Zinc porphyrin, complex with

Zinc porphyrin complexes with coordinated benzaldehyde in the fifth coordination site have also been structurally characterized.347,356... 

There are a reasonable number of structurally characterized zinc compounds with bound THF molecules. For example, a six-coordinate zinc porphyrin complex with axial THF donors and a four-coordinate zinc center with two THF ligands and two phenolate ligands.341,357 Although less common there are other structural examples of ether solvents, such as diethyl ether, coordinated.358 The X-ray structure of zinc chloride with 1,4-dioxane ligands shows a monomeric four-coordinate zinc center with two 1,4-dioxane ligands.359... 

Hunter (60) reported a self-assembled open polymer formed by a zinc porphyrin bearing one para-aniline substituent at the meso position. The ortho- and mela-analogs discussed above form closed dimers, but the geometry of the para-derivative precludes this, and polymerization is the only alternative (76, Fig. 31). Although the dilution experiments could be fitted to a non-cooperative polymerization model with a pairwise association constant (K = 190 M 1) practically identical to that found for simple aniline-zinc porphyrin complexes (K = 130 M 1), broadening of the 4H NMR spectrum at high concentrations is characteristic of oligomerization. 

Square-planar zinc compounds predominate with these ligand types as would be predicted. This is in contrast to the prevalence of tetrahedral or distorted tetrahedral geometries for four-coordinate species that have been discussed thus far. Zinc porphyrin complexes are frequently used as building blocks in the formation of supramolecular structures. Zinc porphyrins can also act as electron donors and antenna in the formation of photoexcited states. Although the coordination of zinc to the porphyrin shows little variation, the properties of the zinc-coordinated compounds are extremely important and form the most extensively structurally characterized multidentate ligand class in the CSD. The examples presented here reflect only a fraction of these compounds but have been selected as recent and representative examples. Expanded ring porphyrins have also... 

The functionalization of zinc porphyrin complexes has been studied with respect to the variation in properties. The structure and photophysics of octafluorotetraphenylporphyrin zinc complexes were studied.762 Octabromoporphyrin zinc complexes have been synthesized and the effects on the 11 NMR and redox potential of 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraarylporphyrin were observed.763 The chiral nonplanar porphyrin zinc 3,7,8,12,13,17,18-heptabromo-2-(2-methoxyphenyl)-5,10,15,20-tetraphenylporphyrin was synthesized and characterized.764 X-ray structures for cation radical zinc 5,10,15,20-tetra(2,6-dichlorophenyl)porphyrin and the iodinated product that results from reaction with iodine and silver(I) have been reported.765 Molecular mechanics calculations, X-ray structures, and resonance Raman spectroscopy compared the distortion due to zinc and other metal incorporation into meso dialkyl-substituted porphyrins. Zinc disfavors ruffling over doming with the total amount of nonplanar distortion reduced relative to smaller metals.766 Resonance Raman spectroscopy has also been used to study the lowest-energy triplet state of zinc tetraphenylporphyrin.767... 

A number of studies concerning zinc complexes of porphyrins or related ligands have also been reported 1193-1196 cadmium complexes of a number of porphyrins have also been investigated,1197-1199 a number of NMR studies of zinc porphyrin complexes have been made1200,1201 and a number of donor-acceptor complexes of zinc tetrapyrrole species with 1,3,5-trinitrobenzene have been described.1202 Recent developments in metallo-phthalocyamine chemistry, including aspects of zinc complexes, have been reviewed.9-15,12026,1468 11... 

Figure 12.7 Various architectures of the porphyrin arrays for light harvesting, (a) Cyclic array with peripheral acceptor (b) cyclic array with integral acceptor (c) tri-branched array with central acceptor (d) starburst array with central acceptor. FB denotes the free base porphyrin and Zn the zinc-porphyrin complex. (Adapted from Van Patten et al. [71])...

Figure 23. ET rate constant (kf) as a function of potential for zinc porphyrin complex and hexacyanoruthenium (III), curve 1. The rate constant for the reverse process is shown in curve 2. (Reprinted with permission from Ref. 177 copyright 1999, American Chemical Society.)...

The C5 position of dU has been used to attach a variety of labels or reporter groups, in particular fluorophores ° (see section 3.5). The pyrene-modified analogue (39) has been used to detect RNA bulge conformations in the HIV-TAR RNA sequence where the fluorescence is greatly enhanced,and as a donor for the red emitter nile red (40) when the two dyes are adjacent in duplex DNA the result is white light that is emitted upon excitation of (39). A zinc-porphyrin complex has been added to C5 of dU for use in electron transfer. Norbornene has been attached via an alkyne linker for post-synthetic modification with nitrile oxides in a copper-free Click reaction, " and various dienes have been attached for Diels-Alder tagging of DNA. The photoaffinity tag (41) has been incorporated into DNA adjacent to a damaged DNA base (8-oxo-dG or thymine dimer) such that when exposed to repair systems, the repair enzyme is trapped by the diazirine for mass spectroscopic characterisation. ... 

Figure 59. Crystal structure of the tetrameric zinc porphyrin complex 102. a, Side view, b, A view perpendicular to the central porphyrin plane showing the crystallographic S4 symmetry and the orthogonal orientation of the four peripheral zinc porphyrins of the covalent cyclotetramer. Reprinted with permission from Anderson, S., Anderson, H. L., Bashail, A., McPartlin, M., Sanders, ]. K. M. Angew. Chem. Ini Ed. Engl. 1995, 34, 1096.

Figure 8-11. Fragment of the crystal structure of the tetrameric zinc porphyrin complex [Zn4(L1797)(H2L1796)] with the disordered methyl ester side chains omitted for clarity.

Self-assembled monolayers of an Os3(CO)s CN(CH2)3Si(OEt)3)(ft3-ri rf if-C6o) cluster on indium-tin oxide or gold surfaces have been shown to be electrochemically stable, being reducible to tetra-anionic species in their cyclic voltammograms. Further derivatization through tethering a zinc porphyrin complex to the cluster generated a high-performance photovoltaic cell with potential applications in artificial photosynthesis. ... 

Phosphite 56 equipped with three zinc porphyrins reacts with l,4-diazabicyclo[2.2.2]octane as the templating agent to give selectively 57 as a bis-phosphite rhodium metal complex. In the absence of the templating diamine, the l b ratio is 2-3 in the rhodium-catalyzed hydroformylation, but after addition of the template, it raised to 15-23, similar to covalently bonded bidentate phosphates with a wide bite angle. 

H NMR data has been reported for the ethylzinc complex, Zn(TPP—NMe)Et, formed from the reaction of free-base N-methyl porphyrin H(TPP—NMe) with ZnEti. The ethyl proton chemical shifts are observed upheld, evidence that the ethyl group is coordinated to zinc near the center of the porphyrin. The complex is stable under N2 in the dark, but decomposed by a radical mechanism in visible light.The complex reacted with hindered phenols (HOAr) when irradiated with visible light to give ethane and the aryloxo complexes Zn(TPP—NMe)OAr. The reaction of Zn(TPP—NMe)Et, a secondary amine (HNEt2) and CO2 gave zinc carbamate complexes, for example Zn(TPP—NMclOiCNEti."" ... 

The aniline-zinc porphyrin interaction has also been exploited to form dimers. Hunter (60) reported the dimerization of porphyrins functionalized at one meso position with ortho or meta aniline groups (47, 48, Fig. 15). Both compounds showed concentration-dependent H NMR spectra with large upfield shifts for the aniline protons. The dimerization constants are 160 and 1080 M-1 respectively for 47 and 48, and these values are an order of magnitude higher than the association constants of simple reference complexes (K — 10 and 130 M 1 respectively), which is indicative of cooperative self-assembly. The complexa-tion-induced changes in chemical shift were used to obtain three-dimensional structures of the dimers. 

A dimer made up of two zinc porphyrins bearing a 7-azabicy-clo[2.2.1]heptadiene fused at the C2-C3 /3-positions was reported by Knapp (61). The compound was designed to dimerize with a pyrrole-over-pyrrole geometry similar to that found in the photosynthetic special pair. Dimerization at KT3 M was confirmed by VPO and JH NMR spectroscopy. Dilution to 10-5 m or addition of DMAP caused disaggregation of the complex. In the solid state, this compound assembles as a cyclic hexamer with the vicinal porphyrin planes almost perpendicular. 

Macrocyclic receptors made up of two, four or six zinc porphyrins covalently connected have been used as hosts for di- and tetrapyridyl porphyrins, and the association constants are in the range 105-106 M-1, reflecting the cooperative multipoint interactions (84-86). These host-guest complexes have well-defined structures, like Lindsey s wheel and spoke architecture (70, Fig. 27a), and have been used to study energy and electron transfer between the chromophores. A similar host-guest complex (71, Fig. 27b) was reported by Slone and Hupp (87), but in this case the host was itself a supramolecular structure. Four 5,15-dipyridyl zinc porphyrins coordinated to four rhenium complexes form the walls of a macrocyclic molecular square. This host binds meso-tetrapyridyl and 5,15-dipyridyl porphyrins with association constants of 4 x 107 M-1 and 3 x 106 M-1 respectively. 

Crossley (89) described the self-assembly of a spherical cage-like structure made up of two zinc porphyrin dimers bound to a tetramine ligand. The 2 1 complex is stable at 10-6m concentrations, but addition of excess of ligand causes dissociation of the capsule with formation of a 1 1 complex. 

Zinc(II) porphyrins form stable complexes with nitrogen donors. This complementary binding motif has been used in a number of variations for the self-assembly combinatorial construction of phosphine and phosphite ligand libraries. 

Switching the roles of the zinc porphyrin template and N-donor adapter provides an alternative mode for the supramolecular construction of biden-tate ligands (Scheme 32). Complex 26 derived from mixing three equivalents of template 24 with two equivalents of monodentate phosphite ligands 23 furnished a rhodium catalyst which displayed good regioselectivity toward... 

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