Iodine complexes, 3-covalent

A very successful example for the use of dendritic polymeric supports in asymmetric synthesis was recently described by Breinbauer and Jacobsen [76]. PA-MAM-dendrimers with [Co(salen)]complexes were used for the hydrolytic kinetic resolution (HKR) of terminal epoxides. For such asymmetric ring opening reactions catalyzed by [Co(salen)]complexes, the proposed mechanism involves cooperative, bimetallic catalysis. For the study of this hypothesis, PAMAM dendrimers of different generation [G1-G3] were derivatized with a covalent salen Hgand through an amide bond (Fig. 7.22). The separation was achieved by precipitation and SEC. The catalytically active [Co "(salen)]dendrimer was subsequently obtained by quantitative oxidation with elemental iodine (Fig. 7.22). 

It is well known that a great variety of biomolecules exist where metals and metalloids are bound to proteins and peptides, coordinated by nucleic acids or complexed by polysaccharides and small organic ligands such as organic acids.55 Most proteins contain amino acids with covalently bonded heteroelements such as sulphur, selenium, phosphorus or iodine.51 Several reviews have been published on the development of mass spectrometric techniques for bioanalysis in metal-lomics , which integrate work on metalloproteins, metalloenzymes and other metal containing biomolecules.1 51 53 54 56-59 The authors consider trace metals, metalloids, P and S (so-called... 

Iodine and bromine NQR studies on the complexes MX2L2 (M = Zn, Cd or Hg L = nitrogen heterocycle) show that the covalency of the M—L bond decreases in the order Cd>Zn> Hg.482 NMR, X-ray photoelectron studies and extended Hiickel calculations on HgCl2py2 indicate a moderate amount of electron transfer to the metal from pyridine relative to ZnCl2py2 filled mercury d orbitals do not participate in bonding.483... 

The first few pentacoordinate cationic silicon complexes (153-155) were discussed in an earlier review2. The first two were described as trivalent silicenium ions stabilized by mtermolecularcoordination183 184, while 155 is an intramolecular silicenium ion21a. Since then, a few other compounds were reported. Oxidation of the dihydrido-hexacoordinate chelate 156 by the addition of excess iodine produced 157185. The X-ray structure of 157 showed a slightly distorted TBP for the cation, with a well separated (Si—I distance 5.036 A) I8 2 anion for every two cations. The nitrogens are in the apical positions, and both Si-N distances (2.08 and 2.06 A) are longer than covalent bonds but well within the coordination distance. 

X-Ray studies of crystals of pyridine complexes with trimethylsilyl bromide and iodide (264) and of N-methylimidazole adducts to trimethyl-chlorosilane (265) were performed. The tetracoordinate silicon structure of these complexes was proved. The distances between the halogen and silicon atoms in pyridine adducts are 4.359 and 4.559 A for bromine and iodine, respectively, which is approximately 2 A greater than the sum of the covalent radii and significantly longer (0.5 A) than the sum of the van der Waals radii. This result is consistent with the ionic structures of the complexes in the solid state. The distance from silicon to nitrogen (1.86 A) is evidently larger than the length of typical Si—N bonds (1.75 A), which... 

Metal-bearing or metal-free phthalocyanines and tetraazaannulenes can be partially oxidized with iodine vapor or in solution . Substituted porphyrins may be partially oxidized with iodine . Phthalocyanines have also been prepared containing a group IIIB (e.g., Al) or group IVB (e.g., Si) main group atom that is part of an Si-O or Al-F covalent polymer. The later materials do not possess a chain of metal atoms however, they are structurally similar and exhibit similar physical properties . Except for the bisglyoximato complexes, the iodine partially oxidized substances are only poorly characterized. 

Molecular substances can be as simple as two iodine atoms linked together as b (bottom) or as complex as this protein, cytochrome c (top), which contains many thousands of atoms of carbon, hydrogen, oxygen, nitrogen, and sulfur linked together by covalent bonds. ... 

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