Schiff base complexes, reaction with

Pd(OAc)2 and an excess of Mel afforded 2,6-dimethylacetanilide (425) by stepwise oft/jo-palladation and methylation twice [179]. However, treatment of the Schiff base complex 426 with trifluoroacetic acid and alkyl iodide produced the 2,6-dialkylbenzaldehyde 427 after hydrolysis. This reaction can be made semi-catalytic [180]. 

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... 

The Schiff bases being derivatives of aldehydes or ketones and various amines have received considerable attention because of their interesting physical and chemical properties, involvement in biologically important reactions and widespread application of their metal complexes. Increasing interest in optically active Schiff bases is connected with the discovery at the beginning of the 1990s of the so-called Jacobsen catalysts used in several asymmetric reactions showing excellent enantioselectivity. 

It was first suggested that the reaction of an alkyl halide with a nickel(I) Schiff base complex yields an alkylnickel(III) intermediate (Equation (56)). Homolytic cleavage of RBr to give an alkyl radical R and a nickel(II) complex (Equation (57)) or, alternatively, one-electron dissociative reduction leading to R (Equation (58)) are possible pathways.254 A mechanism based on the formation of R via dissociative electron transfer of Ni -salen to RX (Equation (59)) has also been proposed.255... 

Glutaraldehyde is the most popular b/s-aldchydc homobifunctional crosslinker in use today. Flowever, a glance at glutaraldehyde s structure is not indicative of the complexity of its possible reaction mechanisms. Reactions with proteins and other amine-containing molecules would be expected to proceed through the formation of Schiff bases. Subsequent reduction with sodium cyanoborohydride or another suitable reductant would yield stable secondary amine... 

Other template cyclizations. In another Schiff-base template reaction, 1,3-diaminopropane monohydrochloride was reacted with biacetyl in methanol in the presence of Ni(n) to yield the nickel complex of the corresponding cyclic tetraimine - see [2.16] (Jackels et al., 1972). The success of the procedure illustrated is quite dependent on the reaction conditions employed. Attempts to isolate the metal-free macrocycle were unsuccessful - this once again emphasizes the stabilizing role of the metal... 

Activation volumes for aquation of Schiff base complexes [Fe(C5H4NCH=NHR)3]2+ (R = Me, Et, nPr, nBu) are between +11 and +14 cm3 mol-1 (107), and thus within the range established earlier (108) for (substituted) tris-l,10-phenanthroline-iron(II) complexes, viz. +11 to +22 cm3 mol-1. These positive values are consistent with dissociative activation. Kinetic studies of the reaction of a CH2S(CH2)3SCH2 -linked bis(terpy) ligand (L6) with [Fe(terpy)2]2+ showed a very slow two-step process. The suggested mechanism consisted of slow loss of one terpy, rapid formation of [Fe(terpy)(L6)], and finally slow displacement of the second terpy as the partially-bonded L6 becomes hexadentate (109). 

Schiff base complexes to aromatic silyl enol ethers/ " olefins/ sugars,Mn ° Schiff base complexes, " and rhenium(III) complexes " has been reported. Similar reactions are observed with the Mn (N)porphyrin complexes. The reaction products are dependant on the nature of the Schiff base ligand, both the yield and the enantiomeric excess being affected. " Salen nitridomanganese(V) complexes have been incorporated into Zeolite... 

A strategy to accelerate p-BL formation was therefore developed, consisting of the synthesis of unsymmetrical tridentate Ci Schiff base) complexes (Fig. 44) that might open a reaction channel for this particular sequence after chloride abstraction with Na[Co(CO)4]. 

L-Canaline is an ineffective antimetabolite of L-ornithine since it has little ability to antagonize ornithine-dependent reactions. On the other hand, it forms a covalently bound Schiff-base complex with the pyridoxal phosphate moiety of Bg-containing enzymes. As such it is a potent inhibitor of many decarboxylases and aminotransferases that utilize this vitamin. 

The susceptibility of the mercaptide groups in these Schiff base complexes to ligand reaction was evaluated by treating these compounds with methyl iodide and benzyl bromide in chloroform solution. The pure compounds isolated from these reaction mixtures were of the composition NiL.2RX, where L represents the tetradendate Schiff base and RX represents the alkyl halide added. These reactions proceed smoothly and the stoichiometry of the products implies that both sufur atoms are reactive. The products are monomeric in dichloroethane. They exhibit magnetic moments consistent with octahedral structures, and they behave as di-univalent electrolytes in coordinating, polar solvents. 

A series of pyridoxal amino acid Schiff base complexes have been prepared in which Al is trigonally coordinated by N and two O atoms.415 These provide a model for the intermediate in the pyridoxal-catalyzed reactions of amino acids. Some Schiff base complexes produced in reactions of the bases with Al(OPri)3 have been assigned a structure with five-coordinate aluminum.416417... 

Alkyl halides would not react with [CrCl2(MeCN)2], but the alkyl derivatives [RCr(salen)(H20)] and [RCr(salphen)(H20)] (R = Me, Ph) are said to form on reaction of the organic hydrazines with the Crm-Schiffs base complexes in MeCN under nitrogen followed by oxidation with oxygen and hydrolysis.1128... 

In Fig. 14-5 the reactions of PLP-amino acid Schiff bases are compared with those of (i-oxo-acids. Beta-hydroxy-a-oxo acids and Schiff bases of PLP with (i-hydroxy-a-amino acids can react in similar ways. The reactions fall naturally into three groups (a,b,c) depending upon whether the bond cleaved is from the a-carbon of the substrate to the hydrogen atom, to the carboxyl group, or to the side chain. A fourth group of reactions of PLP-dependent enzymes (d) also involve removal of the a-hydrogen but are mechanistically more complex. Some of the many reactions catalyzed by these enzymes are listed in Table 14-3. 

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