Impact of ligand bulk on conformational rearrangement in supported organometallic complexes

Measuring the dynamics of surface organometallic species, let alone connecting these to catalysis, is highly challenging. We have applied surface-sensitive proton fast-magic-angle spinning double-quantum sideband NMR methods to probe the dynamics of supported metallocene complexes as a function of ligand size, metal identity, and confinement. It was found that dynamics of these species, which resemble olefin polymerization catalysts, are very sensitive to ligand size and that the complex's orientation is frozen once the bonded alkyl chain reaches a length greater than five carbons. Experimental measurements of motions are quantitatively reproduced by machine learning-accelerated molecular dynamics simulations, which provide clarity into the types of motions that are accessible across the complexes. Metal identity and confinement were found to have a lower influence on dynamics, as compared to ligand bulk.