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A crucial step in the preparation of supported metal catalysts is related to the choice of support, since it regulates the anchoring of the metal species in an environment of strong interactions. In this sense, the binding on the support, which may present defects, as well as induced modifications of the electronic structure, helps to determine efficient metal/support combinations for catalysis applications. In this work, first-principles studies have been carried out to model and describe the geometric and electronic properties of O-functionalized graphene as a model carbon support, in addition to a single Pd atom and Pd13 nanocluster (experimentally observed on various carbon supports) as supported metal catalysts. The carbon-based nanomaterial includes experimentally probed abundant oxygen functional groups and point defects, demonstrating high thermal stability at room temperature. The characterization confirms the structural motifs presented in the model, distinguishing the organic functionalities and various defects using spectroscopy techniques. Interestingly, the oxygenated carbon-based support presents a metallic character when the formal charges in the embedded Pd atom and nanocluster have been determined to be [Pd]+ and [Pd13]3+. The hydrogenation process of the adsorbed cluster is also presented, with the determination of a ratio between the adsorbed hydrides and the surface metal atoms close to unity at room temperature, thanks to ab initio molecular dynamics. [ABSTRACT FROM AUTHOR]

Several NMR and quantum chemical calculations are conducted to explain the properties and reactivities of two different hydrido-ruthenium cluster complexes. The application of these compounds for the different coordination sites on metal surfaces is also demonstrated.

The stabilization of the rare-earth metal alkyl and halide complexes by a cyclen-derived [NNNN] macrocyclic ancillary ligand is studied. The ligand is shown to act as a monoanionic ancillary environment during stabilization.

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]

The 2H quadrupolar interaction is a sensitive tool for the characterization of deuterium-metal binding states. In the present study, experimental solid-state ²H MAS NMR techniques are used in the investigations of two ruthenium clusters, D4Ru4(CO)12 (1) and D2Ru6(CO)18 (2), which serve as model compounds for typical two-fold, three-fold, and octahedral coordination sites on metal surfaces. By line- shape analysis of the ²H MAS NMR measurements of sample 1, a quadrupolar coupling constant of 67 ± 1 kHz, an asymmetry parameter of 0.67 ± 0.1, and an isotropic chemical shift of -17.4 ppm are obtained. In addition to the neutral complex, sample 2 includes two ionic clusters, identified as anionic [DRu6(CO)18] (2-) and cationic [D3Ru6(CO)18]+ (2+). By virtue of the very weak quadrupolar interaction (<2 kHz) and the strong low-field shift (+16.8 ppm) of 2-, it is shown that the deuteron is located in the symmetry center of the octahedron spanned by the six ruthenium atoms. For the cationic 2+, the quadrupolar interaction is similar to that of the neutral 2. Quantum chemical DFT calculations at different model structures for these ruthenium clusters were arranged in order to help in the interpretation of the experimental results. It is shown that the ²H nuclear quadrupolar interaction is a sensitive tool for distinguishing the binding state of the deuterons to the transition metal. Combining the data from the polynuclear complexes with the data from mononuclear complexes, a molecular ruler for quadrupolar interactions is created. This ruler now permits the solid-state NMR spectroscopic characterization of deuterium adsorbed on the surfaces of catalytically active metal nanoparticles. [ABSTRACT FROM AUTHOR]

A salt metathesis synthetic strategy is used to access rare tantalum/coinage metal (Cu, Ag, Au) heterobimetallic complexes. Specifically, complex [Li(THF) 2 ][Ta(C t Bu)(CH 2 t Bu) 3 ], 1 , reacts with (IPr)MCl (M = Cu, Ag, Au, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) to afford the alkylidyne-bridged species [Ta(CH 2 t Bu) 3 (μ-C t Bu)M(IPr)] 2-M . Interestingly, π-bonding of group 11 metals to the Ta─C moiety promotes a rare alkylidyne alkyl to bis-alkylidene tautomerism, in which compounds 2-M are in equilibrium with [Ta(CH t Bu)(CH 2 t Bu) 2 (μ-CH t Bu)M(IPr)] 3-M . This equilibrium was studied in detail using NMR spectroscopy and computational studies. This reveals that the equilibrium position is strongly dependent on the nature of the coinage metal going down the group 11 triad, thus offering a new valuable avenue for controlling this phenomenon. Furthermore, we show that these uncommon bimetallic couples could open attractive opportunities for synergistic reactivity. We notably report an uncommon deoxygenative carbyne transfer to CO 2 resulting in rare examples of coinage metal ketenyl species, ( t BuCCO)M(IPr), 4-M (M = Cu, Ag, Au). In the case of the Ta/Li analogue 1 , the bis(alkylidene) tautomer is not detected, and the reaction with CO 2 does not cleanly yield ketenyl species, which highlights the pivotal role played by the coinage metal partner in controlling these unconventional reactions.

Main-group metal calcium-mediated alkylpyridine benzylic C(sp 3 )-H activation and functionalization have been achieved. The reaction of a calcium hydride complex [{( DIPP nacnac)CaH(thf)} 2 ] ( DIPP nacnac = CH{(CMe)(2,6- i Pr 2 -C 6 H 3 N)} 2 ) with two equivalents of 2,6-lutidine rapidly yields a monomeric calcium alkyl complex with the release of dihydrogen. A hydride/carbon-bridged binuclear calcium complex [{( DIPP nacnac)Ca} 2 (μ-H){2-Me-6-(μ-CH 2 )-Py}(thf)] is obtained from an equimolar treatment of calcium hydride and 2,6-lutidine that is readily converted into mono- or binuclear calcium alkyl complexes upon subsequent addition of 2,6-lutidine. DFT calculations and kinetic studies are conducted to determine their reaction profiles. More significantly, this calcium hydride complex catalyzes regioselective benzylic C-H bond addition of alkylpyridines to a variety of alkenes, affording linear or branched alkylated pyridine derivatives.

The iridium tetrahydride complex Cp*IrH 4 reacts with a range of isobutylaluminum derivatives of general formula Al( i Bu) x (OAr) 3- x ( x = 1, 2) to give the unusual iridium aluminum species [Cp*IrH 3 Al( i Bu)(OAr)] ( 1 ) via a reductive elimination route. The Lewis acidity of the Al atom in complex 1 is confirmed by the coordination of pyridine, leading to the adduct [Cp*IrH 3 Al( i Bu)(OAr)(Py)] ( 2 ). Spectroscopic, crystallographic, and computational data support the description of these heterobimetallic complexes 1 and 2 as featuring strongly polarized Al(III) δ+ -Ir(III) δ- interactions. Reactivity studies demonstrate that the binding of a Lewis base to Al does not quench the reactivity of the Ir-Al motif and that both species 1 and 2 promote the cooperative reductive cleavage of a range of heteroallenes. Specifically, complex 2 promotes the decarbonylation of CO 2 and AdNCO, leading to CO (trapped as Cp*IrH 2 (CO)) and the alkylaluminum oxo ([( i Bu)(OAr)Al(Py)] 2 (μ-O) ( 3 )) and ureate ({Al(OAr)( i Bu)[κ 2 -(N,O)AdNC(O)NHAd]} ( 4 )) species, respectively. The bridged amidinate species Cp*IrH 2 (μ-CyNC(H)NCy)Al( i Bu)(OAr) ( 5 ) is formed in the reaction of 2 with dicyclohexylcarbodiimine. Mechanistic investigations via DFT support cooperative heterobimetallic bond activation processes.

The reduction of U(VI) to U(IV) is rare, especially in one step, and not observed electrochemically as a one-wave, two-electron couple. Here, we demonstrate that reduction of the uranium(VI) bis(imido) complex, (C 5 Me 5 ) 2 U[═N(4-O i PrC 6 H 4 )] 2 , is readily accomplished with Al(C 5 Me 5 ), forming the bridging uranium(IV)/aluminum(III) imido complex (C 5 Me 5 ) 2 U[μ 2 -N(4-O i PrC 6 H 4 )] 2 Al(C 5 Me 5 ). The structure and bonding of the bridging imido complex is examined with electrochemical measurements in tandem with density functional theory calculations.

Reactions of trinuclear rare-earth metal complexes bearing functionalized phosphinidene ligand [L 3 Ln 3 (μ 2 -Me) 2 (μ 3 -Me)(μ 3 -η 1 :η 2 :η 2 -PC 6 H 4 -o)] (L = [PhC(NC 6 H 4 i Pr 2 -2,6) 2 ] - , Ln = Y (1a), Lu (1b)) with phenylacetylene, CO 2 , diisopropyl carbodiimide, isocyanide, or PhSSPh lead to the formation of a series of phosphorus-containing products. The reaction of 1 with CS 2 yields two novel P-methyl-phosphindole-2,3-dithiolate dianion complexes, revealing an unusual tandem desulfurization/coupling/cyclization reaction mode of CS 2 . A possible reaction pathway was determined by density functional theory calculations. This emphasizes the key role of the reduction power of the formal P 2- part of the phosphinidene in the C-S bond cleavage.

We report here a unique example of an in situ generated aluminum initiator stabilized by a C 2 -symmetric salen ligand which shows a hitherto unknown high activity for the ROP of rac-lactide at room temperature. Using a simple and robust catalyst system, which is prepared from a salen complex and an onium salt, this convenient route employs readily available reagents that afford polylactide in good yields with narrow polydispersity indices, without the need for time-consuming and expensive processes that are typically required for catalyst preparation and purification. In line with the experimental evidence, DFT studies reveal that initiation and propagation proceed via an external alkoxide attack on the coordinated monomer.

The synthesis and characterization of Ln(Tp(iPr2))2 (Ln = Sm, 3Sm; Tm, 3Tm) are reported. While the simple (1)H NMR spectra of the compounds indicate a symmetrical solution structure, with equivalent pyrazolyl groups, the solid-state structure revealed an unexpected, "bent sandwich-like" geometry. By contrast, the structure of the less sterically congested Tm(Tp(Me2,4Et))2 (4) adopts the expected symmetrical structure with a linear B-Tm-B arrangement. Computational studies to investigate the origin of the unexpected bent structure of the former compounds indicate that steric repulsion between the isopropyl groups forces the Tp ligands apart and permits the development of unusual interligand C-H···N hydrogen-bonding interactions that help stabilize the structure. These results find support in the similar geometry of the Tm(III) analogue [Tm(Tp(iPr2))2]I, 3Tm(+), and confirm that the low symmetry is not the result of a metal-ligand interaction. The relevance of these results to the general question of the coordination geometry of MX2 and M(C5R5)2 (M = heavy alkaline earth and Ln(II), X = halide, and C5R5 = bulky persubstituted cyclopentadienyl) complexes and the importance of secondary H-bonding and nonbonding interactions on the structure are highlighted.

The experimental design of improved nanocatalysts is usually based on shape control and is surface-ligand dependent. First-principle calculations can guide their design, both in terms of activity and selectivity, provided that theoretical descriptors can be defined and used in a prescreening process. As a consequence of the Sabatier principle and of the Brønsted-Evans-Polanyi relationship, an important prerequisite before optimizing the catalytic properties of nanoparticles is the knowledge of the selective adsorption strengths of reactants at their surface. We report here adsorption energies of X (H, CH3) and L (PH3, CO) ligands at the surface of bare ruthenium nanoclusters Run (n = 55 and 147) calculated at the DFT level. Their dependence on the topology of the adsorption sites as well as on the size and shape of the nanoparticles (NPs) is rationalized with local descriptors derived from the so-called d-band center model. Defining the descriptors involves the determination of the energy of effective d atomic orbitals for each surface atom. Such a ligand field theory-like model is in close relation with frontier molecular orbital theory, a cornerstone of rational chemical synthesis. The descriptors are depicted as color maps which straightforwardly yield possible reactivity spots. The adsorption map of a large spherical hcp cluster (Ru288) nicely confirms the remarkable activity of steps, the so-called B5 sites. The predictive character of this conceptual DFT approach should apply to other transition metal NPs and it could be a useful guide to the design of efficient nanocatalysts bearing sites with a specific activity.

The grafting of an oxo chloro trisalkyl tungsten derivative on silica dehydroxylated at 700 °C was studied by several techniques that showed reaction via W-Cl cleavage, to afford a well-defined precatalyst for alkene metathesis. This was further confirmed by DFT calculations on the grafting process. (17)O labeling of the oxo moiety of a series of related molecular and supported tungsten oxo derivatives was achieved, and the corresponding (17)O MAS NMR spectra were recorded. Combined experimental and theoretical NMR studies yielded information on the local structure of the surface species. Assessment of the (17)O NMR parameters also confirmed the nature of the grafting pathway by ruling out other possible grafting schemes, thanks to highly characteristic anisotropic features arising from the quadrupolar and chemical shift interactions.