Chelating ligands vanadium

Diols derived from substituted monosaccharides have also been shown to bind as chelated heteroligands to L-amino acid-derived Shifif base complexes [17]. The coordination about vanadium in these complexes is octahedral, with the sixth coordination site occupied by an oxo ligand. Vanadium-5 NMR spectra from nonaqueous solvent show the coordination is retained in solution. Evidently, the compound is stable... 

The aqueous speciation of the vanadate-maltol system has been characterized, describing complexes which chelate the vanadium(V) in a bidentate manner (16,17).131 The formation of the corresponding vanadium(V) complex of 2-hydroxycyclohexanone (analogous to 17) has been proposed as an intermediate in the oxidation of cyclohexanone.132 Squaric acid forms a series of mono- and dinuclear complexes with vanadium(IV) and (V).133 Subtle differences in the structure are observed depending on the oxidation state of the vanadium, and are induced by the rigid ligand structure. 

Many complexes can be prepared by electrochemical reduction or oxidation under an inert atmosphere. Exhaustive reduction (coulometry) using a large working electrode can lead to a clean formation of the reduced form, if it is sufficiently stable, since electrons alone are used in the reduction process. As an example, the octahedral vanadium(III) complex [V(phen)3]3+ undergoes a series of sequential and reversible reduction steps (6.36) with retention of the three chelate ligands down to oxidation state of formally vanadium (-1). 

V -0-S-0- rings. 2,2 -bipyridines, symmetrically chelated to vanadium centers, are almost perpendicular to the plane of the equatorial oxygen atoms present in the coordination spheres of the vanadium centers. The metrical parameters are comparable to those observed in [V 202(SO4)2(2,2 -bipyridine)2].The overall composite structure may be viewed as made up of a series of inorganic ladders flanked by 2,2 -bipyridine ligands which also separate the adjacent ladders. 

Splitting of the vanadium perpendicular features into and Ay has only been seen in a few cases and arises from the asymmetry of the chelating ligand 305). In all these cases [Pg.243]

All known X-ray diffraction data indicate that in penta-coordinated pyramidal vanadium chelates the vanadium atom lies out of the basal plane of the ligand macrocycle, i,e.j the plane of the four pyrrole nitrogen atoms. The distance from vanadium... 

As Table 1.3 shows, kn becomes slower as the V-H bonds in (P-P)(CO)4VH become weaker presumably the steric effect of the chelating ligand undermines the effect of the weaker bond. It is worth noting a precedent for the fast transfer of H from vanadium k from the anionic hydride Cp(CO)3VH to a hexenyl radical has been reported to be more than an order of magnitude larger than that measured for BusSnH [59]. 

Elschenbroich C, Hurley J, Metz B (1990) Metal.ic.-complexes of benzene derivatives. 34. Tetraphenylsilane as a chelating ligand synthesis, stmctural characterization, and reactivity of the tilted bis(arene) metal complexes [(C6H5)2Si(.eta.6- C6H5)2]M (M - vanadium, chromium). OrganometaUics 9 889-897... 

Aliwi and coworkers have investigated many vanadium (V) chelate complexes as photoinitiators for vinyl polymerization [36-43]. The mixed ligand complex of chloro-oxo-bis(2,4-pentanedione) vanadium (V). VO(a-cac)2 Cl is used as the photoinitiator of polymerization... 

In another type of mixed ligand oxo-vanadium Schiff base complexes chloro-oxo-bis[N(4-bromophe-nyl) salicylideneiminato] vanadium (V) chelate, VOL2CI, and methoxo-oxobis[N(4-bromophenyl)sali-cylideneimine vanadium (V) chelate, VOL2OCH3 Aiiwi and Salih [43] show that these complexes are active pho-... 

From equation (30), whether a tris chelate is formed depends on the donor ability of the ligand. Several vanadium(IV) complexes with 1,2-dihydroxybenzenes formed from solutions of the ligand, VOSO4 and thallium(I) acetate.498 The compounds are of two types (I) T12[V(RC6H302)3] (R = H, 3-Me, 4-Me, 3-MeO) and (II) T12[V0(RC6H302)2] (R = CHO). 

Where the valency of a metal is not indicated, the normal valency of the metal is assumed. Beryllium probably is placed in the 0=N group because of the stability of its phthalocyanine chelate. Most often Be forms very stable bonds with oxygen as the donor element. Vanadium, nickel, and copper from the N > O group and iron from the ON group are the elements most frequently found in petroleum, chelated with porphyrin ligands. The porphyrin chelate contains four nitrogens as donor elements. 

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