Chelate coordination complexes

Metal Deactivation. Compounds capable of forming coordination complexes with metal ions are needed for this purpose. A chelating agent such as ethylene-diaminetetraacetic acid (EDTA) is a good example. 

Phosphorus Donors. Phosphine coordination complexes of thorium are rare because the hard Th(IV) cation favors harder ligand donor types. The only stable thorium—phosphine coordination complexes isolated as of the mid-1990s contain the chelating ligand,... 

A coordination complex formed by the chelation of a metallic ion. Chemical compound ... 

Notice the loose use of the term octahedral to describe six-coordinate complexes which are based upon an octahedral geometry, but which, by virtue of the presence of different ligand types, are of lower symmetry than Oh. This is a common usage which should give rise to no difficulties. Note also how introduction of chelating... 

In these structures, the cupf assumes its typical chelating coordination pattern and is nearly symmetrically bound to the [Me2Sn(IV)] center. In complex (4) a pentagonal bypiramidal (PBP) geometry containing C2SnOs moiety was found by XRD method. The Bu2Sn(IV)-cup complex proved to be... 

Metal deactivators—Organic compounds capable of forming coordination complexes with metals are known to be useful in inhibiting metal-activated oxidation. These compounds have multiple coordination sites and are capable of forming cyclic strucmres, which cage the pro-oxidant metal ions. EDTA and its various salts are examples of this type of metal chelating compounds. 

The Lewis definition covers all AB cements, including the metal oxide/metal oxysalt systems, because the theory recognizes bare cations as aprotic acids. It is also particularly appropriate to the chelate cements, where it is more natural to regard the product of the reaction as a coordination complex rather than a salt. Its disadvantages are that the definition is really too broad and that despite this it accommodates protonic acids only with difficulty. 

In the four-coordinate complexes (12) (X = Cl, Br) the phenol phosphine is coordinated as a monodentate.151 In the presence of base, the phenolate O atom deprotonates and coordinates to give (13). The five-membered chelate ring in this complex is resistant to protonation, and ringopening is not observed even in the presence of CO or C2H4. 

Cyanide binds to a series of Ni complexes with N302 chelate ligands, and EPR spectra of the adducts indicate quasi-axial symmetry with a g pattern typical of low-spin, six-coordinate complexes with axial elongation and with a 2Ay ground state. No direct spin interaction of the unpaired electron with the carbon atom of the cyanide takes place.70... 

Low valent transition metal centers preferentially coordinate to the phosphorus in diazaphospholes. Accordingly, P-coordinated complexes of [l,2,3]diazapho-spholes with Cr, W, Fe, and Mn carbonyls were obtained as early as 1980 [1, 2,4], Later, Kraaijkamp et al. observed [108] both P- or -coordination modes in complexes of [l,2,3]diazaphospholes with MX2(PEt3) (M = Pt, Pd X = C1, Br). Methanolysis of these complexes led to the diazaphosphole ring opening and formation of five membered metallacyclic P,/V-chelates (103), incorporating P-bonded phosphonite and /V-coordinated hydrazone functionalities (Scheme 32) [109],... 

Chiral bis-(binaphthophosphole) (bis(BNP)) ligands have been used in the asymmetric hydroformylation of styrene. In solution, the free diphospholes display fluxional behavior. Consistent with their structure, the reaction of the bis(BNP) compounds with platinum(II) derivatives gives either cis chelate mononuclear complexes or trans phosphorus-bridged polynuclear derivatives. Coordination to platinum enhances the conformational stability of bis(BNP)s and diastereomeric complexes can be detected in solution. In the presence of SnCl2, the platinum complexes give rise to catalysts that exhibit remarkable activity in the hydroformylation of styrene. Under optimum conditions, reaction takes place with high branched selectivity (80-85%) and moderate enantio-selectivity (up to 45% ee). 

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