Over the last two decades, terminal imido complexes of early transition metals, which contain the M = N double bond, have attracted intensive interest and have been extensively studied. The research on such complexes has revealed rich reactivities and applications in the group transfer and catalytic reactions. In contrast, the chemistry of rare-earthmetal terminal imido complexes remains unexplored. Owing to a relative mismatch in LUMO/HOMO orbital energies between the d 0 rare-earth-metal ions and the imido groups, the Ln=N (Ln = rare-earth metal) bonds are highly polar and reactive. The rare-earth-metal terminal imido species once formed can easily assemble into more stable m or m n (n = 3, 4) bridged bimetallic or multimetallic species, [3, or undergo reactions with solvents by C À H bond activation. Meanwhile, the chemistry of the rare-earth-metal terminal imido complexes is of great interest, as the highly polar and reactive Ln= N bonds should lead to rich reactivity. Recently, we have synthesized and characterized the first rare-earth-metal terminal imido complex, a scandium terminal imido complex. Herein, we uncover reactions of the scandium terminal imido complex with a series of unsaturated substrates that show interesting reactivity and lead to novel products.
When a C 6 D 6 solution of the scandium terminal imido complex, [MeC(NAr)CHC(Me)(NCH 2 CH 2 N(Me)CH 2 CH 2 NMe 2 )Sc = NAr] (Ar = 2,6-(iPr) 2 C 6 H 3 ) (1), was exposed to CO 2 (1.0 atm) at room temperature, the solution changed from red to pale yellow in 30 minutes. Monitoring of the reaction by 1 H NMR spectroscopy revealed that 1 was almost completely converted into a new complex 2. A subsequent scaled-up reaction provided 2 as colorless crystals in 53 % isolated yield. 2 was characterized by NMR spectroscopy, elemental analysis, and X-ray crystallography, confirming that 2 is a scandium dicarboxylate (Scheme 1). Rare-earth-metal carboxylates are common, but to our knowledge, this type of rare-earth-metal dicarboxylate complexes has not been
[*] J.