The Contribution of Organometallic Chemistry and Homogeneous Catalysis to the Understanding of Surface Reactions

A Systematic Approach to Study Complex Ternary Co-Promoter Interactions: Addition of Ir, Li, and Ti to RhMn/SiO2 for Syngas Conversion to Ethanol

The direct conversion of synthesis gas could open up economically viable routes for the efficient production of ethanol. RhMn/SiO2 represents one of the most active systems reported thus far. Potential improvements were reported by added dopants, i.e., Ir, Ti, and Li. Yet, combining these elements leads to contradicting results, owing to the complexity of the interactions in a multi-promoted system. This complexity is often encountered in heterogeneous catalysis. We report a systematic data-driven approach for the assessment of complex multi-promoter interactions based on a combination of design-of-experiment, high-throughput experimentation, statistical analysis, and mechanistic assessment. We illustrate this approach for the system RhMn/SiO2 promoted with Ir, Li, and Ti. Using this approach, we investigate the impact of promoters’ interactions on a mechanistic level. Our analysis depicts the means to learn hidden correlations in the performance data and, additionally, high performance for ethanol yield for the RhMnIr/SiO2 catalyst. The method presented outlines an efficient way to also elucidate co-promoter interactions in other complex environments.

Chemoselective Hydrogenation with Supported Organoplatinum(IV) Catalyst on Zn(II)-Modified Silica

Well-defined organoplatinum(IV) sites were grafted on a Zn(II)-modified SiO₂ support via surface organometallic chemistry in toluene at room temperature. Solid-state spectroscopies including XAS, DRIFTS, DRUV-vis, and solid-state (SS) NMR enhanced by dynamic nuclear polarization (DNP), as well as TPR-H₂ and TEM techniques revealed highly dispersed (methylcyclopentadienyl)methylplatinum(IV) sites on the surface ((MeCp)PtMe/Zn/SiO₂, 1). In addition, computational modeling suggests that the surface reaction of (MeCp)PtMe₃ with Zn(II)-modified SiO₂ support is thermodynamically favorable (Δ G = -12.4 kcal/mol), likely due to the increased acidity of the hydroxyl group, as indicated by NH₃-TPD and DNP-enhanced ¹⁷O{¹H} SSNMR. In situ DRIFTS and XAS hydrogenation experiments reveal the probable formation of a surface Pt(IV)-H upon hydrogenolysis of Pt-Me groups. The heterogenized organoplatinum(IV)-hydride sites catalyze the selective partial hydrogenation of 1,3-butadiene to butenes (up to 95%) and the reduction of nitrobenzene derivatives to anilines (up to 99%) with excellent tolerance of reduction-sensitive functional groups (olefin, carbonyl, nitrile, halogens) under mild reaction conditions.

Synthesis and characterisation of tetranuclear ruthenium polyhydrido clusters with pseudo-tetrahedral geometry

A series of tetranuclear ruthenium polyhydrido complexes with electric charges from +2 to 0 was synthesized.

The electronic structures of small Ni(n) (n=2-4) clusters and their interactions with ethylene and triplet oxygen: a theoretical study

Density functional theory (DFT) calculations of small nickel clusters and their interacting systems are carried out using the BLYP and B97-2 methods, after DFT calibration. All bare nickel clusters in this study have high multiplicities and are paramagnetic. Our results for the interactions between ethylene and oxygen with Ni(n) (n=2-4) clusters at different adsorption modes show that for ethylene, π-orientation is preferred, and that oxygen adsorption in a bridge mode is stronger than on-top coordination. Vibrational frequency analysis reveals that the vibrational modes of ethylene π-coordinated to nickel clusters converge toward the corresponding value for surface-bound ethylene, as the cluster size increases from two to four, showing that finite clusters can be used as localized models for ligand adsorption on nickel surfaces. We also calculate DFT global reactivity descriptors, chemical potential and hardness, and use these to predict the relative stability and reactivity of each bare cluster.

Carbidocarbonyl clusters of iron

Under reducing conditions, at elevated temperatures, coordinated carbon monoxide in transition metal carbonyls may disproportionate to CO 2 and a carbon atom. The carbon atom is trapped in a cage of metal atoms, shielded from further reaction in the core of the resulting carbidocarbonyl clusters. This class of compounds, which has been known for some time, bears some structural resemblance to the binary carbides and may therefore be relevant to Fischer-Tropsch catalysis, in which carbide phases and surface carbon atoms are implicated. The chemical, structural and physical properties of the iron carbidocarbonyIs have been investigated. Reactions are described that lead to C-H and C-C bond formation at the carbide carbon, and these are discussed with regard to the nature of this carbon atom. 13 C n.m.r. spectroscopy reveals large downfield chemical shifts for the carbide carbon, which may be interpreted as either a reflexion of low electron density at the carbon or the influence of paramagnetic contributions to the shift. Reactions of [Fe 4 (CO) 12 C CO 2 CH 3 ]-, [Fe 4 (CO) 12 C C(O)CH 3 ]- and [Fe 4 (CO) 12 C CHO]- with trimethyloxonium fluoborate yield the corresponding vinylidene clusters Fe 4 (CO) 12 - C = C (OCH 3 )R (R = OCH 3 , CH 3 , H).