Bifunctional molecular components

Synthetic supramolecular lyotropic polymer 81 has been prepared from bifunctional molecular components through triply hydrogen bonds [173]. The... 

Figure 3.2 Bifunctional molecular components for longitudinal PLCs assembled with hydrogen bonds.

The possibility of coordinating functionalized TTFs onto polynuclear core is a very stimulating issue because it is now well established that polynuclear cores, with some restrictions of course, can act as SMMs. We started a systematic investigation of polynuclear paramagnetic complexes with TTF CH=CH—py ligands to scan the possibility to access to bifunctional molecules which can act at the same time as SMM and single component metal. We succeeded in coordinating our modified TTFs to several homo- or heteropolynuclear complexes. This opens new perspectives in the field of multifunctional materials. The size of these molecules, which is of the order of 4 nm, is another important aspect in the field of molecular scale electronic. 

Recently, several groups reported molecular squares prepared by an alternative approach, in which bifunctional metalloligands serve as the linkers thereby placing the metal ions into the walls of the container molecules (114—116). Hupp and coworkers, for example, have designed square-shaped macrocycles based on salen-type components (117). Thus, the molecular square 15 was prepared by the directed assembly of cis- [(PEt3)2Pt(OTf)2] and... 

Polymerization. The polymerization of aziridines takes place in the presence of catalytic amounts of acid at elevated temperatures. The molecular weight can be controlled by the monomer—catalyst ratio, the addition of amines as stoppers, or the use of bifunctional initiators. In order to prevent a vigorous reaction, the heat liberated during the highly exothermic polymerization must be removed by various measures, ie, suitable dilution, controlled metering of the aziridine component, or external cooling after the reaction has started. 

Enantioselective synthesis of /3-lactams from enolate and imine components uses a bifunctional Lewis acid/nucleophile strategy.76 A chiral nucleophile is used to form a zwitterionic enolate, and a metal ion coordinates the imine. The postulated mechanism is supported by kinetic, spectroscopic, and molecular modelling evidence. 

If one introduces a component into a polycondensation with a functionality of 3 or more the situation dramatically changes. Branches, branched branches, and crosslinks between polymer chains will cause a more rapid increase in molecular weight as the polymerization proceeds, and ultimately to higher final values than possible from linear polycondensations (see Section 20.2). The extent to which branches and crosslinks will occur will be proportional to the ratio of the polyfunctional to the bifunctional components present, and to the number of functionalities on the polyfunctional component. Usually 3, but up to 8, functionalities per monomer may be used for this component of polyfunctional polycondensations. 

Medium pore aluminophosphate based molecular sieves with the -11, -31 and -41 crystal structures are active and selective catalysts for 1-hexene isomerization, hexane dehydrocyclization and Cg aromatic reactions. With olefin feeds, they promote isomerization with little loss to competing hydride transfer and cracking reactions. With Cg aromatics, they effectively catalyze xylene isomerization and ethylbenzene disproportionation at very low xylene loss. As acid components in bifunctional catalysts, they are selective for paraffin and cycloparaffin isomerization with low cracking activity. In these reactions the medium pore aluminophosphate based sieves are generally less active but significantly more selective than the medium pore zeolites. Similarity with medium pore zeolites is displayed by an outstanding resistance to coke induced deactivation and by a variety of shape selective actions in catalysis. The excellent selectivities observed with medium pore aluminophosphate based sieves is attributed to a unique combination of mild acidity and shape selectivity. Selectivity is also enhanced by the presence of transition metal framework constituents such as cobalt and manganese which may exert a chemical influence on reaction intermediates. 

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