Bis tridentate

The C2-symmetric bifunctional tridentate bis(thiazoline) 222 has been shown to promote the zinc(II)-catalyzed asymmetric Michael addition of nitroalkanes to nitroalkenes in high enantioselectivity <06JA7418>. The corresponding bis(oxazoline) ligand provides comparable enantioselectivity but higher product yield. The same bis(thiazoline) ligand has also been evaluated in the enantioselective Friedel-Crafts alkylation of indoles, but the enantioselectivity is moderate <06OL2115>. 

Evans group has demonstrated that bidentate bis(oxazolinyl)-Cu(II) (86 and 87) and tridentate bis(oxazolinyl)pyridine-Cu(II) (88 and 89) can be used... 

A range of Ru complexes incorporating tridentate bis(pyrazolyl)pyridine or related ligands has been reported. Six complexes of type [RuLL ] (L = L or L L ) in which L and L are ligands (290) have been prepared the oxidation potentials for the Ru /Ru couple decrease as the number of Me substituents increases. The tridentate coordination mode of ligands (291) and (292) have been confirmed by structure determinations of [Ru(291)(N02)(PMe3)][C104] " ... 

A series of chiral C2-symmetric tridentate bis(oxazoline) 110, 112 and bis(thiazoline) 111, in which a diphenylamine unit links the two chiral ox-azolines, was used for a more practical and efficient catalytic asymmetric alkylation of indoles with nitroalkenes (Scheme 31) [104], The alkylation of indole with frarzs-P-nitrostyrene in toluene at room temperature has been accomplished with 110d-Zn(OTf)2 or 113-Zn(OTf)2 as the catalyst. The obtained results show that the NH group in ligands 110-112 is crucial. Indole... 

C2-Symmetric tridentate bis(oxazolinyl)pyri-dine-Cu(Il) complexes, introduced by Evans et al., can function as effective chiral Lewis acid catalysts in the Diels-Alder reaction [15a]. When applied to catalytic asymmetric aldol reactions [15], remarkable results were achieved (Scheme 8) [15a]. Only 0.5 mol % of catalyst 48 was needed for the reaction of 30 with the silylketene thioacetal 47 to yield after deprotection 49 in 99 % chemical yield. The ee values were determined to be 99 %. Today, catalysts... 

Direct arylation of methyl imidazole with 2,7-dichloronaphthyridine leads to a potentially tetradentate and practically tridentate bis-carbene ligand on a naphthyridine scaffold [363]. Reaction of the bis-imidazolium salt with silver(l) oxide in the usual way yields a linear trinuclear silver carbene complex with this tris-bridging hgand (see Figure 3.115). 

Figure 12 Tridentate bis-mer coordination of a trianionic 0,N,0 donor amidodiolate ligand to the rare Co ...

Inoue, M., Suzuki, T., Nakada, M. Asymmetric Catalysis of Nozaki-Hiyama Allylation and Methallylation with A New Tridentate Bis(oxazolinyl)carbazole Ligand. J. Am. Chem. Soc. 2003,125, 1140-1141. 

Treatment of U02C12(THF)3 in THF with 1 equiv. of Na[CH(Ph2P=NSiMe3)2] led to formation of an unusual red uranyl chloro-bridged dimer (70% yield) containing a uranium(vi)-carbon bond as part of a tridentate bis(imino-phosphorano)methanide chelate complex (Scheme 9). This was the first example of a uranyl-methine carbon bond. The methine carbon is displaced significantly from the uranyl equatorial plane.33... 

To fine-tune the metal complex sterics, electronics, and geometries, as well as the stability of the resulting cationic catalysts with respect to ligand degradation due to C-H activation, a series of Zr(iv) and Hf(iv) diamide, dichloride, and dialkyl complexes incorporating tridentate bis(arylamido)amines 145134 135 and a bis(arylamido)pyridine 146136 137 has been synthesized using a combination of standard salt metathesis, amine elimination, and alkylation... 

A hydrocarbyl elimination approach is used to produce the Zr(rv) dibenzyl complex incorporating a tridentate bis(amido) silylether [iV, 0,(V ] complex 18261 (Equation (13)). The molecular structure of 182 features a distorted tbp geometry with an approximately linear ZrN20 unit and the two amido nitrogen atoms occupying approximately axial positions.One benzyl group is -coordinated. When activated with MAO, complex 182 shows moderate activity for ethylene polymerization. 

A tridentate bis(amido)phosphine ligand, (MejSiNFlCFlgCF PPh, is employed to prepare several Zr(iv) complexes including the dichloride, dialkyl, and mixed alkyl complexes 190, via standard amine elimination and alkylation methodologies.165 The mixed methyl benzyl dialkyl complex shows a distorted trigonal bipyramid in which the methyl group is in the apical position trans to phosphorus and the 7]2-benzyl group is cis to phosphorus. Related... 

The reaction of the dilithium salt 225 with ZrCU yields the undesired tetraaryl complex with two dianionic ligands bound to one Zr, irrespective of the ligand-to-Zr ratio employed. However, the reaction of 225 with Zr(CH2Ph)2Gl2(Et20)2 produces the desired dibenzyl complex 226 incorporating one tridentate bis(cr-aryl)amino [C ligand184 (Scheme... 

Fig. 28. Diorganotin dihauaes containing a tridentate bis-anionic ligand resulting in a trigonal bipyramidal coordination geometry at the tin centers.

Figure 8 Zinc complexes featuring tridentate bis(pyrazolyl)amine ligands...

Related monometallic, dimetaUic, and cationic Zn complexes supported by tridentate bis(pyrazolyl)amine ligands have been reported for the polymerization of rac-LA and methyl methacrylate (Figure 8). " All three complexes are active for the polymerization of rac-LA, reaching conversions of >90% in 30h (unoptimized time) at room temperature. Whereas the ethoxide complex is slightly more active and better controlled than the ethyl and cationic complexes, it produces atactic PLA. 

Tridentate bis(phenolate) ligands bridged by NHCs have been reported as supports for Ti and Zr complexes (Figure lO). Both the Zr and Ti complexes show relatively controlled molecular weights with low (<1.1) however, the Ti complex produces atactic PLA whereas the Zr analog produces highly heterotactic PLA with a P > 0.95. "... 

Interesting metal-controlled reversal of enantioselectivity was observed in the asymmetric Henry reaction of a-keto esters catalyzed by tridentate bis(oxazoline) complexes of 172, by changing the Lewis acid center from Cu(II) to Zn(II) <05JOC3712>. 

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