Studies of Carbon-hydrogen and Silicon-hydrogen Bond Activation by Early Transition Metal Complexes PDF Download
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Author: Paige Marie Morse
Publisher:
ISBN:
Category :
Languages : en
Pages : 278
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Book Description
Compounds that contain early transition metals particularly titanium, vanadium, and chromium, are used as catalysts for olefin polymerization in the Ziegler-Natta and Phillips processes. The key intermediates in these catalysts are thought to be six-coordinate metal alkyl/olefin complexes. The synthesis and study of early transition metal alkyl complexes as models of these catalytic centers can provide insight into the mechanism of polymerization processes.
Author: Paige Marie Morse
Publisher:
ISBN:
Category :
Languages : en
Pages : 278
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Book Description
Compounds that contain early transition metals particularly titanium, vanadium, and chromium, are used as catalysts for olefin polymerization in the Ziegler-Natta and Phillips processes. The key intermediates in these catalysts are thought to be six-coordinate metal alkyl/olefin complexes. The synthesis and study of early transition metal alkyl complexes as models of these catalytic centers can provide insight into the mechanism of polymerization processes.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Peter James Alaimo
Publisher:
ISBN:
Category :
Languages : en
Pages : 556
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Author: Chris Patrick Schaller
Publisher:
ISBN:
Category :
Languages : en
Pages : 436
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Author: Ryan Zahn Hinrichs
Publisher:
ISBN: 9780493319186
Category :
Languages : en
Pages : 226
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Book Description
Competition between C-C and C-H bond activation was investigated for prototype organometallic reactions. Energy dependent product branching ratios were measured for the reactions of Y (a2 D), Zr (a3F), Nb (a6D) and Mo* (a 5S2) with several simple hydrocarbons using the crossed molecular beams technique. Ground state Mo (a7S3) atoms were completely unreactive with ethane, whereas excited state Mo* (a 5S2) reactants activated ethane C-H bonds, leading to H2 elimination products. No products associated with C-C bond cleavage were detected for either Mo electronic state, illustrating the relative inertness of saturated alkanes to C-C bond activation. For reactions with cyclopropane, strained C-C bond activation readily competed with C-H bond activation for all metal atoms studied. Periodic trends in the measured product branching ratio (MCH2/MC3H4; M = Y through Mo) were reproduced using a line-of-centers model with ab initio insertion barrier heights. These experiments confirm theoretical predictions that strained C-C insertion barriers lie below C-H insertion barriers for Y and Mo. To further investigate the reactions of M + C3H 6, studies were performed with the propene C3H6 isomer. Only yttrium promoted unstrained C-C bond activation with propene, forming YCH2 + C2H4 products. The efficiency of YCH2 formation, relative to YC3H4 formation, indicated that the largest barrier for unstrained C-C bond activation lies only slightly above the largest barrier for C-H bond activation. Modeling using RRKM theory supports a proposed mechanism involving rearrangement of the Y-propene pi-complex to metallacyclobutane, the intermediate implicated in the cyclopropane reactions. For alkyne reactions, sp3-sp C-C bond cleavage was observed in the reaction Y + propyne & rarr; YC 2H + CH3. While this reaction was thermodynamically prohibited for Zr and Nb, sp3-sp C-C bond cleavage was detected as methane elimination for the reactions of Y, Zr and Nb with 2-butyne. An inverse relationship between C-H insertion barriers and C-H bond strengths has been noted for alkanes, alkenes and alkynes. The reactions presented on the following pages are consistent with an analogous relationship for sp3-sp3, sp3-sp2 and sp3-sp C-C bond insertion. These reactions demonstrating C-C bond cleavage warrant a renewed theoretical interest in C-C bond activation for prototype systems.
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Category :
Languages : en
Pages : 37
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Book Description
We are investigating the fundamental thermodynamic and kinetic factors that influence carbon-hydrogen bond activation at homogeneous transition metal centers and the conversion of hydrocarbons into functionalized products of potential use to the chemical industry. Advances have been made in both understanding the interactions of hydrocarbons with metals and in the functionalization of hydrocarbons. We have found that RhCl(PR3)2(CNR) complexes can catalyze the insertion of isonitriles into the C-H bonds or arenes upon photolysis. The mechanism of these reactions was found to proceed by way of initial phosphine dissociation, followed by C-H activation and isonitrile insertion. We have also examined reactions of a series of arenes with (C5Me5)Rh(PMe3)PhH and begun to map out the kinetic and thermodynamic preferences for arene coordination. The effects of resonance, specifically the differences in the Hueckel energies of the bound vs free ligand, are now believed to fully control the C-H activation/?2-coordination equilibria. We have begun to examine the reactions of rhodium isonitrile pyrazolylborates for alkane and arene C-H bond activation. A new, labile, carbodiimide precursor has been developed for these studies. We have completed studies of the reactions of (C5Me5)Rh(PMe3)H2 with D2 and PMe3 that indicate that both?5 2!?3 ring slippage and metal to ring hydride migration occur more facilely than thermal reductive elimination of H2. We have examined the reactions of heterocycles with (C5Me5)Rh(PMe3)PhH and found that pyrrole and furan undergo C-H or N-H activation. Thiophene, however, undergoes C-S bond oxidative addition, and the mechanism of activation has been shown to proceed through sulfur coordination prior to C-S insertion.
Author: LeGrande Mancel Slaughter (III)
Publisher:
ISBN:
Category :
Languages : en
Pages : 416
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Book Description
Author: Felicia L. Taw
Publisher:
ISBN:
Category : Cations
Languages : en
Pages : 294
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Author: Ryan Zahn Hinrichs
Publisher:
ISBN:
Category :
Languages : en
Pages : 412
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Book Description
Author: Masahiro Murakami
Publisher: John Wiley & Sons
ISBN: 352768011X
Category : Technology & Engineering
Languages : en
Pages : 292
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Book Description
Edited by leading experts and pioneers in the field, this is the first up-to-date book on this hot topic. The authors provide synthetic chemists with different methods to activate carbon-carbon sigma bonds in organic molecules promoted by transition metal complexes. They explain the basic principles and strategies for carbon-carbon bond cleavage and highlight recently developed synthetic protocols based on this methodology. In so doing, they cover cleavage of C-C bonds in strained molecules, reactions involving elimination of carbon dioxide and ketones, reactions via retroallylation, and cleavage of C-C bonds of ketones and nitriles. The result is an excellent information source for researchers in academia and industry working in the field of synthetic organic chemistry, while equally serving as supplementary reading for advanced courses in organometallic chemistry and catalysis.
