10,363 research outputs found
From olefin metathesis to organoruthenium homogeneous catalysis : synthesis, applications and mechanistic understanding
No full textOlefin metathesis is a valuable synthetic tool, widely used in several fields of science. Due to the importance of this transformation several contributions have been made in this field in order to understand mechanistic aspects, reactivity and applicability of this process.
In this topic, ruthenium indenylidene complexes have shown great activity and stability in metathesis, making them very valuable pre-catalysts. However, several aspects of these pre-catalysts have not been evaluated yet. For example, even though reports of active second generation ruthenium indenylidene complexes bearing bulky N-heterocyclic carbenes are present in the literature, no studies have been done to understand how steric hindrance affects the process. For these reasons, [RuCl₂(IPr*)(PPh₃)(3-phenylindenylidene)] (IPr*-PPh₃) and [RuCl₂(IPr*)(Py)(3-phenylindenylidene)] (IPr*-Py), bearing the very bulky ligand, IPr* have been synthesised and compared with [RuCl₂(IPr)(PPh₃)(3-phenylindenylidene)] (IPr-PPh₃) and the new [RuCl₂(IPr)(Py)(3-phenylindenylidene)] (IPr-Py).
Another important aspect, presented in this thesis, is the investigation of the stability of indenylidene pre-catalysts in alcohol solvents. Surprisingly, several different decomposition processes occur depending on the starting complex and the alcohol used. Mechanistic investigation into this decomposition, allowed us to develop a better understanding of this process, and to predict the decomposition product based on the environment. In particular, this study revealed that [RuCl(η⁵-3-phenylindenyl)(PPh₃)₂] (Eta-5) is accessed from [RuCl₂(3-phenylindenylidene)(PPh₃)₂] (M₁₀) via a novel indenylidene to η⁵-indenyl rearrangement. This formal decomposition product has been found to be active in at least 20 different catalytic transformations, rendering it a versatile catalytic tool
N-Heterocyclic Carbenes
No full textThis chapter presents an overview of N-heterocyclic carbenes (NHCs) as chemical species. The electronic characteristics of these ligands are discussed, detailing how pπ–pπ delocalization and σ electron withdrawal stabilizes the carbene center. The bonding to metal centers is also discussed, whereby the potential for σ donation, π donation, and π backbonding is highlighted. The chapter presents a brief introduction to how these species can be classified. In addition, an overview is also presented of how these compounds, and stable adducts thereof, can be prepared in the laboratory. The chapter provides the reader with a foundation from which the myriad applications of NHCs can be appraised and understood, en route to stimulating or developing the use of NHCs in the reader's chemical research
Steven Johnson Author Talk Poster
No full textK-State Book NetworkA poster advertising an author talk by Steven Johnson at Kansas State University on September 3, 2014. Steven Johnson's book "The Ghost Map" was the 2014-2015 common book
Mechanism of CO2 Fixation by IrI–X Bonds (X = OH, OR, N, C)
No full textDensity functional theory calculations have been used to investigate the CO2 fixation mechanism proposed by Nolan et al. for the IrI complex [Ir(cod)(IiPr)(OH)] (1; cod = 1,5-cyclooctadiene;
IiPr = 1,3-diisopropylimidazol-2-ylidene) and its derivatives. For 1, our results suggest that CO2 insertion is the rate-limiting step rather than the dimerization step. Additionally, in agreement with the experimental results, our results show that CO2 insertion into the Ir–OR1 (R1 = H, methyl, and phenyl) and Ir–N bonds is kinetically facile, and the calculated activation energies span a range of only 12.0–23.0 kcal/mol. Substantially higher values (35.0–50.0 kcal/mol) are reported for analogous Ir–C bond
(NHC)copper(I)-catalyzed [3+2] cycloaddition of azides and mono- or disubstituted alkynes
No full textA versatile and highly efficient catalyst for the Huisgen cycloaddition reaction has been developed. Previously isolated or in situ generated azides yielded 1,2,3-triazoles with differently substituted alkynes in the presence of a [(NHC)CuBr] complex (NHC=N-heterocyclic carbene). Extremely high reaction rates and excellent yields were obtained in all cases. This catalytic system fulfils the requirements of "click chemistry" with its mild and convenient conditions, nota-bly in water or solvent free reactions and simple isolation with no purification step. Furthermore, for the first time, an internal alkyne was successfully used in this copper-catalyzed cycloaddition reaction. DFT calculations on this particular system allowed for the proposition of a new mechanistic pathway for disubstituted alkynes
N-heterocyclic carbene complexes of au, pd, and pt as effective catalysts in organic synthesis
No full textN-Heterocyclic carbenes (NHC) have been developed in the last 20 years as effective alternatives to classical tertiary phosphines in transition metal-catalyzed transformations. The rapid development of this area is a result of synergistic interactions between experimental and computational chemists. Indeed, computer modeling has proven extremely useful in rationalizing large amount of experimental data, and thus has permitted to accelerate the pace at which this chemistry has been developed. In this review, we will discuss catalytic transformations involving NHC-containing gold, platinum, and palladium complexes. Particular attention is drawn to the fundamental insights that computational chemistry provided to rationalize mechanistic aspects of these processes
Steven Bialer and Patti Smith, July 1978
No full textMusician, poet, and author Patti Smith sits on a bed in a hotel room in July 1978. The photograph was taken by Don Hamerman as part of a session for "Unicorn Times," an alternative performing arts periodical in Washington, D.C. Steven Bialer, the Design Director for "Unicorn Times," is seated on the bed next to Smith
Steven Garber
No full textSteven Garber speaks on the importance and value of truth.
Steven Garber is the principal of The Washington Institute for Faith, Vocation & Culture, which is focused on reframing the way people understand life, especially the meaning of vocation and the common good. A consultant to foundations, corporations and educational institutions, he is a teacher of many people in many places. The author of The Fabric of Faithfulness: Weaving Together Belief and Behavior, and Visions of Vocation: Common Grace for the Common Good, he is also a contributor to the books, Faith Goes to Work: Reflections from the Marketplace, and Get Up Off Your Knees: Preaching the U2 Catalogue. He lives with his wife Meg in Virginia
Steven Yedinak Interview
No full textLTC (RET) Steven M. Yedinak commissioned in the U. S. Army Infantry in 1963 and subsequently spent 26 years in Special Forces and Airborne Infantry. He served two combat tours in Vietnam (1966-67 & 1971-1972), and started the Mobile Guerrilla Force. He is the author of Hard to Forget: An American with the Mobile Guerrilla Force in Vietnam (Random House, 1998). He retired from the Army in 1989
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