Aminophenolate ligands

Recent work by Wieghardt et al. on complexes of the aminophenolate ligand ( LAP—H )2 (Scheme 1) previously thought to be innocent, showed that the compound [Vv(LAP—H)2(LISQ)] may be oxidized by one electron to [Vv(LAP—H)(LISQ)2]+and reduced by three electrons, first at the ligand, then at the metal, as confirmed by EPR on the Vw species.26 Studies have also been carried out on the related Ni, Pd, and Pt complexes.27... 

As a mimic of the well-studied galactose oxidase [37], a copper(II) thiophenol complex catalyzes the oxidation of primary alcohols to aldehydes in the presence of (Scheme 12) [38]. The latter also promotes the oxidation of secondary alcohols to diols (Scheme 12). The catalytic cycle starts with the oxidation of copper by O, leading to a biradical species. The intermediate 39 is produced from 38 by coordination of two alkoxide substrates. The rate-limiting step is the formation of 40 from 39 by a hydrogen atom transfer from the secondary alcoholate to the oxygen-centered radicals of the aminophenols ligands. The cycle is then closed by radical dimerization which leads the formation of the diol [39]. 

In 2013, chiral imidazoline-aminophenol ligands 138 combined with copper salts were successfully applied by the same group in the AFC reaction of indoles with isatin-derived nitroalkenes 139. By employing the appropriate catalyst, CuOTf/138a or Cu(OTf)2/138a, the reaction of isatin-derived nitroalkene with indole proceeded smoothly to afford 3,3 -bisindole derivatives 140 in up to 99% yield with 92% ee. l,l,l,3,3,3-Hexafluoro-2-propanol (HFIP) was found to be crucial to this transformation, with a positive effect on catalyst activity (Scheme 6.61). 

In the same context, azomethine ylides derived from imino esters were reacted by Arai and Awata with methyleneindolinones in the presence of an in situ generated chiral nickel catalyst derived from their original chiral imid-azoline-aminophenol ligand 11. Remarkably, the process afforded the corresponding chiral spiro[pyrrolidine-3,3 -oxindoles] in excellent yields and exo selectivities, as well as enantioselectivities in almost all cases of substrates studied, as summarised in Scheme 1.11. Since the spiro-oxindole skeleton is... 

In 2014, Arai and Yamamoto described asymmetric nickel-catalysed domino Michael/Henry reactions between 2-sulfanylbenzaldehydes and aromatic nitroalkenes to give the corresponding chiral 2-aryl-3-nitrochroman-4-ols, in most cases in almost quantitative yields and with good to high diastereo- and enantioselectivities of up to >98% de and 95% ee, respectively (R = H, Scheme 4.4). These reactions were promoted by an in situ generated catalyst from 10-11 mol% of chiral imidazoline-aminophenol ligand 1 and... 

Sobota and coworkers described the preparation of monomeric, homoleptic Mg complexes supported by bidentate aminophenolate ligands, Mg tbpca 2 (63) ( tbpca] H=(V-(3,5-di-tert-butylbenzyl-2-hydroxy)-(V-methylcyclohexanamine) and Mg S-tbpmpa 2 (64) ( 5-tbpmpa H=(S)-A(-(3,5-di-tm-butylbenzyl-2-hydroxy)-A(,a-dimethylbenzylamine), the latter one relying on the use of the enantiomerically pure proligand (Fig. 19) [79]. Although on their own these complexes were inactive toward l-LA, in the presence of 1 equiv of BnOH they afforded rapid and quantitative... 

Figure 34 Co(lll) complex based on N-salicylidene-o-aminophenol ligands.

Scheme 5 Synthesis and structural diversity in organoaliuniniun supported by dianionic aminophenolate ligands...

The imidazoline-aminophenol-ligand complex (34) has been developed for the 3 + 2-cycloaddition reaction of methyleneindolinones (32) with iminoesters (33) to produce exo-spiro[pyrrolidin-3,3 -oxindole]s (35) as stable isomers. The reaction proceeds in a stepwise Michael-Mannich reaction sequence (Scheme 12). ... 

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