Controlling Cubic\nversus Octahedral Morphology in\nPlasmonic Aluminum Nanoparticle Synthesis with Titanocene Catalysts:\nA Systematic Study

Ti precatalysts containing the titanocene\nmoiety (Cp<sub>2</sub>Ti–, Cp = cyclopentadienyl) can, under\ncertain conditions,\nselectively produce cubic Al nanocrystals through the dehydrocoupling\nof alane amine adducts such as AlH<sub>3</sub>·NMe<sub>2</sub>Et. A systematic study of reaction conditions reveals that cubic\nAl nanoparticle formation occurs at a higher temperature (e<i>.</i>g., 65 °C) and/or higher catalyst-concentration conditions\n(e<i>.</i>g., 0.5 mol % [Ti]). Kinetic studies reveal that\nunder these conditions nanoparticle formation and alane consumption\nare much faster, and cubic nanoparticle formation takes place under\nkinetically controlled conditions. On the other hand, employing a\nwide suite of TiX<sub>4</sub> (X = anionic ligand)-type precatalysts\nyielded only octahedral-shaped aluminum nanoparticles regardless of\nconditions. Finally, we report the synthesis of a hydride-bridged\nTi–Al heterobimetallic compound from the reaction of Cp<sub>2</sub>TiCl<sub>2</sub> with AlH<sub>3</sub>·NMe<sub>2</sub>Et and characterized it to show that it is a reaction intermediate\nin the Ti-catalyzed aluminum nanoparticle synthesis.