Molecular complexes, diamines

Heating Kemp s acid with appropriate aromatic diamines yields bis-imides with two convergently oriented carboxylic acid groups on the edges of a hydrophobic pocket. Dozens of interesting molecular complexes have been obtained from such compounds and can be traced in the Journal of the American Chemical Society under the authorship of J. Rebek, Jr., (1985 and later e.g. T. Tjivikua, 1990 B). 

It is also easy to see that the dyestuff 2 (diamine green B) can be synthesised by joining the fragments 4 e, f, and g, in this precise order, by controlling the pH of the medium. Such an example illustrates how the molecular magnitude does not necessarily imply greater complexity in the synthetic planning (for a discussion of "molecular complexity" versus "synthetic complexity" see ref. [5]). 

In August 1911 I visited Werner for the first time. On the spot he suggested that I study the synthesis and resolution of diaminediethylene-diamine cobaltic salts (Co(NH3)2en2)X3. Such assymetric molecular complexes had not yet been studied. I solved this problem after one year, and it was published jointly with Werner in Berichte der Deutschen... 

The inclination of diamines 1-6 to form 1 1 molecular complexes (MC) with 1,3,5-trinitrobenzene (TNB) has been pointed out2. The corresponding measurements reveal a lack of any correlation between the basicity of 1,8-diaminonaphthalenes and the ease of MC formation. This would seem to indicate that compounds 1-6 act as jt-donors, and the differences in MC stability, the least stable of which is the 1 TNB complex, are mainly determined by steric factors and the inductive effect of the methyl groups2. 

More recently Noyori developed asymmetric hydrogenation of simple ketones with BlNAP/diamine-ruthenium complexes.In this system the catalytic process contrasted with the conventional mechanism of asymmetric hydrogenation of unsaturated bonds which requires metal-substrate 7t-complexation. In fact with BlNAP/diamine-ruthenium neither the ketone substrate nor the alcohol product interacted with the metallic centre during the catalytic cycle. The enantiofaces of the prochiral ketones were differentiated on the molecular surface of the coordinatively saturated RuH intermediate. 

Sun et al. [51] have further reported the scope of the cyclization reaction of privileged scaffolds, IL-tagged diamines 99. Microwave-assisted IL-supported S5mthesis toward dihydro- and tetrahydroquinazoline analogs was demonstrated in Scheme 14 [50]. In order to conshuct quinazoline framework, IL-supported 99 was condensed with one-carbon electrophile aldehydes and isothiocyanates resulting tetrahydroquinazoline 120 and dihydroquinazoline 122, respectively. To extend the scope of this cyclization reaction, treatment of the same starting material with a-ketobenzoic acids or y-ketoaliphatic acid in the presence of acetic acid afforded isoindolo[l,2-a]quinazoles 119 under microwave irradiation (Scheme 14) [51]. Removal of IL support from quinazolines moiety xmder transesterification conditions furnished heterocycles 119, 121, and 123 with varied molecular complexity. The present methods offer more effective platforms to access structurally diverse heterocycles. 

Polymerization of a dicarbonyl compound, a diamine, and a metal salt, is the most direct route to polymeric metal-Schiff bases (VII-12). One of the earliest uses of this reaction was as a colorimetric analytical method for metal ions (16). This reaction has been carried out in aqueous media, dimethyl-formamide (50), and mixed solvents incorporating benzene (50, 75). As with most chelate polymers, insolubility hampers obtention of high molecular weight. Molecular weights of 2000-11,000 were reported for the products obtained from some halogen-substituted bis(salicy aldehyde)-diamine-uranyl complexes (75). 

SCHEME 30.1. Mechanism of asymmetric reduction of ketones with molecular hydrogen in the presence of Ru(diphosphine)(l,2-diamine)Cl2 complex. 

In homogeneous catalysis using chiral diamine 18 complexed with Rh, the acetophenone was reduced quantitatively with 55% ee, in 7 days. In the case of polymerized complex 36a, acetophenone reduction leads to 33% ee and with its templated analog 43% ee. With 36b, an increase of about 20% ee is observed between polymerized and templated ligand. These increases in ee were ascribed to a favourable molecular imprinting effect of the PM, ereating chiral pockets within the polymer network. 

Silver(I) complexes with polyamines also form molecular aggregates, thus hexamethylenetetramine yields 2D and 3D coordination networks,613 polymeric chains are obtained with diethylene-triamine, tris(2-aminoethyl)amine, or A,A -bis(aminoethyl)propane-l,3-diamine,426 and 2D networks are formed with thiocyanate and bridging polyamines.61... 

Amines such as diethylamine, morpholine, pyridine, and /V, /V, /V, /V -tetramethylethylene-diamine are used to solubilize the metal salt and increase the pH of the reaction system so as to lower the oxidation potential of the phenol reactant. The polymerization does not proceed if one uses an amine that forms an insoluble metal complex. Some copper-amine catalysts are inactivated by hydrolysis via the water formed as a by-product of polymerization. The presence of a desiccant such as anhydrous magnesium sulfate or 4-A molecular sieve in the reaction mixture prevents this inactivation. Polymerization is terminated by sweeping the reaction system with nitrogen and the catalyst is inactivated and removed by using an aqueous chelating agent. 

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