Ligand scaffolds

The redox behavior of Nr1 tetraazaannulene complexes can be tuned by the appropriate choice of substituents bound to the ligand scaffold.158 It is interesting to note that in a series of Jager-type Ni11 complexes, both the type (27) and type (28) systems give reversible oxidation, while (29) does not.159... 

Selected further ligand scaffolds that give relatively stable Nini complexes with thioether or thiolate coordination are (78),301 (79),302 and (80).303 The latter can stabilize Ni111 and NiIV, where the Nilv species is prepared by oxidation with HNO3. 

SCHEME 36. Divalent /J-D-galactopyranosides built on oligopyridine metal ligand scaffolds.275... 

Fig. 2. Tripodal ligand scaffolds with arrows indicating the direction of steric bulk.

Herein we have reported the synthesis, characterization, and reactivity of both transition metal and actinide elements supported by tripodal ligand scaffolds. The carbon-anchored ligands TIME normally form polynuclear species while the nitrogen-anchored ligands TIMEN can coordinate to transition metals in a 1 1, fashion, rendering the coordinated metal centers in well-protected pockets. 

Pincer ligand scaffolds have been shown to possess an extraordinarily useful potential for directing the properhes and reactivity patterns of coordinated metal (M) centers. This is illustrated not only by the sheer number of publications on this topic, but also by the various applications that have been disclosed by using pincer-type ligands, such as highly efficient sensors, switches and catalysts [1]. 

A chemoenzymatic synthesis of di-, tetra-, and octavalent sialyl Lewis X ligands scaffolded on dendrimers has been reported (Scheme 67). 508 Hypervalent L-lysine cores with covalently attached 2-acetamido-2-deoxy-D-glucose residues were chemically prepared and enzymatically transformed into sialyl Lewis X-containing dendrimers using (3-(l— 4) ga-... 

Chirality-Directed Self-Assembly An Enabling Strategy for Ligand Scaffold Optimization... 

Ligand Scaffold Optimization in Palladium-Catalyzed Asymmetric Allylic Amination... 

Ligand Scaffold Optimization in Palladium-Catalyzed Asymmetric Allylic Amination 245 100 I--------------------------------------------------------------------------------zr... 

Ligand Scaffold Optimization in Rhodium-Catalyzed Asymmetric Hydrogenation... 

Figure9.12 Ligand scaffold optimization using SALs in rhodium-catalyzed asymmetric hydrogenation.

---