Schiff base condensation reaction

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. 

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... 

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 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). 

A novel reaction that transfers chirality from an enantiopure tricarbonyl(dienal)iron complex in a Schiff base condensation reaction is followed by an intramolecular Mannich reaction to yield a piperidine which was then manipulated in additional five steps to dienomycin C 40 (Equation 109) <1999EJO 517>. 

Macrocycles that are saturated or have double bonds in only one part of the ring can be made independently or can be made by template synthesis96 where the presence of a metal ion controls the ligand synthesis. An important route is the Schiff base condensation reaction (eq. 9-3),... 

A Schiff base condensation reaction (see also Section 1.12.2.6 for further examples) has recently been used in the preparation of the air-sensitive yellow compound (44) (Scheme 3) from salicy-laldehyde and 2-(phenylphosphino)ethylamine.58... 

Schiff base condensation reactions have also been widely used in the preparation of new imine-functionalized tertiary phosphines (64) (68).122-129 The most frequently used experimental procedure involves the condensation of a carbonyl compound (often 2-Ph2PCeH4CHO)176 and the appropriate amine in ethanol, benzene, or THF under refluxing conditions. To ensure complete reaction, a Dean-Stark trap or the addition of molecular sieves is often necessary, to remove water formed during the reaction. Evaporation of the solvent and recrystallization yield the desired ligand in good to excellent yields. This approach can be used to prepare bis-phosphines, e.g., (66)-(68).127- 29 The iminophosphine (69) was prepared by a series of coupling reactions at a palladium template, and was liberated from the metal by treatment with aqueous cyanide.130... 

A great variety of nitrogen-containing macrocycles5 can be made by employing the Schiff base condensation reaction (21-2), often (but not... 

Scheme 2.7 Schiff-base condensation reactions between dicarbonyl compounds and diamines (a) the formation of a macrocylic Schiff base (b) the formation of a lariat ether Schiff base.

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