DFT Study of Small Palladium Clusters Pdnand Their Interaction with a CO Ligand (n= 1-9)

Synthesis of 2-Alkylaryl and Furanyl Acetates by Palladium Catalysed Carbonylation of Alcohols

The one-pot alkoxycarbonylation of halo-free alkylaryl and furanyl alcohols represents a sustainable alternative for the synthesis of alkylaryl and furanyl acetates. In this paper, the reaction between benzyl alcohol, chosen as a model substrate, CH3OH and CO was tested in the presence of a homogeneous palladium catalyst, an activator (isopropenyl acetate (IPAc) or dimethyl carbonate (DMC)) and a base (Cs2CO3). The influence of various reaction parameters such as the CO pressure, ligand and palladium precursor employed, mmol% catalyst load, temperature and time were investigated. The results demonstrate that decreasing the CO pressure from 50 bar to 5 bar at 130 °C for 18 h increases yields in benzyl acetate from 36% to over 98%. Further experiments were performed in the presence of piperonyl and furfuryl alcohol, interesting substrates employed for the synthesis of various fine chemicals. Moreover, furfuryl alcohol is a lignocellulosic-derived building block employed for the synthesis of functionalized furans such as 2-alkylfurfuryl acetates. Both the alcohols were successfully transformed in the corresponding acetate (yields above 96%) in rather mild reaction conditions (5–0.01 mol% catalyst, 5–2 bar CO pressure, 130 °C, 4–18h), demonstrating that the alkoxycarbonylation of alcohols represents a promising sustainable alternative to more impactful industrial practices adopted to date for the synthesis of alkylaryl and furfuryl acetates.

A sustainable route for the synthesis of alkyl arylacetates via halogen and base free carbonylation of benzyl acetates

The Pd-catalysed carbonylation of benzyl acetates for the synthesis of 2-alkylbenzyl acetates in the absence of base and halogen sources was investigated.

A Perspective on Modelling Metallic Magnetic Nanoparticles in Biomedicine: From Monometals to Nanoalloys and Ligand-Protected Particles

The focus of this review is on the physical and magnetic properties that are related to the efficiency of monometallic magnetic nanoparticles used in biomedical applications, such as magnetic resonance imaging (MRI) or magnetic nanoparticle hyperthermia, and how to model these by theoretical methods, where the discussion is based on the example of cobalt nanoparticles. Different simulation systems (cluster, extended slab, and nanoparticle models) are critically appraised for their efficacy in the determination of reactivity, magnetic behaviour, and ligand-induced modifications of relevant properties. Simulations of the effects of nanoscale alloying with other metallic phases are also briefly reviewed.

Pd nanoparticle growth monitored by DRIFT spectroscopy of adsorbed CO

Synchrotron-based X-ray absorption spectroscopy and scattering are known in situ probes of metal nanoparticles (NPs). A limited number of laboratory techniques allow post-synthesis diagnostics of the active metal surface area. This work demonstrates the high potential of infrared spectroscopy as an in situ laboratory probe for the growth of metal NPs on a substrate. We introduce a small fraction of CO molecules into the reaction mixture as a probe to monitor the reduction kinetics of the Pd2+ precursor on ceria in hydrogen.

On the ligand-free palladium cluster catalysed Suzuki-Miyaura reaction

C-C cross coupling reactions have been widely used for developing synthesis protocols for pharmaceuticals and agricultural products in the past few decades. Of all the reported C-C cross coupling reactions, the Suzuki-Miyaura reaction is preferred because of its mild reaction conditions, the commercial availability of associated reagents and the ease of removal of boron containing by-products. Recently, Corma and co-workers [Leyva-Perez et al., Angew. Chem., 2013, 125, 11768] reported water-stabilized three- and four-atom Pd clusters as highly active catalytic species for C-C coupling reactions. The present work focuses on developing detailed mechanistic insights into the Suzuki-Miyaura reaction with Pd₃ and Pd₄ clusters utilizing density functional theory calculations. The role of the base in the reaction was analysed in this study, which was found to lower the activation barriers of transmetalation over both Pd₃ and Pd₄. Free energy landscapes for Suzuki-Miyaura coupling of bromobenzene and phenylboronic acid over Pd₃ and Pd₄ clusters were developed. The highest free energy barriers of 34.7 and 30.4 kcal mol^-1 were observed for the oxidative addition over Pd₃ and Pd₄, respectively, indicating the oxidative addition as the rate limiting step. Detailed energetics conclusively proved the active nature of small-atom Pd clusters for catalyzing the Suzuki-Miyaura reaction.

Constructing chiral bicyclo[3.2.1]octanes via palladium-catalyzed asymmetric tandem Heck/carbonylation desymmetrization of cyclopentenes

Transition-metal-catalyzed tandem Heck/carbonylation reaction has emerged as a powerful tool for the synthesis of structurally diverse carbonyl molecules, as well as natural products and pharmaceuticals. However, the asymmetric version was rarely reported, and remains a challenging topic. Herein, we describe a palladium-catalyzed asymmetric tandem Heck/carbonylation desymmetrization of cyclopentenes. Alcohols, phenols and amines are employed as versatile coupling reagents for the construction of multifunctional chiral bicyclo[3.2.1]octanes with one all-carbon quaternary and two tertiary carbon stereogenic centers in high diastereo- and enantioselectivities. This study represents an important progress in both the asymmetric tandem Heck/carbonylation reactions and enantioselective difunctionalization of internal alkenes.

Catalytic performance of Pdn (n = 1, 2, 3, 4 and 6) clusters supported on TiO2-V for the formation of dimethyl oxalate via the CO catalytic coupling reaction: a theoretical study

The formation of dimethyl oxalate (DMO) via CO catalytic coupling on a series of catalysts including Pdn (n = 1, 2, 3, 4 and 6) clusters loaded on TiO2-V has been explored by density functional theory (DFT) calculation. The results show that different Pdn clusters have a remarkable influence on DMO formation. The Pd1/TiO2-V catalyst is not suitable for the CO catalytic coupling reaction since CO is easily bound to the O atom on the surface of TiO2-V leading to the formation of CO2. The activity of four catalysts complies with the following order of Pd4/TiO2-V > Pd6/TiO2-V > Pd2/TiO2-V > Pd3/TiO2-V by comparing the activation energy barriers of the rate-determining steps in the optimal paths. Charge analysis implies that less charge is transferred from the Pd4/TiO2-V and Pd6/TiO2-V catalysts to CO than on the other catalysts, which leads to the relatively weak adsorption of CO, and therefore CO has a greater tendency to react with other species on the surface. In addition, Pd6/TiO2-V also exhibits relatively higher selectivity toward DMO than the other three catalysts. Therefore, Pd6 is regarded as a suitable cluster, which is supported on TiO2-V demonstrating high catalytic activity and selectivity to DMO.

Computational screening of carbon monoxide (CO) adsorption over neutral and charged Al7 clusters

A density functional theory study on the structures and chemical bonding of charged (Al7 + and Al7 -) and neutral Al7 clusters is presented. A distorted octahedral structure with an aluminum atom decorating one of the aluminum faces of the octahedron is predicted for these clusters. The AdNDP analysis reveals double (σ- and π-) aromatic and antiaromatic characteristics of Al7 + and Al7 - clusters, respectively. The UV-Vis Spectra of these clusters are also investigated using TD-DFT method. The molecular adsorption of carbon monoxide on the mentioned clusters is also explored. It is found that, the binding of CO through its carbon atom on considered clusters is a physical adsorption and Al7 - cluster shows the most tendency for the CO adsorption. The NBO analysis and density of states spectra confirm the weak interaction between carbon atom of CO and the aluminum atom of these clusters.

Palladium and visible-light mediated carbonylative Suzuki–Miyaura coupling of unactivated alkyl halides and aryl boronic acids

An efficient carbonylative coupling of aryl boronic acids and unactivated alkyl halides under visible-light irradiation and low CO-pressure is presented.

Growth of sub-nanometric palladium clusters on boron nitride nanotubes: a DFT study

Boron nitride nanotubes as a template for the growth of sub-nanometric palladium clusters.

Global optimization of small bimetallic Pd–Co binary nanoalloy clusters: a genetic algorithm approach at the DFT level

The global optimisation of small bimetallic PdCo binary nanoalloys are systematically investigated using the Birmingham Cluster Genetic Algorithm (BCGA).

Theoretical study of catalytic oxidation of CO on free PdxO2+ (x = 4–6) clusters: size dependent comparison of combustion

A DFT study has been adopted to explore the catalytic CO oxidation on a free Pd_xO₂⁺ (x = 4–6) cluster.

Theoretical study for the adsorption of CO on neutral and charged Pd13 clusters

Adsorption of carbon monoxide, CO, on the surface of magnetic Pd13, Pd13–, and Pd13+ clusters, showing magnetic moments of 8, 7, and 7 Bohr magnetons (μB), respectively, was studied by means of density functional methods, allowing partial inclusion of relativistic effects. The favorable adsorption modes are on top, bridge, and threefold, with the binding energy of CO with Pd13– increasing in this same order as 39.4, 48.0 and 50.2 kcal/mol. In addition, the experimental results for the [Pdn–CO]–, n = 4–12, anions show a decrease of the vibrational frequency of CO along this triad of modes, 1940, 1800, and 1680 cm−1, with respect to the free CO value, 2143 cm−1, which conforms to our estimated frequencies, 1956, 1784, and 1679 cm−1, for CO in the [Pd13–CO]– complex. Also, the threefold mode shows a significantly longer bond length for CO, 1.210 Å, with respect to the free case, 1.139 Å. Then the bond of CO is considerably weakened in the negatively charged [Pd13CO]– cluster when the adsorption occurs in a threefold site. These results are mainly accounted for by charge transfer effects from the Pd13 cluster to the CO molecule. Smaller CO activation was found in neutral Pd13–CO and in [Pd13–CO]+, where hollow adsorption yields bigger structural and electronic changes on CO than the respective bridge and on-top modes. Overall, CO adsorption notably quenches the magnetization of neutral and charged Pd13 particles.

Interaction of carbon monoxide with small metal clusters: a DFT, electrochemical, and FTIR study

The adsorption of CO molecules onto small metal clusters was studied using density functional theory (DFT) calculations, and experimental electrochemical and attenuated total reflection-Fourier transform infrared spectroscopic (ATR-FTIR) techniques were used to examine CO adsorbed onto nanostructures of similar composition. The adsorption strengths and CO vibrational stretching frequencies were calculated and analyzed for clusters of the form M–CO for all of the period 4, 5, and 6 d-block transition metals. A direct link between the νCO and the population of d orbitals of the metal was observed. All possible binding sites for CO on clusters of the form Pd4–CO, Pd2Pt2–CO, and Pd2Au2–CO were determined and the corresponding adsorption energies and CO stretching frequencies were examined. Pure Pd and bimetallic PdPt and PdAu nanostructures were fabricated and used as catalysts for the adsorption and electrochemical oxidation of CO. The relative quantities of CO molecules adsorbed to surface of the catalysts decrease in the order of PdPt > Pd > PdAu, consistent with our DFT results. The location of νCO bands of CO adsorbed onto the nanostructured catalysts were determined by means of ATR-FTIR spectroscopy and were found to have values close to that predicted by DFT. This paper shows that DFT calculations on very small metal clusters Mn–CO (n ≤ 4) can be a simple but effective way of screening catalysts for their adsorbing properties.