Controlling Cubic versus Octahedral Morphology in Plasmonic Aluminum Nanoparticle Synthesis with Titanocene Catalysts: A Systematic Study

Ti precatalysts containing the titanocene
moiety (Cp2Ti–, Cp = cyclopentadienyl) can, under
certain conditions,
selectively produce cubic Al nanocrystals through the dehydrocoupling
of alane amine adducts such as AlH3·NMe2Et. A systematic study of reaction conditions reveals that cubic
Al nanoparticle formation occurs at a higher temperature (e.g., 65 °C) and/or higher catalyst-concentration conditions
(e.g., 0.5 mol % [Ti]). Kinetic studies reveal that
under these conditions nanoparticle formation and alane consumption
are much faster, and cubic nanoparticle formation takes place under
kinetically controlled conditions. On the other hand, employing a
wide suite of TiX4 (X = anionic ligand)-type precatalysts
yielded only octahedral-shaped aluminum nanoparticles regardless of
conditions. Finally, we report the synthesis of a hydride-bridged
Ti–Al heterobimetallic compound from the reaction of Cp2TiCl2 with AlH3·NMe2Et and characterized it to show that it is a reaction intermediate
in the Ti-catalyzed aluminum nanoparticle synthesis.