Ln(AlMe4)3 as new synthetic precursors in organolanthanide chemistry:: Efficient access to half-sandwich hydrocarbyl complexes

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 degrees 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. Dub to the steric unsaturation of the large lanthanum metal center, one of the aluminate ligands adopts an unusual distorted mu:eta(3) coordination mode, while the second ligand bonds in a routine mu:eta(2) fashion. An alcoholysis reaction Of (C5Me5)Y(AlMe4)(2) with HOCHtBu(2) gave the heteroleptic complex (C5Me5)Y(OCHtBu(2))(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)LnMe(2)](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.