Hydrovinylation of Olefins Catalyzed by an Iridium Complex via CH Activation

Olefin dimerizations are typically proposed to proceed via a Cossee−Arlman type migratory mechanism involving relatively electron-rich metal hydrides. We provide experimental evidence and theoretical calculations that show, in contrast, relatively electron-poor O-donor Ir complexes can catalyze the dimerization of olefins via a mechanism that involves olefin CH bond activation and insertion into a metal−vinyl intermediate

Benzene C−H Bond Activation in Carboxylic Acids Catalyzed by O-Donor Iridium(III) Complexes: An Experimental and Density Functional Study

The mechanism of benzene C−H bond activation by [Ir(μ-acac-O,O,C^3)(acac-O,O)(OAc)]_2 (4) and [Ir(μ-acac-O,O,C^3)(acac-O,O)(TFA)]_2 (5) complexes (acac = acetylacetonato, OAc = acetate, and TFA = trifluoroacetate) was studied experimentally and theoretically. Hydrogen−deuterium (H/D) exchange between benzene and CD_(3)COOD solvent catalyzed by 4 (ΔH^‡ = 28.3 ± 1.1 kcal/mol, ΔS^‡ = 3.9 ± 3.0 cal K^(−1) mol^(−1)) results in a monotonic increase of all benzene isotopologues, suggesting that once benzene coordinates to the iridium center, there are multiple H/D exchange events prior to benzene dissociation. B3LYP density functional theory (DFT) calculations reveal that this benzene isotopologue pattern is due to a rate-determining step that involves acetate ligand dissociation and benzene coordination, which is then followed by heterolytic C−H bond cleavage to generate an iridium-phenyl intermediate. A synthesized iridium-phenyl intermediate was also shown to be competent for H/D exchange, giving similar rates to the proposed catalytic systems. This mechanism nicely explains why hydroarylation between benzene and alkenes is suppressed in the presence of acetic acid when catalyzed by [Ir(μ-acac-O,O,C^3)(acac-O,O)(acac-C^3)]_2 (3) (Matsumoto et al. J. Am. Chem. Soc. 2000, 122, 7414). Benzene H/D exchange in CF_(3)COOD solvent catalyzed by 5 (ΔH^‡ = 15.3 ± 3.5 kcal/mol, ΔS^‡ = −30.0 ± 5.1 cal K^(−1) mol^(−1)) results in significantly elevated H/D exchange rates and the formation of only a single benzene isotopologue, (C_(6)H_(5)D). DFT calculations show that this is due to a change in the rate-determining step. Now equilibrium between coordinated and uncoordinated benzene precedes a single rate-determining heterolytic C−H bond cleavage step

Synthesis, Structure, and Reactivity of O-Donor Ir(III) Complexes: C−H Activation Studies with Benzene

Various new thermally air- and water-stable alkyl and aryl analogues of (acac-O,O)_2Ir(R)(L), R−Ir−L (acac-O,O = κ^2-O,O-acetylacetonate, −Ir− is the trans-(acac-O,O)_2Ir(III) motif, R = CH_3, C_2H_5, Ph, PhCH_2CH_2, L = Py) have been synthesized using the dinuclear complex [Ir(μ-acac-O,O,C^3)−(acac-O,O)(acac-C^3)]_2, [acac-C−Ir]_2, or acac-C−Ir−H_2O. The dinuclear Ir (III) complexes, [Ir(μ-acac-O,O,C^3)−(acac-O,O)(R)]_2 (R = alkyl), show fluxional behavior with a five-coordinate, 16 electron complex by a dissociative pathway. The pyridine adducts, R−Ir−Py, undergo degenerate Py exchange via a dissociative mechanism with activation parameters for Ph−Ir−Py (ΔH^‡ = 22.8 ± 0.5 kcal/mol; ΔS^‡ = 8.4 ± 1.6 eu; ΔG^‡_(298K) = 20.3 ± 1.0 kcal/mol) and CH_3−Ir−Py (ΔH^‡ = 19.9 ± 1.4 kcal/mol; ΔS^‡ = 4.4 ± 5.5 eu; ΔG^‡_(298K) = 18.6 ± 0.5 kcal/mol). The trans complex, Ph−Ir−Py, undergoes quantitatively trans-cis isomerization to generate cis-Ph−Ir−Py on heating. All the R−Ir−Py complexes undergo quantitative, intermolecular CH activation reactions with benzene to generate Ph−Ir−Py and RH. The activation parameters (ΔS^‡ =11.5 ± 3.0 eu; ΔH^‡ = 41.1 ± 1.1 kcal/mol; ΔG^‡_(298k) = 37.7 ± 1.0 kcal/mol) for CH activation were obtained using CH_3−Ir−Py as starting material at a constant ratio of [Py]/[C_6D_6] = 0.045. Overall the CH activation reaction with R−Ir−Py has been shown to proceed via four key steps:  (A) pre-equilibrium loss of pyridine that generates a trans-five-coordinate, square pyramidal intermediate; (B) unimolecular, isomerization of the trans-five-coordinate to generate a cis-five-coordinate intermediate, cis-R−Ir-□; (C) rate-determining coordination of this species to benzene to generate a discrete benzene complex, cis-R−Ir−PhH; and (D) rapid C−H cleavage. Kinetic isotope effects on the CH activation with mixtures of C_6H_6/C_6D_6 (KIE = 1) and with 1,3,5-C_6H_3D_3 (KIE ∼3.2 at 110 °C) are consistent with this reaction mechanism

Osmotic reflection coefficient

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2009.Includes bibliographical references (leaves 149-152).The presence of a discriminating barrier separating two solutions differing in concentration generates a net volume flux called osmotic flow. The simple case is of the ideal semi-permeable membrane which completely excludes the solute. The flow through such a membrane is directly proportional to the thermodynamic pressure drop less the osmotic pressure drop. For membranes which partially exclude the solute the osmotic contribution to flow is less than that of the semi-permeable membrane, and the reduction is given by the osmotic reflection coefficient [sigma]o,. This work was motivated by understanding the mechanistic aspects of osmotic flow through such membranes, in order to predict [sigma]o. One of the main goals of the research was to develop computational models to predict [sigma]o for charged porous membranes and charged fibrous membranes. The effects of molecular shape on [sigma]o for rigid macromolecules in porous membranes were analyzed using a hydrodynamic model. In this type of model, employed first by Anderson and Malone, steric exclusion of the solute from the periphery of the pore induces a concentration-dependent drop in pressure near the pore wall, which in turn causes the osmotic flow (Anderson and Malone 1974). Results were obtained for prolate spheroids (axial ratio, [gamma] > 1) and oblate spheroids ([gamma] < 1) in cylindrical and slit pores. Two methods, one of which is novel, were used to compute the transverse pressure variation. Although conceptually different, they yielded very similar results; the merits of each are discussed. For a given value of a/R, where a is the prolate minor semiaxis or oblate major semiaxis and R is the pore radius, [sigma]o, increased monotonically with increasing [gamma]. When expressed as a function of aSEIR, where asE is the Stokes-Einstein radius, the effects of molecular shape were less pronounced, but still significant. The trends for slits were qualitatively similar to those for cylindrical pores. When [sigma]o was plotted as a function of the equilibrium partition coefficient, the results for all axial ratios fell on a single curve for a given pore shape, although the curve for cylindrical pores differed from that for slits. For spheres ([gamma]= 1) in either pore shape, [sigma]o was found to be only slightly smaller than the reflection coefficient for filtration (of). That suggests that [sigma]o can be used to estimate of for spheroids, where results are currently lacking. A computational model was developed to predict the effects of solute and pore charge on [sigma]o, of spherical macromolecules in cylindrical pores. Results were obtained for articles and pores of like charge and fixed surface charge densities, using a theory that combined low Reynolds number hydrodynamics with a continuum, point-charge description of the electrical double layers. In this formulation steric and/or electrostatic exclusion of macromolecules from the vicinity of the pore wall creates radial variations in osmotic pressure. These, in turn, lead to the axial pressure gradient that drives the osmotic flow. Due to the stronger exclusion that results from repulsive electrostatic nteractions, ao, with charge effects always exceeded that for an uncharged system with the same solute and pore size. The effects of charge stemmed almost entirely from particle positions within a pore being energetically unfavorable. It was found that the required potential energy could be computed with sufficient accuracy using the linearized Poisson-Boltzmann equation, high charge densities notwithstanding. In principle, another factor that might influence o in charged pores is the electrical body force due to the streaming potential. However, the streaming potential was shown to have little effect on [sigma]o, even when it markedly reduced the apparent hydraulic permeability. A model based on continuum hydrodynamics and electrostatics was developed to predict the combined effects of molecular charge and size on the o, of a macromolecule in a fibrous membrane, such as a biological hydrogel. The macromolecule was represented as a sphere with a constant surface charge density, and the membrane was assumed to consist of an array of parallel fibers of like charge, also with a constant surface charge density. The flow was assumed to be parallel to the fiber axes. The effects of charge were incorporated into the model by computing the electrostatic free energy for a sphere interacting with an array of fibers. It was shown that this energy could be approximated using a pairwise additivity assumption. Results for [sigma]o, were obtained for two types of negatively charged fibers, one with properties like those of glycosaminoglycan chains, and(cont.) the other for thicker fibers having a range of charge densities. Using physiologically reasonable fiber spacings and charge densities, [sigma]o, for BSA in either type of fiber array was shown to be much larger than (often double) that for an uncharged system. Given the close correspondence between [sigma]o and the [sigma]f; the results suggest that the negative charge of structures such as the endothelial surface glycocalyx is important in minimizing albumin loss from the circulation.by Gaurav Bhalla.Ph.D

The Host Scaffolding Protein Filamin A and the Exocyst Complex Control Exocytosis during InlB-Mediated Entry of Listeria monocytogenes.

Listeria monocytogenes is a foodborne bacterium that causes gastroenteritis, meningitis, or abortion. Listeria induces its internalization (entry) into some human cells through interaction of the bacterial surface protein InlB with its host receptor, the Met tyrosine kinase. InlB and Met promote entry, in part, through stimulation of localized exocytosis. How exocytosis is upregulated during entry is not understood. Here, we show that the human signaling proteins mTOR, protein kinase C-α (PKC-α), and RalA promote exocytosis during entry by controlling the scaffolding protein Filamin A (FlnA). InlB-mediated uptake was accompanied by PKC-α-dependent phosphorylation of serine 2152 in FlnA. Depletion of FlnA by RNA interference (RNAi) or expression of a mutated FlnA protein defective in phosphorylation impaired InlB-dependent internalization. These findings indicate that phosphorylation of FlnA by PKC-α contributes to entry. mTOR and RalA were found to mediate the recruitment of FlnA to sites of InlB-mediated entry. Depletion of PKC-α, mTOR, or FlnA each reduced exocytosis during InlB-mediated uptake. Because the exocyst complex is known to mediate polarized exocytosis, we examined if PKC-α, mTOR, RalA, or FlnA affects this complex. Depletion of PKC-α, mTOR, RalA, or FlnA impaired recruitment of the exocyst component Exo70 to sites of InlB-mediated entry. Experiments involving knockdown of Exo70 or other exocyst proteins demonstrated an important role for the exocyst complex in uptake of Listeria Collectively, our results indicate that PKC-α, mTOR, RalA, and FlnA comprise a signaling pathway that mobilizes the exocyst complex to promote infection by Listeria

CH Activation with an O-Donor Iridium−Methoxo Complex

A thermally and air stable O-donor, iridium−methoxo complex is reported that undergoes stoichiometric, intermolecular C−H activation of benzene with co-generation of methanol and the iridium−phenyl complex

IoT-Enhanced Public Safety in Smart Environments: A Comparative Analysis Using the Public Safety IoT Test

The present study does a comparative analysis to evaluate the efficacy of public safety measures boosted by the Internet of Things (IoT) in various smart settings. The "Public Safety IoT Test" methodology is used in the research to evaluate costs, user happiness, and safety improvement percentages. Smart Surveillance devices showed a noteworthy 35% increase in safety in metropolitan City A, while Wearable Health devices showed a surprising 40% increase in safety in rural Village D. At a cost of $500,000 in City A and$10,000 in Village D, these results emphasize the potential of IoT technology to improve public safety and well-being. User satisfaction scores of 4 and 5, respectively, demonstrate the acceptance and efficacy of these devices. Policymakers and urban planners may benefit greatly from this study, which highlights the flexibility of IoT devices in a variety of smart settings and their important role in creating communities that are safer and more resilient

Mechanism of efficient anti-Markovnikov olefin hydroarylation catalyzed by homogeneous Ir(III) complexes

The mechanism of the hydroarylation reaction between unactivated olefins (ethylene, propylene, and styrene) and benzene catalyzed by [(R)Ir(μ-acac-O,O,C^3)-(acac-O,O)_2]_2 and [R-Ir(acac-O,O)_2(L)] (R = acetylacetonato, CH_3, CH_2CH_3, Ph, or CH_2CH_2Ph, and L = H_2O or pyridine) Ir(III) complexes was studied by experimental methods. The system is selective for generating the anti-Markovnikov product of linear alkylarenes (61 : 39 for benzene + propylene and 98 : 2 for benzene + styrene). The reaction mechanism was found to follow a rate law with first-order dependence on benzene and catalyst, but a non-linear dependence on olefin. ^(13)C-labelling studies with CH_3^(13)CH_2-Ir-Py showed that reversible β-hydride elimination is facile, but unproductive, giving exclusively saturated alkylarene products. The migration of the ^(13)C-label from the α to β-positions was found to be slower than the C–H activation of benzene (and thus formation of ethane and Ph-d_5-Ir-Py). Kinetic analysis under steady state conditions gave a ratio of the rate constants for CH activation and β-hydride elimination (k_(CH): k_β) of 0.5. The comparable magnitude of these rates suggests a common rate determining transition state/intermediate, which has been shown previously with B3LYP density functional theory (DFT) calculations. Overall, the mechanism of hydroarylation proceeds through a series of pre-equilibrium dissociative steps involving rupture of the dinuclear species or the loss of L from Ph-Ir-L to the solvento, 16-electron species, Ph-Ir(acac-O,O)_2-Sol (where Sol refers to coordinated solvent). This species then undergoes trans to cis isomerization of the acetylacetonato ligand to yield the pseudo octahedral species cis-Ph-Ir-Sol, which is followed by olefin insertion (the regioselective and rate determining step), and then activation of the C–H bond of an incoming benzene to generate the product and regenerate the catalyst