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- 저자 : Solowey, Douglas P. (검색결과 2 건)
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Solowey, Douglas P.,Mane, Manoj V.,Kurogi, Takashi,Carroll, Patrick J.,Manor, Brian C.,Baik, Mu-Hyun,Mindiola, Daniel J. Nature Publishing Group 2017 Nature chemistry Vol.9 No.11
Selectively converting linear alkanes to α-olefins under mild conditions is a highly desirable transformation given the abundance of alkanes as well as the use of olefins as building blocks in the chemical community. Until now, this reaction has been primarily the remit of noble-metal catalysts, despite extensive work showing that base-metal alkylidenes can mediate the reaction in a stoichiometric fashion. Here, we show how the presence of a hydrogen acceptor, such as the phosphorus ylide, when combined with the alkylidene complex (PNP)Ti=CH<SUP>t</SUP>Bu(CH<SUB>3</SUB>) (PNP=N[2-P(CHMe<SUB>2</SUB>)<SUB>2</SUB>-4-methylphenyl]<SUB>2</SUB><SUP>−</SUP>), catalyses the dehydrogenation of cycloalkanes to cyclic alkenes, and linear alkanes with chain lengths of C<SUB>4</SUB> to C<SUB>8</SUB> to terminal olefins under mild conditions. This Article represents the first example of a homogeneous and selective alkane dehydrogenation reaction using a base-metal titanium catalyst. We also propose a unique mechanism for the transfer dehydrogenation of hydrocarbons to olefins and discuss a complete cycle based on a combined experimental and computational study.
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Room-Temperature Ring-Opening of Quinoline, Isoquinoline, and Pyridine with Low-Valent Titanium
Baek, Seung-yeol,Kurogi, Takashi,Kang, Dahye,Kamitani, Masahiro,Kwon, Seongyeon,Solowey, Douglas P.,Chen, Chun-Hsing,Pink, Maren,Carroll, Patrick J.,Mindiola, Daniel J.,Baik, Mu-Hyun American Chemical Society 2017 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.139 No.36
<P>The complex (PNP)Ti=(CHBu)-Bu-t((CH2Bu)-Bu-t) (PNP = N[2-P(i)p(r2)-4-methylphenyl](2-)) dehydrogenates cyclohexane to cyclohexene by forming a transient low-valent titanium-alkyl species, [(PNP)Ti((CH2Bu)-Bu-t)], which reacts with 2 equiv of quinoline (Q) at room temperature to form (H3CBu)-Bu-t and a Ti(IV) species where the less hindered C-2=N-1 bond of Qis ruptured and coupled to another equivalent of Q, The product isolated from this reaction is an imide with a tethered cycloamide group, (PNP)Ti=N[C18H13N] (1). Under photolytic conditions, intramolecular C-H bond activation across the imide moiety in 1 occurs to form 2, and thermolysis reverses this process. The reaction of 2 equiv of isoquinoline (Iq) with intermediate [(PNP)Ti((CH2Bu)-Bu-t)] results in regioselective cleavage of the C-I=N-2 and C-1-H bonds, which eventually couple to form complex 3, a constitutional isomer of 1. Akin to 1, the transient [(PNP)Ti((CH2Bu)-Bu-t)] complex can ring-open and couple two pyridine molecules, to produce a close analogue of 1, complex (PNP)Ti=N[C10H9N] (4). Multinudear and multidimensional NMR spectra confirm structures for complexes 1-4, whereas solid-state structural analysis reveals the structures of 2, 3, and 4. DFT calculations suggest an unprecedented Mechanism for ring-opening of Q wheat the reactive intermediate in the low-spin manifold crosses over to the high-spin surface to access a low-energy transition state but returns to the low-spin surface immediately. This double spin-crossover constitutes a rare example of a two-state reactivity, which is key for enabling the reaction at room temperature. The regioselective behavior of Iq ring-opening is found to be due to electronic effects, where the aromatic resonance of the bicycle is maintained during the key C-C coupling event.</P>
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