The Experts below are selected from a list of 198 Experts worldwide ranked by ideXlab platform
Michael B Hall - One of the best experts on this subject based on the ideXlab platform.
-
theoretical studies of inorganic and Organometallic Reaction mechanisms 15 catalytic alkane dehydrogenation by iridium iii complexes
Journal of the American Chemical Society, 1999Co-Authors: Shuqiang Niu, Michael B HallAbstract:Alkane dehydrogenation catalyzed by the Ir(III) complexes (PCP‘)Ir(H)2 (1) [PCP‘ = η3-C6H3(CH2PH2)2-1,3] and CpIr(PH3)(H)+ (10) [Cp = η5-C5H5] is investigated with density functional theory (DFT). For both systems the theoretical results show that catalytic alkane dehydrogenation to alkene proceeds through (i) alkane oxidative addition, (ii) dihydride reductive elimination, (iii) β-H transfer from alkyl ligand to metal, and finally (iv) elimination of the olefin. Barriers for steps (i), (ii), and (iv) are critical for the catalytic cycle. The (PCP‘)Ir(H)2 system is special because these three barriers are balanced (16, 15, and 22 kcal/mol, respectively), whereas in the CpIr(PH3)(H)+ system these three barriers are unbalanced (9, 24, and 41 kcal/mol, respectively). Thus, in the catalytic cycle for alkane dehydrogenation by (PCP‘)Ir(H)2 the Reaction endothermicity is achieved gradually. The higher stability of the formally Ir(V) complexes and the η2-alkene complex, which has some Ir(V)-like character, in th...
-
theoretical studies of inorganic and Organometallic Reaction mechanisms 9 intermolecular versus intramolecular carbon hydrogen bond activation in zirconium rhodium and iridium complexes
Organometallics, 1996Co-Authors: Rogelio Jimenezcatano, Michael B HallAbstract:Ab initio quantum mechanical calculations were performed on model Reactions to analyze the behavior of intermolecular versus intramolecular C−H bond activation in zirconium, rhodium, and iridium co...
-
theoretical studies of inorganic and Organometallic Reaction mechanisms 3 the origin of the difference in the barrier for the kinetic and thermodynamic products for the oxidative addition of dihydrogen to a square planar iridium complex
Journal of the American Chemical Society, 1991Co-Authors: Andrew L Sargent, Michael B Hall, Martyn F GuestAbstract:The stereoselective oxidative addition of H2 to IrCl(CO)(dppe) was examined with ab initio theoretical techniques. Reaction coordinates for the two pathways to addition which lead to the formation of the two isomers were constructed from geometry optimization calculations and were augmented by significant portions of the potential energy surfaces near the transition states. The analysis of the Laplacian of the total charge densities revealed that as the complexes evolve from four-coordinate to six-coordinate species, the ligands in the plane of addition move past regions of charge concentration around the metal center. Electron withdrawing ligands in the plan of addition reduce this repulsive interaction by delocalizing a portion of the electronic charge. Electron-donor ligands are unable to function in this capacity and therefore contribute to the repulsive interaction of the five-coordinate transition state to a greater extent. The influence of electron correlation on the Reaction coordinates was examined and found not to significantly alter the conclusions based on the single-determinant calculations.
-
theoretical studies of inorganic and Organometallic Reaction mechanisms 4 the oxidative addition of dihydrogen to d8 square planar iridium complexes with trans phosphines
Inorganic Chemistry, 1991Co-Authors: Andrew L Sargent, Michael B HallAbstract:The oxidative addition of H2 to Vaska-type complexes, transIrX(CO)(PR3)2, are investigated with ab initio quantum chemical calculations. The direction of addition in these complexes is controlled by how the ligands in the plane od addition react to a close encounter with concentrations of charge density around the metal center as the complex evolves from a four-coordinate to a six-coordinate species. Strong electron donating ligands destabilize the five-coordinate transition state while electron withdrawing ligands stabilize the transition state. When X is a weak electron donor ligand such as Cl-, H2 adds in the Cl-Ir-Co plane. When X=Hor Ph-, however, H2 adds in the PR3-IR-PR3 plane; the destabilizing influence of these strong electron donating ligands on the transition state outweigh those of the PR3 ligands. The electronic contribution to the relative stabilities of the six-coordinate final products can be predicted based on the relative orientations of the strongest trans-influence ligands. The isomers in which these ligands are facial are lower in energy than those in which they are meridional.
Andrew L Sargent - One of the best experts on this subject based on the ideXlab platform.
-
Utility of the Nudged Elastic Band Method in Identifying the Minimum Energy Path of an Elementary Organometallic Reaction Step
Organometallics, 2016Co-Authors: Kate E. Mcpherson, Libero J. Bartolotti, Andrew T. Morehead, Andrew L SargentAbstract:The nudged elastic band (NEB) method has been used to re-examine the oxidative addition step in the classic rhodium-catalyzed hydroacylation Reaction. Numerous additional intermediates were found on a pathway that is lower in energy than that originally reported. This study illustrates the potential limitations of the traditional approach to locating transition states in which a chemical-intuition-guided linear or quadratic synchronous transit is used to estimate the high point of the Reaction trajectory. Utilization of that approach constrains the search so that the actual transition state and other possible intermediates and transition states may be missed.
-
theoretical studies of inorganic and Organometallic Reaction mechanisms 3 the origin of the difference in the barrier for the kinetic and thermodynamic products for the oxidative addition of dihydrogen to a square planar iridium complex
Journal of the American Chemical Society, 1991Co-Authors: Andrew L Sargent, Michael B Hall, Martyn F GuestAbstract:The stereoselective oxidative addition of H2 to IrCl(CO)(dppe) was examined with ab initio theoretical techniques. Reaction coordinates for the two pathways to addition which lead to the formation of the two isomers were constructed from geometry optimization calculations and were augmented by significant portions of the potential energy surfaces near the transition states. The analysis of the Laplacian of the total charge densities revealed that as the complexes evolve from four-coordinate to six-coordinate species, the ligands in the plane of addition move past regions of charge concentration around the metal center. Electron withdrawing ligands in the plan of addition reduce this repulsive interaction by delocalizing a portion of the electronic charge. Electron-donor ligands are unable to function in this capacity and therefore contribute to the repulsive interaction of the five-coordinate transition state to a greater extent. The influence of electron correlation on the Reaction coordinates was examined and found not to significantly alter the conclusions based on the single-determinant calculations.
-
theoretical studies of inorganic and Organometallic Reaction mechanisms 4 the oxidative addition of dihydrogen to d8 square planar iridium complexes with trans phosphines
Inorganic Chemistry, 1991Co-Authors: Andrew L Sargent, Michael B HallAbstract:The oxidative addition of H2 to Vaska-type complexes, transIrX(CO)(PR3)2, are investigated with ab initio quantum chemical calculations. The direction of addition in these complexes is controlled by how the ligands in the plane od addition react to a close encounter with concentrations of charge density around the metal center as the complex evolves from a four-coordinate to a six-coordinate species. Strong electron donating ligands destabilize the five-coordinate transition state while electron withdrawing ligands stabilize the transition state. When X is a weak electron donor ligand such as Cl-, H2 adds in the Cl-Ir-Co plane. When X=Hor Ph-, however, H2 adds in the PR3-IR-PR3 plane; the destabilizing influence of these strong electron donating ligands on the transition state outweigh those of the PR3 ligands. The electronic contribution to the relative stabilities of the six-coordinate final products can be predicted based on the relative orientations of the strongest trans-influence ligands. The isomers in which these ligands are facial are lower in energy than those in which they are meridional.
Toshiaki Matsubara - One of the best experts on this subject based on the ideXlab platform.
-
Application of the ONIOM-molecular dynamics method to the Organometallic Reaction cis-(H)2Pt(PR3)2 --> H2 + Pt(PR3)2 (R=H, Me, Ph, and t-Bu). An insight into the dynamical environmental effects.
The journal of physical chemistry. A, 2008Co-Authors: Toshiaki MatsubaraAbstract:The ONIOM-molecular dynamics (MD) method, which we recently developed, is applied to one of representative Organometallic Reactions, cis-(H) 2 Pt(PR 3 ) 2 → H 2 + Pt(PR 3 ) 2 (R = H, Me, Ph, and t-Bu) to give an insight into the dynamical effects of the environment on the Reaction. We adopted the two-layered ONIOM methodology and divided the system into the inner part of cis-(H) 2 Pt(PH 3 ) 2 and the outer part of the others. The inner and outer parts are treated by the quantum mechanics (QM) method at the HF level of theory and the molecular mechanics (MM) method with the MM3 force field, respectively. The ONIOM-MD simulations show that the thermal motion of the outer part increases the magnitude of the energy fluctuations of the inner part and promotes the H 2 elimination Reaction. These dynamical environmental effects increase in the order, t-Bu > Ph > Me > H, indicating that the reactivity of cis-(H) 2 Pt(PR 3 ) 2 increases in the same order. These results are also supported by an equation derived from the Arrhenius' equation (Matsubara's equation). The snapshots of the Reaction for R = t-Bu clearly indicate the new feature of the H 2 elimination process.
-
application of the new integrated mo mm imomm method to the Organometallic Reaction pt pr3 2 h2 r h me t bu and ph
The Journal of Physical Chemistry, 1996Co-Authors: Toshiaki Matsubara, Feliu Maseras, Nobuaki Koga, Keiji MorokumaAbstract:An application of the newly developed “Integrated MO + MM (IMOMM)” method to the oxidative addition of H2 to Pt(PR3)2 (R = H, Me, t-Bu, and Ph) complex is presented. In the IMOMM method, an active part of the system is handled by the MO method, the remainder is treated by the molecular mechanics force field, and the geometry is optimized fully using the sum of MO and MM energies. A comparison of full MO(RHF) results with the IMOMM(RHF:MM3) results indicates that the IMOMM method can reproduce the MO optimized geometry and energetics very well. The transition state structure for the sterically congested system changes substantially from that of the less congested system. The energetics at the more reliable IMOMM(MP2:MM3) level shows that, while for R = H, Me, and Ph the early coplanar transition state with a low barrier leads to the cis-product, for R = t-Bu the relatively late nonplanar transition state has a high barrier, making the oxidative addition Reaction difficult to take place.
Charles B Harris - One of the best experts on this subject based on the ideXlab platform.
-
ultrafast infrared studies of the role of spin states in Organometallic Reaction dynamics
Accounts of Chemical Research, 2014Co-Authors: Justin P Lomont, Son C Nguyen, Charles B HarrisAbstract:ConspectusThe importance of spin state changes in Organometallic Reactions is a topic of significant interest, as an increasing number of Reaction mechanisms involving changes of spin state are consistently being uncovered. The potential influence of spin state changes on Reaction rates can be difficult to predict, and thus this class of Reactions remains among the least well understood in Organometallic chemistry. Ultrafast time-resolved infrared (TRIR) spectroscopy provides a powerful tool for probing the dynamics of spin state changes in Organometallic catalysis, as such processes often occur on the picosecond to nanosecond time scale and can readily be monitored in the infrared via the absorptions of carbonyl reporter ligands. In this Account, we summarize recent work from our group directed toward identifying trends in reactivity that can be used to offer predictive insight into the dynamics of coordinatively unsaturated Organometallic Reaction intermediates.In general, coordinatively unsaturated 16-...
-
reactivity of tempo toward 16 and 17 electron Organometallic Reaction intermediates a time resolved ir study
Journal of the American Chemical Society, 2013Co-Authors: Justin P Lomont, Son C Nguyen, Charles B HarrisAbstract:The (2,2,6,6-tetramethylpiperidin-1-yl)oxyl radical (TEMPO) has been employed for an extensive range of chemical applications, ranging from Organometallic catalysis to serving as a structural probe in biological systems. As a ligand in an Organometallic complex, TEMPO can exhibit several distinct coordination modes. Here we use ultrafast time-resolved infrared spectroscopy to study the reactivity of TEMPO toward coordinatively unsaturated 16- and 17-electron Organometallic Reaction intermediates. TEMPO coordinates to the metal centers of the 16-electron species CpCo(CO) and Fe(CO)4, and to the 17-electron species CpFe(CO)2 and Mn(CO)5, via an associative mechanism with concomitant oxidation of the metal center. In these adducts, TEMPO thus behaves as an anionic ligand, characterized by a pyramidal geometry about the nitrogen center. Density functional theory calculations are used to facilitate interpretation of the spectra and to further explore the structures of the TEMPO adducts. To our knowledge, this ...
Roger Alberto - One of the best experts on this subject based on the ideXlab platform.
-
direct synthesis of tricarbonyl cyclopentadienyl rhenium and tricarbonyl cyclopentadienyl technetium units from ferrocenyl moieties preparation of 17α ethynylestradiol derivatives bearing a tricarbonyl cyclopentadienyl technetium group
European Journal of Inorganic Chemistry, 2004Co-Authors: Stephane Masi, Siden Top, Leila Boubekeur, Gerard Jaouen, Stefan Mundwiler, Bernhard Spingler, Roger AlbertoAbstract:The preparation of new tricarbonyl(cyclopentadienyl)rhenium and tricarbonyl(cyclopentadienyl)technetium derivatives is described. The approach used was applied to a cold target model, 17α-ethynylestradiol substituted at the 17α position by a ketotricarbonyl(cyclopentadienyl)rhenium group. The novel Organometallic Reaction applied here, when extended to potential radiopharmaceuticals, consists of a cyclopentadienyl-ligand transfer between ketoferrocenes and fac-[99mTc(H2O)3(CO)3]+ in a water/DMSO 1:1 mixture. This Reaction lead to the synthesis of a new estradiol derivative, labeled with 99mTc. The synthesis of another product was performed by using [99TcCl3(CO)3]2− as the Tc precursor and its X-ray crystal structure was determined. In each case high yields were obtained. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)