Thibault Cantat

Recycling of Carbon and Silicon Wastes: Room Temperature Formylation of N–H Bonds Using Carbon Dioxide and Polymethylhydrosiloxane

A highly active organocatalytic system based on N-heterocyclic carbenes has been designed for the formylation of N-H bonds in a large variety of nitrogen molecules and heterocycles, using two chemical wastes: CO(2) and polymethylhydrosiloxane (PMHS).

CO2 as a C1-building block for the catalytic methylation of amines

A novel catalytic reaction has been designed to utilize, for the first time, CO2 as a C1 feedstock in the synthesis of N-methylamines. Simple zinc catalysts, based on commercially available zinc salts and ligands, prove highly efficient in promoting both a 6 electron reduction of carbon dioxide and the formation of a C–N bond, using hydrosilanes and amines.

Reductive functionalization of CO2 with amines: an entry to formamide, formamidine and methylamine derivatives

CO2 utilization for the production of C1-containing molecules is a desirable route to value-added chemicals. In this perspective, we summarize the recent results devoted to the formation of nitrogen compounds obtained by reductive functionalization of CO2 in the presence of amines. Using mild reductants, such as molecular hydrogen, hydrosilanes and hydroboranes, novel catalytic reactions have been designed in the last few years to facilitate the reductive functionalization of CO2 to formamide, formamidine and methylamine derivatives. While early efforts were devoted to the formylation of N–H bonds, efficient organic and metal catalysts have been developed lately to promote the complete deoxygenation of CO2 to benzimidazoles, quinazolinones, formamidines and methylamines. Finally, the opportunities and challenges facing the practical use of CO2 in the production of nitrogen-containing molecules are discussed.

Uranium azide photolysis results in C–H bond activation and provides evidence for a terminal uranium nitride

Uranium nitride [U[triple bond]N](x) is an alternative nuclear fuel that has great potential in the expanding future of nuclear power; however, very little is known about the U[triple bond]N functionality. We show, for the first time, that a terminal uranium nitride complex can be generated by photolysis of an azide (U-N=N=N) precursor. The transient U[triple bond]N fragment is reactive and undergoes insertion into a ligand C-H bond to generate new N-H and N-C bonds. The mechanism of this unprecedented reaction has been evaluated through computational and spectroscopic studies, which reveal that the photochemical azide activation pathway can be shut down through coordination of the terminal azide ligand to the Lewis acid B(C(6)F(5))(3). These studies demonstrate that photochemistry can be a powerful tool for inducing redox transformations for organometallic actinide complexes, and that the terminal uranium nitride fragment is reactive, cleaving strong C-H bonds.

The U═C Double Bond: Synthesis and Study of Uranium Nucleophilic Carbene Complexes

Treatment of U(BH(4))(4) with 1 or 3 equiv of Li(2)(SCS) x 1.5 Et(2)O, 1, afforded the actinide carbene complexes U(mu-SCS)(3)[U(BH(4))(3)](2) (4) and U(mu-SCS)(3)[Li(Et(2)O)](2) (6), respectively [SCS = (Ph(2)P = S)(2)C]. In THF, complex 4 was transformed into the mononuclear derivative (SCS)U(BH(4))(2)(THF)(2) (5). The multiple bond character of the uranium-carbon bond was first revealed by the X-ray crystal structures of the three complexes. The U=C bond in these complexes present a nucleophilic character, as shown by their reaction with a carbonyl derivative. Finally, DFT calculations prove the involvement of both 5f and 6d orbitals in both the sigma and the pi U-C bonds.

Carbon Dioxide Reduction to Methylamines under Metal‐Free Conditions

The first metal-free catalysts are reported for the methylation of amines with carbon dioxide. Proazaphosphatrane superbases prove to be highly active catalysts in the reductive functionalization of CO2, in the presence of hydroboranes. The new methodology enables the methylation of N-H bonds in a wide variety of amines, including secondary amines, with increased chemoselectivity.

Structural and kinetic effects of chloride ions in the palladium-catalyzed allylic substitutions

Addition of ligands to (Pd(h 3 -RCH/CH/CH2)(m-Cl))2 or chloride ions to cationic ((h 3 -RCHCHCH 2 )PdL 2 ) � BFinduces the formation of neutral complexes h 1 -RCH/CH/CH2/PdClL2 (R � /H with L � /(4-Cl/C6H4)3P, (4-CH3/C6H4)3P, (4-CF3/C6H4)3P or L2� /1,2-bis(diphenylphosphino)butane (dppb), 1,1?-bis(diphenylphosphino)ferrocene (dppf); R � /Ph with L� /(4-Cl/C6H4)3P), instead of the expected cationic complexes ((h 3 -RCH/CH/CH2)PdL2) � Cl � . In the presence of chloride ions, the reaction of morpholine with the cationic complexes ((h 3 -allyl)Pd(PAr3)2) � BF � (Ar� /4-Cl/C6H4, 4-CH3/C6H4) goes slower and involves both cationic ((h 3 -allyl)Pd(PAr3)2) � and neutral h 1 -allyl-PdCl(PAr3)2 complexes as reactive species in equilibrium with Cl � . The cationic complex is more reactive than the neutral one. However, their relative contribution in the reaction strongly depends on the chloride concentration, which controls their relative concentration. The neutral h 1 -allyl-PdCl(PAr3)2 may become the major reactive species at high chloride concentration. Consequently, (Pd(h 3 -allyl)(m-Cl))2 associated with ligands or cationic ((h 3 -allyl)PdL2) � BF � ; used indifferently as precursors in palladium-catalyzed allylic substitutions, are not equivalent. In both situations, the mechanism of the Pd-catalyzed allylic substitution depends on the concentration of the chloride ions, delivered by the precursor or purposely added, that determines which species, ((h 3 -allyl)PdL2) � or/and h 1 -allyl-PdClL2 are involved in the nucleophilic attack with consequences on the rate of the reaction and probably on its regioselectivity. Consequently, the chloride ions of the catalytic precursors (Pd(h 3 -

Exploring the uranyl organometallic chemistry: from single to double uranium-carbon bonds.

Uranyl organometallic complexes featuring uranium(VI)-carbon single and double bonds have been obtained from uranyl UO(2)X(2) precursors by avoiding reduction of the metal center. X-ray diffraction and density functional theory analyses of these complexes showed that the U-C and U=C bonds are polarized toward the nucleophilic carbon.

Iron-catalyzed hydrosilylation of CO2: CO2 conversion to formamides and methylamines

Catalytic hydrosilylation of CO2 is an efficient and selective approach to form chemicals. Herein, we describe the first iron catalysts able to promote the reductive functionalization of CO2 using hydrosilanes as reductants. Iron(II) salts supported by phosphine donors enable the conversion of CO2 to formamide and methylamine derivatives under mild reaction conditions.

Metal-free reduction of CO2 with hydroboranes: two efficient pathways at play for the reduction of CO2 to methanol.

Guanidines and amidines prove to be highly efficient metal-free catalysts for the reduction of CO2 to methanol with hydroboranes such as 9-borabicyclo[3.3.1]nonane (9-BBN) and catecholborane (catBH). Nitrogen bases, such as 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (Me-TBD), and 1,8-diazabicycloundec-7-ene (DBU), are active catalysts for this transformation and Me-TBD can catalyze the reduction of CO2 to methoxyborane at room temperature with TONs and TOFs of up to 648 and 33 h(-1) (25 °C), respectively. Formate HCOOBR2 and acetal H2C(OBR2)2 derivatives have been identified as reaction intermediates in the reduction of CO2 with R2BH, and the first C-H-bond formation is rate determining. Experimental and computational investigations show that TBD and Me-TBD follow distinct mechanisms. The N-H bond of TBD is reactive toward dehydrocoupling with 9-BBN and affords a novel frustrated Lewis pair (FLP) that can activate a CO2 molecule and form the stable adduct 2, which is the catalytically active species and can facilitate the hydride transfer from the boron to the carbon atoms. In contrast, Me-TBD promotes the reduction of CO2 through the activation of the hydroborane reagent. Detailed DFT calculations have shown that the computed energy barriers for the two mechanisms are consistent with the experimental findings and account for the reactivity of the different boron reductants.