- Heteroorganic betaines 1. Synthesis of betaines containing the +P-C-Si-S- and +P-C-C-S- fragments and their characterization by multinuclear NMR spectroscopy
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A method for the synthesis of a new class of betaines, viz., R13P+CR2R3SiR4S-, was developed. The experimental evidence for the intermediate formation of betaines R13P+-CR2R3-CR4R5-S- in the Wittig reaction for a series of thiocarbonyl compounds was obtained. A comparative analysis of the NMR spectra of betaines containing the +P-C-Si-S- and +P-C-C-S- fragments was performed.
- Borisova, I. V.,Zemlyanskii, N. N.,Shestakova, A. K.,Ustynyuk, Yu. A.,Chernyshev, E. A.
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p. 920 - 928
(2007/10/03)
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- Hexanuclear iron-sulfur basket clusters: Topological isomers of prismanes. Synthesis, structure, and reactions
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The new set of cluster molecules Fe6S6(PEt3)4X2 (X = Cl- (1), Br-, I-) has been prepared by the reaction of Fe(PEt3)2X2 (2) with (i) (Me3Si)2S or Li2S in THF, (ii) the cubane clusters [Fe4S4X4]2- in acetonitrile, and (iii) the prismane clusters [Fe6S6X6]3- in acetonitrile. Also prepared by similar means were Fe6S6(PMe3)4Cl2, Fe6Se6(PEt3)4Cl2, and Fe6S6(P-n-Bu3)4Cl2 (3). The compounds were obtained as black crystalline solids, usually in purified yields of 50-65%. Precursor complex 2 (X = Br-) was isolated as pale yellow crystals with monoclinic space group Pn, a = 7.316 (1) ?, b = 12.316 (2) ?, c = 11.356 (2) ?, β = 97.15 (2)°, and Z = 2. The expected (distorted) tetrahedral structure was confirmed, with a notably open Br-Fe-Br angle (121.9 (1)°) presumably set by steric interactions. This angle is one of the largest in the tetrahedral series M(PR3)2X2, all of which thus far have X-M-X angles ≥105°; no previous structural data have been reported for type 2 complexes. Compound 3 crystallizes in tetragonal space group I41 with a = 33.78 (1) ?, c = 12.362 (7) ?, and Z = 8. It contains a [Fe6(μ2-S)(μ3-S)4(μ 4-S)]2+ core, formally including 2 Fe(III) + 4 Fe(II), and is built by the fusion of six nonplanar Fe2S2 rhombs to form an open basket with a bridging group Fe-(μ2-S)-Fe of bond angle 75.5° as the handle . The core has idealized C2v symmetry with the 2-fold axis containing the μ2-S and μ4-S atoms. Each Fe atom is four-coordinate; the two FeS3Cl sites have trigonally distorted tetrahedral geometry whereas the four FeS3P sites resemble very distorted trigonal pyramids with the Fe atoms only ca. 0.11 ? above the S3 planes and expanded S-Fe-S angles, one at each site (mean 127.5°), which form edges of the basket and handle in the form of two chairlike Fe3S3 rings or open faces . A simple conceptual relationship among 6-Fe core structures is presented as a scheme wherein different cores are transformed by formal addition (or subtraction) of Fe and S atoms. Arguments based on electrochemical properties are provided to show that basket and prismane ([Fe6(μ3-S)6]) cores do not interconvert even in the same oxidation level and are therefore topological isomers. The typical cluster 1 exhibits a versatile reaction chemistry that includes unique transformations that result in core conversions. In addition to being formed from [Fe6S6Cl6]3- (4) in a reductive-substitution reaction and from [Fe4S4Cl4]2- (5) in a process of core enlargement and reductive substitution, it is also spontaneously generated in solution from Fe7S6(PEt3)4Cl3. Further, in the presence of sulfur and chloride, the phosphines of 1 are removed in the form of Et3PS in high yield. In acetone solution in the presence of (Me4N)Cl, (Me4N)2[5] was isolated, whereas the use of (PPN)Cl resulted in isolation of the (PPN)+ salts of 4 and [Fe2S2(S5)2]2-, the latter in low yield. (PPN)3[4] could be identified securely only by X-ray crystallography. This compound crystallizes in monoclinic space group C2/c with a = 28.929 (8) ?, b = 15.296 (5) ?, c = 28.898 (6) ?, β = 122.39 (2)°, and Z = 4. The anion has a slightly distorted hexagonal prismatic structure with dimensions comparable to those found previously for another salt. In these conversions 85% of the Fe content of 1 is accounted for in the products. The basket and prismane Fe6S6 cores are the only open or closed polyhedral cores of this stoichiometry. The open faces of the prismane can be capped by certain metal fragments. These faces of the basket core have the same potential, but their less regular shape and longer S?S separations (3.93-4.10 ?) presumably will require core structural adjustment in the event of formation of a stable capped product.
- Snyder, Barry S.,Holm
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p. 2339 - 2347
(2008/10/08)
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