Bis chelating

Biological and medicinal chemistry of bi-heterocycles and bi-chelates 97CB669. 

A bis(chelate) structure was found for the closely related germylene [MeC(NPr )2]2Ge, which was also made from GeCl2(dioxane) and 2 equivalents of the lithium amidinate (colorless crystals, 81%). The same synthetic approach was used to make bis(amidinato) metal dichlorides of silicon and germanium in high yields (83-95%). Rapid oxidative addition of chalcogen atom sources (styrene sulfide and elemental Se) to the germylene derivatives resulted in a series... 

Figure 9J2a Hydrolysis of the zinc eugenolate bis chelate to the hydrogen bonded eugenol dimer and zinc hydroxide. After Wilson Mesley (1974).

Very recently, Chant et al. (65) reported the existence of a bis-chelated Fe(III) cation, obtained by titrating Fe(i-Pr2 tc)3 with Fe(III)-ions to the endpoint corresponding with [FeO —Pr2perchlorate acid hydrolysis of Q i Pr2dtc. ... 

Many bis-chelate Pd11 complexes possessing a m-arrangcmcnt of the phosphinoalkylsilyl ligands have been synthesized,386-389 but comparatively few /ranx-bis-chelates are known. The kinetic stability of trans-bis-chelates can be greatly enhanced by placing a bulky o-carborane unit in the ligand backbone.390... 

Optical activity in metal complexes may also arise either if one of the ligands bound to the metal in the first co-ordination sphere is itself optically active or if the complex as a whole lacks a centre of inversion and a plane of symmetry. Thus all octahedral cts-complexes of the tris-or bis-chelate type have two isomeric forms related by a mirror plane, the d- and /-forms. These species have circular dichroism spectra of identical intensities but opposite in sign. The bands in the circular dichroism spectrum are, of course, modified if ligand exchange occurs but they are also exceedingly sensitive to the environment beyond the first co-ordination sphere. This effect has been used to obtain association constants for ion-pair formation. There also exists the possibility that, if such compounds display anti-tumour activity, only one of the mirror isomers will be effective. 

Phosphinoalkylsilanes as chelate ligands with transition metals have been studied, principally to provide a better understanding of metal-catalyzed industrial reactions such as hydrosilylation.51 Although many examples of bis-chelate metal complexes possessing a cA-arrangement of the phosphinoalkylsilyl ligands in a typical square-planar M(II)(M = Pd, Pt) environment have been synthesized,52... 

Salicylaldiminato ligands have also been studied and the bis(chelate) complex (101) has been reported to produce high molecular weight PE with an activity of 96gmmol 1 h 1bar 1267... 

Reaction of the bis-chelate complex 149 and various bis(arylalkyl)barium complexes generates heteroleptic barium complexes with one chelate and one reactive arylalkyl ligand 164. The homoleptic and heteroleptic barium complexes both induce living polymerization of styrene to atactic polystyrene in cyclohexane solution. The fact that no stereocontrol is observed during polymerization despite the presence of the chiral carbanionic ligands is... 

Scheme 4 Proposed reaction of Pd-H moiety reacting with excess ligand to form the inactive bis-chelated complex...

Addition of LiAlMe4 to 64 yields the adduct [ LiN(SiMe2CH2PPr )2 LiAlMe4]2, which is dimeric in the solid state. Two of the lithium atoms are bound by the ligand in a P2N bis-chelate mode, the other... 

Carbonylations involving catalytic amounts of Pd(n) and substoichiometric Cu(n) have been developed for the synthesis of lactams. This Wacker-type process is assumed to proceed via C-H functionalization involving a palladacycle intermediate such a hypothesis is backed by the high degree of regioselectivity attained, when using a bis-chelating substrate (Equation (114)).104... 

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