Geometric Isomers



Modules for Introducing Organometallic Reactions: A Bridge between Organic and Inorganic ChemistrySupporting InformationChris P. Schaller,* Kate J. Graham, Brian J. Johnson Department of Chemistry, College of Saint Benedict and Saint John’s University, Saint Joseph, MN, 56374, USA Table of contentsOrganometallic Topics within a traditional curriculum2Organometallic Topics within CSB/SJU Courses3Modules:Coordination Compounds: Structure and Geometry4Coordination Compounds: Electron Counting7Coordination Compounds: Isomerism13Reaction Mechanisms: Lewis Acid/Lewis Base 19Reaction Mechanisms: Ligand Exchange 23Reaction Mechanisms: Insertions/Eliminations 27Reaction Mechanisms: Oxidative Addition/Reductive Elimination 39Catalytic Cycles43Olefin Metathesis58Sample QuizzesGeometry, Ligands & e- count64Insertion and Elimination66Catalytic Cycles69Organotransition Metal Chemistry within A Traditional CUrriculumGeneral Chemistry 1 Matter & MeasurementAtoms, Molecules and IonsStoichiometryAqueous ReactionsThermochemistryElectronic Structure of AtomsPeriodic Properties of the ElementsBasic Concepts of BondingMolecular GeometryCoordination Compounds: Geometry and Bonding GasesIntermolecular Forces, Liquids and SolidsGeneral Chemistry 2 (or Gen Chem 1 “Atoms First”)Modern MaterialsProperties of SolutionsChemical KineticsChemical EquilibriumAcid-Base EquilibriaAdditional Aspects of Aqueous EquilibriaChemistry of the EnvironmentChemical ThermodynamicsElectrochemistryNuclear ChemistryMetals and MetallurgyCoordination Compounds: Electron Counting Organic Chemistry 1Reactivity: Acid-Base ChemistryCoordination Compounds: Lewis Acid Base ReactionsStructural Topics – Bonding and Conformation of HydrocarbonsStereochemistryCoordination Compounds: IsomersAssociation/Dissociation MechanismsSubstitution and Elimination Mechanisms Redox reactions (organic and inorganic)Oxidative Addition and Reductive EliminationElectrophilic AdditionIntroduction to Polymers (Cationic Polymerizations)Organic Chemistry 2SpectroscopyConjugated SystemsAromaticityElectrophilic Aromatic SubstitutionNucleophilic Additions to CarbonylsNucleophilic Substitutions to Acid DerivativesOrganometallic Insertion/Elimination ReactionsOrganometallic Catalytic CyclesRadicals Radical PolymerizationsPericyclic ReactionsRearrangementsOlefin MetathesisOrganotransition Metal Chemistry within CSB/SJU Foundational CoursesChem 125: Structure and PropertiesAtomic Structure and Periodic TrendsMetallic Structure and PropertiesIonic Structure and PropertiesMolecular Structure: Bonding and GeometryMolecular Structure: Isomers and StereochemistryIntermolecular ForcesBiological Structures and BiopolymersNetwork SolidsCoordination Compounds: Electron Counting, Geometry and IsomersMolecular Bonding revisited: Molecular OrbitalsReactivity: Acid-Base ChemistryChem 250: Reactivity 1Nucleophilic Additions to CarbonylsNucleophilic Substitutions to Acid DerivativesIntroduction to Thermodynamics of ReactionsLigand Field TheoryOrganometallic Insertion/Elimination ReactionsConjugate AdditionsEnzyme CatalysisGlycolysis, TCA Cycle and Fatty Acid BiosynthesisThermodynamics of PathwaysEnzyme RegulationIntroduction to Condensation Polymers Chem 251: Reactivity 2Introduction to Kinetics & Collision TheoryAssociation/Dissociation MechanismsSubstitution and Elimination MechanismsSubstitution in SynthesisOxidative Addition and Reductive EliminationOrganometallic Catalytic CyclesEnzyme KineticsElectrophilic AdditionElectrophilic Aromatic SubstitutionCationic PolymerizationsEyring PlotsChem 315: Reactivity 3Redox reactionsReduction Potentials & Cell PotentialsBiological Redox: Binding & Reduction of O2 and N2Radicals Radical PolymerizationsOxidative PhosphorylationAtmospheric ChemistryPhotochemistry (inorganic and organic compounds)Pericyclic ReactionsRearrangementsOlefin MetathesisCoordination Compounds: Bonding and Geometry Coordination Compounds: Structures of Transition MetalsIn a coordination compound, a central metal ion is attached to a group of surrounding molecules or ions (called ligands).Practice Predicting Geometry and Drawing Coordination ComplexesConventions for Representing Coordination Complexes:The coordination complex is inside the brackets. A ligand that binds to the metal is inside the parentheses.In front of the brackets is a cation. Behind the brackets are negative anions. Cations and anions float nearby but do not affect the coordination number.What would the coordination number be for these different compounds? Draw each of these the compounds in the predicted geometry using wedges and dashes.g. [Cu(NCCH3)4]BF4h. K3[Fe(CN)6]Ligand BindingA dative bond (also called a coordinate covalent bond) is a bond where one species provides both electrons for the covalent bond. A ligand donates at least one pair of electrons to the metal.Ligands may be anions or neutral.Draw structures of these neutral ligands and circle the lone pair that will be donated: H2O (aqua)NH3 (ammine)CO (carbonyl) (pyridine, py) PPh3(triphenylphosphine)Draw structures of these anionic ligands and circle the lone pair that will be donated: Cl- (chloride)CH3- (methyl)OH- (hydroxide)H- (hydride)CH2CHCH2- (allyl)PhO- (phenoxide)Polydentate LigandsDenticity is the number of donor atoms per ligand. If there is only one donor atom the ligand is monodentate (meaning “one – toothed”).Polydentate ligands are also known as chelating agents. These agents bond to metal ions and “trap” them as very stable complexes. What would bidentate imply?What would tridentate imply?What would tetradentate imply?What would polydentate imply?Ethylenediamine (H2NCH2CH2NH2 , often abbreviated as en) is a common ligand. What are the donor atoms on this ligand? How many times will this ligand bind?Draw Ni(en)(H2O)4+2Draw Mg+2 complexed with propylenediamine (H2NCH2CH2CH2NH2). What shape will this complex adopt?Hydrazine (NH2NH2) has two e- pairs but is NOT bidentate. Explain why.Determine how many times each of these ligands might bind a metal:Label the donor atoms: Coordination Compounds: Electron CountingElectron Counting on Coordination ComplexesElectron count on a metal in a complex can be accomplished as follows:Decide whether any anionic ligands are present (just cover up the metal, assume the donor atom in the ligand has an octet, and determine whether that atom has a formal charge). If so, adjust the charge on the metal atom to keep the overall charge balanced.Count the number of electrons on the metal, given its oxidation state (charge on the metal).Count the number of electrons donated by ligands.Total the electrons.342900023622000A worked example: (PPh3)4PdDraw this compound. Disconnect the ligands assuming the pair in the dative bond remains with the ligand.36576004000500Calculate the charge on each ligand. Determine the charge on the metal. Fill in the following table:Charge on the ligands:_______Valence electrons on Metal: 10 Charge on the Metal: 0 Revised Count on the Metal (accounting for charge): 10 Number of electrons donated from the ligands:______Two per dative bond to the metalTotal electrons in this complex:______A more complicated example: K[Ru(CN)4(NH3)2]342900020574000Draw this compound (remember the complex is inside the brackets). Disconnect the ligands assuming the pair in the dative bond remains with the ligand.36576002095500Calculate the charge on each ligand. NH3 ________CN ________Total charge on ligands: -4 Determine the charge on the metal. Charge on complex = charge on metal + charge on ligands-1 = ________ + (-4)Fill in the following table:Valence electrons on Metal:_______Charge on the ligands:_______Charge on the Metal:_______Revised Count on the Metal (accounting for charge):______Number of electrons donated from the ligands: ______Two per dative bond to the metalTotal electrons in this complex: ______Count the electrons on the metals in these complexes.[Mo(CO)6]Valence electrons on Metal:_______Charge on the ligands:_______Charge on the Metal:_______Revised Count on the Metal (accounting for charge):______Number of electrons donated from the ligands:______Total electrons in this complex:______[Ni(CO)4]Valence electrons on Metal:_______Charge on the ligands:_______Charge on the Metal:_______Revised Count on the Metal (accounting for charge):______Number of electrons donated from the ligands:______Total electrons in this complex:______ [Co(NH3)6] (Cl)3 Valence electrons on Metal:_______Charge on the ligands:_______Charge on the Metal:_______Revised Count on the Metal (accounting for charge):______Number of electrons donated from the ligands:______Total electrons in this complex:______[(PPh3)2Rh(CO)Cl]Valence electrons on Metal:_______Charge on the ligands:_______Charge on the Metal:_______Revised Count on the Metal (accounting for charge):______Number of electrons donated from the ligands:______Total electrons in this complex:______ K3[Fe(C2O4)3] (hint: bidentate oxalate ligands)Valence electrons on Metal:_______Charge on the ligands:_______Charge on the Metal:_______Revised Count on the Metal (accounting for charge):______Number of electrons donated from the ligands:______Total electrons in this complex:______[Ni(en)2(Cl)2]Valence electrons on Metal:_______Charge on the ligands:_______Charge on the Metal:_______Revised Count on the Metal (accounting for charge):______Number of electrons donated from the ligands:______Total electrons in this complex:______[Re(CO)5(PF3)]ClValence electrons on Metal:_______Charge on the ligands:_______Charge on the Metal:_______Revised Count on the Metal (accounting for charge):______Number of electrons donated from the ligands:______Total electrons in this complex:______[(PPh3)3RhCl] (Wilkinson's catalyst)Valence electrons on Metal:_______Charge on the ligands:_______Charge on the Metal:_______Revised Count on the Metal (accounting for charge):______Number of electrons donated from the ligands:______Total electrons in this complex:______ [(NH3)2PtCl2] (cis-platin)Valence electrons on Metal:_______Charge on the ligands:_______Charge on the Metal:_______Revised Count on the Metal (accounting for charge):______Number of electrons donated from the ligands:______Total electrons in this complex:______[Pd(en)2(NO2)2](PF6)2Valence electrons on Metal:_______Charge on the ligands:_______Charge on the Metal:_______Revised Count on the Metal (accounting for charge):______Number of electrons donated from the ligands:______Total electrons in this complex:______[Co(NH3)3Cl3]Valence electrons on Metal:_______Charge on the ligands:_______Charge on the Metal:_______Revised Count on the Metal (accounting for charge):______Number of electrons donated from the ligands:______Total electrons in this complex:______18 Electron RuleAlthough the majority of metal complexes do not satisfy the 18-electron rule, the rule predicts formulas for many organometallic complexes of the Cr, Mn, Fe, and Co triads. Compounds that obey the 18 VE rule are typically "exchange inert." Complexes with fewer than 18 valence electrons tend to show enhanced reactivity. plexes with bulky ligands often do not complete the 18 e- configuration.Draw these complexes in the correct geometry and count the electrons.Co(norbornyl)4 Pt(PtBu3)2 ((CH3)3CCH2)3TaCl2 Note: What prevents these compounds from binding to more ligands and achieving a full valence shell?Coordination Compounds: IsomerismIsomers of Coordination Complexes Linkage isomers occur when there is a choice between connecting the metal to one atom or another atom in the same ligand.Draw the two best Lewis structures for SCN - (same connectivity) and assign formal charges to each atom.In SCN -, which atoms are most likely to donate a pair of electrons. Explain your reasoning.Show two pictures of SCN- binding to a metal (M).Geometric Isomers in Coordination ComplexesWe have looked at cis and trans before in the context of carbon compounds. Define cis and trans: This same type of relationship can also be applied to transition metal complexes.Draw the two geometric isomers of the square planar complex Pt(NH3)2Cl2Which structure would be considered cis and which one trans? Why did you label them as such?Draw the two geometric isomers of the octahedral complex [Co(NH3)4Cl2].Which structure would be considered cis and which one trans? Why did you label them as such?Another diastereoisomeric relationship is fac and mer. These occur when there are three identical ligands Draw the geometric isomers of the octahedral complex [Co(NH3)3Cl3].How would you describe the relationship between the two (i.e. what is different between the two)? StereoisomersReview: Define enantiomer.Square Planar vs TetrahedralCompare the two mirror images of a metal complex in four coordinate shapes -- tetrahedral and square planar. Label the tetrahedral pair and the square planar pair. Are these pairs of enantiomers? Or pairs of identical complexes?If achiral, show a plane of symmetry.Octahedral StereoisomersWill any of these pairs of octahedral complexes be chiral?Draw a plane of symmetry through any complex that is achiral.Additional Practice with Types of IsomersLabel the type of isomeric relationship between these compounds (fac/mer, cis/trans, enantiomers, linkage or identical)Finding all the isomers in Octahedral Transition Metal ComplexesTo determine the number of possible isomers (geometric and optical) for an octahedral transition metal complex using the “trans pair” naming system method.See Structure and Reactivity, SC18 for more detail: See Structure and Reactivity, SC18 for more detail: . Draw 1 isomer with the ligands arranged in any order. Remember bidentate ligands can only occupy cis sites.2. Write out the 3 pairs of trans ligands.3. Switch a pair of cis ligands and again write out the 3 pairs of trans ligands. If the 2 isomers do not have the same pairs of trans ligands then they are geometric isomers of one another.4. Examine each geometric isomer for an internal plane of symmetry (or draw mirror image). If there is an internal plane, or its mirror image is superimposable, then it does not have an enantiomer. If there is no internal plane of symmetry, or its mirror image is non-superimposable, then it does have an enantiomer.Determine the number of geometric isomers for [Cr(H2O)3(OH)2Cl].Which of these isomers have enantiomers?Reaction Mechanisms: Lewis AcID/Lewis Base ReactionsDefinitions and Introduction to Lewis Acids and BasesLewis Acid: electron acceptorLewis Base: electron pair donorLewis Acid/Base Complexes (Dative bonds)What structural feature would be required for a Lewis Base?What structural feature(s) would be required for a Lewis Acid?Which of these compounds is most likely to behave as a Lewis acid?a) BH3b) NH3c) CH4d) H2OWhich of the central atoms is most likely to behave as a Lewis base?a) BH3b) BeH2c) CH4d) H2OFor the molecules below:Add lone pairs of electrons Circle those that are Lewis acidsUnderline those that are Lewis BasesExplain your choicesStrengths of Lewis AcidsRank the following Lewis acids in order of increasing acidity and explain your ranking:Fe+3Fe+2Fe+1Same question, new molecules:Same question, new molecules:MO of Lewis Acid-Lewis Base ReactionsDraw an MO diagram showing the overlap of these two orbitals resulting in the sigma and sigma* orbitals on the product. Curved Arrow Notation for Lewis Acid-Lewis Base ReactionsRules for Arrows:Arrows always begin at the source of electrons (nucleophile or Lewis Base). Arrows always end at the electrophilic (electron deficient or Lewis Acid).This accounting of bonds formed and broken is called a reaction mechanism.Predict the products for the following Lewis Acid-Lewis Base Reactions.Use curved arrows to show the mechanism of the following reactions). Label the Nucleophile (Lewis Base) and the Electrophile (Lewis Acid) in the starting materials.Two Step Lewis Acid-Lewis Base ReactionsSometimes there are two arrows for these Lewis acid:Lewis base reactions. Use curved arrows to show the mechanism of the following reactions. Propose a reason why these reactions need a second arrow.Reaction Mechanisms: Ligand ExchangesAssociation / Dissociation 274320017780000One ligand in a transition metal complex is replaced by another ligand.Draw the possible mechanisms for the ligand substitution.Associative:Dissociative:Label the two mechanisms above with molecularity.Challenge:Draw a third possible mechanism for the ligand substitution where the bond-making and bond-breaking steps occur simultaneously. This is called Ia (Associative Interchange).What would the reaction potential diagram look like?What would the molecularity for this reaction be?Factors Affecting Ligand Substitution Mechanism TypeTransition metal complexes have flexible geometry / coordination environment, so predicting a mechanism can be difficult. However, there are some general observations.1. Electron countThe order of steps may be influenced by electron saturation at the metal.Explain how the electron count in an 18-electron complex may influence the order of steps in a ligand substitution.Explain how things may be different in a 16-electron complex.Draw square planar (NH3)2PtCl2. Count the electrons on the metal in the complex. Replace one of the amines with PH3. Show a mechanism with arrows.2. Electron FillingComplexes containing metals such as Cr+3 or Mo+3 are often resistant to association.Provide an octahedral ligand splitting diagram for Cr(acac)3 (acac is a bidentate anionic ligand).Using the splitting diagram, explain why this complex may not be willing to bind another ligand.3. GeometryThe order of steps may be influenced by the geometry at the metal.Four coordinate complexes of Ni2+ and Pt2+ often have two different geometries. What is the geometry of each? Why?Which of these two metal ions might be more likely to undergo substitution via association followed by dissociation: (NH3)2NiCl2 or (NH3)2PtCl2? Why?4. StericsOrder of steps may also be influenced by crowding at the metal.What is the electron count of the metal in the tetrahedral complex, (PPh3)4Pd?Replace a triphenylphosphine with a tricyclohexylphosphine. Show a mechanism with arrows.5. Metal LabilityThe order of steps may be influenced by the lability of the metal.If a metal is labile, the complex would be more likely to undergo an ( associative / dissociative ) mechanism.Which of these two metal ions might be more likely to undergo substitution via association followed by dissociation: L6V2+ or high spin L6Fe2+? Show why using a d orbital splitting diagram.6. Ligand LabilityThe order of steps may be influenced by the coordinating ability of the ligand.If a ligand is labile, the complex would be more likely to undergo an ( associative / dissociative ) pare the coordinating ability of water to carbon monoxide.Which of these two ligands might be more likely to undergo substitution via dissociation followed by association?7. Jahn-TellerJahn-Teller distortions can lead to increased lability and, hence increased ligand exchange, in some complexes.Explain why [Cr(H2O)6]2+ undergoes substitution more easily than [Cr(H2O)6]3+. Reaction Mechanisms: Insertions/EliminationsCarbonyl Binding and Migratory InsertionBinding CO to transition metalDraw the Lewis structure for CO.Show, with mechanism arrows, CO binding to a nickel atom.What type of ligand (? only, ? acceptor or ? donor) is CO?CO binding usually involves two events:a) donation of lone pair electrons to an empty metal p orbital (??bond)b) donation of metal d electrons to a pi* orbital (? bond)Sketch these two orbital interactions as two separate drawings.Label the type of bond formed in each picture.Explain what happens to the ??bond when the CO binds. Is this consistent with your above drawing of the bound CO? Draw a new Lewis structure to support the MO picture of bonding.Ni(CO)4 absorbs near 2057 cm-1. C-O absorbs around 1250C=O absorbs around 1700C=Oabsorbs around 2150When CO is bound to the metal, approximately what is the Bond Order?11.522.53Why?Migratory Insertion or 1,1-InsertionReview: A more familiar reaction is addition to carbonyl. Draw the product.Identify the nucleophile and the electrophile in the above reaction.A migratory insertion is related to the reaction above. Fill in the boxes below and follow directions.Migratory insertion is the addition of an alkyl or hydride to a coordinated carbonyl.Draw mechanism arrows in the drawing below.Draw mechanism arrows and fill in the products of the following reactions.1,2-Insertion and -EliminationInsertion is the addition of a metal-hydride to a ? bond.Elimination is the reverse reaction, from right to left.Insertion: CarbonylsThe following scheme describes the reaction of methanal with a metal hydride to give a metal methoxide. Fill in the intermediate, the product and mechanism arrows.?-Elimination: CarbonylsShow the reaction of methoxide ion with a metal cation to give methanal and a metal hydride (the reverse of the above reaction).Representations of Metal Alkene Binding Show mechanism arrows for the following step and show the product, with formal charges.Sometimes, a bound alkene is shown this way, as a metallacyclopropane. Can you explain why using Lewis structures?Alkene binding usually involves two events:a) donation of pi electrons to an empty metal p orbitalb) donation of metal d electrons to a pi* orbital.Sketch these two orbital interactions as two separate drawings.Explain what happens to the pi bond when the alkene binds. How is this consistent with the above drawings of the bound alkene?Insertion: Alkenes: Alkenes are not usually electrophiles. Why is the alkene bound to a metal an electrophile?In the following drawing, complete the reaction by showing mechanism arrows for each step, showing the intermediate as a metallacyclopropane and filling in the product. Application Problems1. Hydride transfer reduction Catalytic reductions are ubiquitous in industrial reactions.Show how, in the presence of a weak amine base, benzaldehyde can be reduced to benzyl alcohol. This is hydrogen transfer reduction, and it takes place in alcohol solvent, such as isopropanol.Fill in the boxes in the following scheme.Asymmetric 1,2-insertionReview: Cation Stability (from acid-base chemistry)Rank the following Lewis acids in order of increasing stability and explain your ranking:Same question, new molecules:Cationic Intermediates in 1,2-insertionDraw the bound complex and the insertion product for the generic reaction below. Two different insertion products are possible. Show them. Is there a preferred product? Why or why not?Provide an explanation based on steric effects (suppose the M is Wilkinson's catalyst, (PPh3)3RhCl):Provide an explanation based on electronic effects / ion stabilities:Practice ProblemsCircle the more stable cation intermediate (consider resonance structures).Draw the insertion product. Is there a preferred product? Why or why not?Draw the bound complex and the insertion product. Is there a preferred product? Why or why not?Hydroformylation can be performed using HCo(CO)4 as a catalyst. However, some branching of the longer-chain aldehyde occurs. To limit branching and encourage straight-chain aldehyde formation, promoters such as Ph3P are sometimes added to the reaction.Explain, using the pictures of the cationic intermediates, how that change promotes formation of a straight-chain aldehyde.The Heck Reaction MechanismDraw arrows where indicated.Fill in boxes with appropriate products.Provide a name for Complex A.Count the electrons on Complex B.Valence electrons on Metal:_______Charge on the ligands:_______Charge on the Metal:_______Electrons on Metal ion: _______Ligand electrons donated:_______Total electron count:_______Geometry of Complex B: Use LFT splitting diagrams, to explain why this complex is square planar NOT tetrahedral.Application of The Heck ReactionThe alkaloid, huperzine A, is isolated from the clubmoss, Lycopodium. It has shown potential as a treatment for Alzheimer’s disease which has heightened synthetic interest in this family of natural products.Bisai and Sarpong, “Methoxypyridines in the Synthesis of Lycopodium Alkaloids: Total Synthesis of Lycoposerramine R”, Org. Lett., 2010, 12(11), 2551-2553.Fill in the blanks in the synthesis shown below. Don’t use the same reagent twice.Reaction Mechanisms: Oxidative Addition/Reductive EliminationsOxidative Addition and Reductive EliminationOxidative addition is the addition of a bond to a metal center.Reductive elimination is the reverse reaction.Why is the forward reaction called an oxidative addition? What is the oxidation state on the metal in the reactants and the products of this reaction?Ni + Cl2 Explain why this is an oxidation (remember: lose e- oxidize, gain reduce).Draw the reverse reaction.On the previous page, label the oxidative addition in the cycle.On the previous page, label the reductive elimination in the cycle.Oxidative Addition MechanismsThere are two possible mechanisms.The metal can donate a pair of electrons to one of the atoms, displacing the other atom as an ion. This ion recombines with the metal.The addition can be concerted.1. Stepwise Polar AdditionThis mechanism is really an example of an SN2 mechanism. BUT in this reaction, the metal is the nucleophile. That should seem very strange. Why? To do an SN2 on a substrate, what structural characteristics does the substrate need?Show the mechanism with arrows for addition of a) HCl and b) CH3CH2Br to nickel.a.b.Polar Oxidative Additions are much faster in polar solvents. Propose a reason for this phenomenon.The addition of H2 to nickel does not follow this mechanism. Explain why.2. Concerted Oxidative AdditionUnderstanding how the alternative, concerted mechanism works (both atoms add at the same time) may require some MO theory. Draw an occupied molecular orbital on hydrogen (H2) and its interaction with an unoccupied p orbital on nickel.Draw an occupied metal d orbital and its interaction with an empty molecular orbital on hydrogen (H2).Explain how these interactions combine to break the H-H bond.Draw a mechanism for this reaction using arrows. The mechanism should reflect what you know about the MO situation.Practice ProblemsChoose the most likely mechanism for the following cases (one-step or two-step).Explain why you chose this mechanism for these cases.Catalytic CyclesCatalytic CyclesCatalytic Cycle is a term for a multistep reaction mechanism that involves a catalyst. Since catalysts are regenerated, catalytic cycles are usually written as a sequence of chemical reactions in the form of a loop. Fill in the blanks on the cycle below:Classic Organometallic Catalytic CyclesDuPont Hydrocyanation (nylon synthesis)Count electrons for each metal complex in the cycle shown below.Label each step with the type of reaction (association, dissociation, migratory insertion, 1,2-insertion, ?-elimination, oxidative addition, reductive elimination).Draw the arrows for each step.How many turns on the cycle to make the precursor for Nylon-6,6?Reppe Carbonylation (Very similar to DuPont Hydrocyanation)Fill in the missing metal complexes.Label each step with the type of reaction (association, dissociation, migratory insertion, 1,2-insertion, ?-elimination, oxidative addition, reductive elimination).Predict the product if ethanol (CH3CH2OH) is used rather than H2O.2971800-34290000Monsanto Acetic Acid ProcessEfforts to establish organic syntheses on the basis of C1 building blocks from coal resources include the Monsanto Acetic Acid Process. This cycle involves homogeneous catalysis: carbonylation of methanol.Count electrons for each metal complex in the cycle shown below.Label each step with the type of reaction (association, dissociation, migratory insertion, 1,2-insertion, ?-elimination, oxidative addition, reductive elimination).Draw the arrows for each step.Fill in missing products.Sonogashira CouplingSonogashira (1975) developed a method to form a carbon-carbon bond between a terminal alkyne and an aryl or vinyl halide.Count electrons for each metal complex in the cycle shown below.Label each step with the type of reaction (association, dissociation, migratory insertion, 1,2-insertion, ?-elimination, oxidative addition, reductive elimination).Draw the arrows for each step.Label the cis-trans isomerization step.Why did the square planar Pd complex have to undergo isomerization for this cycle?Sonogashira ApplicationSonogashira reaction also has a carbonylation variation. The following example shows the synthesis of a pyridone in which the carbonylation and cyclization occur in tandem (Kalinin, Tet. Lett., 1992, 33, 373). Propose a cycle for this process.Buchwald-Hartwig CouplingCount electrons for each metal complex in the cycle shown below.Fill in the missing metal complexes.Draw the arrows for each step.Stille Coupling Count electrons for each metal complex in the cycle shown below.Fill in the missing metal complexes.Draw the arrows for each step.3657600-22860000HydrogenationIn a hydrogenation reaction, two hydrogen atoms are added across the double bond of an alkene. Hydrogenation is used in the food industry to make a large variety of manufactured goods, like Crisco or margarine from liquid oils. Hydrogenation is also used in coal processing. Solid coal is converted to a liquid through the addition of hydrogen.?Liquefying coal makes it available to be used as fuel.The catalyst can be a homogeneous catalyst or a heterogeneous catalyst.Homogeneous Catalytic Cycle:Fill in the blanks on this cycle using a Pd catalyst.Calculate charges on each metal complex.Label each step as: binding, reductive elimination, oxidative addition, or 1,2-insertion.The rate of reduction is partially based on the availability of the π-bond electrons and the stability of the alkene.Rank the following π-bonds in order of π-electron availability (1 = most reactive).Based on your answer to the above question, how could an alkyne be selectively hydrogenated to an alkene. (i.e. How strong of a catalyst would the Lindlar catalyst be?)StrongMediumWeakWhat strength of a catalyst would be needed to reduce a tetrasubstituted alkene? Circle one. StrongMediumWeakApplication Problems1. Compare the selectivity of these two catalysts.Which Catalyst is stronger?Crabtree’s Catalyst ORWilkinson’s CatalystDraw both catalysts.Draw both catalysts after the H2 is added.Provide the geometry and electron count for each catalyst (before and after H2 addition).COD is a sacrificial ligand. What happens to the COD on Crabtree's catalyst with the hydride? Draw the product of this reaction. Now what is the geometry and electron count?Explain the difference in selectivity between the two hydrogenation catalysts. Heterogeneous Catalytic HydrogenationOn solid metal catalysts, the accepted mechanism is the Horiuti-Polanyi mechanism.Some of the most common metal catalysts are:Pt, Pd, and NiThese are usually placed on a highly dispersed powder support with large surface area (Carbon or alumina)With this mechanism, explain the following results. Hydrogenation Practice ProblemsFill in the products (be sure to include stereochemistry).Electrophilic Addition with Catalytic CyclesSuzukiFirst published in 1979 by Akira Suzuki, the Suzuki reaction couples boronic acids (containing an organic substituent) to halides (2010 Nobel Prize). Provide a mechanism for the reaction of catecholborane with the alkyne.Fill in the blanks on the following catalytic cycle for the Suzuki coupling.Roadmap with SuzukiWhite and Choi, (-)-Ibogamine Org. Lett., 2000, 2(15), 2373-2376.Fill in the boxes in the following synthesis of Ibogamine.Olefin MetathesisOlefin MetathesisIn olefin (or alkene) metathesis, a C=C bond is split in half and reattached with another partner.One application of olefin metathesis is found in the Shell Higher Olefin Process (SHOP), which supplies raw materials for making soaps (sodium lauryl sulfate, etc).Provide a mechanism for the oligomerization step.Describe what is happening in the metathesis step.SHOP allows the statistical distribution of olefins produced in oligomerization to be adjusted and optimized. The desired fractions are then subject to hydroformylation, reduction, and sulfonation.Suggest reagents to complete the preparation of sodium lauryl sulfate.Olefin Metathesis: Overall ReactionYves Chauvin, Dick Schrock and Bob Grubbs shared the 2005 Nobel Prize in Chemistry for their work in this area.Show the products of the following olefin metatheses:Chauvin was working as a bachelor’s-level chemist at the French Petroleum Institute in the 1960’s. He was an avid reader of the chemical literature, and these two reports caught his eye:Fill in the products of the olefin metathesis reactions.Olefin Metathesis: Making Better Catalysts on the East CoastBy 1980, Schrock had moved from DuPont to MIT, where his lab was developing better metathesis catalysts.Propose reagents for each step in the pounds of this type (lower left) are effective metathesis catalysts. The analogous molybdenum compounds are among the fastest metathesis catalysts; options are available that offer excellent control over cis vs. trans bond formation.Similar catalysts were developed for alkyne metathesis.Propose a synthesis of the catalyst from plete the following synthesis of the perfume, civetone.Olefin Metathesis: Making Better Catalysts on the West Coast Meanwhile, Bob Grubbs at CalTech sought metathesis catalysts that were more tolerant of air, moisture and oxygen/nitrogen-containing functional groups.Classify in terms of hard/soft acid/baseTungstenMolybdenumRutheniumOxygenNitrogenExplain briefly why unwanted hard/soft acid/base interactions may interfere with catalysis.The new catalyst was based on a precursor, below right, from Geoff Wilkinson’s lab at Imperial College. Wilkinson shared Fischer’s 1973 Nobel Prize.What is the oxidation state of ruthenium (a) before and (b) after the reaction?What is the electron count on ruthenium in the brown dichloride complex? Show your work.Triphenylphosphine is a new ligand in the reaction. What is its other role?The first generation of catalysts from the Grubbs lab are stable to air and water. Their ease of use quickly made them the preferred catalysts worldwide for routine metatheses.Olefin Metathesis: Application1. Professor Hoye and others (Organic Letters, 1999, 2, 277-279) were looking at synthesizing a natural product (±)-Differolide (compound 1). A) The first step is an olefin metathesis mechanism. It is postulated that it can occur two different ways (“yne-then-ene” or “ene-then-yne”). Evidence for the “ene-then-yne” mechanism is the production of an aromatic side product. Propose a mechanism (catalytic cycle) for this “ene-then-yne” reaction. Hint: Compound 4 is an initiator and two molecules of compound 3 are needed to generate compound 2.B) What is the structure of the aromatic side product that is produced from this reaction?C) Compound 4 is referred to as a carbene complex. Draw a resonance structure of 4 and explain how it is a carbene.The last step in this mechanism to produce compound 1 is a dimerization of compound 2. Propose a mechanism for this last pound 3 can be synthesized as outlined below. Provide reagents for the steps.Sample Quiz: Geometry, Ligands and Electron CountsQuiz: Coordination CompoundsChem 125: Chemical Structure and PropertiesCoordination Compounds(2 pts each) Make a perspective drawing for each of the following coordination compounds. (1 pts each) Provide the name of the geometry for each compound.(5 pts each) Count the valence electrons on each metal and the total electrons donated by the ligands in the tables provided.a. Na[AuCl4] b. K2[Zn(CN)4] c. [Ni(ox)2(H2O)(NH3)]a. Geometry:_______________Valence electrons on Metal:_______Charge on the ligands:_______Charge on the Metal:_______Electrons on Metal ion: _______Ligand electrons donated:_______Total electron count:_______c. Geometry:_______________Valence electrons on Metal:_______Charge on the ligands:_______Charge on the Metal:_______Electrons on Metal ion: _______Ligand electrons donated:_______Total electron count:_______b. Geometry:_______________Valence electrons on Metal: _______Charge on the ligands:_______Charge on the Metal:_______Electrons on Metal ion: _______Ligand electrons donated:_______Total electron count:______________/24Stereochemistry of Coordination Compounds (4 pts) Draw the fac and mer geometric isomers of the octahedral complex [Mn(NH3)3(F)3]. Label them.(4 pts) Draw the two geometric isomers of the square planar complex [Rh(Cl)2(PPh3)2]. Label them as cis and trans.(2 pts) What is the relationship between these two compounds?EnantiomersDiastereomersIdenticalConstitutional Isomers/10Sample Quiz: Insertions and EliminationsQuiz: Insertions and EliminationsChem 250: Reactivity 1Synthesis of MethoxyfumimycinGross, Hartmann, Nieger and Brase, J. Org. Chem., 2010, 75, 229-232.Due to bacterial resistance to common classes of antibiotics, a continuing discovery of antibiotics with new modes of action is critical. One target of special interest is the bacterial peptide deformylase (PDF). In the course of screening for PDF inhibitors, fumimycin was isolated from cultures of the mildew Aspergillus fumisynnematus F746.(2 pts) Fill in the boxes with appropriate reagents or products.______/10In one of the key steps of the synthesis of fumimycin, the alkene is isomerized with a rhodium catalyst.The rhodium trichloride reacts with the EtOH to form the following catalyst.(2 pts) What is the geometry of the rhodium in this complex?Geometry: _________________(4 pts) What is the total electron count on Rh in this complex? Valence electrons on Metal:_______Charge on the ligands:_______Charge on the Metal:_______Revised Count on the Metal (accounting for charge): _______Number of electrons donated from the ligands:_______Total electrons in this complex:_______(3 pts) Draw a d orbital splitting diagram (see Appendix). (2 pts) Will this complex be High SpinORLow Spin ______/11In one of the key steps of the synthesis of fumimycin, the alkene is isomerized with a rhodium catalyst.The rhodium trichloride reacts with the EtOH to form the following catalyst.(6 pts) In this isomerization reaction, propose a mechanism for how this catalyst effects this reaction.(3 pts) Label each of the steps of your mechanism with the appropriate type of mechanism (migratory insertion, 1,2-insertion, ?-elimination, association, dissociation).(2 pts) Considering structure and thermodynamics, why is this the final product? ______/11Sample Quiz: Catalytic CyclesQuiz: Catalytic CyclesChem 251: Reactivity 2 Hydrosilylation with Biscarbene Rhodium ComplexesGigler, Bechlars, Herrmann and Kühn, J. Am. Chem. Soc., 2011, 133, 1589-1596.Rhodium complexes are commonly used catalysts for the hydrosilylation of ketones. Only a few mechanistic studies on rhodium-based hydrosilylation reactions have been published. Ojima proposed a mechanism shown below.(2 pts each) Label the mechanistic steps with the type of reaction (association, dissociation, migratory insertion, 1,2-insertion, ?-elimination, oxidative addition, reductive elimination).(2 pts) Fill in the blank box for the product. (2 pts each) Provide the charge and e- count for each of the metal complexes:Complex 1: charge ______e- count___________Complex 2: charge ______e- count___________Complex 3: charge ______e- count___________Complex 4: charge ______e- count__________________/18A different mechanism was proposed by Zheng and Chan where the ketone is thought to coordinate to the silicon atom rather than the Rh.(6 pts) Propose a catalytic cycle for the Zheng mechanism.(1 pt) In the Ojima mechanism, when is the C-H bond formed?3 4 OR 4 1(1 pt) In contrast, when is the C-H bond formed in the Zheng mechanism?3 4 OR 4 1_______/8 ................
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