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

Reactions of [La(AlMe 4 ) 3 ] and [Y(AlMe 4 ) 3 ] with PMe 3 show that the phosphine can cleave LnCH 3 Al linkages, separating Me 3 Al(PMe 3 ). PMe 3 (3 mol equiv) reacts with [Y(AlMe 4 ) 3 ] to give [(YMe 3 ) n ] contaminated with by‐products containing phosphorus and aluminum. The La‐based analog, [(LaMe 3 ) n ], is not formed selectively from the reaction of [La(AlMe 4 ) 3 ] with PMe 3 or Et 2 O, which rather yields insoluble La/Al heterobimetallic products. Three multi‐nuclear La‐based clusters were obtained from a reaction of [La(AlMe 4 ) 3 ] with PMe 3 (1 equiv) and identified by X‐ray structure analyses. Each cluster exhibits extensive methyl group degradation and contains methylene, methine, or carbide moieties. [La 4 Al 8 (CH) 4 (CH 2 ) 2 (CH 3 ) 20 (PMe 3 )] has a {La 4 (CH) 4 } cuboid core supported by AlMe 3 , Me 2 AlCH 2 AlMe 2 , and PMe 3 ligands. [La 4 Al 8 (C)(CH) 2 (CH 2 ) 2 (CH 3 ) 22 (toluene)] also contains a cuboid core, {La 3 Al(C)(CH) 2 (CH 2 )}, which includes one exo cubic lanthanum atom, and is supported by AlMe 3 , Me 3 AlCH 2 AlMe 2 , (AlMe 4 ) − , and toluene ligands. The lanthanum atoms in [La 5 Al 9 (CH) 6 (CH 3 ) 30 ] are arranged in a trigonal bipyramidal fashion with (CH) functionalities capping each face. The {La 5 (CH) 6 } 3− core is formally balanced by three AlMe 2 + moieties and is additionally supported by six AlMe 3 ligands. The unit cell contains two independent La 5 clusters, one with pseudo ‐ C 3h and the other with pseudo ‐ D 3 symmetry, as well as two molecules of the separation co‐product Me 3 Al(PMe 3 ).