Organometallic complexes of scandium and yttrium supported by a bulky salicylaldimine ligand

Organometallic derivatives of scandium and yttrium supported by a bulky salicylaldiminato ligand were prepared from the tris(alkyl) precursors [M(CH2SiMe2R)(3)(THF)(2)] (M = SC, 1-Sc-R; M = Y, 1-Y-R; R = CH3, Ph) via alkane elimination. The new precursors 1-M-Ph are convenient alternatives to the 1-M-Me derivatives, due to their higher thermal stability and crystallinity; 1-Sc-Ph has been characterized crystallographically. Reaction of these compounds with 1 equiv of protio ligand gives isolable mono(ligand) bis(alkyl) derivatives only for 1-Y; for other derivatives 1-Sc, mixtures were obtained. The products of the former reaction retain either two (2-yPh) or one (3-yPb) THF ligands; both of these compounds have been characterized crystallographically. In solution, both exhibit fluxional exchange between two geometric isomers which were characterized by variable-temperature NMR spectroscopy. Heating solutions of either compound leads to facile ligand redistribution. Reactions of tris(alkyls) 1 with 2 equiv of protio ligand gives the five-coordinate, THF-free bis(ligand) mono(alkyl) complexes 4-M-R. These compounds are highly thermally stable, decomposing at temperatures above 140 degreesC via a pathway involving metalation of one of the N-aryl isopropyl methyl groups. The derivatives 4-Sc-Me and 4-Y-Ph have been structurally characterized, as well as the product of thermolysis of 4-Sc-Me, the nonorganometallic four-coordinate complex 5-Sc. Both 4-Sc-Me, and 4-Y-Ph react slowly but cleanly with H-2. The former yields a product, 7-Sc, derived from transfer of the in situ formed scandium hydride to the aldimine carbon of one of the ligands. The yttrium product, however, is the D-2-symmetric dimeric mu-hydride complex 6-Y, characterized by spectroscopic and crystallographic methods. A survey of 6-Y's reactivity toward deuterated solvents, d(2)-6-Y, ethylene, (trimethylsilyl)acetylene, [HB(C6F5)(2)](2), benzophenone, pyridine, and THF suggests that it does not dissociate into a monomeric hydride but reacts as a dimer. Nonetheless, products from the reactions of (trimethylsilyl)acetylene, [HB(C6F5)(2)](2), benzophenone, pyridine, and THF were isolated and characterized spectroscopically and, in the case of the product from the benzophenone reaction, crystallographically. Finally, reactions of mono(alkyls) 4-Sc-Me, and 4-yPh with a further 1 equiv of protio ligand gave nonorganometallic tris(ligand) coordination complexes, both of which were structurally and spectroscopically characterized. The scandium derivative 8-Sc contained an O-bound k(1)-salicylaldiminato ligand, while for 8-Y, containing the larger Y nucleus, all three ligands were chelating in the normal k(2) bonding mode.