Formation and the nature of activity of Ziegler systems based on palladium β-diketonate complexes in hydrogenation catalysis

Iridium Ziegler-Type Hydrogenation Catalysts Made from [(1,5-COD)Ir(μ-O2C8H15)]2 and AlEt3: Spectroscopic and Kinetic Evidence for the Irn Species Present and for Nanoparticles as the Fastest Catalyst

“…5% of the activity) and transition to heterogeneous catalysis during hydrogenation. That said, we wish to emphasize once again (vide supra; the Introduction) the important, recent contributions of, especially, Shmidt and co-workers and Bönnemann and co-workers , that also provide evidence for the presence of nanoclusters under Ziegler-type hydrogenation catalysis conditions.…”

“…(ii) Multiple variables are important in catalyst synthesis, including the specific components used, the cocatalyst/transition metal ratio (Al/M), the amount of H 2 O present (widely observed to be connected to the amount of cocatalyst), and the order of addition of the catalyst components, and (iii) these variables influence the nature of the resulting catalysts and their catalytic properties. Other insights are (iv) a central, unanswered question in the area of Ziegler-type industrial hydrogenation catalysts is whether the true catalyst is a homogeneous (e.g., single metal organometallic) or heterogeneous (e.g., polymetallic M(0) n nanocluster) catalyst, and that (v) the most recent, especially noteworthy prior workthat of Shmidt and co-workers, and Bönnemann and co-workers , is starting to suggest that Ziegler-type hydrogenation catalysts are transition metal nanoclusters, what we have coined in our review as “Ziegler nanoclusters” . However, (vi) compelling or even highly suggestive evidence concerning the homogeneous versus heterogeneous catalysis question for Ziegler-type hydrogenation catalysts has remained elusive due to the use of often poorly defined precursors or the lack of application of the best current, previously successful approaches for addressing the historically perplexing “is it homogeneous or heterogeneous catalysis?” question …”

Formation of the cobalt hydrogenation catalysts at the action of lithium aluminum hydride and lithium tri(tert-butoxy)aluminohydride and their properties

“…To date, experimentally has been shown that the coreagents in the Ziegler type systems are involved in the formation of hydride or an organic derivative of the transition metal, reduction of the transition metal compound, most often to the metal in the zero oxidation state, formation of adducts with the reduced form of the transition metal of the type of acid-base interaction, and stabilization of nanoparticles [6][7][8]. However, some aspects of this problem have not yet been substantiated experimentally.…”

“…However, some aspects of this problem have not yet been substantiated experimentally. These include the role of the decomposition reactions of the I-III group metal compounds catalyzed by the transition metals [8,9].We have previously shown [10] that in the formation of nickel-based hydrogenation catalysts using lithium aluminum hydride LiAlH 4 , the function of the latter is not limited to the reduction of the nickel precursor. The tetrahydroaluminate anions adsorbed on the surface act as a stabilizer of the nickel nanoparticles.…”

“…However, some aspects of this problem have not yet been substantiated experimentally. These include the role of the decomposition reactions of the I-III group metal compounds catalyzed by the transition metals [8,9].…”