Scandium diketiminate complexes

Since Piers and coworkers [80] reported the first scandium P-diketiminate complexes by using category B ligands in 1999, a few scandium P-diketiminate complexes have been revealed to be highly active catalysts for the polymerization of ethylene and the intramolecular hydroamination [81,82]. 

SCANDIUM TRICHLORIDE TRIS(TETRAHYDROFURAN) AND 0-DIKETIMINATE-SUPPORTED SCANDIUM CHLORIDE COMPLEXES... 

Transition metal p-diketiminate complexes are typically prepared by one of three routes. In one, these complexes are prepared by the reaction of a metal halide with an alkali metal P-diketiminate generated from the reaction of the p-diketiminate with an alkali metal base. An example of this synthesis is shown for the scandium system in Equation 4.51 In a second method, these complexes are prepared by the reaction of a transition metal complex containing a basic ligand, such as an alkyl or amido group, with the neutral p-diketimine. Two examples of this route for zirconium systems are shown in Equations 4.52 and 4.53, 3... 

The second approach is a popular route to cationic lanthanide alkyl complexes, which have proven to be the important intermediates for ethylene polymerization and the stereospecific polymerization of diene [5]. Various monocationic lanthanide monoalkyl complexes have been synthesized by the alkyl abstraction/elimination reaction of lanthanide dialkyl complexes. The reaction of a bisbenzyl scandium complex supported by P-diketiminate with B(C6Fs)3 affords the cationic complex with a contact ion pair structure, in which a weak bonding between the cation and the anion exists (Figure 8.21) [77]. The reaction of an amidinate... 

Additional catalytic investigation of p-diketiminate scandium complexes by Piers and coworkers showed that well-characterized complexes 121 and 122 with the bulky ligand L27 were highly active catalysts for intramolecular hydroamination to form nitrogen heterocycles. The catalytic reaction was monitored by determining starting material and product with NMR. Both the neutral complex 121 and the CIP complex 122 are effective catalysts (10 mol%) for the intramolecular hydroamination of 5-phenyl-4-pentyl-l-amine (R = H, R = Ph, n = 1 in Scheme 42). However, they are not active catalysts for the potential application to the intermolecular hydroamination of 1-hexyne with alkylamines [82],... 

FIGURE 44 The structure of [(LMgBr)2ScBr] (L = pentane-2,4-di(2-diethylaminoethyl) diketiminate), prepared by the reaction of [LScBr2] with two equivalents of allylmagnesium bromide. Theoretical studies are consistent with the monovalent nature of scandium in this complex. Figure was redrawn after Neculai et al. (2002). 

---