Search

Polynuclear metal hydride clusters play important roles in various catalytic processes, with most of the reported polynuclear metal hydride clusters adopting a polyhedral three‐dimensional structure. Herein, we report the first example of a planar tetranuclear uranium hydride cluster [(CpCMe2CMe2Cp)U]4(μ2‐H)4(μ3‐H)4 (U4H8). It was synthesized by reacting an ansa‐bis(cyclopentadienyl) ligand‐supported uranium chloride precursor [(CpCMe2CMe2Cp)U]3(μ2‐Cl)3(μ3‐Cl)2 with NaHBEt3. The presence of hydrides in U4H8 was confirmed by NMR spectroscopy and its reactivity with phenol and carbon tetrachloride. DFT calculations also facilitated the determination of the hydrides' positions in U4H8, featuring four bridging μ2‐H ligands and four face‐capping μ3‐H ligands, with the four U centers arranged in a rhombic geometry. The U4H8 represents not only the first example of planar polynuclear actinide metal hydride cluster but also the uranium hydride cluster with the highest nuclearity reported to date. [ABSTRACT FROM AUTHOR]

Polynuclear metal hydride clusters play important roles in various catalytic processes, with most of the reported polynuclear metal hydride clusters adopting a polyhedral three‐dimensional structure. Herein, we report the first example of a planar tetranuclear uranium hydride cluster [(CpCMe2CMe2Cp)U]4(μ2‐H)4(μ3‐H)4 (U4H8). It was synthesized by reacting an ansa‐bis(cyclopentadienyl) ligand‐supported uranium chloride precursor [(CpCMe2CMe2Cp)U]3(μ2‐Cl)3(μ3‐Cl)2 with NaHBEt3. The presence of hydrides in U4H8 was confirmed by NMR spectroscopy and its reactivity with phenol and carbon tetrachloride. DFT calculations also facilitated the determination of the hydrides' positions in U4H8, featuring four bridging μ2‐H ligands and four face‐capping μ3‐H ligands, with the four U centers arranged in a rhombic geometry. The U4H8 represents not only the first example of planar polynuclear actinide metal hydride cluster but also the uranium hydride cluster with the highest nuclearity reported to date. [ABSTRACT FROM AUTHOR]

Hydrogenolysis of the half-sandwich penta-arylcycopentadienyl-supported rare-earth metal dibenzyl complexes [(CpAr5)Ln(p-CH2-C6H4-Me)2(THF)] (CpAr5 = C5Ar5, Ar = 3,5-iPr2-C6H3; Ln = Sc, La) afforded a bimetallic scandium complex [(CpAr5)Sc(H)(μ-OC4H9)]2 (2) with two terminal hydrido ligands, and a double-sandwich bimetallic lanthanum hydride complex [(CpAr5)La(μ-H)]2 (4) bearing the reduced CpAr5 ligand. DFT calculations were conducted to elucidate the reaction profiles. [ABSTRACT FROM AUTHOR]

An efficient tandem hydrosilylation of CO2, which uses a combination of a simple, homoleptic lanthanum aryloxide and B(C6F5)3, was performed. Use of a less sterically hindered silane led to an exclusive reduction of CO2 to CH4, with a turnover frequency of up to 6000 h−1 at room temperature. The catalytic system is robust, and 19 400 turnovers could be achieved with 0.005 mol% loading of lanthanum. The reaction outcome depended highly on the nature of the silane reductant used. Selective production of the formaldehyde equivalent, i.e., bis(silyl)acetal, without over-reduction, was observed when a sterically bulky silane was used. The reaction mechanism was elucidated by stoichiometric reactions and DFT calculations. [ABSTRACT FROM AUTHOR]

A rare heterobimetallic oxidative addition of X–H (X = C, O) bonds is reported. DFT suggests that steric constraints around the bimetallic core play a critical role to synergistically activate C–H bonds across the two metals and thus explains the exceptional H/D exchange catalytic activity of unhindered surface organometallic Ta/Ir species observed experimentally. [ABSTRACT FROM AUTHOR]

We report intramolecular proton transfer reactions to functionalize carbon monoxide and tert‐butyl nitrile from a bis(phosphido) thorium complex. The reaction of (C5Me5)2Th[PH(Mes)]2, Mes=2,4,6‐Me3C6H2, with 1 atm of CO yields (C5Me5)2Th(κ2‐(O,O)‐OCH2PMes‐C(O)PMes), in which one CO molecule is inserted into each thorium–phosphorus bond. Concomitant transfer of two protons, formerly coordinated to phosphorus, are now bound to one of the carbon atoms from one of the inserted CO molecules. DFT calculations were employed to determine the lowest energy pathway. With tert‐butyl nitrile, tBuCN, only one nitrile inserts into a thorium–phosphorus bond, but the proton is transferred to nitrogen with one phosphido remaining unperturbed affording (C5Me5)2Th[PH(Mes)][κ2‐(P,N)‐N(H)C(CMe3)P(Mes)]. Surprisingly, reaction of this compound with KN(SiMe3)2 removes the proton bound to nitrogen, not phosphorus. [ABSTRACT FROM AUTHOR]

We report intramolecular proton transfer reactions to functionalize carbon monoxide and tert‐butyl nitrile from a bis(phosphido) thorium complex. The reaction of (C5Me5)2Th[PH(Mes)]2, Mes=2,4,6‐Me3C6H2, with 1 atm of CO yields (C5Me5)2Th(κ2‐(O,O)‐OCH2PMes‐C(O)PMes), in which one CO molecule is inserted into each thorium–phosphorus bond. Concomitant transfer of two protons, formerly coordinated to phosphorus, are now bound to one of the carbon atoms from one of the inserted CO molecules. DFT calculations were employed to determine the lowest energy pathway. With tert‐butyl nitrile, tBuCN, only one nitrile inserts into a thorium–phosphorus bond, but the proton is transferred to nitrogen with one phosphido remaining unperturbed affording (C5Me5)2Th[PH(Mes)][κ2‐(P,N)‐N(H)C(CMe3)P(Mes)]. Surprisingly, reaction of this compound with KN(SiMe3)2 removes the proton bound to nitrogen, not phosphorus. Building on CO: A primary bis(phosphido) complex gives both hydrogen atoms from each phosphorus center to a single carbon atom when treated with carbon monoxide. This is a rare example of the conversion of CO into a formyl‐like species through intramolecular proton transfer. [ABSTRACT FROM AUTHOR]

Working closely with experimentalists on the comprehension of the surface properties of catalytically active organometallic nanoparticles (NPs) requires the development of several computational strategies which significantly differ from the cluster domain where a precise knowledge of their optimal geometry is a mandatory prerequisite to computational modeling. Theoretical simulations can address several properties of organometallic nanoparticles: the morphology of the metal core, the surface composition under realistic thermodynamic conditions, the relationship between adsorption energies and predictive descriptors of reactivity. It is in such context that an integrated package has been developed or adapted in our group: (i) one tool aims at building a wide variety of the typical shapes exhibited by nanoparticles. Using Reverse Monte Carlo modeling, a given shape can be optimized in order to fit pair distribution function data obtained from X-ray diffraction measurements; (ii) trends in density functional theory (DFT) adsorption energies of surface species can be rationalized and predicted by making use of simple descriptors. This is why we have proposed an extension of the d-band center model, that leads to the formulation of a generalized ligand-field theory. A comparison between cobalt and ruthenium is proposed in the case of a 55-atoms nanocluster. The accuracy of the generalized coordination number [Angew. Chem., Int. Ed., 2014, 53, 8316], a very simple coordination-activity criterion, is also assessed; (iii) the builder package is completed by the steric-driven grafting of ligands on the surface of metal NPs. It easily generates structures with adjustable surface composition values and coordination modes; (iv) after a local optimization at the DFT level of theory, DFT energies and normal modes of vibration can feed a general tool based on the ab initio thermodynamics method. This method aims at easily calculating an optimal surface composition under realistic temperature and pressure conditions. In addition to that, we also show to what extent knowledge of the density of states (DOS) and of the crystal overlap Hamilton population (COHP), both projected from a plane-wave basis set to a local basis set, sheds light on metal core–ligand chemical bonding. [ABSTRACT FROM AUTHOR]

Cluster models of SiO2-200 are proposed and compared with spectroscopic (IR and NMR) experimental data. Five models describing the variety of surface silanols (isolated, vicinal and germinal) at the SiO2-200 surface have then been derived and used to study the grafting reaction of homoleptic silylamide lanthanum(iii) complexes. Three different grafting modes have been obtained (mono-, bi- and tri-grafted) in line with the experimental knowledge. In terms of energetic stability as well as spectroscopic properties of coordinated OPPh3 (as a probe), all modes could coexist at the surface. The analysis of the δ(31P) chemical shifts for the coordinated OPPh3 indicates some possible important differences in Lewis acidity of the lanthanide centre, which may impact the catalysis. [ABSTRACT FROM AUTHOR]

The speciation of compounds [Cp*2M2O5] (M=Mo, W; Cp*=pentamethylcyclopentadienyl) in different protic and aprotic polar solvents (methanol, dimethyl sulfoxide, acetone, acetonitrile), in the presence of variable amounts of water or acid/base, has been investigated by 1H NMR spectrometry and electrical conductivity. Specific hypotheses suggested by the experimental results have been further probed by DFT calculations. The solvent (S)-assisted ionic dissociation to generate [Cp*MO2(S)]+ and [Cp*MO3]− takes place extensively for both metals only in water/methanol mixtures. Equilibrium amounts of the neutral hydroxido species [Cp*MO2(OH)] are generated in the presence of water, with the relative amount increasing in the order MeCN≈acetone

Grafting catalysts on a surface leads to heterogeneous catalysts with well-defined active sites. However, the grafting mode of a lanthanum complex onto silica remains unknown. To shed light on this grafting reaction, different studies have been achieved in the framework of density functional theory. The silica substrate hydroxylated at 700 °C has been simulated both by molecular and periodic models. The created molecular models are in agreement with the rigidity of the ligand, the surface density of silanol groups, and the different spectroscopic data of a silica surface partially dehydroxylated at 700 °C. Two possible models of surface have henceforth been considered: the first one with one isolated silanol and the second one with two vicinal silanols linked by a siloxane bridge. The thermodynamics of a grafting reaction of lanthanum catalysts on these models has also been investigated. This reaction leads to thermodynamically stable structures that reveal different types of grafting: monografted, bigrafted, or bigrafted after breaking of a Si−O−Si bridge. Similarly to experimental approaches, coordination of triphenylphosphine oxide (OPPh3) has also been considered as a probe of the grafting mode. A good agreement between the theoretical and the experimental spectroscopic values has systematically been found, but none of the grafting modes seem to be more relevant. Accordingly, it is necessary to consider in subsequent studies that all grafting modes coexist, increasing the difficulty to theoretically investigate multistep reactions. [ABSTRACT FROM AUTHOR]

A novel Ta/Os heterobimetallic complex, [Ta(CH2tBu)3(μ-H)3OsCp*], 2, is prepared by protonolysis of Ta(CHtBu)(CH2tBu)3 with Cp*OsH5. Treatment of 2 and its iridium analogue [Ta(CH2tBu)3(μ-H)2IrCp*], 1, with CO2 under mild conditions reveal the efficient cleavage of CO2, driven by the formation of a tantalum oxo species in conjunction with CO transfer to the osmium or iridium fragments, to form Cp*Ir(CO)H2 and Cp*Os(CO)H3, respectively. This bimetallic reactivity diverges from more classical CO2 insertion into metal–X (X = metal, hydride, alkyl) bonds. [ABSTRACT FROM AUTHOR]

Two‐electron oxidative addition is one of the most important elementary reactions for d‐block transition metals but it is uncommon for f‐block elements. Here, we report the first examples of intermolecular oxidative addition of E−H (E=C, N) bonds to uranium(II) centers. The transient U(II) species was formed in‐situ by reducing a heterometallic cluster featuring U(IV)‐Pd(0) bonds with potassium‐graphite (KC8). Oxidative addition of C−H or N−H bonds to the U(II) centers was observed when this transient U(II) species was treated with benzene, carbazole or 1‐adamantylamine, respectively. The U(II) centers could also react with tetracene, biphenylene or N2O, leading to the formation of arene reduced U(IV) products and uranyl(VI) species via two‐ or four‐electron processes. This study demonstrates that the intermolecular two‐electron oxidative addition reactions are viable for actinide elements. [ABSTRACT FROM AUTHOR]

Two‐electron oxidative addition is one of the most important elementary reactions for d‐block transition metals but it is uncommon for f‐block elements. Here, we report the first examples of intermolecular oxidative addition of E−H (E=C, N) bonds to uranium(II) centers. The transient U(II) species was formed in‐situ by reducing a heterometallic cluster featuring U(IV)‐Pd(0) bonds with potassium‐graphite (KC8). Oxidative addition of C−H or N−H bonds to the U(II) centers was observed when this transient U(II) species was treated with benzene, carbazole or 1‐adamantylamine, respectively. The U(II) centers could also react with tetracene, biphenylene or N2O, leading to the formation of arene reduced U(IV) products and uranyl(VI) species via two‐ or four‐electron processes. This study demonstrates that the intermolecular two‐electron oxidative addition reactions are viable for actinide elements. [ABSTRACT FROM AUTHOR]

The first part of this study aims at evaluating the accuracy of DFT calculations of acids and their conjugate bases in periodic boundary conditions and plane-wave basis sets. The resulting gas-phase acidities are compared to experimental data. Calculations done with the PBE functional are accurate, with a ∼ 4 kcal mol - 1 mean average deviation (MAD) with respect to experiments and a ∼ 1 kcal mol - 1 MAD with respect to non-periodic DFT calculations done in the aug-cc-pvtz basis set with the same functional. In the second part, the relative stability of Ru 13 - isomers is also successfully compared to previous calculations done using local basis sets (Waldt et al. in J Chem Phys 142:024319, 2015). Finally, several carboxylic acids and their conjugate bases are adsorbed on two Ru 13 clusters, showing a linear correlation between adsorption energies and experimental gas-phase acidities. [ABSTRACT FROM AUTHOR]

• Two routes to prepare Ta-Ir/SiO 2 catalysts via surface organometallic chemistry. • In-depth structural characterization of Ta, Ta-Ir and Ta-Ir 2 surface sites. • Improved catalytic performances in H/D isotope exchange and propane metathesis. A stepwise surface organometallic chemistry (SOMC) methodology consisting in using a silica-supported tantalum species, [(≡SiO)Ta(CH t Bu)(CH 2 t Bu) 2 ], as a reactive center to coordinate an iridium site, was developed to construct tantalum/iridium heterobimetallic edifices. The resulting material, MAT-2 , exhibits enhanced catalytic performances - both in H/D isotopic exchange and alkane metathesis reactions - in comparison to MAT-1 , which was prepared from the direct grafting on silica of a well-defined heterobimetallic Ta/Ir complex. We projected that the difference in catalytic activity was due to the presence of distinct active sites and we used a combination of advanced spectroscopic methods (IR, solid-state NMR and XAS spectroscopies) as well as modeling (computational studies and molecular models) to identify the structure of these surface species. These investigations point towards the presence of three types of active sites at the surface of MAT-2 : the heterobimetallic surface species, [≡SiOTa(CH 2 t Bu) 2 {IrH 2 (Cp*)}] 2-s , which is also found in MAT-1 , as well as an unanticipated heterotrimetallic species, [≡SiOTa(CH 2 t Bu) 2 {IrH 2 (Cp*)}], 3-s along with some unreacted monometallic Ta sites [(≡SiO)Ta(CH t Bu)(CH 2 t Bu) 2 ], 1-s. The well-defined trimetallic surface species 3-s was independently prepared and characterized to support this hypothesis. This study highlights the importance of the synthetic methodology used for the preparation of heterobimetallic species through SOMC, and the difficulty to obtain true single-sites surface species. [ABSTRACT FROM AUTHOR]

We have re‐examined the reactivity of the manganese dinitrogen complex [Cp(CO)2Mn(N2)] (1, Cp=η5‐cyclopentadienyl, C5H5) with phenylithium (PhLi). By combining experiment and density functional theory (DFT), we have found that, unlike previously reported, the direct nucleophilic attack of the carbanion onto coordinated dinitrogen does not occur. Instead, PhLi reacts with one of the CO ligands to provide an anionic acylcarbonyl dinitrogen metallate [Cp(CO)(N2)MnCOPh]Li (3) that is stable only below −40 °C. Full characterization of 3 (including single crystal X‐ray diffraction) was performed. This complex decomposes quickly above −20 °C with N2 loss to give a phenylate complex [Cp(CO)2MnPh]Li (2). The latter compound was erroneously formulated as an anionic diazenido compound [Cp(CO)2MnN(Ph)=N]Li in earlier reports, ruling out the claimed and so‐far unique behavior of the N2 ligand in 1. DFT calculations were run to explore both the hypothesized and the experimentally verified reactivity of 1 with PhLi and are fully consistent with our results. Direct attack of a nucleophile on metal‐coordinated N2 remains to be demonstrated. [ABSTRACT FROM AUTHOR]

We have re‐examined the reactivity of the manganese dinitrogen complex [Cp(CO)2Mn(N2)] (1, Cp=η5‐cyclopentadienyl, C5H5) with phenylithium (PhLi). By combining experiment and density functional theory (DFT), we have found that, unlike previously reported, the direct nucleophilic attack of the carbanion onto coordinated dinitrogen does not occur. Instead, PhLi reacts with one of the CO ligands to provide an anionic acylcarbonyl dinitrogen metallate [Cp(CO)(N2)MnCOPh]Li (3) that is stable only below −40 °C. Full characterization of 3 (including single crystal X‐ray diffraction) was performed. This complex decomposes quickly above −20 °C with N2 loss to give a phenylate complex [Cp(CO)2MnPh]Li (2). The latter compound was erroneously formulated as an anionic diazenido compound [Cp(CO)2MnN(Ph)=N]Li in earlier reports, ruling out the claimed and so‐far unique behavior of the N2 ligand in 1. DFT calculations were run to explore both the hypothesized and the experimentally verified reactivity of 1 with PhLi and are fully consistent with our results. Direct attack of a nucleophile on metal‐coordinated N2 remains to be demonstrated. [ABSTRACT FROM AUTHOR]

Alkyl and hydrido scandium complexes of the dianionic pentadentate ligand B2Pz4Py are reported. The key starting material (B2Pz4Py)ScCl is readily prepared and alkylated with organolithium reagents RLi (R = CH3, CH2SiMe3, CH2SiMe2Ph, CH2CH2CH3 and CH2CHMe2) to form alkyl derivatives in 61-93% yields. These compounds are very thermally stable and do not undergo sigma bond metathesis reactions with dihydrogen. The hydrido complex was prepared from (B2Pz4Py)ScCl and NaHBEt3 in 80% yield and was found to be more stable by 28 kcal mol-1 as a dimer, rather than a monomeric hydrido complex. However, the monomer is accessible through dissociation of the dimer at 80 °C. All of the compounds (B2Pz4Py)ScR react with water to form the bridging oxo dimer (B2Pz4Py)ScOSc(B2Pz4Py). The reactivity of the hydrido and methyl complexes towards carbon dioxide was explored; heating to 80 °C results in the formation of κ2 formato and acetate complexes, respectively. The mechanisms were studied via density functional theory and distinct transition states for insertion of CO2 into the Sc-R (R = H, CH3) were found, with the insertion into Sc-CH3 being more enthalpically difficult (by 18 kcal mol-1) than insertion into Sc-H. The slow rate of reaction between [(B2Pz4Py)ScH]2 and CO2 is attributed to the barrier associated with dimer dissociation. In both insertion reactions, the kinetic products are κ1 formato or acetate complexes that are only slightly less stable than the observed κ2 derivatives. The κ1 compounds can therefore be trapped by treating the κ2 isomers with tris-pentafluorophenyl borane. [ABSTRACT FROM AUTHOR]

[Display omitted] • CNT supported Ru single atoms have been associated to Ru, Pd and Ni particles. • Hydrogen spillover induced a cooperative catalysis between supported Pd and Ni particles and Ru single atoms. • The RuNi/CNT catalyst contains a cocktail of catalytic species including isolated Ru single atoms and Ru single atoms on Ni particles. • The RuNi/CNT catalyst shows much better performances in terms of activity and selectivity compared to the monometallic systems. • DFT calculations revealed that the active species is a Ru SA @Ni NP single atom alloy. Reaching high selectivity at high conversion and high rate in the industrially important selective hydrogenation of α,β-unsaturated aldehydes is a challenging task. Among current approaches reported in the literature, high selectivity towards the unsaturated alcohol or saturated aldehyde is generally achieved at the expense of activity. The use of bimetallic systems can lead either to selectivity or to activity enhancement, but generally not to both. Herein, we show that, for cinnamaldehyde hydrogenation, combining Ni nanoparticles (Ni NP) and Ru single atoms (Ru SA) on CNTs allows improvement of the hydrocinnamaldehyde selectivity, while obtaining a remarkable activity. The STY of Ru SA -Ni NP /CNT is approximately 60 times higher than that of the Ru SA /CNT and 10 times higher than that of the Ni NP /CNT. Importantly, the resulting catalyst shows 94% selectivity at 99% conversion and a good stability in flow. Insights into the cooperative "cocktail"-type catalysis between Ni NP and Ru SA were revealed from density functional theory calculations. [ABSTRACT FROM AUTHOR]

This work reports the synthesis, characterization, and reactivity of the first example of a well‐defined zinc α‐diazoalkyl complex. Treatment of zinc(I)‐zinc(I) bonded compound L2Zn2 [L=CH3C(2,6‐iPr2C6H3N)CHC(CH3)(NCH2CH2PPh2)] or zinc(II) hydride LZnH with trimethylsilyldiazomethane affords zinc diazoalkyl complex LZnC(N2)SiMe3. This complex liberates N2 in the presence of a nickel catalyst to form an α‐zincated phosphorus ylide by reacting with the pendant phosphine. It selectively undergoes formal [3+2] cycloaddition with CO2 or CO to form the corresponding product with a five‐membered heterocyclic core. Notably, the use of CO in such a [3+2] cycloaddition reaction is unprecedented, reflecting a novel CO reaction mode. [ABSTRACT FROM AUTHOR]

This work reports the synthesis, characterization, and reactivity of the first example of a well‐defined zinc α‐diazoalkyl complex. Treatment of zinc(I)‐zinc(I) bonded compound L2Zn2 [L=CH3C(2,6‐iPr2C6H3N)CHC(CH3)(NCH2CH2PPh2)] or zinc(II) hydride LZnH with trimethylsilyldiazomethane affords zinc diazoalkyl complex LZnC(N2)SiMe3. This complex liberates N2 in the presence of a nickel catalyst to form an α‐zincated phosphorus ylide by reacting with the pendant phosphine. It selectively undergoes formal [3+2] cycloaddition with CO2 or CO to form the corresponding product with a five‐membered heterocyclic core. Notably, the use of CO in such a [3+2] cycloaddition reaction is unprecedented, reflecting a novel CO reaction mode. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hydrogen spillover induced a cooperative catalysis between Pd particles and Pd single atoms supported on carbon supports. • Few-layer graphene (FLG) support allows more extended H-spillover than multi-walled carbon nanotubes (CNT) • Pd/FLG is more active for solvent-free total hydrogenation of squalene than Pd/CNT but deactivated. • A new mechanism of thermal catalyst deactivation induced by H-spillover is proposed. General interest in solvent-free catalytic processes is driven by the development of environmentally and economically acceptable procedures. Such processes require the use of highly active and stable catalysts. This study reports on the synthesis, characterization, and kinetic evaluation of two highly active Pd catalysts supported on different carbons support, i.e., multi-walled carbon nanotubes (CNT) and few-layer graphene (FLG). These catalysts, with similar Pd loading (∼2 wt%) and containing both Pd single atoms (Pd SA) and nanoparticles (Pd NP), were systematically tested for solvent-free total hydrogenation of squalene (SQE) to obtain high-purity squalane (SQA). Thanks to the unique cooperative catalysis between Pd SA and Pd NP involving H-spillover, the activities of both catalysts were high compared to catalysts described in the literature. Solvent-free total hydrogenation of SQE could be performed under mild conditions (120 °C, 20 bar H 2 , 4 h) using ultralow Pd loading (60 ppm). However, since this reduction reaction is highly exothermic (ΔH R = − 765 kJ.mol−1), heat management during the reactor operation with these highly active catalysts is crucial to avoid deactivation and thermal runaway. Under these conditions, Pd/FLG was highly active but deactivated, unlike Pd/CNT, which still has high activity, but does not deactivate. Characterizations (ICP, XPS, Raman, TPD-MS, HAADF-STEM) of the Pd/FLG catalyst before and after reaction, supported by calculations based on density functional theory, allowed us to propose a new mechanism of catalyst deactivation involving the chemical reduction of specific surface oxygen groups of the carbon support induced by H-spillover. [ABSTRACT FROM AUTHOR]

Reduction of a range of amido‐ and aryloxy‐aluminum dihydride complexes, e.g. [AlH2(NR3){N(SiMe3)2}] (NR3=NMe3 or N‐methylpiperidine (NMP)), with β‐diketiminato dimagnesium(I) reagents, [{(ArNacnac)Mg}2] (ArNacnac=[HC(MeCNAr)2]−, Ar=mesityl (Mes) or 2,6‐xylyl (Xyl)), have afforded deep red mixed valence aluminum hydride cluster compounds, [Al6H8(NR3)2{Mg(ArNacnac)}4], which have an average Al oxidation state of +0.66, the lowest for any well‐defined aluminum hydride compound. In the solid‐state, the clusters are shown to have distorted octahedral Al6 cores, having zero‐valent Al axial sites and mono‐valent AlH2− equatorial units. Several novel by‐products were isolated from the reactions that gave the clusters, including the Mg−Al bonded magnesio‐aluminate complexes, [(ArNacnac)(Me3N)Mg−Al(μ‐H)3[{Mg(ArNacnac)}2(μ‐H)]]. Computational analyses of one aluminum hydride cluster revealed its Al6 core to be electronically delocalized, and to possess one unoccupied, and six occupied, skeletal molecular orbitals. [ABSTRACT FROM AUTHOR]

Reduction of a range of amido‐ and aryloxy‐aluminum dihydride complexes, e.g. [AlH2(NR3){N(SiMe3)2}] (NR3=NMe3 or N‐methylpiperidine (NMP)), with β‐diketiminato dimagnesium(I) reagents, [{(ArNacnac)Mg}2] (ArNacnac=[HC(MeCNAr)2]−, Ar=mesityl (Mes) or 2,6‐xylyl (Xyl)), have afforded deep red mixed valence aluminum hydride cluster compounds, [Al6H8(NR3)2{Mg(ArNacnac)}4], which have an average Al oxidation state of +0.66, the lowest for any well‐defined aluminum hydride compound. In the solid‐state, the clusters are shown to have distorted octahedral Al6 cores, having zero‐valent Al axial sites and mono‐valent AlH2− equatorial units. Several novel by‐products were isolated from the reactions that gave the clusters, including the Mg−Al bonded magnesio‐aluminate complexes, [(ArNacnac)(Me3N)Mg−Al(μ‐H)3[{Mg(ArNacnac)}2(μ‐H)]]. Computational analyses of one aluminum hydride cluster revealed its Al6 core to be electronically delocalized, and to possess one unoccupied, and six occupied, skeletal molecular orbitals. [ABSTRACT FROM AUTHOR]

The article offers information on a study related to the significance of the 2H solid-state nuclear magnetic resonance (NMR) technique to study metallic nanostructures of ruthenium-containing hydrogenation catalysts published in a 2013 issue of the journal "ChemPhysChem."

Pd/C catalysts are widely used for hydrogenation reactions in the chemical industry. One of the reasons for their high activity is the ability of Pd nanoparticles (PdNP) to dissociate H2 and promote H‐spillover. Nevertheless, for selective hydrogenation unpromoted Pd/C catalysts show disappointing results. The use of supported Pd single atom (PdSA) catalysts permits to achieve high selectivity. However, PdSA show low activity because they have difficulty in activating H2. A cooperative catalysis between PdNP and PdSA operates for the hydrogenation of alkenes thanks to the H‐spillover, which makes it possible to obtain active isolated PdSA−H species. Here, we present experimental and computational results obtained for phenylacetylene hydrogenation on Pd/CNT catalysts showing different PdSA/PdNP ratios. Tuning this ratio allows doubling the activity while reaching high selectivity to styrene at high conversion. DFT calculations suggest that the first coordination sphere of PdSA has a pronounced effect on their reactivity. [ABSTRACT FROM AUTHOR]

The use of the hypervalent iodine reagents in oxidative processes has become a staple in modern organic synthesis. Frequently, the reactivity of λ³ iodanes is further enhanced by acids (Lewis or Brønsted). The origin of such activation, however, has remained elusive. Here, we use the common combination of PhI(OAc)2 with BF3⋅Et2O as a model to fully explore this activation phenomenon. In addition to the spectroscopic assessment of the dynamic acid-base interaction, for the first time the putative PIDA⋅BF3 complex has been isolated and its structure determined by X-ray diffraction. Consequences of such activation are discussed from a structural and electronic (DFT) points of views, including the origins of the enhanced reactivity. [ABSTRACT FROM AUTHOR]

The activation of CH bonds has revolutionized modern synthetic chemistry. However, no general strategy for enantiospecific CH activation has been developed to date. We herein report an enantiospecific CH activation reaction followed by deuterium incorporation at stereogenic centers. Mechanistic studies suggest that the selectivity for the α-position of the directing heteroatom results from a four-membered dimetallacycle as the key intermediate. This work paves the way to novel molecular chemistry on nanoparticles. [ABSTRACT FROM AUTHOR]

The activation of CH bonds has revolutionized modern synthetic chemistry. However, no general strategy for enantiospecific CH activation has been developed to date. We herein report an enantiospecific CH activation reaction followed by deuterium incorporation at stereogenic centers. Mechanistic studies suggest that the selectivity for the α-position of the directing heteroatom results from a four-membered dimetallacycle as the key intermediate. This work paves the way to novel molecular chemistry on nanoparticles. [ABSTRACT FROM AUTHOR]

Polymer diols are a class of polymeric building blocks of high interest for the synthesis of complex macromolecular edifices. Rare-earth borohydride complexes are known as efficient initiators for the ring-opening polymerization (ROP) of cyclic esters, directly affording α,ω-dihydroxy-telechelic polyesters. Here, were report the direct synthesis of poly(benzyl β-malolactonate) (PMLABe) diols, from the ROP of racemic (benzyl β-malolactonate) ( rac-MLABe), a valuable and renewable monomer, initiated by the homoleptic [Ln(BH4)3(thf)3] (Ln=La, Nd, and Sm) complexes. These initiators enabled the controlled ROP of this β-lactone, affording well-defined syndiotactic-enriched ( Pr≈0.83) PMLABes ( Mn up to 21 300 g mol−1, ÐM≈1.5) as evidenced by size exclusion chromatography, 1H and 13C NMR spectroscopy, and MALDI-ToF mass spectrometry analyses. The first and second insertions of rac-MLABe, as assessed by DFT calculations, revealed more favorable stationary front-side than migratory back-side insertions, the thermodynamically and kinetically competitive ROP on two distinct arms with that on a one arm-only, and the thermodynamically slightly favored formation of syndiotactic-enriched PMLABes. [ABSTRACT FROM AUTHOR]

Breslow intermediates are very often elusive species whose application in frustrated Lewis pair (FLP) chemistry is unprecedented. Described herein is the use of a masked form of an O‐borylated Breslow (OBB) intermediate that performs FLP‐type activation of the carbonyl function of five different benzaldehyde derivatives with complete diastereoselectivity. The resulting compounds are characterised in solution by NMR spectroscopy (compounds 4–8) and in solid state by X‐ray diffraction analysis (compounds 4–6). A combined kinetic and theoretical investigation reveals the associative nature of the rate determining step and suggests that the OBB intermediate part is never released during the whole process. [ABSTRACT FROM AUTHOR]

The direct access to (mesityl)(alkyl)haloboranes (Mes(Alk)BX) (X = Br, Cl) from mesitylborane dimer and vinyl halides is presented. The involved hydroboration reaction results in the transfer of the halogen atom from the carbon of the starting material to the boron in the final product. The reactivity of the obtained Mes(Alk)BX has been evaluated for the synthesis of the bipyridyl boronium cations and 2-arylpyridine derived boron N^C-chelates. The formation mechanism of Mes(Alk)BX is apprended by DFT-calculations which shows that their formation involves two concomitant pathways derived from the regioslectivity of the hydroboration reaction. [ABSTRACT FROM AUTHOR]

This work reports the first catalyzed synthesis of d-block metalmetal bonded complexes. The treatment of terminal zinc hydrides [LZnH] [L = CH3C(2,6-iPr2C6H3N)CHC(CH3) (N(CH2)nCH2PR2); n = 1, 2; R = Ph, iPr] in the presence of 5 mol% Ni(CO)2(PPh3)2 afforded Zn(I)-Zn(I) bonded compounds [L2Zn2] in high isolated yields with concomitant elimination of dihydrogen. Stoichiometric reactions, kinetic studies and DFT calculations were conducted to elucidate the reaction mechanism. [ABSTRACT FROM AUTHOR]

RuNi nanoparticles (NP) were prepared by decomposition of [Ru(η4-C8H12)(η6-C8H10)] and [Ni(η4-C8H12)2] by H2 in the presence of polyvinylpyrrolidone (PVP) at 85 °C using several Ru/Ni ratios. The nanoparticles display a segregated structure in which Ni is on the surface, as ascertained by wide angle X-ray scattering (WAXS). The catalytic activity in the selective hydrogenation of furfural of these RuNi NP was correlated with the Ru content. High selectivity towards the partially hydrogenated product 2-(hydroxymethyl)furan (HF) was found when carrying out the reaction in tetrahydrofuran (THF). A different scenario was found when using a protic polar solvent, 1-propanol. Catalysts displaying Ru on the surface were able to hydrogenate the heteroaromatic ring, while those with Ni on the surface were highly selective towards the partially hydrogenated product. In addition, Ru surfaces were prone to catalyse the acetalization reaction in the presence of the alcoholic solvent, while the addition of Ni supressed this reactivity. Density functional theory (DFT) calculations performed on hydrogenated Ru nanoparticles (Ru55H70) show differences in the adsorption energies of several reagents, products, reaction intermediates, and solvents onto the Ru NP surface, which are in line with the experimental catalytic results. [ABSTRACT FROM AUTHOR]

Recently, we disclosed the uncatalyzed formation of polyaminoboranes (PABs) from monomeric diisopropylaminoborane (iPr2N−BH2) and primary amines (RNH2). Their structure is studied through a detailed multinuclear NMR study and their full spectroscopic characterization is presented revealing that N‐alkyl substituted PABs exhibit magnetically non‐equivalent methylenic protons in the close vicinity of the BN‐backbone. We also performed an in‐depth theoretical study of this global chemical process. The mechanism is fully apprehended and the strong influence of the temperature on the outcome of the reaction is unveiled. DFT‐calculations clearly show that the formation of the polyaminoboranes (RNH−BH2)n results from a kinetically controlled step‐growth polymerization reaction that can be globally viewed as a head‐to‐tail association process of the in situ generated transient monomeric monoalkylamino‐borane [RNH−BH2]. [ABSTRACT FROM AUTHOR]

The reactivity of rare-earth complexes RE(BH4)2(C3H5)(THF)x (RE = La, Nd, Sm, Y, Sc) toward the Ring-Opening Polymerization (ROP) of ε-caprolactone (ε-CL) was rationalized by Density Functional Theory (DFT) calculations. Even if the polymerization reaction can be initiated by both RE-(BH4) and RE-allyl bonds, experimental investigations have shown that the initiation via the borohydride ligand was favored, as no allyl group could be detected at the chain-end of the resulting polymers. DFT studies could confirm these observations, as it was highlighted that even if the activation barriers are both accessible, the allyl group is not active for the ROP of ε-CL due to the formation of a highly stable intermediate that disfavors the subsequent ring-opening. [ABSTRACT FROM AUTHOR]

Hydrogenolysis of alkyl‐substituted cyclopentadienyl (CpR) ligated thorium tribenzyl complexes [(CpR)Th(p‐CH2‐C6H4‐Me)3] (1–6) afforded the first examples of molecular thorium trihydrido complexes [(CpR)Th(μ‐H)3]n (CpR=C5H2(tBu)3 or C5H2(SiMe3)3, n=5; C5Me4SiMe3, n=6; C5Me5, n=7; C5Me4H, n=8; 7–10 and 12) and [(Cp#)12Th13H40] (Cp#=C5H4SiMe3; 13). The nuclearity of the metal hydride clusters depends on the steric profile of the cyclopentadienyl ligands. The hydrogenolysis intermediate, tetra‐nuclear octahydrido thorium dibenzylidene complex [(Cpttt)Th(μ‐H)2]4(μ‐p‐CH‐C6H4‐Me)2 (Cpttt=C5H2(tBu)3) (11) was also isolated. All of the complexes were characterized by NMR spectroscopy and single‐crystal X‐ray analysis. Hydride positions in [(CpMe4)Th(μ‐H)3]8 (CpMe4=C5Me4H) were further precisely confirmed by single‐crystal neutron diffraction. DFT calculations strengthen the experimental assignment of the hydride positions in the complexes 7 to 12. [ABSTRACT FROM AUTHOR]

Hydrogenolysis of alkyl‐substituted cyclopentadienyl (CpR) ligated thorium tribenzyl complexes [(CpR)Th(p‐CH2‐C6H4‐Me)3] (1–6) afforded the first examples of molecular thorium trihydrido complexes [(CpR)Th(μ‐H)3]n (CpR=C5H2(tBu)3 or C5H2(SiMe3)3, n=5; C5Me4SiMe3, n=6; C5Me5, n=7; C5Me4H, n=8; 7–10 and 12) and [(Cp#)12Th13H40] (Cp#=C5H4SiMe3; 13). The nuclearity of the metal hydride clusters depends on the steric profile of the cyclopentadienyl ligands. The hydrogenolysis intermediate, tetra‐nuclear octahydrido thorium dibenzylidene complex [(Cpttt)Th(μ‐H)2]4(μ‐p‐CH‐C6H4‐Me)2 (Cpttt=C5H2(tBu)3) (11) was also isolated. All of the complexes were characterized by NMR spectroscopy and single‐crystal X‐ray analysis. Hydride positions in [(CpMe4)Th(μ‐H)3]8 (CpMe4=C5Me4H) were further precisely confirmed by single‐crystal neutron diffraction. DFT calculations strengthen the experimental assignment of the hydride positions in the complexes 7 to 12. [ABSTRACT FROM AUTHOR]

A hybrid material made of mononuclear organophosphorus polypyridyl ruthenium complexes covalently bonded to ruthenium nanoparticles has been synthesized via a one-pot organometallic procedure and finely characterized. These results open new avenues to access unique hybrid transition metal nanomaterials. [ABSTRACT FROM AUTHOR]

Enantiopure poly(lactic acid) (PLA) can form stereocomplexes when enantiomeric PLA chains are mixed in equivalent amounts. Such materials provide interesting features that might be suitable for numerous applications. Despite several advantages, the main drawback of PLA is its narrow window of processing, thus limiting its use for industrial applications. Reported herein are achiral iron complexes, that are highly active, productive, and stereoselective under mild reaction conditions for the ring‐opening polymerization of lactide. The corresponding catalytic systems enable the production of stereoblock polymers with high molecular weights, allowing the formation of thermally stable and industrially relevant stereocomplexes. [ABSTRACT FROM AUTHOR]

Enantiopure poly(lactic acid) (PLA) can form stereocomplexes when enantiomeric PLA chains are mixed in equivalent amounts. Such materials provide interesting features that might be suitable for numerous applications. Despite several advantages, the main drawback of PLA is its narrow window of processing, thus limiting its use for industrial applications. Reported herein are achiral iron complexes, that are highly active, productive, and stereoselective under mild reaction conditions for the ring‐opening polymerization of lactide. The corresponding catalytic systems enable the production of stereoblock polymers with high molecular weights, allowing the formation of thermally stable and industrially relevant stereocomplexes. [ABSTRACT FROM AUTHOR]

The monomeric actinide dihydrido complex [(CpAr*)(Cp*)ThH2(THF)] (2) bearing the super-bulky penta-arylcyclopentadienyl (CpAr* = C5Ar*5, Ar* = 3,5-tBu2-C6H3) and pentamethylcyclopentadienyl (Cp* = C5Me5) ligands was obtained for the first time. Complex 2 underwent unique Th–H addition reactions with various unsaturated compounds to afford the corresponding five-membered metallacycles, including the first example of actinide metallacyclopentyne [(CpAr*)(Cp*)Th(PhCH–C≡C–CHPh)] (4). [ABSTRACT FROM AUTHOR]

The amine elimination reaction of equimolar amounts of ansa-bis(amidine) C6H4-1,2-{NC(tBu)NH(2,6-iPr2C6H3)}2 (L1H) and [(Me3Si)2N]2Yb(THF)2 affords a bis(amidinate) YbII complex [C6H4-1,2-{NC(tBu)N(2,6-iPr2C6H3)}2]Yb(THF) (1) in 68% yield. Complex 1 features a rather rare η1-amido:η6-arene coordination of both amidinate fragments to the YbII ion, resulting in the formation of a bent bis(arene) structure. Oxidation of 1 by I2 regardless of the molar ratio of reagents (2 : 1 or 1 : 1) leads to the formation of the YbIII species [{(2,6-iPr2C6H3)=NC(tBu)NH}-C6H4-1,2-{NC(tBu)N(2,6-iPr2C6H3)}]YbI2(THF)2 (2) in which only one amidinate fragment is coordinated to the ytterbium ion in κ2-N,N′-chelating coordination mode, while the second NCN fragment is protonated in the course of the reaction and is not bound to the metal ion. The outcome of the salt metathesis reaction of LaCl3 with lithium amidinates [C6H4-1,2-{NC(tBu)N(2,6-R2C6H3)}2Li2] (R = Me, iPr) is proven to be strongly affected by the substituent 2,6-R2C6H3 on the amidinate nitrogens. When R = iPr, the salt metathesis reaction occurs smoothly and results in the formation of an ate-chloro-amidinate complex [C6H4-1,2-{NC(tBu)N(2,6-iPr2C6H3)}2]La(μ2-Cl)Li(THF)(μ2-Cl)2Li(THF)2 (3) in which the LaIII ion is coordinated by both amidinate fragments in a “classic”κ2-N,N′-chelating fashion. In the case of R = Me, the reaction requires prolonged heating for completion. Moreover, the salt metathesis reaction is accompanied by the fragmentation of the ligand and affords a trinuclear chloro-amidinate complex [C6H4-1,2-{NC(tBu)N(2,6-Me2C6H3)}2]La{[(tBu)C(N-2,6-Me2C6H3)2]La(THF)}2(μ2-Cl)4(μ3-Cl)2 (4) containing one dianionic ansa-bis(amidinate) and two monoanionic [(tBu)C(N-2,6-Me2C6H3)2] amidinate fragments. DFT calculations are conducted to determine the factor that governs this change in coordination mode and, in particular, the effect of the metal oxidation state. [ABSTRACT FROM AUTHOR]

The new bisamido aluminum species [AlCl{N(SiMe3)2}2(THF)] (1) was prepared and fully characterized by 27Al and 35Cl solid-state NMR, along with X-ray diffraction studies. 1 was grafted on silica partially dehydroxylated at 700 °C, affording silica-supported Al species. The resulting material (2) was characterized by IR, elemental analysis and 1H, 13C and 27Al solid-state MAS NMR. The 1D and 2D 27Al MAS NMR studies showed the occurrence of two types of species, where the Al center adopts a tetracoordinated coordination sphere, with as an additional coordinated Lewis base, either a THF ligand or a silica-surface siloxane moiety. DFT calculations allowed understanding the grafting mechanism and the spectroscopic properties of the material. [ABSTRACT FROM AUTHOR]

To use carbon dioxide as a source of carbon, recent progress has been made toward the synthesis of higher value chemicals and in particular toward Cn compounds. In this context, we report here the synthesis of a borylated C3‐carbohydrate from CO2 as the only source of carbon. This result corresponds to the unprecedented formation of a polyol chain and of asymmetric carbon atoms from CO2. The adopted strategy involves the Fe‐catalysed selective 4e− reduction of CO2 into bis(boryl)acetal followed in one‐pot by a carbene‐mediated C−C coupling reaction. Boron is shown to play a key role in the coupling step enabling to observe the first diastereoselective formose‐type reaction. This result is in addition obtained under mild reaction conditions (T<80 °C, 1 atm of CO2) and short reaction time (t<2 h). Such a boron: The combination of organometallic catalysis and carbene‐mediated C−C homocoupling enables the unprecedented generation of asymmetric carbon centres from CO2. [ABSTRACT FROM AUTHOR]

Abstract: The preferential substitution of oxo ligands over alkyl ones of rare‐earth complexes is commonly considered as “impossible” due to the high oxophilicity of metal centers. Now, it has been shown that simply assembling mixed methyl/oxo rare‐earth complexes to a rigid trinuclear cluster framework cannot only enhance the activity of the Ln‐oxo bond, but also protect the highly reactive Ln‐alkyl bond, thus providing a previously unrecognized opportunity to selectively manipulate the oxo ligand in the presence of numerous reactive functionalities. Such trimetallic cluster has proved to be a suitable platform for developing the unprecedented non‐redox rare‐earth‐mediated oxygen atom transfer from ketones to CS2 and PhNCS. Controlled experiments and computational studies shed light on the driving force for these reactions, emphasizing the importance of the sterical accessibility and multimetallic effect of the cluster framework in promoting reversal of reactivity of rare‐earth oxo complexes. [ABSTRACT FROM AUTHOR]

Abstract: The preferential substitution of oxo ligands over alkyl ones of rare‐earth complexes is commonly considered as “impossible” due to the high oxophilicity of metal centers. Now, it has been shown that simply assembling mixed methyl/oxo rare‐earth complexes to a rigid trinuclear cluster framework cannot only enhance the activity of the Ln‐oxo bond, but also protect the highly reactive Ln‐alkyl bond, thus providing a previously unrecognized opportunity to selectively manipulate the oxo ligand in the presence of numerous reactive functionalities. Such trimetallic cluster has proved to be a suitable platform for developing the unprecedented non‐redox rare‐earth‐mediated oxygen atom transfer from ketones to CS2 and PhNCS. Controlled experiments and computational studies shed light on the driving force for these reactions, emphasizing the importance of the sterical accessibility and multimetallic effect of the cluster framework in promoting reversal of reactivity of rare‐earth oxo complexes. [ABSTRACT FROM AUTHOR]

The grafting of a lanthanum trisbenzyl derivative onto dehydroxylated silica affords a mixture of [(≡SiO)2La(CH2Ph)(THF)n] and [(≡SiO)La(CH2Ph)2(THF)m] surface sites, in respective proportions of 80 and 20%, as evidenced from mass balance analyses, IR and ¹H, 13C and 29Si 1D and 2D solid-state NMR spectroscopy. Significant transfer of alkyl groups from lanthanum to the surface was demonstrated. The grafting mechanism was also probed by DFT calculations, which confirm that benzyl group transfer from the lanthanum to the surface (via Si-O-Si cleavage) occurs readily. This material proved to be active in alkyne dimerization and in ethylene, styrene, and ε-caprolactone homopolymerization. [ABSTRACT FROM AUTHOR]

In the present study, we report the first silver-dependent enantiodivergent gold-catalysed reaction. The asymmetric intramolecular hydroamination of alkenes catalysed by the combination of a single chiral binuclear gold(I) chloride complex and silver perchlorate can afford both enantiomers of the products by a simple solvent change from toluene to methanol. Such an enantiodivergent reaction is strictly independent of the reaction temperature or of the nature of the catalyst anion and displays the same first-order kinetic rate law with respect to substrate concentration in both solvents. Beyond a simple solvent effect the enantioinversion is controlled by gold-silver chloride adducts which occur only in methanol and allow a dual activation of the reagent. While one single gold atom activates the alkene moiety, the other gold atom forms an oxophilic gold-silver chloride adduct which is likely to interact with the carbamate function. By comparison with toluene, which affords ( S)-enantiomer, this proximal and bimetallic activation would allow an opposite stereodifferentiation of the two diastereomeric intermediates during the final protodeauration step and lead therefore to the ( R)-enantiomer. [ABSTRACT FROM AUTHOR]