Imprinted metal complex

In addition to imprinted acid-base catalysts [49-55], attempts to imprint metal complexes have been reported and constitute the current state of the art [46, 47]. In most cases of metal-complex imprinting, ligands of the complexes are used as template molecules, which aims to create a cavity near the metal site. Molecular imprinting of metal complexes exhibits several notable features (i) attachment of metal complex on robust supports (ii) surrounding of the metal complex by polymer matrix and (iii) production of a shape selective cavity on the metal site. Metal complexes thus imprinted have been appHed to molecular recognition [56, 57], reactive complex stabilization [58, 59], Hgand exchange reaction [60] and catalysis [61-70]. 

Using Co as the metal centre, 1-vinyl imidazole as the functional monomer and amino acids as the templates, Leonhardt and Mosbach prepared imprinted metal-complexing polymers [14]. These polymers were aimed at being used as enzyme-like substrate specific catalysts (for more details, see Section 6.5.3.). 

Leonhardt and Mosbach prepared metal-complexing imprinted polymers by polymerising Co " complexes of N-vinyl imidazole and A-protected amino acids [14]. After work-up of the polymer and removal of the amino acid templates, the catalytic activities of the resulting imprinted metal-complexing polymers were evaluated by following the hydrolysis of the p-nitrophenyl esters of various amino acids. Assessment of the rate of hydrolysis revealed a clear preference for the substrates used as the templates. The polymers could be used several times without any deterioration of the catalytic activities and true turnover was observed. 

Fig. 6.7. Molecularly imprinted metal-complexing polymer as a glucose sensor.

Molecular-Imprinted Metal Complexes for the Design of Catalytic Structures... 

Abstract Recent progresses in molecularly imprinted metal-complex catalysts are highlighted in this chapter. Molecular imprinting is a technique to produce a cavity with a similar shape to a particular molecule (template), and the molecularly imprinted cavity acts as shape-selective reaction space for the particular reactant. The application of the molecular-imprinting technique to heterogeneous metal-complex catalysts is focused in the viewpoint of a novel approach in the design of shape-selective catalysis mimicking enzymatic catalysis. 

A ligand of a metal complex is one of the most appropriate templates for a molecular-imprinted metal-complex catalyst. Several ligands have been reported as candidates because of their analogy to transition states or reaction intermediates for target reactions [51-64], Several metal complexes with single-site Co, Cu, Zn, Ti, Ru, Rh, and Pd species have been used as active metal sites coordinated with template ligands (Table 22.1). Acrylate polymers [54, 55, 60, 63, 64] or polystyrene-divinylbenzene (DVB) polymers [51, 53, 56] are common polymer supports for molecularly imprinted catalysts. 

Tada M, Iwasawa Y (2003) Design of molecular-imprinting metal-complex catalysts. J Mol Catal AChem 199 115... 

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