PubMed · 14051929
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J D WOFFORD. 1963. PROGRESSIVE SYSTEMIC SCLEROSIS.. https://pubmed.ncbi.nlm.nih.gov/14051929/
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Five-coordinate phenylsilicates are formed from the reaction of trimethoxy(phenyl)silane with monosaccharides in methanol in the presence of a stoichiometric amount of base. Five complexes have been isolated and characterized with two ketoses and three aldopentoses. The silicon central atom in [K([18]crown-6)][PhSi(beta-D-Fruf 2,3H-2)2].MeOH (1, Fru=fructose) is part of two chelate rings, with the ligands being beta-D-fructofuranose-O2,O3 dianions. The beta-furanose isomer is best suited for silicon ligation because it exhibits a torsion angle close to 0 degrees for the most acidic diol function, thus assuring a flat chelate ring. The same structural principles are also found in [K([18]crown-6)][PhSi(beta-D-Araf1,2H-2)2].2 MeOH (2, Ara=arabinose), [K([18]crown-6)][PhSi(alpha-D-Ribf1,2H-2)2] (3, Rib=ribose), [K([18]crown-6)][PhSi(alpha-D-Xylf1,2H-2)2]. acetone (4, Xyl=xylose), and [K([18]crown-6)][PhSi(alpha-D-Rulf2,3H-2)2] (5, Rul=ribulose).
The ligand TMPA (tris(2-pyridylmethyl)amine) and its copper complexes have played a prominent role in recent (bio)inorganic chemistry studies; the copper(I) complex [CuI(TMPA)(CH3CN)]+ possesses an extensive dioxygen reactivity, and it is also known to effect the reductive dechlorination of substrates such as dichloromethane and benzyl and allyl chlorides. In this report, we describe a set of new analogues of TMPA, ligand 6TMPAOH, binucleating Iso-DO, and trinucleating SYMM. Copper(I) complexes with these ligands and a previously described binucleating ligand DO react with chloroform, resulting in reductive dechlorination and production of [CuIIx(L)Clx]x+ (x = 1, 2, or 3). X-ray crystal structures of [CuII(6TMPAOH)Cl]PF6, [CuII2(Iso-DO)Cl2](PF6)2, [CuII2(DO)Cl2](PF6)2, and [Cu3(SYMM)Cl3](PF6)3 are presented, and the compounds are also characterized by UV-vis and EPR spectroscopies as well as cyclic voltammetry. The steric influence of a pyridyl 6-substituent (in the complexes with 6TMPAOH, Iso-DO, and SYMM) on the solid state and solution structures and redox potentials are compared and contrasted to those chlorocopper(II) complexes with a pyridyl 5'-substituent (in [CuII2(DO)Cl2](PF6)2 and in [CuII(TMPA)Cl]+). Some insights into the reductive dechlorination process have been obtained by using 2H NMR spectroscopy in following the reaction of [Cu2(Iso-DO)(CH3CN)2](PF6)2 with CDCl3, in the presence or absence of a radical trap, 2,4-di-tert-butylphenol.
The N-protonated bismercaptoethanediazacyclooctane serves as a bidentate dithiolate ligand to oxidized Fe(NO)(2) of Enemark-Feltam notation, E-F [Fe(NO)(2)],(9) mimicking Cys-X-Cys binding of Fe(NO)(2) to proteins or thio-biomolecules. The neutral compound is characterized by the well-known g = 2.03 EPR signal which is a hallmark of dinitrosyl iron complexes, DNIC's. The Fe(NO)(2) unit can be removed from the chelate by excess PhS(-), producing (PhS)(2)Fe(NO)(2)(-). Transfer of NO from Fe(H(+)bme-daco)(NO)(2) (nu(NO) = 1740, 1696 cm(-)(1)) to Fe(II) of [(bme-daco)Fe](2) yields the five-coordinate, square-pyramidal N(2)S(2)Fe(NO) (nu(NO) = 1649 cm(-)(1)), where NO is in the apical position. Its isotropic EPR signal at g = 2.05 is consistent with E-F [Fe(NO)](7) formulation. In excess NO, Roussin's red ester-type molecules are formed as dinuclear or tetranuclear species, [(micro-SRS)[Fe(2)(NO)(4)]](n)() (n =1, 2). These well-characterized molecules furnish reference points for positions and patterns in nu(NO) vibrational spectroscopy expected to be useful for in vivo studies of NO degradation of iron-sulfur clusters in ferredoxins.