Elusive Trimethyllanthanum: Snapshots of Extensive Methyl Group Degradation in LaAl Heterobimetallic Complexes

• Published in: Chemistry : a European journal 2008-10, Vol.14 (31), p.9555-9564
• Main Authors: Gerber, Laura C. H., Le Roux, Erwan, Törnroos, Karl W., Anwander, Reiner
• Format: Article
• Language: English
• Subjects: aluminum; bond activation; cluster compounds; lanthanum; methine; methylene
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200801174

Reactions of [La(AlMe4)3] and [Y(AlMe4)3] with PMe3 show that the phosphine can cleave LnCH3Al linkages, separating Me3Al(PMe3). PMe3 (3 mol equiv) reacts with [Y(AlMe4)3] to give [(YMe3)n] contaminated with by‐products containing phosphorus and aluminum. The La‐based analog, [(LaMe3)n], is not formed selectively from the reaction of [La(AlMe4)3] with PMe3 or Et2O, which rather yields insoluble La/Al heterobimetallic products. Three multi‐nuclear La‐based clusters were obtained from a reaction of [La(AlMe4)3] with PMe3 (1 equiv) and identified by X‐ray structure analyses. Each cluster exhibits extensive methyl group degradation and contains methylene, methine, or carbide moieties. [La4Al8(CH)4(CH2)2(CH3)20(PMe3)] has a {La4(CH)4} cuboid core supported by AlMe3, Me2AlCH2AlMe2, and PMe3 ligands. [La4Al8(C)(CH)2(CH2)2(CH3)22(toluene)] also contains a cuboid core, {La3Al(C)(CH)2(CH2)}, which includes one exo cubic lanthanum atom, and is supported by AlMe3, Me3AlCH2AlMe2, (AlMe4)−, and toluene ligands. The lanthanum atoms in [La5Al9(CH)6(CH3)30] are arranged in a trigonal bipyramidal fashion with (CH) functionalities capping each face. The {La5(CH)6}3− core is formally balanced by three AlMe2+ moieties and is additionally supported by six AlMe3 ligands. The unit cell contains two independent La5 clusters, one with pseudo‐C3h and the other with pseudo‐D3 symmetry, as well as two molecules of the separation co‐product Me3Al(PMe3). Metal‐promoted C1 cannibalism: Separation of Me3Al(PMe3) occurs slowly when [La(AlMe4)3] reacts with trimethylphosphine and prolonged reaction periods lead to multiple CH bond activation as evidenced by the isolation of two distinct cuboid La4Al8 clusters and an La5Al9 cluster (see figure) bearing methylene, methine, and carbide units.