Indium chelates

Figure 15.17 An amino-PEG-pyrrolidine derivative of carbon nanotubes can be used to couple metal chelating groups, such as DTPA. Subsequent coordination of mIn results in an indium chelate that can be used for imaging applications.

Deshpande, S.V., Subramanian, R., McCall, M.J., DeNardo, S.J., DeNardo, G.L. and Meares, C.F. (1990) Metabolism of indium chelates attached to monoclonal antibody minimal transchelation of indium from benzyl-EDTA chelate... 

Apart from PAR, many other azo reagents have been applied as spectrophotometric reagents for indium. l-(2-Pyridylazo)-2-naphthol (PAN) has been applied widely as analytical reagent for indium [24,36-38]. The indium chelate with PAN is extractable into chloroform from solutions of pH 6 (e = 1.9-10 ). Indium has also been determined with PAN by derivative spectrophotometry [39]. Other azo reagents proposed for indium include 2-(2-pyridylazo)-l-hydroxynaphthalene-4-sulphonic acid [40], TAR (formula 4.7) [41], Lumogallion (e = 5.4-10 at 510 nm) (formula 21.1) [42], Sulpharsazen [43], Thoron I [44], and Eriochrome Black T (extraction into n-butanol in the presence of diphenylguanidine, = 3.6-10 ) [45], Picramine M [46], 2-(2-thiazolylazo)-p-cresol (TAC) [47], and 2,4,6-tris(2-hydroxy-4-sulphonaphthylazo)l,3,5-triazine (e = 8.4-10 [48]. 

In summary, the groups of Espenson and Loh observe catalysis of Diels-Alder reactions involving monodentate reactants by Lewis acids in water. If their observations reflect Lewis-acid catalysis, involvirg coordination and concomitant activation of the dienophile, we would conclude that Lewis-acid catalysis in water need not suffer from a limitation to chelating reactants. This conclusion contradicts our observations which have invariably stressed the importance of a chelating potential of the dienophile. Hence it was decided to investigate the effect of indium trichloride and methylrhenium trioxide under homogeneous conditions. 

The synthesis and characterization of the monomeric amidinato-indium(I) and thallium(I) complexes [Bu C(NAr)2]M[But(NAr(NHAr)] (M = In, Tl Ar = 2,6-Pr2CgH3) have been reported. Both compounds were isolated as pale yellow crystals in 72-74% yield. These complexes, in which the metal center is chelated by the amidinate ligand in an N, j -arene-fashion (Scheme 33), can be considered as isomers of four-membered Group 13 metal(I) carbene analogs. Theoretical studies have compared the relative energies of both isomeric forms of a model compound, In[HC(NPh)2]. ... 

Reagent-controlled stereoselectivity can provide stereochemical relationships over several centers when a combination of acyclic and chelation control and cyclic TS resulting from transmetallation is utilized. In reactions mediated by BF3 or MgBr2 the new centers are syn. Indium reagents can be used to create an anti relationship between two new chiral centers. The indium reagents are formed by transmetallation and react... 

Normally, the addition of C-nucleophiles to chiral a-alkoxyaldehydes in organic solvents is opposite to Cram s rule (Scheme 8.15). The anti-Cram selectivity has been rationalized on the basis of chelation control.142 The same anti preference was observed in the reactions of a-alkoxyaldehydes with allyl bromide/indium in water.143 However, for the allylation of a-hydroxyaldehydes with allyl bromide/indium, the syn isomer is the major product. The syn selectivity can be as high as 10 1 syn anti) in the reaction of arabinose. It is argued that in this case, the allylindium intermediate coordinates with both the hydroxy and the carbonyl function leading to the syn adduct. 

The same coordination is used to account for the observed anti preference in the allylation of (t-hydroxybutanal with allyl bromide/indium in water (Scheme 8.16). The intermediate leads to the anti product. In support of the intramolecular chelation model, it is found that if the hydroxy group is converted to the corresponding benzyl or t-butyldimethylsilyl ether, the reaction is not stereoselective at all and gives nearly equal amounts of syn and anti products. 

Investigation of the coordination of tetradentate N2S2 ligands has been reported for gallium and indium.79 This type of chelate had previously been incorporated into many technetium complexes for biomedical applications. 

Open-chain ligands were the first evaluated for complexation studies with indium and yttrium. The use of diethylenetriaminepentaacetic acid (DTPA) anhydride permitted early evaluation of labeled chelate-conjugates (Figure 2).80 The use of this activated chelating agent was quite popular, until the drawbacks associated with its crosslinking of proteins became apparent. 

Singh et al. (2006) also used cycloaddition to prepare carbon nanotubes containing indium labeled diethylenetriamine pentaacetic acid (DTPA) derivatives (Figure 15.17). In the initial modification, a SWNT was derivatized to contain a primary amine at the end of a short PEG spacer. The resultant water-soluble nanotube then was reacted with DTPA to create a metal chelating group at the end of the chain. Subsequent loading of the chelate with mIn created a radionuclide-SWNT complex for in vivo biodistribution studies. 

Figure 20.18 The bifunctional chelating reagent DTPA may be used to modify amine groups on antibody molecules, forming amide bond linkages. Indium-111 then may be complexed to the chelator group to create a radiolabeled-targeting reagent.

A poly(acrylaminophosphamic-dithiocarbamate) chelating fibre hasbeen used to preconcentratrate several trace metals in seawater by a factor of 200 [957]. The elements included beryllium, bimuth, cobalt, gallium, silver, lead, cadmium, copper, manganese, and indium. ICP-MS was used for detection. 

Addition of the indium reagent derived from the foregoing (P)-allenylstannane to /8-benzyloxy-a-methylpropanal as the aldehyde substrate at low temperature afforded a 70 30 mixture of anti,anti and anti,syn adducts (Eq. 9.141). The improved dia-stereoselectivity in this case can be attributed to substrate control, reflecting the chelating ability of an OBn versus an ODPS group. The lower temperature may also account for the improved diasteroselectivity. 

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