Porphyrin complexes structures

Structural aspects and coordination chemistry of metal porphyrin complexes with emphasis on axial ligand binding to carbon donors and mono- and di-atomic nitrogen and oxygen donors. P. D. Smith, B. R. James and D. H. Dolphin, Coord. Chem. Rev., 1981,39, 31-75 (170). 

Mechanisms of micellar reactions have been studied by a kinetic study of the state of the proton at the surface of dodecyl sulfate micelles [191]. Surface diffusion constants of Ni(II) on a sodium dodecyl sulfate micelle were studied by electron spin resonance (ESR). The lateral diffusion constant of Ni(II) was found to be three orders of magnitude less than that in ordinary aqueous solutions [192]. Migration and self-diffusion coefficients of divalent counterions in micellar solutions containing monovalent counterions were studied for solutions of Be2+ in lithium dodecyl sulfate and for solutions of Ca2+ in sodium dodecyl sulfate [193]. The structural disposition of the porphyrin complex and the conformation of the surfactant molecules inside the micellar cavity was studied by NMR on aqueous sodium dodecyl sulfate micelles [194]. 

For the purposes of this review the criterion has been refined to include only those porphyrin complexes where there is direct structural or spectroscopic evidence for a metal-carbon interaction. This interaction will not, however, be limited to covalent bonds. The last decade has seen the rise in importance of supramolecular chemistry and non-covalent interactions, and a small set of examples involving porphyrin complexes will be included as the last section in the review. 

To date, the only organometallic lanthanide porphyrin complexes to be reported contain yttrium and lutetium, and they will be considered in the section on scandium. Representative structural types of porphyrin complexes containing groups 3 and 4 metals are shown in Fig. 3 and selected data for all the structurally characterized complexes are given in Table 11. 

The electronic absorption spectra of the products of one-electron electrochemical reduction of the iron(III) phenyl porphyrin complexes have characteristics of both iron(II) porphyrin and iron(III) porphyrin radical anion species, and an electronic structure involving both re.sonance forms Fe"(Por)Ph] and tFe "(Por—)Ph has been propo.sed. Chemical reduction of Fe(TPP)R to the iron(II) anion Fe(TPP)R) (R = Et or /7-Pr) was achieved using Li BHEt3 or K(BH(i-Bu)3 as the reductant in benzene/THF solution at room temperature in the dark. The resonances of the -propyl group in the F NMR spectrum of Fe(TPP)(rt-Pr) appear in the upfield positions (—0.5 to —6.0 ppm) expected for a diamagnetic porphyrin complex. This contrasts with the paramagnetic, 5 = 2 spin state observed... 

Only a handful of rr-bonded iron porphyrin complexes have been structurally characterized, listed in Table HI, and four of these contain porphycene. corrolc. or phthalocyanine ligands rather than porphyrins. " "" Selected data arc given in Table III, and X-ray crystal structures of methyl- and phenyliron porphyrin complexes are shown in Fig. 4. All of the iron(III) porphyrin complexes exhibit... 

Only a small number of structurally characterized organometallic cobalt porphyrin complexes have been reported, and selected data for these are collected... 

The syntheses and spectroscopic and electrochemical characterization of the rhodium and iridium porphyrin complexes (Por)IVI(R) and (Por)M(R)(L) have been summarized in three review articles.The classical syntheses involve Rh(Por)X with RLi or RMgBr, and [Rh(Por) with RX. In addition, reactions of the rhodium and iridium dimers have led to a wide variety of rhodium a-bonded complexes. For example, Rh(OEP)]2 reacts with benzyl bromide to give benzyl rhodium complexes, and with monosubstituted alkenes and alkynes to give a-alkyl and fT-vinyl products, respectively. More recent synthetic methods are summarized below. Although the development of iridium porphyrin chemistry has lagged behind that of rhodium, there have been few surprises and reactions of [IrfPorih and lr(Por)H parallel those of the rhodium congeners quite closely.Selected structural data for rr-bonded rhodium and iridium porphyrin complexes are collected in Table VI, and several examples are shown in Fig. 7. ... 

The X-ray structures are known of a number of ketone ligands, including hexanedione and 4-methylcyclohexanone, that have bound as monodentate ligands in the fifth coordination site of zinc porphyrin complexes.347,348 Oxaphlorin dimeric compounds are also known where the oxygen from a neighboring porphyrin ring coordinates in the fifth coordination site of a neighboring zinc porphyrin unit.349... 

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... 

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... 

The Ru porphyrin complex (8) has also been used as a catalyst for the cyclization of allylic diazoacetates,258 albeit with limited success only the cyclization of F-cinnamyl diazoacetate shows high enantioselectivity (Scheme 81). It is noteworthy that a carbenoid species prepared from allyl o-phenyl-o-diazoacetate and complex (8) has been isolated and subjected to X-ray diffraction analysis, though it does not undergo the desired cyclization. In the structure, the carbene plane lies almost halfway between the two adjacent Ru—N bonds. 

Unusual arene-cadmium 7r-complexes have been recently prepared and structurally characterized. For example, the /w /zz-bcn/i porphyrin complex 194, which can be obtained by reaction of the free base with CdCl2, possesses a cadmium atom that is bound to the Mfez-phcnylcnc unit of the ligand in an apparent /-fashion (Figure 32). The resulting Cd-C distance of 2.71 A is shorter than the sum of the van der Waals radii.252 Despite this relatively short contact, DFT calculations and AIM analysis point to the weakness of the interaction. Comparable weak arene-cadmium 7r-interactions are also observed in the /wra-benziporphyrin cadmium chloride complex 195.253... 

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