Bidendate ligands

Anthracene can be selectively oxidized to anthraquinone by molecular oxygen in the presence of copper(II) bromide in an ethylene glycol solution. Ethylene glycol (EG) acts as a bidendate ligand for copper and prevents the formation of bromoanthracene as a by-product (equation 267).596... 

Asymmetric -methylation of a, -enones. Chiral bidendate ligands derived from L-prolinol can be used for asymmetric Michael additions to a, 3-enones with cuprates of the type CH,L CuMgBr (10, 266). The highest optical yield in conjugate addition to chalcone is observed when L is (S)-N-methylprolinol (88% ee). The tridentate chiral ligand 1 is equally effective for asymmetric 3-methylation of chalcone with CH,L CuLi and CuBr the chemical yield is 95%. Reduction of the amide carbonyl group of 1 results in practically total loss of chiral induction. 

In photosynthetic bacteria, the four histidine residues coordinated to the iron atom are supplemented by a bidendate ligand. However, a corresponding glutamyl residue is not present in the D2 protein. Michel and Deisenhofer reasoned that since the D- and E-helices in Dl and D2 are of equal length, it is rather... 

Ethene complex 339 is much more prone to ligand exchange reactions than carbonyl complex 327. Treatment with the bidendate ligands 1,5-cyclooctadiene, bis(diisopropylphosphanyl)ethane, 2,2 -bipyridyl, and norbornadiene at 20 °C results in the formation of unchelated complexes 336 and 340—342 in 82—93% yield no irradiation is necessary ° (Chart 18). 

Another 0,0 -bidendate ligand class with a more constrained bisphenol backbone based on 2,7-dimethyl-l,8-biphenylenediol has been comprehensively investigated by the group of Ooi and Maruoka. The ligands were reacted with trimethyl aluminium as precursor to afford, after controlled alcoholysis, highly efficient aluminium catalysts, as shown in Scheme 18.14. ... 

It should be added that in the vast majority of the recently reported kinetic studies of the ROP of cyclic esters, the first-order kinetic internal order in the monomer was observed, that is, the experimental plots ln ([M]o- [M]eq)/([M]o- [M]) versus time were linear. Atypically, in LA polymerization initiated with Zn alkoxide bearing 2-[(2-methoxyphenyl) amino]-4-[(2-methoxyphenyl)imino]pent-2-ene bidendate ligand, the second-order kinetics was observed for LA (based on the linearity of the (1/[LAJ) - (l/[LA]o) vs. time plot). A mechanistic explanation of this result, however, has not been given. 

Some fulvalene complexes have served as the backbone of chiral bidendate ligands for asymmetric synthesis [125-127]. 

Tris-chelated compounds with three symmetrical bidendate ligands (in inorganic chemistry these are the prototypical tris-chelate complexes of transition metals) can also be conceived as three-bladed propellers with their helicities specified accordingly. 

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