Dinucleating Schiff base

A heterobimetallic transition metal/rare earth metal system with a dinucleating Schiff base is also a promising... 

Scheme 10 A catalytic asymmetric 5yn-selective nitro-Mannich reaction promoted by heterobimetallic Cu/Sm/dinucleating Schiff base complexes...

As expected, suitable selection of a metal combination for each targeted reaction was important to achieve high stereoselectivity. For a sy -selective nitro-Maimich-type reaction, a heterobimetallic complex prepared from Cu(OAc)2, Sm(0-/Pr)3, and dinucleating Schiff base la was the best [12]. Other metal combinations resulted in much lower selectivity. Either Cu or Sm alone also resulted in poor reactivity and selectivity. Thus, both Cu and Sm are essential for high catalytic activity and selectivity. After optimization studies, the addition of achiral phenol source and the use of oxo-samarium alkoxide, Sm50(0-jPr)i3, with a well-ordered structure, gave the superior reactivity and stereoselectivity. Under the optimized reaction cmiditions, 1-10 mol% of the Cu/Sm catalyst promoted asymmetric... 

To incorporate a cationic rare earth metal into the outer cavity of a dinucleating Schiff base, we used Schiff base 2 derived from o-vanilUn (Fig. 5). We selected a-additions of a-isocyanoacetamides to aldehydes as a model reaction because a salen-Al catalyst gave only modest enantioselectivity and reactivity [16]. The working hypothesis for bimetallic Schiff base catalysis is shown in Fig. 6. We assumed that the bimetallic Schiff base complex would not only activate the aldehyde with one metal, but might also interact with the a-isocyanoacetamide through the other metal to effectively control the orientation of the two substrates in the enantio-discriminating step. 

Scheme 3 Preparation of bench-stable Ni2-Schiff base lb, Co2-lb, and Mn2-lb catalysts from (R)-binaphthyldiamine-based dinucleating Schiff base lh-H4...

By varying the nature of the heterocyclic dicarbonyl ( head unit ) and the l,n-diamine ( lateral unit ), a wide range of dinucleating tetraimine Schiff base macrocycles can be synthesised. 

Phenolate based molecules as templates for dinucleating ligands have been around for more than 40 years [1—3]. The term di- or binucleating ligands was first used by Robson in 1970 who reported a Schiff-ha.se copper complex with a phenol core [3]. While the numbers of applications are vast, the purpose of the phenolic... 

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