Cobalt phthalocyanine dendrimers

Phthalocyanines and their metal complexes have interesting catalytic, electronic, and optical properties.172 Kimura et al.173 synthesized a phthalocyanine-centered dendrimer possessing Newkome-type dendrons,174 and subsequently used the second-generation cobalt-metalated phthalocyanine dendrimer as the catalyst for the oxidation of mercaptoethanol by dioxygen... 

The possibility of using the thermotropic properties of macromolecular complexes of dendrimers was demonstrated by the example of oxidation of disulfides in the presence of a macromolecular complex of cobalt phthalocyanine with a polyisopropylacrylamide-based (PIPAAm-based) dendrimer characterized by temperature-dependent solubility. The oxidation rate is almost tripled by increasing the temperature from 34 to 36 °C [129]. These temperatures are close to... 

A water-soluble hydroformylation catalyst was developed by Xi and co-workers [65]. Third generation PAMAM dendritic ligands, with hydrophilic amine or sulfonic acid end groups, were phosphonated and the rhodium complexes thus formed were found to catalyse efficiently the hydroformylation of 1-octene and styrene, under very mild conditions. Water-soluble dendritic cobalt phthalocyanines that exhibited catalytic activities and oxidised thiols in the presence of oxygen, have been synthesised by Kimura and co-workers [66]. The catalytic activity of the phthalocyanines was influenced by a egation of the catalytic sites that results fi om strong intermolecular cohesive forces. It was proposed that steric isolation, enforced by the addition of a bulky dendritic coaf around the active phthalocyanine unit, could improve the catalytic activity. Acid terminated polyamide dendrimers were coupled to a phthalocyanine core to produce the desired water-soluble cobalt phthalocyanines, which were tested subsequently for catalytic activity and stability. The results obtained showed that the aggregation of phthalocyanines was reduced the catalytic activity was improved and the stability of the catalyst was improved by addition of the dendritic substituents. 

A poly(propylenamine) dendrimer (11, Fig. 6.37) functionalised with poly-(N-isopropylacrylamide) (PIPAAm) (see Section 4.1.2) was used as dendritic host for anionic cobalt(II)-phthalocyanine complexes (a, b) as guests, which are held together by supramolecular (electrostatic and hydrophobic) interactions [57]. These dendritic complexes were investigated as catalysts in the above-mentioned oxidation of thiols, where they show a remarkable temperature dependence the reaction rate suddenly increases above 34°C. One attempted explanation assumes that the dendritic arms undergo phase separation and contraction above the Lower Critical Solubility Temperature (LCST). At this temperature the phthalocyanine complex site is more readily accessible for substrates and the reaction rate is therefore higher. 

It has been shown that this catalyst is selective in epoxidation of linear alkenes the linear epoxide yield was two to four times higher than in catalysis by ordinary porphyrin. It was also demonstrated that, in catalysis by the dendrimers, cyclic alkenes are oxidized three times more rapidly than similar linear 1-alkenes are. The catalyst activity decreases only by 10% at a turnover number (TON) of 1000, which is much higher than that for the monomolecular analogue. A cobalt complex with dendrimer phthalocyanine was much more stable, while remaining active, in... 

In addition to porphyrins, phthalocya-nines have been placed in the middle of hyperbranched molecules. Cobalt phthalo-cyanines with dendritic branches have been synthesized, and the analysis of their electrochemical behavior suggests that electron transfer between the phthalocya-nine core and an electrode is considerably hindered by the dendritic structure [51]. Dendrimers with phthalocyanine cores and electroactive tetrathiafulvalene (TTF) branches have also been synthesized and examined [52]. 

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