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901.
Dr. Kuppuswamy Arumugam C. Daniel Varnado Jr. Dr. Stephen Sproules Dr. Vincent M. Lynch Prof. Dr. Christopher W. Bielawski 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(33):10866-10875
High yielding syntheses of 1‐(ferrocenylmethyl)‐3‐mesitylimidazolium iodide ( 1 ) and 1‐(ferrocenylmethyl)‐3‐mesitylimidazol‐2‐ylidene ( 2 ) were developed. Complexation of 2 to [{Ir(cod)Cl}2] (cod=cis,cis‐1,5‐cyclooctadiene) or [Ru(PCy3)Cl2(?CH‐o‐O‐iPrC6H4)] (Cy=cyclohexyl) afforded 3 ([Ir( 2 )(cod)Cl]) and 5 ([Ru( 2 )Cl2(?CH‐o‐O‐iPrC6H4)]), respectively. Complex 4 ([Ir( 2 )(CO)2Cl]) was obtained by bubbling carbon monoxide through a solution of 3 in CH2Cl2. Spectroelectrochemical IR analysis of 4 revealed that the oxidation of the ferrocene moiety in 2 significantly reduced the electron‐donating ability of the N‐heterocyclic carbene ligand (ΔTEP=9 cm?1; TEP=Tolman electronic parameter). The oxidation of 5 with [Fe(η5‐C5H4COMe)Cp][BF4] as well as the subsequent reduction of the corresponding product [ 5 ][BF4] with decamethylferrocene (Fc*) each proceeded in greater than 95 % yield. Mössbauer, UV/Vis and EPR spectroscopy analysis confirmed that [ 5 ][BF4] contained a ferrocenium species, indicating that the iron center was selectively oxidized over the ruthenium center. Complexes 5 and [ 5 ][BF4] were found to catalyze the ring‐closing metathesis (RCM) of diethyl diallylmalonate with observed pseudo‐first‐order rate constants (kobs) of 3.1×10?4 and 1.2×10?5 s?1, respectively. By adding suitable oxidants or reductants over the course of a RCM reaction, complex 5 was switched between different states of catalytic activity. A second‐generation N‐heterocyclic carbene that featured a 1′,2′,3′,4′,5′‐ pentamethylferrocenyl moiety ( 10 ) was also prepared and metal complexes containing this ligand were found to undergo iron‐centered oxidations at lower potentials than analogous complexes supported by 2 (0.30–0.36 V vs. 0.56–0.62 V, respectively). Redox switching experiments using [Ru( 10 )Cl2(?CH‐o‐O‐iPrC6H4)] revealed that greater than 94 % of the initial catalytic activity was restored after an oxidation–reduction cycle. 相似文献
902.
903.
Dr. Baoshun Liu Dr. Xuelei Wang Dr. Liping Wen Prof. Dr. Xiujian Zhao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(32):10751-10759
The in situ open‐circuit voltages (Voc) and the in situ photoconductivities have been measured to study electron behavior in photocatalysis and its effect on the photocatalytic oxidation of methanol. It was observed that electron injection to the conduction band (CB) of TiO2 under light illumination during photocatalysis includes two sources: from the valence band (VB) of TiO2 and from the methanol molecule. The electron injection from methanol to TiO2 is slower than that directly from the VB, which indicates that the adsorption mode of methanol on the TiO2 surface can change between dark and illuminated states. The electron injection from methanol to the CB of TiO2 leads to the upshift of the Fermi level of electrons in TiO2, which is the thermodynamic driving force of photocatalytic oxidation. It was also found that the charge state of nano‐TiO2 is continuously changing during photocatalysis as electrons are injected from methanol to TiO2. Combined with the apparent Langmuir–Hinshelwood kinetic model, the relation between photocatalytic kinetics and electrons in the TiO2 CB was developed and verified experimentally. The photocatalytic rate constant is the variation of the Fermi level with time, based on which a new method was developed to calculate the photocatalytic kinetic rate constant by monitoring the change of Voc with time during photocatalysis. 相似文献
904.
905.
906.
Dr. Jacorien Coetzee Dr. Deborah L. Dodds Prof. Jürgen Klankermayer Sandra Brosinski Prof. Walter Leitner Prof. Alexandra M. Z. Slawin Prof. David J. Cole‐Hamilton 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(33):11039-11050
Hydrogenation of amides in the presence of [Ru(acac)3] (acacH=2,4‐pentanedione), triphos [1,1,1‐tris‐ (diphenylphosphinomethyl)ethane] and methanesulfonic acid (MSA) produces secondary and tertiary amines with selectivities as high as 93 % provided that there is at least one aromatic ring on N. The system is also active for the synthesis of primary amines. In an attempt to probe the role of MSA and the mechanism of the reaction, a range of methanesulfonato complexes has been prepared from [Ru(acac)3], triphos and MSA, or from reactions of [RuX(OAc)(triphos)] (X=H or OAc) or [RuH2(CO)(triphos)] with MSA. Crystallographically characterised complexes include: [Ru(OAc‐κ1O)2(H2O)(triphos)], [Ru(OAc‐κ2O,O′)(CH3SO3‐κ1O)(triphos)], [Ru(CH3SO3‐κ1O)2(H2O)(triphos)] and [Ru2(μ‐CH3SO3)3(triphos)2][CH3SO3], whereas other complexes, such as [Ru(OAc‐κ1O)(OAc‐κ2O,O′)(triphos)], [Ru(CH3SO3‐κ1O)(CH3SO3‐κ2O,O′)(triphos)], H[Ru(CH3SO3‐κ1O)3(triphos)], [RuH(CH3SO3‐κ1O)(CO)(triphos)] and [RuH(CH3SO3‐κ2O,O′)(triphos)] have been characterised spectroscopically. The interactions between these various complexes and their relevance to the catalytic reactions are discussed. 相似文献
907.
Dr. Benjamin Frank Dr. Thomas P. Cotter Dr. Manfred E. Schuster Prof. Dr. Robert Schlögl Dr. Annette Trunschke 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(50):16938-16945
The effect of the gas‐phase chemical potential on surface chemistry and reactivity of molybdenum carbide has been investigated in catalytic reactions of propane in oxidizing and reducing reactant mixtures by adding H2, O2, H2O, and CO2 to a C3H8/N2 feed. The balance between surface oxidation state, phase stability, carbon deposition, and the complex reaction network involving dehydrogenation reactions, hydrogenolysis, metathesis, water‐gas shift reaction, hydrogenation, and steam reforming is discussed. Raman spectroscopy and a surface‐sensitive study by means of in situ X‐ray photoelectron spectroscopy evidence that the dynamic formation of surface carbon species under a reducing atmosphere strongly shifts the product spectrum to the C3‐alkene at the expense of hydrogenolysis products. A similar response of selectivity, which is accompanied by a boost of activity, is observed by tuning the oxidation state of Mo in the presence of mild oxidants, such as H2O and CO2, in the feed as well as by V doping. The results obtained allow us to draw a picture of the active catalyst surface and to propose a structure–activity correlation as a map for catalyst optimization. 相似文献
908.
Maria A. Lebedeva Dr. Thomas W. Chamberlain Dr. E. Stephen Davies Dr. Dorothée Mancel Bradley E. Thomas Dr. Mikhail Suyetin Dr. Elena Bichoutskaia Prof. Dr. Martin Schröder Prof. Dr. Andrei N. Khlobystov 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(36):11999-12008
A covalently‐linked salen–C60 (H2L) assembly binds a range of transition metal cations in close proximity to the fullerene cage to give complexes [M(L)] (M=Mn, Co, Ni, Cu, Zn, Pd), [MCl(L)] (M=Cr, Fe) and [V(O)L]. Attaching salen covalently to the C60 cage only marginally slows down metal binding at the salen functionality compared to metal binding to free salen. Coordination of metal cations to salen–C60 introduces to these fullerene derivatives strong absorption bands across the visible spectrum from 400 to 630 nm, the optical features of which are controlled by the nature of the transition metal. The redox properties of the metal–salen–C60 complexes are determined both by the fullerene and by the nature of the transition metal, enabling the generation of a wide range of fullerene‐containing charged species, some of which possess two or more unpaired electrons. The presence of the fullerene cage enhances the affinity of these complexes for carbon nanostructures, such as single‐, double‐ and multiwalled carbon nanotubes and graphitised carbon nanofibres, without detrimental effects on the catalytic activity of the metal centre, as demonstrated in styrene oxidation catalysed by [Cu(L)]. This approach shows promise for applications of salen–C60 complexes in heterogeneous catalysis. 相似文献
909.
910.
Dr. Srijit Biswas Dr. Christian Dahlstrand Rahul A. Watile Dr. Marcin Kalek Prof. Dr. Fahmi Himo Prof. Dr. Joseph S. M. Samec 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(52):17939-17950
Gold(I)‐chloride‐catalyzed synthesis of α‐sulfenylated carbonyl compounds from propargylic alcohols and aryl thiols showed a wide substrate scope with respect to both propargylic alcohols and aryl thiols. Primary and secondary aromatic propargylic alcohols generated α‐sulfenylated aldehydes and ketones in 60–97 % yield. Secondary aliphatic propargylic alcohols generated α‐sulfenylated ketones in yields of 47–71 %. Different gold sources and ligand effects were studied, and it was shown that gold(I) chloride gave the highest product yields. Experimental and theoretical studies demonstrated that the reaction proceeds in two separate steps. A sulfenylated allylic alcohol, generated by initial regioselective attack of the aryl thiol on the triple bond of the propargylic alcohol, was isolated, evaluated, and found to be an intermediate in the reaction. Deuterium labeling experiments showed that the protons from the propargylic alcohol and aryl thiol were transferred to the 3‐position, and that the hydride from the alcohol was transferred to the 2‐position of the product. Density functional theory (DFT) calculations showed that the observed regioselectivity of the aryl thiol attack towards the 2‐position of propargylic alcohol was determined by a low‐energy, five‐membered cyclic protodeauration transition state instead of the strained, four‐membered cyclic transition state found for attack at the 3‐position. Experimental data and DFT calculations supported that the second step of the reaction is initiated by protonation of the double bond of the sulfenylated allylic alcohol with a proton donor coordinated to gold(I) chloride. This in turn allows for a 1,2‐hydride shift, generating the final product of the reaction. 相似文献