Dialkylscandium complexes supported by beta-diketiminato ligands: Synthesis, characterization, and thermal stability of a new family of organoscandium complexes

Several diorganoscandium complexes stabilized by the beta -diketiminato lig ands (Ar)NC(R)CHC(R)N(Ar) (Ar = 2,6-iPr-C6H3; R = CH3 (ligand a), R = rBu ( ligand b)) have been synthesized. Reaction of the lithium salts of the liga nds with ScCl3. 3THF leads to the complexes LScCl2(THF)(n), which may be re adily alkylated to form the dialkyl derivatives. Most are isolated as base- free, four-coordinate complexes. Several have been characterized via X-ray crystallography, and a detailed discussion of their structures is presented . Steric interactions between Ar and the Sc-alkyl groups force the scandium to adopt an out-of-plane bonding mode. In solution, this is manifested via a fluxional process which equilibrates the two diastereotopic alkyl groups and ligand groups as well. The barriers to this process roughly correlate with the steric bulk of the alkyl substituents. At elevated temperatures, t he dialkyl derivatives LScR2 undergo a metalation process whereby one of th e alkyl groups is eliminated as RH, and a ligand iPr group is metalated in the methyl position. These reactions are first order in scandium complex, a nd activation parameters of DeltaH(double dagger) = 19.7(6) kcal mol(-1) an d DeltaS(double dagger) = -17(2) cal mol(-1) K-1 were measured for the loss of Me4Si from (Ligb)Sc(CH2SiMe3)(2).