• Oxidative Addition • Reductive Elimination • Migratory Insertion • Β - Hydrogen Elimination AJELIAS L7-S2 Oxidative Addition
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Crystal Structures
Crystal Structures Academic Resource Center Crystallinity: Repeating or periodic array over large atomic distances. 3-D pattern in which each atom is bonded to its nearest neighbors Crystal structure: the manner in which atoms, ions, or molecules are spatially arranged. Unit cell: small repeating entity of the atomic structure. The basic building block of the crystal structure. It defines the entire crystal structure with the atom positions within. Lattice: 3D array of points coinciding with atom positions (center of spheres) Metallic Crystal Structures FCC (face centered cubic): Atoms are arranged at the corners and center of each cube face of the cell. FCC continued Close packed Plane: On each face of the cube Atoms are assumed to touch along face diagonals. 4 atoms in one unit cell. a 2R 2 BCC: Body Centered Cubic • Atoms are arranged at the corners of the cube with another atom at the cube center. BCC continued • Close Packed Plane cuts the unit cube in half diagonally • 2 atoms in one unit cell 4R a 3 Hexagonal Close Packed (HCP) • Cell of an HCP lattice is visualized as a top and bottom plane of 7 atoms, forming a regular hexagon around a central atom. In between these planes is a half- hexagon of 3 atoms. • There are two lattice parameters in HCP, a and c, representing the basal and height parameters Volume respectively. 6 atoms per unit cell Coordination number – the number of nearest neighbor atoms or ions surrounding an atom or ion. For FCC and HCP systems, the coordination number is 12. For BCC it’s 8. -
Crystal Structure of a Material Is Way in Which Atoms, Ions, Molecules Are Spatially Arranged in 3-D Space
Crystalline Structures – The Basics •Crystal structure of a material is way in which atoms, ions, molecules are spatially arranged in 3-D space. •Crystal structure = lattice (unit cell geometry) + basis (atom, ion, or molecule positions placed on lattice points within the unit cell). •A lattice is used in context when describing crystalline structures, means a 3-D array of points in space. Every lattice point must have identical surroundings. •Unit cell: smallest repetitive volume •Each crystal structure is built by stacking which contains the complete lattice unit cells and placing objects (motifs, pattern of a crystal. A unit cell is chosen basis) on the lattice points: to represent the highest level of geometric symmetry of the crystal structure. It’s the basic structural unit or building block of crystal structure. 7 crystal systems in 3-D 14 crystal lattices in 3-D a, b, and c are the lattice constants 1 a, b, g are the interaxial angles Metallic Crystal Structures (the simplest) •Recall, that a) coulombic attraction between delocalized valence electrons and positively charged cores is isotropic (non-directional), b) typically, only one element is present, so all atomic radii are the same, c) nearest neighbor distances tend to be small, and d) electron cloud shields cores from each other. •For these reasons, metallic bonding leads to close packed, dense crystal structures that maximize space filling and coordination number (number of nearest neighbors). •Most elemental metals crystallize in the FCC (face-centered cubic), BCC (body-centered cubic, or HCP (hexagonal close packed) structures: Room temperature crystal structure Crystal structure just before it melts 2 Recall: Simple Cubic (SC) Structure • Rare due to low packing density (only a-Po has this structure) • Close-packed directions are cube edges. -
Tetrahedral Coordination with Lone Pairs
TETRAHEDRAL COORDINATION WITH LONE PAIRS In the examples we have discussed so far, the shape of the molecule is defined by the coordination geometry; thus the carbon in methane is tetrahedrally coordinated, and there is a hydrogen at each corner of the tetrahedron, so the molecular shape is also tetrahedral. It is common practice to represent bonding patterns by "generic" formulas such as AX4, AX2E2, etc., in which "X" stands for bonding pairs and "E" denotes lone pairs. (This convention is known as the "AXE method") The bonding geometry will not be tetrahedral when the valence shell of the central atom contains nonbonding electrons, however. The reason is that the nonbonding electrons are also in orbitals that occupy space and repel the other orbitals. This means that in figuring the coordination number around the central atom, we must count both the bonded atoms and the nonbonding pairs. The water molecule: AX2E2 In the water molecule, the central atom is O, and the Lewis electron dot formula predicts that there will be two pairs of nonbonding electrons. The oxygen atom will therefore be tetrahedrally coordinated, meaning that it sits at the center of the tetrahedron as shown below. Two of the coordination positions are occupied by the shared electron-pairs that constitute the O–H bonds, and the other two by the non-bonding pairs. Thus although the oxygen atom is tetrahedrally coordinated, the bonding geometry (shape) of the H2O molecule is described as bent. There is an important difference between bonding and non-bonding electron orbitals. Because a nonbonding orbital has no atomic nucleus at its far end to draw the electron cloud toward it, the charge in such an orbital will be concentrated closer to the central atom. -
Bimetallic Catalyst Catalyzed Carbonylation of Methanol to Acetic Acid
materials Article Study on Rh(I)/Ru(III) Bimetallic Catalyst Catalyzed Carbonylation of Methanol to Acetic Acid Shasha Zhang 1, Wenxin Ji 1,2,*, Ning Feng 2, Liping Lan 1, Yuanyuan Li 1,2 and Yulong Ma 1,2 1 College of Chemistry and Chemical Engineering, Ningxia University, Yinchuan 750021, China; [email protected] (S.Z.); [email protected] (L.L.); [email protected] (Y.L.); [email protected] (Y.M.) 2 State Key Laboratory of High-efficiency Utilization of Coal and Green Chemical Engineering, Ningxia University, Yinchuan 750021, China; [email protected] * Correspondence: [email protected]; Tel.: +86-135-1957-9989; Fax: +86-951-206-2323 Received: 13 July 2020; Accepted: 3 September 2020; Published: 11 September 2020 Abstract: In this study, a Rh(I)/Ru(III) catalyst with a bimetallic space structure was designed and synthesized. The interaction between the metals of the bimetallic catalyst and the structure of the bridged dimer can effectively reduce the steric hindrance effect and help speed up the reaction rate while ensuring the stability of the catalyst. X-ray photoelectron spectroscopy (XPS) results show that rhodium accepts electrons from chlorine, thereby increasing the electron-rich nature of rhodium and improving the catalytic activity. This promotes the nucleophilic reaction of the catalyst with methyl iodide and reduces the reaction energy barrier. The methanol carbonylation performance of the Rh/Ru catalyst was evaluated, and the results show that the conversion rate of methyl acetate and the yield of acetic acid are 96.0% under certain conditions. Furthermore, during the catalysis, no precipitate is formed and the amount of water is greatly reduced. -
Oxidative Addition & Reductive Elimination
3/1/2021 Oxidative Addition & Reductive Elimination Robert H. Crabtree: Pages 159 – 182 and 235 - 266 1 Oxidative Addition Change in Example Group configuration • Oxidative addition is a key step in many transition-metal catalyzed reactions 10 8 I III • Basic reaction: d d Cu Cu 11 X X Pd0 PdII 10 LnM + LnM Pt0 PtII 10 Y Y d8 d6 PdII PdIV 10 • The new M-X and M-Y bonds are formed using the electron pair of the X-Y PtII PtIV 10 bond and one metal-centered lone pair IrI IrIII 9 RhI RhIII 9 • The metal goes up in oxidation state (+2), X-Y formally gets reduced to X-, Y- d6 d4 ReI ReIII 7 • The ease of addition (or elimination) can be tuned by the electronic and 0 II steric properties of the ancillary ligands Mo Mo 6 • OA favored by strongly e-donating L d4 d2 MoII MoIV 6 • The most common applications involve: a) Late transition metals (platinum metals: Ru, Rh, Pd, Ir, Pt) - not d7 d6 2CoII 2CoIII 9 too sensitive to O2 and H2O; routinely used in organic synthesis b) C-Halogen, H-H or Si-H bonds d4 d3 2CrII 2CrIII 6 • Common for transition metals, rare for main-group metals but: Grignard reagents! 2 1 3/1/2021 Oxidative addition – concerted mechanism Concerted addition - mostly with non-polar X-Y bonds X X X LnM + LnM LnM Y Y Y A Cr(CO)5: • H2, silanes, alkanes, ... coordinatively Cr(PMe3)5: • Arene C-H bonds more reactive than alkane C-H bonds unsaturated, but metal- centered lone pairs not phosphines are better • H-H, C-H strong bond, but M-H and M-C bonds can be very available donors, weaker acceptors full oxidative -
Chemical Kinetics HW1 (Kahn, 2010)
Chemical Kinetics HW1 (Kahn, 2010) Question 1. (6 pts) A reaction with stoichiometry A = P + 2Q was studied by monitoring the concentration of the reactant A as a function of time for eighteen minutes. The concentration determination method had a maximum error of 6 M. The following concentration profile was observed: Time (min) Conc (mM) 1 0.9850 2 0.8571 3 0.7482 4 0.6549 5 0.5885 6 0.5183 7 0.4667 8 0.4281 9 0.3864 10 0.3557 11 0.3259 12 0.3037 13 0.2706 14 0.2486 15 0.2355 16 0.2188 17 0.2111 18 0.1930 Determine the reaction order and calculate the rate constant for decomposition of A. What can be said about the mechanism or molecularity of this reaction? Question 2. (4 pts) Solve problem 2 on pg 31 in your textbook (House) using both linear and non-linear regression. Provide standard errors for the rate constant and half-life based on linear and non-linear fits. Below is the data set for your convenience: dataA = {{0, 0.5}, {10, 0.443}, {20,0.395}, {30,0.348}, {40,0.310}, {50,0.274}, {60,0.24}, {70,0.212}, {80,0.190}, {90,0.171}, {100,0.164}} Question 3. (3 pts) Solve problem 3 on pg 32 in your textbook (House). Question 4. (7 pts) The authors of the paper “Microsecond Folding of the Cold Shock Protein Measured by a Pressure-Jump Technique” suggest that the activated state of folding of CspB follows Hammond- type behavior. -
Oxidative Addition of Polar Reagents
OXIDATIVE ADDITION OF POLAR REAGENTS Organometallic chemistry has vastly expanded the practicing organic chemist’s notion of what makes a good nucleophile or electrophile. Pre-cross-coupling, for example, using unactivated aryl halides as electrophiles was largely a pipe dream (or possible only under certain specific circumstances). Enter the oxidative addition of polarized bonds: all of a sudden, compounds like bromobenzene started looking a lot more attractive as starting materials. Cross-coupling reactionsinvolving sp2- and sp-hybridized C–X bonds beautifully complement the “classical” substitution reactions at sp3electrophilic carbons. Oxidative addition of the C–X bond is the step that kicks off the magic of these methods. In this post, we’ll explore the mechanisms and favorability trends of oxidative additions of polar reagents. The landscape of mechanistic possibilities for polarized bonds is much more rich than in the non-polar case—concerted, ionic, and radical mechanisms have all been observed. Concerted Mechanisms 2 Oxidative additions of aryl and alkenyl Csp –X bonds, where X is a halogen or sulfonate, proceed through concertedmechanisms analogous to oxidative additions of dihydrogen. Reactions of N–H and O–H bonds in amines, alcohols, and water also appear to be concerted. A π complex involving η2-coordination is an intermediate in the mechanism of insertion into aryl halides at least, and probably vinyl halides too. As two open coordination sites are necessary for concerted oxidative addition, loss of a ligand from a saturated metal complex commonly precedes the actual oxidative addition event. Concerted oxidative addition of aryl halides and sulfonates. Trends in the reactivity of alkyl and aryl (pseudo)halides toward oxidative addition are some of the most famous in organometallic chemistry. -
Graphene Supported Rhodium Nanoparticles for Enhanced Electrocatalytic Hydrogen Evolution Reaction Ameerunisha Begum1*, Moumita Bose2 & Golam Moula2
www.nature.com/scientificreports OPEN Graphene Supported Rhodium Nanoparticles for Enhanced Electrocatalytic Hydrogen Evolution Reaction Ameerunisha Begum1*, Moumita Bose2 & Golam Moula2 Current research on catalysts for proton exchange membrane fuel cells (PEMFC) is based on obtaining higher catalytic activity than platinum particle catalysts on porous carbon. In search of a more sustainable catalyst other than platinum for the catalytic conversion of water to hydrogen gas, a series of nanoparticles of transition metals viz., Rh, Co, Fe, Pt and their composites with functionalized graphene such as RhNPs@f-graphene, CoNPs@f-graphene, PtNPs@f-graphene were synthesized and characterized by SEM and TEM techniques. The SEM analysis indicates that the texture of RhNPs@f- graphene resemble the dispersion of water droplets on lotus leaf. TEM analysis indicates that RhNPs of <10 nm diameter are dispersed on the surface of f-graphene. The air-stable NPs and nanocomposites were used as electrocatalyts for conversion of acidic water to hydrogen gas. The composite RhNPs@f- graphene catalyses hydrogen gas evolution from water containing p-toluene sulphonic acid (p-TsOH) at an onset reduction potential, Ep, −0.117 V which is less than that of PtNPs@f-graphene (Ep, −0.380 V) under identical experimental conditions whereas the onset potential of CoNPs@f-graphene was at Ep, −0.97 V and the FeNPs@f-graphene displayed onset potential at Ep, −1.58 V. The pure rhodium nanoparticles, RhNPs also electrocatalyse at Ep, −0.186 V compared with that of PtNPs at Ep, −0.36 V and that of CoNPs at Ep, −0.98 V. -
Organometallic Chemistry BASIC PRINCIPLES, APPLICATIONS, and a FEW CASE STUDIES
Safety Moment TYLER LAB GROUP MEETING 1 Safety Moment TYLER LAB GROUP MEETING 2 Metal Hydrides: Benchtop vs. Box Hydride = :H- Hydrides are powerful Lewis bases and reducing agent ◦ Exothermically form H2 (this should scare you) ◦ Heating leads to faster reactivity ◦ H evolution leads to rapid increase in pressure2 ◦ Uncontrolled reactions easily cause runaway exotherm, class D fire, explosion, and death/unemployment LiAlH is the #1 chemical cause of fatality in chemical4 industry 3 Metal Hydrides: “I want to commit the murder I was imprisoned for†.” LiAlH4 ◦ Insanely irritating (serious safety hazard) ◦ Extremely moisture sensitive (don’t leave out for >2 minutes) ◦ Ethereal mixtures are pyrophoric! DiBuAl-H ◦ Pyrophoric – it will explode upon exposure to oxygen NaEt3BH ◦ Pyrophoric in solution LiH and NaH ◦ Can be handled on the benchtop (not >2 minutes) ◦ Parrafin oil dispersions much safer KH ◦ Pyrophoric if not in a dispersion ◦ Handle with extreme care! † Sirius Black, Harry Potter and the Prisoner of Azkaban 4 Metal Hydrides: “I want to commit the murder I was imprisoned for†.” CaH2 ◦ Very safe to handle on the benchtop Pt-H, Pd-H, Ni-H ◦ All very pyrophoric NaBH4 ◦ Very safe in general Other hydrides ◦ Treat as pyrophoric ◦ Transition metal hydrides vary in hydridic strength ◦ General rule of thumb: if it does hydrogenations, it is probably pyrophoric ◦ If they’re in organics of any kind, they are probably pyrophoric † Sirius Black, Harry Potter and the Prisoner of Azkaban 5 Organometallic Chemistry BASIC PRINCIPLES, APPLICATIONS, -
18- Electron Rule. 18 Electron Rule Cont’D Recall That for MAIN GROUP Elements the Octet Rule Is Used to Predict the Formulae of Covalent Compounds
18- Electron Rule. 18 Electron Rule cont’d Recall that for MAIN GROUP elements the octet rule is used to predict the formulae of covalent compounds. Example 1. This rule assumes that the central atom in a compound will make bonds such Oxidation state of Co? [Co(NH ) ]+3 that the total number of electrons around the central atom is 8. THIS IS THE 3 6 Electron configuration of Co? MAXIMUM CAPACITY OF THE s and p orbitals. Electrons from Ligands? Electrons from Co? This rule is only valid for Total electrons? Period 2 nonmetallic elements. Example 2. Oxidation state of Fe? The 18-electron Rule is based on a similar concept. Electron configuration of Fe? [Fe(CO) ] The central TM can accommodate electrons in the s, p, and d orbitals. 5 Electrons from Ligands? Electrons from Fe? s (2) , p (6) , and d (10) = maximum of 18 Total electrons? This means that a TM can add electrons from Lewis Bases (or ligands) in What can the EAN rule tell us about [Fe(CO)5]? addition to its valence electrons to a total of 18. It can’t occur…… 20-electron complex. This is also known Effective Atomic Number (EAN) Rule Note that it only applies to metals with low oxidation states. 1 2 Sandwich Compounds Obeying EAN EAN Summary 1. Works well only for d-block metals. It does not apply to f-block Let’s draw some structures and see some new ligands. metals. 2. Works best for compounds with TMs of low ox. state. Each of these ligands is π-bonded above and below the metal center. -
NEW TANDEM REACTIONS INVOLVING NUCLEOPHILIC AROMATIC SUBSTITUTION by JAMES ERVIN SCHAMMERHORN III Associates of Science Murray
NEW TANDEM REACTIONS INVOLVING NUCLEOPHILIC AROMATIC SUBSTITUTION By JAMES ERVIN SCHAMMERHORN III Associates of Science Murray State College Tishomingo, Oklahoma 2003 Bachelor of Science in Chemistry Oklahoma State University Stillwater, Oklahoma 2006 Submitted to the Faculty of the Graduate College of the Oklahoma State University in partial fulfillment of the requirements for the Degree of DOCTOR OF PHILOSOPHY May, 2011 1 NEW TANDEM REACTIONS INVOLVING NUCLEOPHILIC ARMOMATIC SUBSTITUTION Thesis Approved: Dr. Richard Bunce Thesis Adviser Dr. K. Darrell Berlin Dr. Ziad El-Rassi Dr. Nicholas Materer Dr. Andrew Mort Dr. Mark E. Payton Dean of the Graduate College ii ACKNOWLEDGMENTS I would like to express my sincere gratitude to Dr. R. A. Bunce, my research advisor, my graduate committee chairman and my friend. I have learned many valuable lessons working alongside him in his research laboratory. His ability to teach both organic theory and laboratory techniques have been instrumental in my research at Oklahoma State University. I am immensely thankful for his support, guidance and patience to me during the course of this research. His unique sense of humor always makes me laugh and makes it a joy to come to lab. I would also like to thank my committee members, Drs. K. D. Berlin, Z. El Rassi, N. F. Materer, and A. J. Mort their acceptance to be on my committee. Their insights into research and graduate life have been invaluable during my graduate career. I am especially grateful to Dr. Berlin for sharing his wealth of organic chemistry knowledge with me during the course of my research. Also, to Dr. -
Anagostic Interactions Under Pressure: Attractive Or Repulsive? Wolfgang Scherer *[A], Andrew C
Manuscript Click here to download Manuscript: manuscript_final.pdf ((Attractive or repulsive?)) DOI: 10.1002/anie.200((will be filled in by the editorial staff)) Anagostic Interactions under Pressure: Attractive or Repulsive? Wolfgang Scherer *[a], Andrew C. Dunbar [a], José E. Barquera-Lozada [a], Dominik Schmitz [a], Georg Eickerling [a], Daniel Kratzert [b], Dietmar Stalke [b], Arianna Lanza [c,d], Piero Macchi*[c], Nicola P. M. Casati [d], Jihaan Ebad-Allah [a] and Christine Kuntscher [a] The term “anagostic interactions” was coined in 1990 by Lippard preagostic interactions are considered to lack any “involvement of 2 and coworkers to distinguish sterically enforced M•••H-C contacts dz orbitals in M•••H-C interactions” and rely mainly on M(dxz, yz) (M = Pd, Pt) in square-planar transition metal d8 complexes from o V (C-H) S-back donation.[3b] attractive, agostic interactions.[1a] This classification raised the fundamental question whether axial M•••H-C interaction in planar The first observation of unusual axial M•••H-C interaction in 8 8 d -ML4 complexes represent (i) repulsive anagostic 3c-4e M•••H-C planar d -ML4 complexes was made by S. Trofimenko, who interactions[1] (Scheme 1a) or (ii) attractive 3c-4e M•••H-C pioneered the chemistry of transition metal pyrazolylborato hydrogen bonds[2] (Scheme 1b) in which the transition metal plays complexes.[5,6] Trofimenko also realized in 1968, on the basis of the role of a hydrogen-bond acceptor (Scheme 1b). The latter NMR studies, that the shift of the pseudo axial methylene protons in 3 bonding description is related to another bonding concept which the agostic species [Mo{Et2B(pz)2}(K -allyl)(CO)2] (1) (pz = describes these M•••H-C contacts in terms of (iii) pregostic or pyrazolyl; allyl = H2CCHCH2) “is comparable in magnitude but [3] preagostic interactions (Scheme 1c) which are considered as being different in direction from that observed in Ni[Et2B(pz)2]2” (2) “on the way to becoming agostic, or agostic of the weak type”.[4] (Scheme 2).[6,7] Scheme 1.