Condensation, Schiff base

The bidentate ligands were prepared by the Schiff-base condensation of two equivalents of the desired 2,6-dialkyl substituted anilines with acenaphthenequinone as in the scheme 1, The pre-catalysts, formed by addition of the ligand to (DME)NiBr2 are isolated and purified. The products were characterized by h, C NMR, GPC, DSC and Elemental Analysis. 

Bis(ethylenediamine)gold(III) chloride reacts with a variety of -diketonates in aqueous base, via Schiff base condensation, to form 14-membered tetraaza 12jt macrocyclic species [78[. The parent member of the series [AuL ]" being 22 (where H2L = 5,7,12,14-tetramethy]-l,4,8,ll-tetraazacydotetradeca-4,6,ll,13-tetra-ene) (Figure 2.15). The X-ray structure shows the cation to be nearly planar. 

One method of solving the kinetics dilemma is well known in coordination chemistry that is, start with a labile metal ion and render it inert during the course of the synthetic reaction. We have accomplished this in the case of zirconium(IV) by starting with tetrakis(salicylaldehydo)zirconium(IV), which is quite labile, and polymerization with 1,2,4,5-tetraaminobenzene in a Schiff-base condensation reaction in situ (6). The polymeric product contains a "double-headed" quadridentate ligand, which is much more inert to substitution. However, 1,2,4,5-tetraaminobenzene has become very expensive. Therefore, the synthesis of a zirconium polymer with 3,3, 4,4 -tetraaminobiphenyl (commercially 3,3 -diami nobenzidine) with zirconium salicylaldehyde, Zr(sal)4 (7) has been undertaken as shown below ... 

See structure 1. The reaction is conducted in dimethyl sulfoxide (DMSO), because DMSO is a very good solvent for the growing oligomers and its strong interaction with water prevents hydrolysis of the zirconium(IV) and favors the forward Schiff-base condensation reaction. 

The reaction of 2,2 -dithiodibenzaldehyde with Ni11 complexes containing coordinated primary amines results in Schiff base condensation and cleavage of the disulfide bond to form a chelating... 

Similarly, by Schiff-base condensation reactions have been used to generate free cryptands from triamines and dicarbonyls in [2+3] condensation mode. These ligands react with silver(I) compounds to give dinuclear or trinuclear macrocyclic compounds where Ag Ag interactions may be present. Thus, with a small azacryptand a dinuclear complex with a short Ag- Ag distance (55) is found.498 With bigger azacryptand ligands also dinuclear complexes as (56) are achieved but without silver-silver interaction. 65,499-501 A heterobinuclear Ag1—Cu1 cryptate has also been... 

Bis(ethylenediamine)gold(III) chloride reacts with /3-diketonates in aqueous base via Schiff base condensation to form complexes of gold(III) with a 14-membered macrocyclic tetraaza ligand such as (292).1711-1713 The X-ray structure showed the cation to be nearly planar. Delocalization of -electrons within the six-membered /3-diketonate rings was indicated by the observed pattern of C—C and C—N distances. Open-chain tetraaza ligand complexes in which condensation of only one /3-diketonate has occurred, can be isolated as intermediates in this reaction. They may be used for further condensation with a different /3-diketonate. Oxidation of this complex with trityl tetrafluoroborate introduces a double bond in position C2C3.1712,1714... 

Earlier work demonstrated that rhena-j8-diketones readily undergo Schiff-base condensation with ammonia or primary amines to give rhena-0-ketoimines 24 and 25 [Eq. (3)] (1). When R is i-Pr, condensation occurs... 

In related work, complexes 32 and 33 have been synthesized (41). The precursor complex in each preparation is the rhenaacetylacetonimine complex 25, where R = CH2CH2OH. This complex is formed by direct Schiff-base condensation with 2-aminoethanol. Complex 32 is formed when this precursor compound is treated with MeP(0)F2, and complex 33 is formed similarly by treatment with N,N -carbonyldiimidazole. The... 

A selection from the large number of template reactions published following the original report by Curtis will now be described. Schiff-base and related condensations have figured prominently in these reactions. For ease of presentation, it is convenient to separate examples involving non-Schiff-base condensation from those involving Schiff-base formation. The next two subsections are devoted to descriptions of examples from each of these respective types. 

As mentioned previously, Schiff-base condensations between amines and aldehydes or ketones have played a prominent role in metal-ion template chemistry. A generalized Schiff-base condensation (to produce an imine linkage) is given by [2.15],... 

A number of pendant arm ligand derivatives based on hexamine macrocyclic backbones have been reported." One such species was formed by the [2 -f 2] Schiff base condensation between 3,3-iminobis(propylamine) and diformyl-p-cresol followed by sodium borohydride reduction of the four imine functions so generated. Potentiometric studies indicate that a range of both mononuclear and dinuclear species are formed in solution with manganese(II) incorporating various both protonated and nonprotonated forms of the ligand. 

Fig. 19. Schiff base condensation of glutaraldehyde with enzyme amino...

Aspinall, H. C. Black, J. Dodd, I. Harding, M. M. Winkley, S. J. A lanthanide-templated Schiff-base condensation reaction to give a trinuclear macrocyclic complex. J. Chem. Soc., Dalton Trans. 1993, 709—714. 

The Ni(II) complex of a 16-membered macrocycle, 2,7-dimethyl-3,6 -(1,1 - (2,2 - biimidazole) -1,3,6,8,11,14 - hexaazacyclohexadeca -1,7 -diene, 22, was synthesized by Schiff base condensation of the Ni(II)-triethylenetetramine complex and 1,1 -diacetyl-2,2 -bisimidazole (29). The Ni(II) complex formed square-planar geometry with iodide or perchlorate anions and an octahedral structure with chloro or bromo ligands. 

A kinetic study of the Schiff base condensation of //z-toluidinc with salicylaldehyde has examined the effects of proton, hydroxide, general base, and transition metal catalysts, and also solvent effects.25... 

High yields have been achieved via Schiff base condensation of 2-aminophenol 115 and fluorinated benzaldehyde... 

The standard synthesis for cyclam was developed by Barefield and Wagner in 1976.29 They used similar starting materials to the van Alphen procedure but the cyclisation yield is improved through the use of a nickel (II) template. Glyoxal completes the macrocycle by a Schiff base condensation reaction. The resulting imine functionalities are reduced with sodium borohydride to leave the complexed macrocycle. The metal ion is then removed by reaction with cyanide and the free ligand extracted with chloroform (Scheme 3.19). Yields are typically in the region of 60%. 

A vast range of Schiff base macrocycles and macrobicycles exist and have been of great importance in macrocyclic coordination chemistry, particularly of the transition metals, from the very beginning of supramolecular chemistry. The key Schiff base condensation reaction involves simply the reaction of an amine with an aldehyde to eliminate (condense) water and give an imine. If desired, the product may be reduced (e.g. with NaBH4) to give an amine or a secondary amine-based macrocycle (Scheme 3.21). 

Scheme 3.21 The Schiff base condensation and the reduction of the product to give an amine.

Amine-aldehyde condensations. Sometimes known as a Schiff base condensation, the reaction of dialdehydes with diamines has been used extensively in the preparation of macrocyciic ligands for metal cations. Reduction of the resulting imine (C = N) group with NaBH4 gives the corresponding aliphatic amine (Section 3.10.6). 

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