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1Author    Prof Sonderdruckanforderungen, M. Dr, HerberholdRequires cookie*
 Title    Monosubstituierte Derivate des Halbsandwich-Komplexes Cp*Ta(CO)4 - Vergleich mit den analogen Vanadiumverbindungen Cp*V(CO)3L und Röntgenstrukturanalyse des y-Picolin-Komplexes Cp*V(CO)3(NC5H4-Me(4))  
 Abstract    M onosubstituted D erivatives o f the H alfsandw ich C om plex C p*T a(C O)4 -C om parison with the A nalogous V anadium C om pounds C p*V (C O)3L and X -R ay Structural Analysis of the y-Picoline C om plex C p*V (C O)3(N C 5H 4-M e(4)) M ax H erberhold*, G udrun F rohm ader, Jürgen P eu k ert und W olfgang Milius The photo-induced substitution of a CO ligand in Cp*Ta(CO)4 (1) has been used to pre­ pare a series of Cp*Ta(CO)3L (2) complexes, in which the two-electron ligand L includes, e.g., isonitriles, sulfanes, cyclic ethers, phosphanes and pyridines. The complexes (2 a -y) were characterized by their v(CO) frequencies and their 'H and 13C NM R spectra, and were compared -if possible -with the corresponding vanadium complex, C p*V(C O)4 (3) and its derivatives, C p*V(C O)3L (4). The molecular structure o f the 4-picoline complex Cp*V(C O)3(NC5H 4-M e(4)) (4r) has been determ ined by X-ray crystal structure analysis. 
  Reference    Z. Naturforsch. 55b, 1188—1194 (2000); eingegangen am 21. August 2000 
  Published    2000 
  Keywords    Halfsandwich Complexes, Carbonylmetal Compounds, Photoreactions 
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 TEI-XML for    default:Reihe_B/55/ZNB-2000-55b-1188.pdf 
 Identifier    ZNB-2000-55b-1188 
 Volume    55 
2Author    D. Bryce-Smith, A. Gilbert, N. Al-Jalal, R. R. Deshpande, J. Grzonka, M. A. Hems, P. YianniRequires cookie*
 Title    Acid and Polarity Effects in Benzene Photoreactions with Alkenes and Alkynes  
 Abstract    The effects of polar solvents and proton donors on various photoreactions of the benzene ring with electron-acceptor alkenes and alkynes are described and discussed in relation to the various electronic excitation mechanisms involved. Proton donors prove valuable as mechanistic probes for polar intermediates in such processes, and can in some systems both initiate and divert reaction pathways. In 1970 we observed that the course of the photo-chemical cycloadditions of certain ethylenic and acetylenic compounds to benzene, earlier reported by us [1, 2], was profoundly altered in the presence of proton donors, leading to a type of photochemical Friedel-Crafts reaction [3]. Since then, we have described, mostly in preliminary form, numerous further examples of acid catalysis in the photo-reactions of benzene, viz. with amines [4], ethers [5], a ketone [6], a carboxylic acid [6], and hexa-fluorobenzene [7]. Our objective in this present paper is to bring together the previous preliminary reports on acid catalysis in the photoreactions of ethylenic and acetylenic compounds with benzene in conjunction with unpublished recent findings, and to provide a mechanistic rationale together with relevant experimental details. But before we proceed to consider the acid-cata-lysed processes, it is desirable to summarise the main types of reaction that have been shown to occur in the absence of acids. Ethylenes and/or acetylenes photoadd to benzene in the following four main ways: (a) ortho cycloaddition; (b) meto-cycloaddi-tion; (c) £>ara-cycloaddition; and (d) para-ene addi-tion [8, 9]. The mode of addition varies with the addend, and in some cases more than one pathway may be followed. In the case of (a), the adducts (1) of ethylenes may be obtained as such when the ethylenic addend is not a strong thermal dienophile, e.g. acrylonitrile [10], 2,3-dihydropyran [11]. When it is a strong dienophile, as in the case of maleic * Reprint requests to Prof. D. Bryce-Smith. 0340-5087/83/0900-1101/$ 01.00/0 anhydride and certain maleimides, a second mole-cule may add thermally to give the remarkably 
  Reference    Z. Naturforsch. 38b, 1101—1112 (1983); received May 2 1983 
  Published    1983 
  Keywords    Photoreactions, Benzene, Alkenes, Alkynes, Acid Effects 
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 TEI-XML for    default:Reihe_B/38/ZNB-1983-38b-1101.pdf 
 Identifier    ZNB-1983-38b-1101 
 Volume    38 
3Author    Claudia Bäk, Klaus PraefckeRequires cookie*
 Title    und dessen Cycloreversion Organic Sulfur Compounds, XLVII [1] Dimerization of Monothiobenzil to a 1,3-Dithietane and its Cycloreversion  
 Abstract    The thermal dimerization of monothiobenzil (lc) to a 1,3-dithietane (2c) and the photochemical cycloreversion of this heterocycle to 1 c is described. 
  Reference    Z. Naturforsch. 35b, 372—375 (1980); eingegangen am 26. November 1979 
  Published    1980 
  Keywords    Heterocycles, Organic Sulfur Compounds, a-Oxothiones, 1, 3-Dithietans, 1, 3-Oxathiols, Photoreactions 
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 TEI-XML for    default:Reihe_B/35/ZNB-1980-35b-0372.pdf 
 Identifier    ZNB-1980-35b-0372 
 Volume    35