Chiral ligands nitrogen-containing

Cobalt(II) complexes prepared in situ from (AcO Co and two novel chiral spiro nitrogen-containing ligands, 7,7/-bis(2-pyridinecarboxamido)-l,l/-spirobiindane (SIPAD) and 7,7/-bis(2-quinolinecarboxamido)-l,l/-spirobiindane (SIQAD), are efficient cata- lysts for the asymmetric Michael addition of malonates to chalcone derivatives. The alkylation products were obtained in high yields with moderate enantioselectives.169... 

Pyridine-based N-containing ligands have been tested in order to extend the scope of the copper-catalyzed cyclopropanation reaction of olefins. Chelucci et al. [33] have carefully examined and reviewed [34] the efficiency of a number of chiral pyridine derivatives as bidentate Hgands (mainly 2,2 -bipyridines, 2,2 6, 2 -terpyridines, phenanthrolines and aminopyridine) in the copper-catalyzed cyclopropanation of styrene by ethyl diazoacetate. The corresponding copper complexes proved to be only moderately active and enantios-elective (ee up to 32% for a C2-symmetric bipyridine). The same authors prepared other chiral ligands with nitrogen donors such as 2,2 -bipyridines 21, 5,6-dihydro-1,10-phenanthrolines 22, and 1,10-phenanthrolines 23 (see Scheme 14) [35]. 

The cobalt complexes are all diamagnetic and behave as 1 1 electrolytes in methanol.7 The infrared spectra of the complexes contain sharp, strong N—H stretching absorptions (Table I). The electronic spectral data are also shown in Table I. Isomers I and II differ in the chiralities of nitrogen atoms in the macro-cyclic ligands.7 Both chemical and physical properties are dependent on ring... 

Mattay et al. employed asymmetric copper(I)-catalyzed intramolecular [2 + 2]-photocycloaddition reactions in a synthetic approach to (+)- and (— )-grandisol [56]. Racemic dienol 33 was irradiated in the presence of CuOTf and a chiral ligand to yield mainly cyclobutanes 34 and ent-34 as a mixture of enantiomers. Other 1,6-dienes were also employed. A number of chiral nitrogen-containing bidentate ligands were tested, the most effective of which, (4S,4 S)-4,4 -diisopropyl-2,2 -bisoxazoline (35) and (4R,47 )-4,4 -diethyl-2,2 -bisoxazoline (36), ensured a minor enantiomeric excess of <5% ee (Scheme 12). The coordination of the diene to the chiral Cu(I) complex under formation of a complex of type 37 was proved by CD analysis. The authors suggest a lower reactivity of the chiral complex compared to the copper ion coordinated to solvent molecules as the reason for the low enantioselectivities observed. 

In the second approach, a chiral nitrogen-containing compound has most often been used as the ligand to achieve enantioselectivity. Thus, oxidation of ( )-stilbene (22 equation 9) with a stoichiometric quantity of osmium tetroxide in toluene at room temperature, in the presence of dihydroquinine acetate (23), yielded r/ireo-hydrobenzoins (24) after reductive hydrolysis, with an enantiomeric excess of 83.2% in favor of the (15,25)-(-)-isomer performing the reaction at -78 C increased the eiuuitiomeric excess to 89.7%. 

Amines containing a Chiral carbon center in the aliphatic residue attached to the nitrogen atom, for example, o -methyl benzylamine (24), (25), are of considerable interest to the coordination chemist as, when coordinated, these ligands induce chirality in the metal-ligand chromophore. Methods for the resolution of more than 1000 racemic nitrogen containing organic compounds have been described. ... 

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