Chelate complexes amine

Diamine chelate complexes are more stable than the monodentate amine heterocycles and, therefore, can be studied under physiological conditions. The imidazole complexes are unstable in aqueous solution and decompose rapidly to technetium oxide hydrate. Six-membered ring chelates are significantly less stable than five-membered ones. Lesser flexibility of the ligand, such as 1.2-diamino-cyclohexane, parallels somewhat lower stability of the complex [53] ... 

Figure 7.23 Chelating groups such as the isothiocyanate derivative of DTPA can be used to create multivalent chelating complexes with amine-dendrimers. Such complexes are able to coordinate multiple metal ions for detection, imaging, or radioimmunotherapy purposes.

A similar reaction mechanism was proposed by Chin et al. [32] for the hydrolysis of the biological phosphate monoester adenosine monophosphate (AMP) by the complex [(trpn) Co (OH2)]2+ [trpn = tris(ami-nopropyl)amine]. Rapid cleavage is observed only in the presence of 2 equiv metal complex. It is evident from 31P NMR spectra that on coordination of 1 equiv (trpn)Co to AMP a stable four-membered chelate complex 4 is formed. The second (trpn)Co molecule may bind to another oxygen atom of the substrate (formation of 5) and provide a Co-OH nucleophile which replaces the alkoxy group. The half-life of AMP in 5 is about 1 h at pD 5 and 25 °C. 

A comparison of the initial rates obtained with various cobalt complexes (Table I) reveals that the chelate complexes of Co(II) are more efficient than the simple salts, the catalytic activity of Co(III) is lower than that of Co(II) and the reaction becomes slower by increasing the number of N atoms in the coordination spheres in both oxidation states. In general, the addition of amine derivatives increased the activity of the catalysts. 

This new process has one unexpected benefit the rates and turnover numbers are increased substantially with the result that the amount of the toxic and expensive 0s04 is considerably reduced (usually 0.002 mole %). The rate acceleration is attributed to formation of an Os04-alkaloid complex, which is more reactive than free osmium tetroxide. Increasing the concentration of 1 or 2 beyond that of 0s04 produces only negligible increase in the enantiomeric excess of the diol. In contrast quinuclidine itself substantially retards the catalytic reaction, probably because it binds too strongly to osmium tetroxide and inhibits the initial osmylation. Other chelating tertiary amines as well as pyridine also inhibit the catalytic process. 

Since carbohthiations usually proceed as syn additions, 458 is expected to be formed first. Due to the configurationally labile benzylic centre it epimerizes to the trani-substitu-ted chelate complex epi-45S. The substitution of epi-458 is assumed to occur with inversion at the benzylic centre. Sterically more demanding reagents (t-BuLi) or the well-stabilized benzyllithium do not add. The reaction works with the same efficiency when other complexing cinnamyl derivatives, such as ethers and primary, secondary, or tertiary amines, are used as substrates . A substoichiometric amount (5 mol%) of (—)-sparteine (11) serves equally well. The appropriate (Z)-cinnamyl derivatives give rise to ewf-459, since the opposite enantiotopic face of the double bond is attacked . 

Chelate complexes of the type [PdX2(diene)] (X = Cl, Br) are readily formed by the dienes hexa-1,5-diene (124), bicyclo 2,2,lJhepta-2,5-diene (1, 7) tricyclo[4,2,2,0]-deca-triene and -diene derivatives (10), cyclo-octa-1,5-diene and dicyclopentadiene, but not dipentene (43). These may be converted to complexes of the types [Pd2X2(dieneOR)2] and [PdCl(dieneOR)-(amine)] (R = alkyl) (43), and their properties indicate that they have similar structures to the platinum complexes (XXXI) and (XXXIII). 

Diaminoethane (en), H2NCH2CH2NH2, forms tris- and bis-chelate complexes. The tris-chelate [Ni(en)3]2+ cation (94) has been known since 1899.658 It is considerably more stable than the six-coordinate complexes formed with monodentate amines as shown in Table 39 where the stability constants of some six-coordinate complexes are reported. 

In addition to chelate complexes, the cyclic amine 1,4,7-triazacyclononane will complex to platinum(II) and (IV). The hexacoordinate platinum(IV) complexes are bonded to two molecules of the tridentate ligand, but platinum(II) complexes with the ligand monodentate and bidentate.988 Also the formation of platinum(II) ammine complexes from chloride complexes is a reversible process. The rate constants decrease as the basicity of the leaving amine increases.989... 

The second mechanism requires a preliminary displacement of chloride by the oxygen of the ester to give a chelated complex which may be attacked by external hydroxide as seen in Chapter 3. In practice, the displacement of chloride from cobalt(m) is very slow and this mechanism proceeds by the SNlcb mechanism, in which loss of chloride ion is aided by deprotonation of the amine. The first step involves deprotonation of the en ligand followed by chloride loss to give a five co-ordinate intermediate (Fig. 5-63). 

Propyl, ethylene diamine Si-O-Si-C -CH2CH2CH2-NHCH2CH2NH2 Ion exchange Weak anion exchange phase for aqueous and biological samples incorporates a bidentate ligand to form chelate complexes useful for metal separations less polar than the propyl amine bonded phase... 

Chelate complexation through both amine and carboxylate... 

Due to the position of their free electron pairs in the colorless form, the 2-quinolylmethanes and -amines are able—in contrast to the 2,4 and 4,4 compounds—to form chelate complexes with suitable transition metal compounds. However, the formation of these complexes is dependent on sterical effects.10,11 While, for example,... 

FIGURE 12. Structure of a binuclear Fe(III)Fe(IV) chelate complex used as a model for Q. L=tris(5-ethyl-2-pyridylmethyl)amine. The structure shown is based on the X-ray crystal structure of the complex (Hsu et al., 1999). 

The reaction of palladium reagents with amines, phosphines, and other organic ligands to produce chelated complexes with Pd-C bonds is the Cyclometalation reaction (equation 7). It has been used to synthesize thousands of complexes with Pd-alkyl and Pd-aryl bonds. These complexes are beginning to be used as very stable, high turnover number catalysts and as intermediates in the synthesis of complex natural products. The scope and limitations of this reaction are detailed in Section 8. 

---