Chelating tridentate

Cationic complexes of rran.s-chelating tridentate ligand, (/ ,/ )-4,6-dibenzo-furandiyl-2,2 -bis(4-phenyloxazoline), with transition metal(II) perchlorates as effective catalysts for asymmetric cycloaddition of nitrones 98YGK368. 

The cationic aqua complexes prepared from traws-chelating tridentate ligand, R,R-DBFOX/Ph, and various transition metal(II) perchlorates induce absolute enantio-selectivity in the Diels-Alder reactions of cyclopentadiene with 3-alkenoyl-2-oxazoli-dinone dienophiles. Unlike other bisoxazoline type complex catalysts [38, 43-54], the J ,J -DBFOX/Ph complex of Ni(C104)2-6H20, which has an octahedral structure with three aqua ligands, is isolable and can be stored in air for months without loss of catalytic activity. Iron(II), cobalt(II), copper(II), and zinc(II) complexes are similarly active. 

To have sufficient stability for commercial application, chelating tridentate azo ligands (5) are required.7 The most important and widely used tridentate azo ligands are the ortho,ortho -dihydroxy azo dyes, i.e., (5, X = Y = OH). Other tridentate azo ligands are ortho-carboxy-ortho -hydroxyazo and or tho-hydvoxy-ort ho - Ammo zo. 

The cationic aqua complexes of the C2-symmetric trans-chelating tridentate ligand 447 proved also highly effective chiral catalysts. The complexes involving the metal(II) perchlorates of iron, cobalt, nickel, copper and zinc produced the main endo adduct of cyclopentadiene and N - aery loy 1-1,3 -oxazo I i din -2 -one with very high ee values281. 

The reaction of [Mn(CH3)(CO)5] with chelating tridentate phosphorus ligands (denoted P-P-P) gives [Mn(COCH3)(CO)2(P-P-P)] species (7i7,732). Equation (31) represents an example of this type of reaction (130). 

King has recently studied the first examples of chelating tridentate phosphine-phosphite ligands, i.e., i P[CH2CH2P(OCH3)2]2 (R = CH3 and These ligands react with metal(II) chlorides of Fe, Co, and Ni in methanol solution to form the [MC1(P3 ligand)] cations, which are planar for nickel and tetrahedral for cobalt and iron. ... 

Other jAjA-chelating tridentate ligands have also been employed for preparation of the mononuclear and dinuclear complexes containing these ligands. 

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