Ziegler-Natta Olefin Polymerization Catalyst Systems: “Emergent” Unidirectional Molecular Machines

Unidirectional biomolecular machines are at the heart of many biological processes, and many machines mimicking such behavior have now been synthesized in the laboratory. What the current work showcases is a new class of unidirectional molecular machines that are neither biological nor consciously designed but are, instead, the outcome of “emergent” behavior in chemical systems. This is shown to be the case in Ziegler-Natta (Z-N) heterogeneous olefin polymerization systems. Calculations with DFT, as well as stochastic simulations, show that the oxygen containing Lewis basic molecule, the “internal donor”, successfully and repeatedly finds the active titanium-based catalyst on the MgCl2 surface, due to an “energy ratchet” unidirectional molecular machine being created during the catalysis. Since the presence of the donor at the catalyst centre is a prerequisite for improved stereoselectivity, the formation of “emergent” molecular machines is crucial in Z-N catalyst systems.