Evaluating the effects of carbon nanoreactor diameter and internal structure on the pathways of the catalytic hydrosilylation reaction.

Three different types of carbon nanoreactors, double-walled nanotubes (DWNT), multi-walled nanotubes (MWNT) and graphitised carbon nanofibers (GNF) have been appraised for the first time as containers for the reactions of phenylacetylene hydrosilylation catalysed by a confined molecular catalyst [Rh₄(CO)₁₂]. Interactions of [Rh₄(CO)₁₂] with carbon nanoreactors determining the ratio of β-addition products are unchanged for all nanoreactors and are virtually unaffected by the confinement of [Rh₄(CO)₁₂] inside carbon nanostructures. Conversely, the relative concentrations of reactants affecting the ratio of addition and dehydrogenative silylation products is very sensitive to nanoscale confinement, with all nanoreactors demonstrating significant effects on the distribution of reaction products as compared to control experiments with the catalyst in bulk solution or adsorbed on the outer surface of nanoreactors. Surprisingly, the widest nanoreactors (GNF) change the reaction pathway most significantly, which is attributed to the graphitic step-edges inside GNF providing effective anchoring points for the catalyst and creating local environments with greatly altered concentrations of reactants as compared to bulk solution. Possessing diameters significantly wider than molecules, GNF impose no restrictions on the transfer of reactants while providing the strongest confinement effects for the reaction. Furthermore, GNF facilitate the effective recyclability of the catalyst and thus represents a superior nanoreactor system to carbon nanotubes.