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]ScCl 2 } n (Ar = 2,6- i Pr 2 -C 6 H 3; R = CH 3, 1a, n = 2; R = t Bu, 1b, n = 1) with 1 equiv of a lithium amide reagent LiN(H)R‘ (R‘ = t Bu, 2,6- i Pr 2 -C 6 H 3 ) gave scandium amido derivatives. For 1a, use of LiN(H) t Bu 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‘ = t Bu) and 3b (R‘ = 2,6- i Pr 2 -C 6 H 3 ) are obtained in good yields, and these compounds can be alkylated with MeLi to provide mono-amido methyl compounds 4b (R‘ = t Bu) and 5b (R‘ = 2,6- i Pr 2 -C 6 H 3 ). 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 CH 4 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.