Olefin Ring-Closing Metathesis Under Spatial Confinement: Morphology-Transport Relationships

Spatial confinement effects on hindered transport in mesoporous silica particles are quantified using reconstructions of their morphology obtained by electron tomography as geometrical models in direct diffusion simulations for passive, finite-size tracers. We monitor accessible porosity and effective diffusion coefficients resulting from steric and hydrodynamic interactions between tracers and pore space confinement as a function of lambda=d(tracer)/d(meso), the ratio of tracer to mean mesopore size. For lambda=0, pointlike tracers reproduce the true diffusive tortuosities. For lambda 0, derived hindrance factors quantify the extent to which diffusion through the materials is hindered compared with free diffusion in the bulk liquid. Morphology-transport relationships are then discussed with respect to the immobilization, formation, and transport of key molecular species in the ring-closing metathesis of an alpha,omega-diene to macro(mono)cyclization product and oligomer, with a 2(nd)-generation Hoveyda-Grubbs type catalyst immobilized inside the mesopores of the particles.