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(CH 2 SiMe 2 R) 3 (THF) 2 ] (M = Sc, 1-Sc R; M = Y, 1-Y R; R = CH 3, 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-Y Ph ) or one ( 3-Y Ph ) 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 °C 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 μ-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(C 6 F 5 ) 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(C 6 F 5 ) 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-Y Ph 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 κ 1 -salicylaldiminato ligand, while for 8-Y, containing the larger Y nucleus, all three ligands were chelating in the normal κ 2 bonding mode.