aromatic and aliphatic amines to methylamines. The reaction proceeds via a formylation/transfer hydrogenation pathway over a solid Pd/In$_2$O$_3$ catalyst without the need for any additive

Catalytic deoxygenation of alcohols and ketones promoted by a new scandium / hydrosilane system

International audienceThe rarefaction of carbon fossil resources calls for the use of alternative raw material sources for the production of fuels and chemicals. In this context, biomass waste constitutes a renewable source of carbon and is considered one of the most promising feedstock to the sustainable production of chemicals, both from an economic and environmental standpoint. Nevertheless, molecules derived from biomass present a higher degree of functionalization than petrochemicals and they possess numerous oxidized groups, such as alcohols, carbonyls, ethers, etc. The selective reduction and deoxygenation of C-O and C=O bonds is thus a challenge to benefit from biomass derived product

Synthèse de nouveaux catalyseurs pour la dismutation de l’acide formique

International audienceLa pétrochimie fournit aujourd’hui carburants, plastiques, médicaments, etc. Pourrons-nous utiliser demain un déchet, le dioxyde de carbone (CO$_2$), pour fabriquer les mêmes produits ? Les enjeux scientifiques sont importants car le recyclage du CO$_2$ en produits chimiques et carburants présente le double avantage d’économiser des ressources fossiles tout en évitant une augmentation des émissions de ce gaz à effet de serre par leur utilisation