21,441 research outputs found
Intermolecular C-H bond activation reactions promoted by transient titanium alkylidynes. Synthesis, reactivity, kinetic, and theoretical studies of the Ti C linkage
No full textThe neopentylidene-neopentyl complex (PNP)(TiCHBu)-Bu-t((CH2Bu)-Bu-t) (2;PNP- = N[2-P(CHMe2)(2)-4-methylphenyl](2)), prepared from the precursor (PNP)(TiCHBu)-Bu-t(OTf) (1) and (LiCH2Bu)-Bu-t, extrudes neopentane in neat benzene under mild conditions (25 degrees C) to generate the transient titanium alkylidyne, (PNP)(TiCBu)-Bu-t (A), which subsequently undergoes 1,2-CH bond addition of benzene across the TiC linkage to generate (PNP)(TiCHBu)-Bu-t(C6H5) (3). Kinetic, mechanistic, and theoretical studies suggest the C-H activation process to obey pseudo-first-order in titanium, the alpha-hydrogen abstraction to be the rate-determining step (KIE for 2/2-d(3) conversion to 3/3-d(3) = 3.9(5) at 40 degrees C) with activation parameters Delta H = 24(7) kcal/mol and Delta S = -2(3) cal/mol center dot K, and the post-rate-determining step to be C-H bond activation of benzene (primary KIE = 1.03(7) at 25 degrees C for the intermolecular C-H activation reaction in C6H6 vs C6D6). A KIE of 1.33(3) at 25 degrees C arose when the intramolecular C-H activation reaction was monitored with 1,3,5-C6H3D3. For the activation of aromatic C-H bonds, however, the formation of the sigma-complex becomes rate-determining via a hypothetical intermediate (PNP)(TiCBu)-Bu-t(C6H5), and C-H bond rupture is promoted in a heterolytic fashion by applying standard Lewis acid/base chemistry. Thermolysis of (3) in C6D6 at 95 degrees C over 48 h generates 3-d(6), thereby implying that 3 can slowly equilibrate with A under elevated temperatures with k = 1.2(2) x 10(-5) s(-1), and with activation parameters Delta H = 31(16) kcal/mol and Delta S = 3(9) cal/mol.K. At 95 degrees C for one week, the EIE for the 2-3 reaction in 1,3,5-C6H3D3 was found to be 1.36(7). When 1 is alkylated with LiCH2SiMe3 and KCH2Ph, the complexes (PNP)(TiCHBu)-Bu-t(CH2SiMe3) (4) and (PNP)(TiCHBu)-Bu-t(CH2Ph) (6) are formed, respectively, along with their corresponding tautomers (PNP)TiCHSiMe3((CH2Bu)-Bu-t) (5) and (PNP)TiCHPh((CH2Bu)-Bu-t) (7). By means of similar alkylations of (PNP)TiCHSiMe3(OTf) (8), the degenerate complex (PNP)TiCHSiMe3(CH2SiMe3) (9) or the non-degenerate alkylidene-alkyl complex (PNP)TiCHPh(CH2SiMe3) (11) can also be obtained, the latter of which results from a tautomerization process. Compounds 4/5 and 9, or 6/7 and (11), also activate benzene to afford (PNP)TiCHR(C6H5) (R = SiMe3 (10), Ph (12). Substrates such as FC6H5, 1,2-F2C6H4, and 1,4-F2C6H4 react at the aryl C-H bond with intermediate A, in some cases regioselectively, to form the neopentylidene-aryl derivatives (PNP)(TiCHBu)-Bu-t(aryl). Intermediate A can also perform stepwise alkylidene-alkyl metatheses with 1,3,5-Me<INF>3</INF>C<INF>6</INF>H<INF>3</INF>, SiMe<INF>4</INF>, 1,2-bis(trimethylsilyl)alkyne, and bis(trimethylsilyl)ether to afford the titanium alkylidene-alkyls (PNP)TiCHR(R') (R = 3,5-Me<INF>2</INF>C<INF>6</INF>H<INF>2</INF>, R' = CH<INF>2</INF>-3,5-Me<INF>2</INF>C<INF>6</INF>H<INF>2</INF>; R = SiMe<INF></INF>, R' = CH<INF>2</INF>SiMe<INF>3</INF>; R = SiMe<INF>2</INF>CCSiMe<INF>3</INF>, R' = CH<INF>2</INF>SiMe<INF>2</INF>CCSiMe<INF>3</INF>; R = SiMe<INF>2</INF>OSiMe<INF>3</INF>, R' = CH<INF>2</INF>SiMe<INF>2</INF>OSiMe<INF>3</INF>)
Report to Governor Neil Goldschmidt of Judge John C. Warden's corrections investigation
No full text"In accordance with Executive Order No. EO-89-12, on September 6, 1989 ..."--Page 1.Title from PDF title page (viewed on December 20, 2017).This archived document is maintained by the State Library of Oregon as part of the Oregon Documents Depository Program. It is for informational purposes and may not be suitable for legal purposes.Includes bibliographical references (page ).Mode of access: Internet from the Oregon Government Publications Collection.Text in English
Synthetic and Mechanistic Studies of the Ring Opening and Denitrogenation of Pyridine and Picolines by Ti−C Multiple Bonds
No full textThe neopentylidene-neopentyl complex (PNP)Ti=CH(t)Bu(CH(2)(t)Bu) (1; PNP(-) = N[2-P(CHMe(2))2-4-methylphenyl]2) extrudes neopentane in neat pyridine or picoline (3- or 4-picoline) under mild conditions (25 degrees C), to generate the transient titanium alkylidyne intermediate (PNP)Ti C(1)Bu (A), which subsequently ring-opens the pyridine by ring-opening metathesis of the aromatic N=C bond across the Ti C linkage, generating the metallaazabicycles (PNP)Ti(C((t)Bu)C(5)H(3)RNH) (R = H (2), 3-Me (3), 4-Me (4)). Kinetic studies suggest that the C N activation process obeys a pseudo-first-order process in titanium, with a-hydrogen abstraction being the rate-determining step (the KIE for 1/1-d(3) conversion to 2 was 3.8(3) at 25 degrees C). The activation parameters are Delta H* = 23(3) kcal/mol and Delta S* = -4(3) cal/(mol K). The intermolecular k(H)/k(D) ratio is close to unity, 1.07(3) at 25 C, for the conversion of 1 to 2 in pyridine versus pyridine-d(5). Detailed theoretical studies suggest the 1 -> 2 transformation proceeds in the following order: (i) formation of A in an overall endergonic step by a-hydrogen abstraction, (ii) an exergonic binding of pyridine, and (iii) concerted, exergonic 1,2 + 21 cycloaddition followed by (iv) exergonic ring-opening metathesis and finally (v) a concerted hydrogen atom migration. Complexes 2-4 can denitrogenate, that is, completely remove N of the heterocycle at 65 C over 7211, when treated with silyl chlorides such as ClSi R(3) (R = Me, (i)Pr, Ph) to cleanly afford the titanium silylimides (PNP)Ti=NSiR(3)(Cl) (R = Me (8), (i)Pr (9), Ph (10)) and the corresponding (1)Bu-arene organic byproduct. [Et(3)Si][B(C(6)F(5))(4)] also promotes denitrogenation of 2 to yield (t)Bu-benzene, but the metal complex could not be characterized from such a reaction. The conversion 2 -> 8 was found to have activation parameters Delta H* = 30(6) kcal/mol and Delta S* = 10(2) cal/(mol K), therefore yielding activation parameters Delta H* = 30(6) kcal/mol and Delta S* = 10(2) cal/(mol K), therefore yielding Delta G*approximate to kcal/mol at 298.15 K. A KIE of 1.6(2) at 85 degrees C was observed when 2/2-d(5) were denitrogenated to 8 in the presence of ClSiMe(3), with the rate of the reaction being insensitive to both the steric nature and concentration of the trialkylsilyl chloride. Denitrogenation leading to 8-10 is proposed to occur via a series of steps including a 1,3-hydrogen migration, an electrocyclic rearrangement, a retrocycloaddition, and a Si-Cl addition. The transformations 1 -> 2/3/4 and 2/3/4 -> 8 can be made cyclic by a series of steps such as deimination of the imide moiety in 8 with 2 equiv of MoCl(5), followed by reduction and transmetalation with LiCH(2)(t)Bu and then oxidatively induced a-hydrogen abstraction. The reactivity of 1 with other heterocycles such as THF, thiophene, and piperidine is also discussed
Thoughts on civil liberty, [electronic resource] : on licentiousness, and faction. By the author of Essays on the characteristics, &c.
No full textAuthor of Essays on the characteristics, &c = John Brown.Electronic reproduction.English Short Title Catalog,Reproduction of original from British Library
A Co2N2 diamond-core resting state of cobalt(I): A three-coordinate Co-I synthon invoking an unusual pincer-type rearrangement
No full textJohn Brent (1808-1882)
No full textAuthor, poet, campaigner and antiquarian John Brent was born in Rotherhithe in 1808, to a shipbuilder and his wife Susannah. The latter was from Sturry, and the family moved back to Canterbury in around 1821.
Biography for Kent Maps Online
Correspondence, C. W. Tayleure to John Brown, Jr., June 18, 1879
No full textA letter to C. W. Tayleure to John Brown, Jr. concerning the death of Brown's brother, Watson. 5 pages
The construction of Karen Karnak: The multi-author-function
No full textThis thesis is situated within the comparatively recent developments of Web 2.0 and the emergence of interactive WikiMedia, and explores the mode of authorship within a Read/Write culture compared to that of a Read/Only tradition. The hypothesis of this study is that the role of the audience has become merged with the author, and as such, represents new functions and attributes, distinct from a more conventional concept of authorship, in which the roles of audience and author are more separate. Read/Write and participatory culture, as defined by this study, is focused on collaboration, and includes the influences of D.I.Y. culture, Open-Source practices and the production of text by multiple authors. Multi-authorship presents a re-thinking of several concepts which support the notion of the individual author, since the focus of multi-authorship is not on attribution and ownership of a finished text, but on the continued malleability of a text. Modes of multi-authorship, demonstrated in the use of the pseudonyms Alan Smithee and Karen Eliot, represent declarative authors whose names signify multiple origins, whilst concurrently indicating a distinct body of work. The function of these names form an important context to this study, since primary research involves the construction of an experimental mode of multi-authorship utilising WikiMedia technology and the interaction of thirty nine participants, who are invited to create a body of work under the collective pseudonym Karen Karnak. The data generated by this experiment is analysed using aspects of Michel Foucault's author-function to identify and determine power structures inherent in the WikiMedia context. The interplay of power structures, including concepts such as identity, ownership and the body of work, affect the resulting mode of authorship and contribute to the construction of Karen Karnak, suggesting further areas of research into the emerging multi-author
Search for the decay
No full textA search for the fully reconstructed → μμγ decay is performed at the LHCb experiment using proton-proton collisions at = 13 TeV corresponding to an integrated luminosity of 5.4 fb. No significant signal is found and upper limits on the branching fraction in intervals of the dimuon mass are setat 95% confidence level. Additionally, upper limits are set on the branching fraction in the [2m, 1.70] GeV/c dimuon mass region excluding the contribution from the intermediate ϕ(1020) meson, and in the region combining all dimuon-mass intervals.[graphic not available: see fulltext]A search for the fully reconstructed decay is performed at the LHCb experiment using proton-proton collisions at TeV corresponding to an integrated luminosity of . No significant signal is found and upper limits on the branching fraction in intervals of the dimuon mass are set \begin{align} {\cal B}(B_s^0 \rightarrow \mu^+\mu^-\gamma) < 4.2\times10^{-8},~&m(\mu\mu)\in[2m_\mu,~1.70]\,\mathrm{GeV/c^2} ,\nonumber {\cal B}(B_s^0 \rightarrow \mu^+\mu^-\gamma) < 7.7\times10^{-8},~&m(\mu\mu)\in[1.70,~2.88]\,\mathrm{GeV/c^2},\nonumber {\cal B}(B_s^0 \rightarrow \mu^+\mu^-\gamma) < 4.2\times10^{-8},~&m(\mu\mu)\in[3.92 ,~m_{B_s^0}]\,\mathrm{GeV/c^2},\nonumber \end{align} at 95% confidence level. Additionally, upper limits are set on the branching fraction in the dimuon mass region excluding the contribution from the intermediate meson, and in the region combining all dimuon-mass intervals
- …
