β-Diketiminato Scandium Chemistry: Synthesis, Characterization, and Thermal Behavior of Primary Amido Alkyl Derivatives

Treatment of the β-diketiminato-supported scandium dichlorides {[ArNC(R)CHC(R)NAr]ScCl2}n (Ar = 2,6-iPr2-C6H3; R = CH3, 1a, n = 2; R = tBu, 1b, n = 1) with 1 equiv of a
lithium amide reagent LiN(H)R‘ (R‘ = tBu, 2,6-iPr2-C6H3) gave scandium amido derivatives.
For 1a, use of LiN(H)tBu leads to the bis-amido derivative (6a) regardless of the equivalency
of amide reagent employed, suggesting that facile ligand redistribution processes are
operative when the ligand is the less bulky methyl-substituted example. For 1b, mono-amido
chlorides 2b (R‘ = tBu) and 3b (R‘ = 2,6-iPr2-C6H3) are obtained in good yields, and these
compounds can be alkylated with MeLi to provide mono-amido methyl compounds 4b (R‘ =
tBu) and 5b (R‘ = 2,6-iPr2-C6H3). All four of these compounds were characterized crystallographically. The amido ligand occupies the exo coordination site exclusively, and there is no
evidence in solution for a diastereomer with the amido group in the endo site. DFT
calculations suggest that there is a strong steric preference and a slight electronic bias for
the amido ligand to assume the exo position. Thermolysis of the amido methyl complex 4b
leads to loss of CH4 and production of a scandacylic product, 7, formed via metalation with
one of the N-aryl isopropyl methyl groups. This compound was characterized crystallographically. Deuterium labeling experiments suggest that 7 is produced via direct metalation
and does not form via a scandium imido intermediate.