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Papers by Kumar Vanka
Comptes Rendus Chimie, Sep 1, 2005
Cp2Zr(CH3)R and its derivatives can serve as powerful olefin polymerization catalysts after activ... more Cp2Zr(CH3)R and its derivatives can serve as powerful olefin polymerization catalysts after activation by a Lewis acid A to form the ion-pair [Cp2ZrR]+[CH3A]– (I) which is held together by a Zr-μ-CH3A– bridge. It is generally assumed that the cation Cp2ZrR+ (II) of I is the active species whereas the influence of the anion CH3A– (III) is less well understood. We
Inorganic Chemistry, Dec 8, 2011
The possibility of metal-metal cooperativity in improving the yield of the homogeneous Water Gas ... more The possibility of metal-metal cooperativity in improving the yield of the homogeneous Water Gas Shift reaction (WGSR) has been investigated through full quantum mechanical (QM) density functional theory (DFT) calculations. The calculations indicate that bi-metallic catalysts would be likely to be more highly active than mono-nuclear metal based catalysts for the WGSR. The results have implications for the design of improved WGSR catalysts in the future.
![Research paper thumbnail of A Combined Density Functional Theory and Molecular Mechanics (QM/MM) Study of Single-Site Ethylene Polymerization Catalyzed by [(C 6 H 5 NCH)C 4 H 3 N] 2 -RM + {M = Ti, Zr} in the Presence of the Counterion CH 3 B(C 6 F 5 ) 3](https://attachments.academia-assets.com/41934738/thumbnails/1.jpg)
](Organometallics, 2004
Molecular oscillations of ligand motions at the active site of carbonmonoxy myoglobin have been c... more Molecular oscillations of ligand motions at the active site of carbonmonoxy myoglobin have been calculated in a protein environment using the combined QM/MM approach. In these calculations, the active site was calculated at a quantum mechanical (QM) level of theory using the B3LYP/6-31 + G* method, while the remaining protein was calculated at the molecular mechanical (MM) level utilizing the AMBER force field. The presence of a torsion mode and the second component of the bending vibration are proof of a bent CO geometry in the heme pocket.
PrTi+ (R = F, H) and [bis(eta(5)-1-indenyl)dimethylsilane]PrZr+ in the presence of the counterion CH3B(C6F5)(3)(-)](https://attachments.academia-assets.com/41934772/thumbnails/1.jpg)
](Organometallics
Molecular oscillations of ligand motions at the active site of carbonmonoxy myoglobin have been c... more Molecular oscillations of ligand motions at the active site of carbonmonoxy myoglobin have been calculated in a protein environment using the combined QM/MM approach. In these calculations, the active site was calculated at a quantum mechanical (QM) level of theory using the B3LYP/6-31 + G* method, while the remaining protein was calculated at the molecular mechanical (MM) level utilizing the AMBER force field. The presence of a torsion mode and the second component of the bending vibration are proof of a bent CO geometry in the heme pocket.
![Research paper thumbnail of A combined density functional theory and molecular mechanics (QM/MM) study of single site ethylene polymerization catalyzed by [Cp{NC((BU)-B-t)(2)}TiR+] in the presence of the counterion, CH3B(C6F5)(3)(-)](https://attachments.academia-assets.com/41934736/thumbnails/1.jpg)
](Macromolecular Symposia
Molecular oscillations of ligand motions at the active site of carbonmonoxy myoglobin have been c... more Molecular oscillations of ligand motions at the active site of carbonmonoxy myoglobin have been calculated in a protein environment using the combined QM/MM approach. In these calculations, the active site was calculated at a quantum mechanical (QM) level of theory using the B3LYP/6-31 + G* method, while the remaining protein was calculated at the molecular mechanical (MM) level utilizing the AMBER force field. The presence of a torsion mode and the second component of the bending vibration are proof of a bent CO geometry in the heme pocket.
Dalton Trans., 2015
The protolytic cleavage of the O-H bond in water and alcohols is a very important reaction, and a... more The protolytic cleavage of the O-H bond in water and alcohols is a very important reaction, and an important method for producing dihydrogen. Full quantum chemical studies with density functional theory (DFT) reveal that germanium based complexes, such as HC{CMeArB}2GeH (Ar = 2,6-(i)Pr2C6H3), with the assistance of silicon based compounds such as SiF3H, can perform significantly better than the existing state-of-the-art post-transition metal based systems for catalyzing dihydrogen generation from water and alcohols through the protolysis reaction.
Inorganic chemistry, Jan 6, 2015
In biological oxidations, the intermediate Fe(V)(O)(OH) has been proposed to be the active specie... more In biological oxidations, the intermediate Fe(V)(O)(OH) has been proposed to be the active species for catalyzing the epoxidation of alkenes by nonheme iron complexes. However, no study has been reported yet that elucidates the mechanism of direct O-atom transfer during the reaction of Fe(V)(O) with alkenes to form the corresponding epoxide. For the first time, we study the mechanism of O-atom transfer to alkenes using the Fe(V)(O) complex of biuret-modified Fe-TAML at room temperature. The second-order rate constant (k2) for the reaction of different alkenes with Fe(V)(O) was determined under single-turnover conditions. An 8000-fold rate difference was found between electron-rich (4-methoxystyrene; k2 = 216 M(-1) s(-1)) and electron-deficient (methyl trans-cinnamate; k2 = 0.03 M(-1) s(-1)) substrates. This rate difference indicates the electrophilic character of Fe(V)(O). The use of cis-stilbene as a mechanistic probe leads to the formation of both cis- and trans-stilbene epoxides ...
Journal of Computational Chemistry, 2015
There is considerable interest presently in the chemistry of allenes. The current computational i... more There is considerable interest presently in the chemistry of allenes. The current computational investigation looks into the possibility of using allenes and their derivatives as leaving groups. As it is well known, leaving groups are significant in catalytic processes for generating the active site. A full quantum mechanical study using density functional theory shows that allenes and their derivatives can function as excellent leaving groups. Indeed, the calculations show that they can be several orders of magnitude more effective than existing ligands for this purpose. The modification of second generation Grubbs' catalysts with these ligands suggests that the allene ligand cases that would be most effective are those having electron withdrawing groups, especially those that have the potential for supramolecular interactions between the substituent groups in the free state. © 2015 Wiley Periodicals, Inc.
For the past few decades, a large number of catalysts have been reported for selective ethylene o... more For the past few decades, a large number of catalysts have been reported for selective ethylene oligomerization to give mostly the C4-C20 range of α-olefins [5]. These α-olefins are used primarily in production of detergents, plasticizers and linear low density polyethylene (LLDPE) [3,4, ...
Comptes Rendus Chimie, Sep 1, 2005
Cp2Zr(CH3)R and its derivatives can serve as powerful olefin polymerization catalysts after activ... more Cp2Zr(CH3)R and its derivatives can serve as powerful olefin polymerization catalysts after activation by a Lewis acid A to form the ion-pair [Cp2ZrR]+[CH3A]– (I) which is held together by a Zr-μ-CH3A– bridge. It is generally assumed that the cation Cp2ZrR+ (II) of I is the active species whereas the influence of the anion CH3A– (III) is less well understood. We
Inorganic Chemistry, Dec 8, 2011
The possibility of metal-metal cooperativity in improving the yield of the homogeneous Water Gas ... more The possibility of metal-metal cooperativity in improving the yield of the homogeneous Water Gas Shift reaction (WGSR) has been investigated through full quantum mechanical (QM) density functional theory (DFT) calculations. The calculations indicate that bi-metallic catalysts would be likely to be more highly active than mono-nuclear metal based catalysts for the WGSR. The results have implications for the design of improved WGSR catalysts in the future.
Organometallics, 2004
Molecular oscillations of ligand motions at the active site of carbonmonoxy myoglobin have been c... more Molecular oscillations of ligand motions at the active site of carbonmonoxy myoglobin have been calculated in a protein environment using the combined QM/MM approach. In these calculations, the active site was calculated at a quantum mechanical (QM) level of theory using the B3LYP/6-31 + G* method, while the remaining protein was calculated at the molecular mechanical (MM) level utilizing the AMBER force field. The presence of a torsion mode and the second component of the bending vibration are proof of a bent CO geometry in the heme pocket.
Organometallics
Molecular oscillations of ligand motions at the active site of carbonmonoxy myoglobin have been c... more Molecular oscillations of ligand motions at the active site of carbonmonoxy myoglobin have been calculated in a protein environment using the combined QM/MM approach. In these calculations, the active site was calculated at a quantum mechanical (QM) level of theory using the B3LYP/6-31 + G* method, while the remaining protein was calculated at the molecular mechanical (MM) level utilizing the AMBER force field. The presence of a torsion mode and the second component of the bending vibration are proof of a bent CO geometry in the heme pocket.
Macromolecular Symposia
Molecular oscillations of ligand motions at the active site of carbonmonoxy myoglobin have been c... more Molecular oscillations of ligand motions at the active site of carbonmonoxy myoglobin have been calculated in a protein environment using the combined QM/MM approach. In these calculations, the active site was calculated at a quantum mechanical (QM) level of theory using the B3LYP/6-31 + G* method, while the remaining protein was calculated at the molecular mechanical (MM) level utilizing the AMBER force field. The presence of a torsion mode and the second component of the bending vibration are proof of a bent CO geometry in the heme pocket.
Dalton Trans., 2015
The protolytic cleavage of the O-H bond in water and alcohols is a very important reaction, and a... more The protolytic cleavage of the O-H bond in water and alcohols is a very important reaction, and an important method for producing dihydrogen. Full quantum chemical studies with density functional theory (DFT) reveal that germanium based complexes, such as HC{CMeArB}2GeH (Ar = 2,6-(i)Pr2C6H3), with the assistance of silicon based compounds such as SiF3H, can perform significantly better than the existing state-of-the-art post-transition metal based systems for catalyzing dihydrogen generation from water and alcohols through the protolysis reaction.
Inorganic chemistry, Jan 6, 2015
In biological oxidations, the intermediate Fe(V)(O)(OH) has been proposed to be the active specie... more In biological oxidations, the intermediate Fe(V)(O)(OH) has been proposed to be the active species for catalyzing the epoxidation of alkenes by nonheme iron complexes. However, no study has been reported yet that elucidates the mechanism of direct O-atom transfer during the reaction of Fe(V)(O) with alkenes to form the corresponding epoxide. For the first time, we study the mechanism of O-atom transfer to alkenes using the Fe(V)(O) complex of biuret-modified Fe-TAML at room temperature. The second-order rate constant (k2) for the reaction of different alkenes with Fe(V)(O) was determined under single-turnover conditions. An 8000-fold rate difference was found between electron-rich (4-methoxystyrene; k2 = 216 M(-1) s(-1)) and electron-deficient (methyl trans-cinnamate; k2 = 0.03 M(-1) s(-1)) substrates. This rate difference indicates the electrophilic character of Fe(V)(O). The use of cis-stilbene as a mechanistic probe leads to the formation of both cis- and trans-stilbene epoxides ...
Journal of Computational Chemistry, 2015
There is considerable interest presently in the chemistry of allenes. The current computational i... more There is considerable interest presently in the chemistry of allenes. The current computational investigation looks into the possibility of using allenes and their derivatives as leaving groups. As it is well known, leaving groups are significant in catalytic processes for generating the active site. A full quantum mechanical study using density functional theory shows that allenes and their derivatives can function as excellent leaving groups. Indeed, the calculations show that they can be several orders of magnitude more effective than existing ligands for this purpose. The modification of second generation Grubbs' catalysts with these ligands suggests that the allene ligand cases that would be most effective are those having electron withdrawing groups, especially those that have the potential for supramolecular interactions between the substituent groups in the free state. © 2015 Wiley Periodicals, Inc.
For the past few decades, a large number of catalysts have been reported for selective ethylene o... more For the past few decades, a large number of catalysts have been reported for selective ethylene oligomerization to give mostly the C4-C20 range of α-olefins [5]. These α-olefins are used primarily in production of detergents, plasticizers and linear low density polyethylene (LLDPE) [3,4, ...