Phthalocyanines Schiff bases

Square planar complexes are also well authenticated if not particularly numerous and include [Co(phthalocyanine)] and [Co(CN)4] as well as [Co(salen)] and complexes with other Schiff bases. These are invariably low-spin with magnetic moments at room temperature in the range 2.1-2.9 BM, indicating 1 unpaired electron. They are primarily of interest because... 

Calcium-binding proteins, 6, 564, 572, 596 intestinal, 6, 576 structure, 6, 573 Calcium carbonate calcium deposition as, 6, 597 Calcium complexes acetylacetone, 2, 372 amides, 2,164 amino acids, 3, 33 arsine oxides, 3, 9 biology, 6, 549 bipyridyl, 3, 13 crown ethers, 3, 39 dimethylphthalate, 3, 16 enzyme stabilization, 6, 549 hydrates, 3, 7 ionophores, 3, 66 malonic acid, 2, 444 peptides, 3, 33 phosphines, 3, 9 phthalocyanines, 2,863 porphyrins, 2, 820 proteins, 2, 770 pyridine oxide, 3,9 Schiff bases, 3, 29 urea, 3, 9... 

The major types of complexes under intense investigation are the tetraden-tate Schiff base, for example, CoSalen, and phthalocyanine, for example, iron phthalocyanine complexes (Fig. 7.1).69... 

Catalytic activity of the aluminum-Schiff base system is dramatically enhanced by adding a bulky Lewis acid (Table 2). Inoue et al. reported that a combination of 3 with 2c led to over 1000 times acceleration in the polymerization of PO at room temperature compared with the polymerization in the absence of 2c.The resulting polymers have narrow MWDs, molecular weights close to those estimated, assuming that every molecule of 3 forms one polymer chain. The same accelerating effect of 2c is also demonstrated in the polymerization of PO by using aluminum-phthalocyanine and aluminum-tetraazaannulene complexes, 4 and 5, which exhibit very low catalytic activities without 2c. 

The key point of the high-speed living polymerization is the steric suppression of an undesired reaction between the nucleophilic growing species and the Lewis acid, for which not only the steric bulk of the Lewis acid but also that of the porphyrin ligand is considered important. The benefit of using a Lewis acid holds even for the aluminum complexes with phthalocyanine (11), tetraazaannulene (12), and. Schiff bases (13-15). As initiators, these complexes exhibit much lower activity for the polymerization of PO than aluminum porphyrin 1 (X=C1). 

Mitchell and Valero (1982, 1983) studied VO-phthalocyanine (VO-PC) and a Schiff base complex, VO-salen, as model vanadium compounds. The VO-PC provides a metal coordination environment comprised of four nitrogens, similar to the porphyrin. The benzo rings at the /3-pyrrolic positions contribute to enhanced aromaticity in the metal ligand. 

Both porphyrins and phthalocyanines are prepared by template Schiff base type condensation rections. For example, the use of a large template is evident in the synthesis of the superphthalocyanine 3.83, in which five repeat units are organised about the pentagonal bipyramidal U022+ core, instead of four as in more traditional phthalocyanine complexes such as 3.82. Smaller templates result in the formation of the trimeric subphthalocyanine 3.84. The reversible nature of the condensation reaction means that both 3.83 and 3.84 can be converted into normal tetrameric phthalocyanine, 3.85, Scheme 3.23. 

Schiff base macrocycles and phthalocyanines are readily prepared and pre-date crown ethers and cryptands but are more suitable for binding transition metals or softer main group ions. 

Complexation of macrocyclic ligands to lanthanide cations has been studied extensively [207,208], One main reason for the current interest in those macro-cyclic complexes are their intrinsic paramagnetic and luminescent properties. There is also the steadily increasing number of tailor-made macrocyclic ligands [209], This section will focus on complexes which contain macrocycles as discrete counterions and in particular on the coordination chemistry of phthalocyanine (Pc) and porphyrin (Por) ligands. Schiff base ligands which display another source of amine functionalities are usually not deprotonated under the prevailing reaction conditions [210]. 

Oxidative coupling of phenols to give diphenoquinones is a particularly well-studied reaction. Simple O2 can be used as the oxidant, and the process is accelerated by Co porphyrins, phthalocyanines, and Schiff bases. The most frequently used immobilization technique is anion exchange, requiring... 

In addition there has been a recent review of manganese porphyrin chemistry (19) as well as of the aqueous and chloro complexes of the porphyrin species (20). These discussions are complemented by a discussion of the electrochemistry of manganese porphyrin compounds (21). Related studies include the phthalocyanine complexes (22), the manganese (III)-hemoglobin structure (23), and the characterization of macrocyclic complexes of manganese (24, 25). Other relevant chemistry involves the Schiff-base complexes of Mn(III) (26, 27, 28). 

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