Ln(AlMe4)3 as New Synthetic Precursors in Organolanthanide Chemistry: Efficient Access to Half-Sandwich Hydrocarbyl Complexes

Abstract

The homoleptic complexes Ln(AlMe4)3 (Ln = Y, La, Nd, Lu) were reacted with pentamethylcyclopentadiene to yield the corresponding half-sandwich complexes (C5Me5)Ln(AlMe4)2 in high yield and purity. NMR spectroscopic investigations revealed a highly dynamic nature of the bridging and terminal alkyl groups, even at −85 °C. In the solid state, the tetramethylaluminato ligands coordinate differently to the metal center, as shown by an X-ray structure analysis of the lanthanum derivative. Due to the steric unsaturation of the large lanthanum metal center, one of the aluminate ligands adopts an unusual distorted μ:η3 coordination mode, while the second ligand bonds in a routine μ:η2 fashion. An alcoholysis reaction of (C5Me5)Y(AlMe4)2 with HOCHtBu2 gave the heteroleptic complex (C5Me5)Y(OCHtBu2)(AlMe4). (C5Me5)Nd(AlMe4)2 was reacted with dehydrated periodic mesoporous silica MCM-41, affording surface-grafted (C5Me5)Nd(AlMe4)2@MCM-41. The half-metallocene bis(aluminate) complexes were converted into donor-free [(C5Me5)LnMe2]3 (Ln = Y, Lu) via stoichiometric THF-induced cleavage and reversibly regenerated by addition of trimethylaluminum. The organolanthanide complexes were fully characterized by NMR and FTIR spectroscopy and elemental analysis. The organometallic−inorganic hybrid materials were characterized by FTIR spectroscopy, elemental analysis, and nitrogen physisorption.