Flexible tripods

Note This compound can be prepared in a well-ventilated laboratory but will stain easily take care when handling the product. 

Place 4,4-methylenedianiline (1.6 g, 8 mmol) and ethanol (25 mL) in a 100 mL conical flask equipped with a stirrer bar. Stir at room temperature for about 20 min or until all the solid has dissolved. Add a solution of salicylaldehyde (1.9 g, 1.7 mL, 15 mmol) in ethanol (25 mL) and continue to stir. The solution turns an intense yellow colour before the product precipitates over 30 min as a yellow powder. The product is isolated in quantitative yield by filtration and washed with small quantities of ethanol to remove any unreacted starting materials. N,N -(4,4 -methylenebiphenyl)bis(salicylideneimine) (6) is isolated as a yellow microcrystal-line powder. Further purification should not be necessary, however, the product can be recrystallized from a minimum volume of boiling ethanol. 

Tris(2-aimnoethyl)amine tren) S alicylaldehyde Ethanol [FLAMMABLE] 

Round-bottomed flask (250 mL) Heater/stirrer and stirrer bar Reflux condenser Rotary evaporator 

Note Wherever possible this reaction should be carried out in a fume hood. 

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The similar, but more flexible, tripodal ligand (275) forms an Fe + complex with log K 28. Rate... 

Mukherjee, P. S., Das, N., and Stang, P. J. 2004. Self-assembly of nanoscopic coordination cages using a flexible tripodal amide containing linker, Org Chem 69, 3526-3529. 

Scheme 13 Flexible tripodal ligand TCPSB, used for studying multiple substitution reactions at the metal centers. (Reproduced with permission from Ref 83. Copyright 2011 American Chemical Society.)...

Despite their simplified structures, most of the tripodal based chelators exhibit iron binding with pronounced affinity, facilitate synthesis and allow fast screening of a variety of related structures with a number of bacterial types in a relatively short time. There is, however, a clear distinction between the flexible and the rigid templates. While the former generally exhibit broad spectrum microbial activity, the latter are generally less active and frequently show no biological activity at all. 

In order to limit flexibility, three tridentate binding units similar to L3 have been connected to a covalent tri(2-aminoethyl)amine (TREN) tripod to give the nonadentate podand L4. Upon reaction with /J(III) (R = La-Eu, Yb, Lu, Y) in acetonitrile/nitromethane (1 1), the NMR spectra confirm the formation of the expected C3-symmetrical complexes [/ (L4)]3+ (Re-naud et al., 1999). The methylene protons are systematically diastereotopic at 298 K. For the diamagnetic cations R = Y, Lu, no coalescence is observed in the accessible temperature range (233-343 K), but the rate of helical interconversion increases with increasing ionic radii and [La(L4)]3+ shows coalescence at 323 K, thus pointing to a fast /J- Ea(L4)]3+ = M-... 

Flexible imidazole-containing tripodal ligands [e.g., l,3,5-tris(imidazol-l-yl-methyl)benzene and l,3,5-tris(imidazol-l-ylmethyl)-2,4,6-trimethylbenzene (1)]... 

Treatment of 5-thioxo-4,5-dihydro-3,4-dimethyl-l,2,4-triazole with sodium tetrahydroborate at 210 °C provides the new N3S3-donor tripod ligand Tt as its sodium complex salt [Na(H20)6] [Na(Tt)2]. Bailey also describes some Tt bismuth(III), tin(IV) and manganese complexes, which illustrated the flexible Tt offering a combination of the properties ot the Tp and Tm ligands.163... 

Some rigid tripodal ligands have been synthesized for the construction of various novel cage- or box-like complexes, and have demonstrated their potential use in supramolecular chemistry. The relatively flexible amide-type ligand (136) was prepared by the replacement reaction of 1,1,1-tris(p-tosyloxymethyl)propane and /V-benzylsalicylamide.217... 

Several analogous tripodal (amido)zirconium compounds 202170 and 203171 were prepared earlier using salt metathesis. Only when X in compound 202 is small, such as Me, the spectroscopic data and structural considerations indicate all three F-donors at ortho-positions of the aryl rings are bonded to Zr, demonstrating the coordinative flexibility of the ancillary donor functions in the tripodal amido complexes. 

Database analysis and molecular mechanics were used to determine the conformational flexibility of tridentate scorpionate ligands. It has been reported that tris(pyrazolyl)borate ligands act like molecular vises, opening their tripodal structure for larger metals and closing around smaller metal ions. The Tpx ligand conformation... 

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