Atropisomeric amides: Achiral ligands with chiral conformations

Abstract

A new class of achiral ligands with atropisomeric conformations has been coordinated to titanium(IV). The ligands are ortho-hydroxy benzamide derivatives which are deprotonated on reaction with titanium tetraisopropoxide to furnish Ti(L)(2)(O-iPr)(2) complexes (L=ortho-phenoxy benzamide). In these octahedral titanium compounds, the ortho-phenoxy benzamide ligands chelate to titanium, bonding through the phenoxide oxygen and the amide carbonyl oxygen. The benzamide ligands adopt atropisomeric conformations with an angle between the aryl and amide groups of approximately 35 degrees. The ligand precursor, ligand, and titanium complexes have been characterized by X-ray crystallography. Only one diastereomer of each titanium complex was observed in the solid state structures.

A titanium salicylate, Na4[Ti(C7H4O3)3]2·11H2O

“…The Ti-O distances (Table 1) range between 1.846 (4) and 2.077 (4) Å in complex A, and between 1.847 (4) and 2.042 (4) Å in complex B. Similar Ti-O distances are found in many recently determined crystal structures of titanium complexes (Honda et al, 2003;Thurston et al, 2004). The bite angles of the ligands (Table 1) range between 84.3 (2) and 85.1 (2) .…”

Modular N,O‐Chelating Ligands: Group‐4 Amidate Complexes for Catalytic Hydroamination

“…Initial investigations into catalytic hydroamination began using three different proligands: N-tert-butyl-2-methylpropanamide (26), N-tert-butylbenzamide (27), and N-tert-butylperfluorophenylamide (28). Bis(amidate) bis(amido)-titanium and -zirconium complexes were synthesized and the tunable reactivity accessible through modification of the [64]…”

“…Examples of several complexes that are used for bioinorganic [22][23][24] and lanthanide coordination chemistry display these coordination modes, [25,26] however, these are outside the scope of this review, and only a few select examples will be discussed. Also, there are several examples of catalytically relevant complexes with coordinated neutral amides as ligands, [22,27,28] which will be largely excluded from our discussion. In summary, this microreview highlights recent contributions that have used the modular amidate ligand framework to advantage in the facile synthesis of catalytically active complexes.…”

Biocatalytic Desymmetrization of an Atropisomer with both an Enantioselective Oxidase and Ketoreductases

“…Atropisomeric diaryl ethers9 form part of the structure of vancomycin10 and are promising scaffolds for the construction for new chiral ligands 11. Dialdehyde 3 and diol 1 were made by our published route 9.…”