ZfN: Search Results

1	Author	Prof Sonderdruckanforderungen, M. Dr, Herberhold	Requires cookie*
	Title	Monosubstituierte Derivate des Halbsandwich-Komplexes CpTa(CO)4 - Vergleich mit den analogen Vanadiumverbindungen CpV(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 pT a(C O)4 -C om parison with the A nalogous V anadium C om pounds C pV (C O)3L and X -R ay Structural Analysis of the y-Picoline C om plex C pV (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 CpTa(CO)4 (1) has been used to pre pare a series of CpTa(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 pV(C O)4 (3) and its derivatives, C pV(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

2	Author	D. Bryce-Smith, A. Gilbert, N. Al-Jalal, R. R. Deshpande, J. Grzonka, M. A. Hems, P. Yianni	Requires 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

3	Author	Claudia Bäk, Klaus Praefcke	Requires 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