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Cyclopentadienyl free radical

Relatively few ir—electron problems involve molecules that permit use of D2y symmetry in fact, many substances of interest have no useable symmetry whatsoever. However, quite a few have one two—fold axis. The procedure for utilizing this is quite simple. Consider the cyclopentadienyl free radical the five equivalent resonance forms suggest fivefold symmetry ... [Pg.70]

Group VIA (Cr, Mo, W). y-Radiolysis studies have been carried out for the simple hexacarbonyls (31,32) and for certain carbonyl iodides (33) and cyclopentadienyl carbonyl iodides (34). In the case of the hexacarbonyls (31,32), two free-radical products have been detected and characterized for Cr(C0)6, weak unidentified EPR signals have been observed for Mo(C0)6, but irradiated W(C0)6 apparently contains no detectable paramagnetic centres. [Pg.180]

Fluxional and Nonrigid Behavior of Transition Metal Organometallic ir-Complexes, 16, 211 Free Radicals in Organometallic Chemistry, 14, 345 Functionally Substituted Cyclopentadienyl Metal Compounds, 21,1... [Pg.323]

For the lanthanide metals, Sm, Eu, and Yb, which have a readily accessible ( + 2) oxidation state, oxidative addition reactions of M(1I) complexes with halogens and organic halides are dominated by the atom transfer or free radical mechanism (cf. 5.S.2.9.1.) in which two metal ions are each oxidized to the -I- 3 state. Numerous examples illustrate the ability of cyclopentadienyl or indenyl Ln(II) complexes (Ln = Sm, Eu, Yb) to abstract halogen atoms from molecular halogens ", halogenated solvents sueh as CH2CI2 and and alkyl halides . An archetypieal example is ... [Pg.385]

Numerous reactions have been observed for cyclopentadienyl Ln(II) complexes (Ln = Yb or Sm) where the products are suggestive of free radical oxidative addition (cf. 5.8.2.9.1). Some of these reactions are listed (rj -Cp = j/ -CjMes) ... [Pg.391]

The reactivity of water with both carbanion and carbocation intermediates is well known and recognised, but until recently it was generally believed that water is inert towards free radicals. Some years ago, Cuerva et al. by chance observed that tertiary radicals were reduced effectively in the presence of bis(cyclopentadienyl)titanium(III) chloride and water. Now the authors have solid evidence to show that water really acts as a complete hydrogen atom source rather than a simple proton donor for radical reductions mediated by Ti(III) and, presumably, other metals that react by single electron transfer (Scheme 8.7).6... [Pg.96]

Selective generation of free radicals from epoxides promoted by (cyclopentadienyl) titanium (III) chloride, followed by trapping, usually with olefin. [Pg.269]

Valuable insight of multiple additions of free radicals came from the ESR spectroscopic investigations of benzyl radicals, C-labeled at the benzylic positions [97,98]. These radicals can be prepared in situ by photolysis of saturated solutions of Cgo in labeled toluene containing about 5% di-ferf-butyl peroxide. Thereby, the photochemically generated ferf-butoxy radicals readily abstract a benzylic hydrogen atom from the toluene. Two radical species with a different microwave power saturation behavior can be observed. One radical species can be attributed to an allylic radical 63 and the other to a cyclopentadienyl radical 65 formed by the addition to three and five adjacent [5]radialene double bonds, respectively (Scheme 11). In these experiments no evidence for the radical 61 is found, which is very likely a short-lived species. [Pg.45]

Methylsilanol ascorbate free radical scavenger Amaranth Apple (Pyrus malus) extract Bis (cyclopentadienyl) chromium Bis (cyclopentadienyl) vanadium dichloride p-Glucan... [Pg.5331]

Formation of a siloxane network via hydrosilylation can also be initiated by a free-radical mechanism (300-302). A photochemical route makes use of photosensitizers such as peresters to generate radicals in the system. Unfor-timately, the reaction is quite sluggish. Several complexes of platinum such as (jj-cyclopentadienyl)trialkylplatinum(rV) compoimds have been found to be photoactive. The mixture of silicone polymer containing alkenyl functional groups with silicon hydride cross-linker materials and a catalytic amoimt of a cy-clopentadienylplatinum(IV) compound is stable in the dark. Under UV radiation, however, the platinum complex imdergoes rapid decomposition with release of platinum species that catalyze rapid hydrosilylation and network formation (303-308). Other UV-active hydrosilylation catalyst precursors include (acetylacetonate)Pt(CH3)3 (309), (acetylacetonate)2Pt (310-312), platinum tri-azene compounds (313,314), and other sytems (315,316). [Pg.7595]

Atom abstraction reactions also occur with // -cyclopentadienyl substituted metal carbonyl complexes. Laser photolysis (460-490 nm) of [ / -cpM(CO)3]2 in the presence of organic halides (RX) leads to the formation of the halo compounds / -cpM(CO)3X (M = Mo, W). The reactivity trends RI > RBr > RCl, and benzyl > allyl > 3 > 2 > 1 > CH3, follow those expected for a free radical pathway. The reaction involves formation of the 17-electron intermediate / -cpM(CO)3, which then abstracts a halogen atom from the substrate (Scheme 6.9). The cpM(CO)3 radical is trapped by oxygen at a rate that is close to diffusion controlled. [Pg.245]

Uranium.—Uranium alkyls of the type [U(Bu )(A -C6H6)3] are thermally stable and appear to resist jS-elimination and probably decompose by a free-radical pathway. Decomposition of [U(Bu")(A -C5H5)3] in [ Hgltoluene produces butane with only about 5 % incorporation of deuterium, suggesting that hydrogen abstraction occurs principally within a solvent cage from the cyclopentadienyl rings. ... [Pg.383]

Table 9 IR spectra of free cyclopentadienyl radical," cyclopentadienyl ligand and free cyclopentadienyl anion. Table 9 IR spectra of free cyclopentadienyl radical," cyclopentadienyl ligand and free cyclopentadienyl anion.

See other pages where Cyclopentadienyl free radical is mentioned: [Pg.936]    [Pg.936]    [Pg.308]    [Pg.936]    [Pg.936]    [Pg.308]    [Pg.248]    [Pg.450]    [Pg.45]    [Pg.665]    [Pg.91]    [Pg.789]    [Pg.91]    [Pg.165]    [Pg.165]    [Pg.257]    [Pg.88]    [Pg.191]    [Pg.165]    [Pg.1083]    [Pg.13]    [Pg.338]    [Pg.91]    [Pg.345]    [Pg.240]    [Pg.91]    [Pg.665]    [Pg.259]    [Pg.199]    [Pg.5591]    [Pg.334]    [Pg.411]    [Pg.2]    [Pg.272]    [Pg.235]    [Pg.44]   


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Cyclopentadienyl radical

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