Capturing the dynamic behavior of active sites on complex, amorphous supports is a significant challenge in modeling single-site catalysts, particularly in surface organometallic catalysts. These systems are characterized by a well-defined chemical bonding pattern that coexists with the fluxionality of ancillary ligands and the inherent complexity of the support. Here, we present a conceptual workflow that integrates reactive molecular dynamics with advanced graph theory-based analysis to systematically explore the configurational space of supported catalysts. First, we used enhanced molecular dynamics to overcome local energy barriers and generate a diverse ensemble of structures. Then, we applied graph-based algorithms to distinguish truly distinct isomers from mere conformers and rotamers. Applying this approach to the model system of 1,1′-bis(n-butyl-cyclopentadienyl) zirconium dihydride on a dehydrated amorphous silica model, our method reveals the significant role of local silica strain in shaping the ensemble of active site configurations: catalysts grafted on silanol groups with strained confinement exhibit a diverse array of reaction pathways and significant energy stabilization, whereas less-strained environments yield a more restricted set of accessible configurations. This work demonstrates that combining molecular dynamics with graph theory provides an intuitive framework for unraveling the complex, fluxional behavior of supported catalysts.

Sulfated zirconium oxide (SZO) catalyzes the hydrogenolysis of isotactic polypropylene (iPP, Mw=13.3 kDa, Đ=2.4, <mmmm>=94 %) or high-density polyethylene (HDPE, Mn=2.5 kDa, Đ=3.6) to branched alkane products. We propose that this reactivity is driven by the pyrosulfate sites SZO, which open under mild conditions to transiently form adsorbed SO3 and sulfate groups. This adsorbed SO3 is a very strong Lewis acid that binds 15N-pyridine or triethylphosphineoxide (TEPO) (ΔEads>−39 kcal mol−1), reacts with Ph3CH to form Ph3C+, and mediates H/D exchange in dihydroanthracene-d4. DFT studies show that pyrosulfate sites open with a modest 26.1 kcal mol−1 barrier to form the adsorbed SO3 and sulfate in the presence of a tetramer of propylene. Hydride abstraction from the tertiary C−H in this model is exothermic and subsequent β-scission forms cleaved products. Analysis of the energetics provided here brackets the hydride ion affinity (HIA) of the adsorbed SO3 between 226.2 to 237.9 kcal mol−1, among largest values reported for a formally neutral Lewis acid. This study explains how SZO, a classic heterogeneous catalyst, can form carbocations by a redox neutral hydride abstraction reaction by very strong Lewis sites.

Heterogeneous derivatives of catalysts discovered by Ziegler and Natta are important for the industrial production of polyolefin plastics. However, the interaction between precatalysts, alkylaluminum activators, and oxide supports to form catalytically active materials is poorly understood. This is in contrast to homogeneous or model heterogeneous catalysts that contain resolved molecular structures that relate to activity and selectivity in polymerization reactions. This study describes the reactivity of triisobutylaluminum with high surface area aluminum oxide and a zirconocene precatalyst. Triisobutylaluminum reacts with the zirconocene precatalyst to form hydrides and passivates -OH sites on the alumina surface. The combination of passivated alumina and zirconium hydrides formed in this mixture generates ion pairs that polymerize ethylene.

Lutidine-derived bis-N-heterocyclic carbene (NHC) ruthenium CNC-pincer complexes (Ru-CNC's) were prepared. Depending on the synthetic procedure, normal (1, 2) or mixed normal/abnormal NHC-complexes (3) are formed. In the presence of phosphazene base, Ru-CNC complexes activate nitriles to give ketimino compounds 4-6. Nitrile adduct 4 shows reactivity toward strong bases to yield dearomatized complex 7, which heterolytically activates H₂ to form the bis-hydrido complex 8. Finally, these Ru-CNC's are active in catalytic hydrogenation of CO₂ to formate salts, and unlike the phosphine-containing Ru-PNP counterpart, they also catalyze the selective hydrogenation of esters to alcohols.

The metal-ligand cooperative activation of CO₂ with pyridine-based ruthenium PNP pincer catalysts leads to pronounced inhibition of the activity in the catalytic CO₂ hydrogenation to formic acid. The addition of water restores catalytic performance by activating alternative reaction pathways and leads to unprecedented Ru-catalyzed CO₂ hydrogenation activity. The mechanism of the underlying chemical transformations is proposed on the basis of DFT calculations, kinetic experiments, and NMR reactivity studies.