Metal Catalyzed Outer Sphere Alkylations of Unactivated Olefins and Alkynes

Total Page:16

File Type:pdf, Size:1020Kb

Metal Catalyzed Outer Sphere Alkylations of Unactivated Olefins and Alkynes Metal Catalyzed Outer Sphere Alkylations of Unactivated Olefins and Alkynes Stephen Goble Organic Super-Group Meeting Literature Presentation October 6, 2004 1 Outline I. Background • Introduction to Carbometallation • “Inner Sphere” vs. “Outer Sphere” • Review of Seminal Work II. Catalytic Palladium Systems III. Catalytic Platinum Systems IV. Catalytic Gold Systems 2 I. Background: Carbometallation is the formal addition of a metal and a carbon atom across a double bond. • Cis addition would involve olefin insertion in to an σ-alkyl-metal species. This is an “Inner Coordination Sphere” process. cis addition [M] [M] R olefin insertion R • The alkyl-metal species could arise from: 1. Oxidative addition of the metal to an electrophile. 2. Transmetallation of a nucleophile to the metal. 3. Direct nucleophilic attack on the palladium. • Trans addition would involve an “Outer Coordination Sphere” nucleophilic attack on the metal-olefin coordination complex. trans addition [M] [M] R- R 3 First Example: Carbopalladation of an Olefin Tsuji, J. and Takahashi, H. J. Am. Chem. Soc. 1965. 87(14), 3275-3276. [Pd] O O RO2C CO R PdCl2 RO OR 2 Na2CO3 [Pd] Cl • Amino and Oxo-palladations (i.e. Wacker Process) were previously known and have since been much more widely studied. • No distinction between cis and trans nucleophilic addition made. 4 Carbopalladation on Styrene: Different Modes of Attack Proposed different modes of attack based on different observed products with MeLi vs. Na-Malonate: Murahashi, S. et. al. J. Org. Chem. 1977. 42 (17), 2870-2874. Nucleophilic Attack on Pd Olefin Insertion B-Hydride Elimination CH3Li [Pd] [Pd] CH3 PdX2 CH3 [Pd]-H Inner Sphere Mechanism Palladium Coordination Nucleophilic Attack B-hydride elimination CO R CO2R 2 NaCH(CO2R) CO R [Pd] CO2R 2 PdX2 [Pd] [Pd]-H • Outer Sphere attack usually occurs at the more substituted carbon - more stabilization of + + charge (In intermolecular processes). [Pd]- • Stoichiometric in Pd 5 First Direct Evidence of Trans Addition Kurosawa, H. et. al. Tetrahedron Lett. 1979. 3, 255-256. [Pd] O O D D THF D H + J=4.2 Hz -19 C [Pd] D H Na CHAc2 5 + - [Pd] = [Pd(n -C5H5)(PPh3)] ClO4 [Pd] O O D THF D H + J=12.3 Hz -19 C [Pd] D H D Na CHAc2 5 + - [Pd] = [Pd(n -C5H5)(PPh3)] ClO4 6 Palladium-Assisted Alkylation of Unactivated Olefins Hegedus, L. S. et. al. J. Am. Chem. Soc. 1980. 102, 4973-4979. • Wanted general procedure for Outer Sphere carbopalladations on unactivated olefins – but reduction of Pd (II) was a problem. • Overcame problem of nucleophilic reduction of Pd (II) by using NEt3, in a step- wise, one pot procedure. R' Pd(0) H R H2 flush 1. PdCl2(MeCN)2, THF, RT -60 C 2. NEt3 (2 Eq), THF, -78 C R 3. CH(Na)CO2R', THF, -60 C -60 to RT R = alkyl R' R Cl-Pd-H CH(Na)CO R' PdCl2(MeCN)2 2 THF RT THF, -60 C Pd (0) NEt3 (2 Eq) -78 C Cl Cl NEt Pd Pd 3 Cl Et3N 7 R R Palladium-Assisted Alkylation of Unactivated Olefins (Continued) Hegedus, L. S. et. al. J. Am. Chem. Soc. 1980. 102, 4973-4979. • Worked well on a variety of terminal olefins. • Internal alkenes gave only traces of reaction. • Worked with a variety of malonates. • Without triethylamine, reductive dimerization predominates. • Using HMPA as an additive the reaction works on a variety of un-stabilized nucleophiles: Enolates of ketones and esters. • Un-stabilized nucleophiles are usually ineffective because they attack the palladium first – Inner Sphere. • First Intramolecular case: CO Me PdCl2(MeCN) CO Me 2 2 42% Yield CO2Me CO2Me NEt3, THF (H2 flush) • In all cases the reaction is stoichiometric in Palladium. 8 Problems with Catalysis • Since the process is a formal reduction of the metal (Pd (II) to Pd (0) – re-oxidation of the metal is necessary. • Problem: Carbanions are very easily oxidized. – Reductive dimerization is a problem in carbopalladations: MeO2C CO2Me Pd (0) + Pd (II) + 2 MeO2C CO2Me MeO2C CO2Me – Therefore, any oxidant strong enough to oxidize the metal will probably oxidize the carbanion – preventing any desired reaction. 9 Palladium-Promoted Alkylation of Olefins by Silyl Enol Ethers • Silyl enol ethers transmetallate to Pd (II), β-H Elimination gives α,β-unsaturation: Ito, Y., Aoyama, H., Hirao, T. Mochizuki, A., and Saegusa, T. J. Org. Chem. 1978. 43(5), 1011-1013. OTMS Pd(OAc)2 O [Pd] O MeCN observed intermediate [Pd]-H oxo-π-allylpalladium • When an olefin is present, a formal insertion product is recovered : Ito, Y., Aoyama, H., Hirao, T. Mochizuki, A., and Saegusa, T. J. Am. Chem. Soc. 1979. 101(2), 494-496. O O R OTMS 2 Pd(OAc)2 + R 1 n MeCN R1 R1 R2 R2 • Works on a variety of substrates. • Since silyl enol ethers don’t get oxidized by Pd (II), they could get some weak catalysis (0.5 Molar Equiv) using a benzoquinone re-oxidant – but yields suffered. 10 Palladium-Promoted Alkylation of Olefins by Silyl Enol Ethers Ito, Y., Aoyama, H., Hirao, T. Mochizuki, A., and Saegusa, T. J. Am. Chem. Soc. 1979. 101(2), 494-496. By analogy they proposed this “Inner Sphere” mechanism: O R2 OTMS Pd(OAc) 2 R2 O [Pd] olefin R 1 MeCN R1 n n insertion n [Pd] R1 R2 [Pd] R2 Beta-H Elim R1 O n O O Isomerism OTMS n n But in a footnote they R1 R1 R2 R2 noted another possibility: R1 R 2[Pd] 11 Palladium-Promoted Alkylation of Olefins by Silyl Enol Ethers During the synthesis of (+/-)-Quadrone, the mechanism of this cyclization was explored: Kende, A. S. et al. J. Am. Chem. Soc. 1982. 104, 1784-1785. CO2Et Pd(OAc)2 OTMS MeCN O O O CO2Et O Product distributions in a model system are consistent an Outer Sphere process: O O Pd(OAc)2 MeO TMSO Pd(OAc)2 MeCN No Reaction A D O O 58% MeO Pd(OAc) 14% 2 MeCN C MeCN O O TBSO Pd(OAc) 40% LiO O 2 20% Pd(OAc)2 B MeCN E MeCN 45% 22% • If desilylation is first step: A and B and E should give same distribution, and C should not react (because it doesn’t form an enone in D). • Cyclization and enone formation does not proceed through same intermediate. 12 • Evidence supports an Outer Sphere mechanism. Pt (II) Additions to Ethylene Fanizzi, F. P et. al. J. Chem. Soc. Dalton Trans. 1992. 309-312. N Cl Cl CH2(CO2Et) Pt CO Et N Pt N 2 N Na2CO3 CO2Et DCM, RT • Addition is irreversible. - - - • Also works with inorganic nucleophiles (NO2 , N3 , NCO ). • Heating to 50 ºC gives β-hydride elimination. • Treatment of product with acids results in the facile cleavage of the Pt-C bond, regenerating Pt (II). N 0.5 M HCl Cl CO2Et Pt CO2Et N H2O CO2Et CO2Et or HCl/CHCl 3 13 Summary – Up to ~2001 • “Outer Sphere” carbopalladations are stoichiometric in palladium. • Pd/amine and Pt/amine complexes are the only known promoters. • The products of carbopalladations (alkyl-palladium complexes) undergo β- hydride elimination above -20 ºC. • The carbopalladation products can be quenched with H2 by simply flushing the system below -20 ºC. • Stabilized and non-stabilized carbon nucleophiles work well. • Using silyl enol ethers as the nucleophile allows weak catalysis (50 mol%), but technical problems with the system limit its utility. • One isolated example of a Pt (II) cationic complex adding to ethylene. No other late TM system is known. • Hegedus: “[The process] is unlikely to find extensive use in synthesis” Hegedus, L. S. Transition Metals in the Synthesis of Complex Organic Molecules. 1999. University Science Books, Sausalito, California. 14 II. First Example of TM (Pd) Catalysis - Hydroalkylation Pei, T. and Widenhoefer, R. A. J. Am. Chem. Soc. 2001. 123, 11290-11291. Looking at carbopalladations to get cyclopentanones: O O O O O O PdCl2(MeCN)2 (1 Eq) 70 % THF, 25 C expected • Surprising results: No net oxidation and endo ring closure. If no net oxidation, then Pd (II) would not be reduced and catalysis is possible: O O O O PdCl (MeCN) (5%) 2 2 81% Dioxane, 25 C • Mono terminal substitution on olefin is well tolerated. • α-substitution is tolerated. • β-keto esters give lower yields. But using TMSCl as an additive gives comparable yields (Pei. T and Widenhoefer, R. A. Chem. Comm. 2002. 650-651.) 15 Mechanistic Investigation Qian, H. and Widenhoefer, R. A. J. Am. Chem. Soc. 2003. 125, 2056-2057. 2 possible mechanisms: “Outer” vs. “Inner” Sphere O O Inner Sphere O H + Ac Path H Ac Ac H D D [Pd] D O O D D [Pd] H H D trans D OH O O D Ac Ac Ac H+ H H Outer Sphere D D Path [Pd] D D [Pd] D H D cis Br PhO S O O O O 2 Br O D H PdCl2(MeCN)2 (5%) NaOMe Dioxane, 25 C H D D D MeO C PhO S D D 2 2 16 Results are consistent with an outer coordination sphere mechanism. Mechanistic Investigation (Continued) Qian, H. and Widenhoefer, R. A. J. Am. Chem. Soc. 2003. 125, 2056-2057. Other labeling experiments: O O O O O O O O D D D D D D D O O O O O O O O D D D CD3 CD3 D D D D D • Palladium migration around the ring must occur. 17 Mechanistic Investigation (Continued) Qian, H. and Widenhoefer, R. A. J. Am. Chem. Soc. 2003. 125, 2056-2057. Plausible mechanism with palladium migration: O O O O Ac Ac [Pd] + [Pd]-H O O HCl O O Ac Ac [Pd] [Pd] [Pd] L L Pd Cl O O O Cl [Pd] Ac Ac Ac O O [Pd] [Pd] HCl 18 Extension to Non-Stabilized Enolates Wang, X., Pei, t., Han, X.
Recommended publications
  • 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
    [Show full text]
  • 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.
    [Show full text]
  • 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.
    [Show full text]
  • NIH Public Access Author Manuscript J Am Chem Soc
    NIH Public Access Author Manuscript J Am Chem Soc. Author manuscript; available in PMC 2013 August 29. NIH-PA Author ManuscriptPublished NIH-PA Author Manuscript in final edited NIH-PA Author Manuscript form as: J Am Chem Soc. 2012 August 29; 134(34): 14232–14237. doi:10.1021/ja306323x. A Mild, Palladium-Catalyzed Method for the Dehydrohalogenation of Alkyl Bromides: Synthetic and Mechanistic Studies Alex C. Bissember†,‡, Anna Levina†, and Gregory C. Fu†,‡ †Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States ‡Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States Abstract We have exploited a typically undesired elementary step in cross-coupling reactions, β-hydride elimination, to accomplish palladium-catalyzed dehydrohalogenations of alkyl bromides to form terminal olefins. We have applied this method, which proceeds in excellent yield at room temperature in the presence of a variety of functional groups, to a formal total synthesis of (R)- mevalonolactone. Our mechanistic studies establish that the rate-determining step can vary with the structure of the alkyl bromide, and, most significantly, that L2PdHBr (L=phosphine), an often- invoked intermediate in palladium-catalyzed processes such as the Heck reaction, is not an intermediate in the active catalytic cycle. INTRODUCTION The elimination of HX to form an olefin is one of the most elementary transformations in organic chemistry (eq 1).1,2 However, harsh conditions, such as the use of a strong Brønsted acid/base or a high temperature (which can lead to poor functional-group compatibility and to olefin isomerization) are often necessary for this seemingly straightforward process.
    [Show full text]
  • Tutorial on Oxidative Addition Jay A
    Tutorial pubs.acs.org/Organometallics Tutorial on Oxidative Addition Jay A. Labinger* Beckman Institute and Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States ABSTRACT: This tutorial introduces oxidative addition as a reactivity pattern and organizing principle for organometallic chemistry. The history, characteristics, and scope of oxidative addition are briefly surveyed, followed by a detailed examination of the variety of mechanisms found for the oxidative addition of alkyl halides and their relevance to practical applications. ■ INTRODUCTION comprehensive review but rather as an introduction to the The recognition of oxidative addition as a common pattern of topic, such as might be presented in a lecture, as part of a reactivity has played a central role in the development of course on organometallic chemistry. Accordingly, the tone is organometallic chemistry over the second half of the 20th rather informal, and citations have been limited to a moderate number of historically significant papers. Those interested in century. The starting point for modern organotransition-metal following up on any aspects can find more details and thorough chemistry is usually taken as the discovery and structural referencing elsewhere; Hartwig’s recent textbook5 is a good characterization of ferrocene in the early 1950s (of course, starting point. there were many important earlier contributions). That inspired a large amount of new chemistry during
    [Show full text]
  • Intramolecular Ene Reactions of Functionalised Nitroso Compounds
    INTRAMOLECULAR ENE REACTIONS OF FUNCTIONALISED NITROSO COMPOUNDS A Thesis Presented by Sandra Luengo Arratta In Partial Fulfilment of the Requirements for the Award of the Degree of DOCTOR OF PHILOSOPHY OF UNIVERSITY COLLEGE LONDON Christopher Ingold Laboratories Department of Chemistry University College London 20 Gordon Street London WC1H 0AJ July 2010 DECLARATION I Sandra Luengo Arratta, confirm that the work presented in this thesis is my own. Where work has been derived from other sources, I confirm that this has been indicated in the thesis. ABSTRACT This thesis concerns the generation of geminally functionalised nitroso compounds and their subsequent use in intramolecular ene reactions of types I and II, in order to generate hydroxylamine derivatives which can evolve to the corresponding nitrones. The product nitrones can then be trapped in the inter- or intramolecular mode by a variety of reactions, including 1,3-dipolar cycloadditions, thereby leading to diversity oriented synthesis. The first section comprises the chemistry of the nitroso group with a brief discussion of the current methods for their generation together with the scope and limitations of these methods for carrying out nitroso ene reactions, with different examples of its potential as a powerful synthetic method to generate target drugs. The second chapter describes the results of the research programme and opens with the development of methods for the generation of functionalised nitroso compounds from different precursors including oximes and nitro compounds, using a range of reactants and conditions. The application of these methods in intramolecular nitroso ene reactions is then discussed. Chapter three presents the conclusions which have been drawn from the work presented in chapter two, and provides suggestions for possible directions of this research in the future.
    [Show full text]
  • Appendix I: Named Reactions Single-Bond Forming Reactions Co
    Appendix I: Named Reactions 235 / 335 432 / 533 synthesis / / synthesis Covered in Covered Featured in problem set problem Single-bond forming reactions Grignard reaction various Radical couplings hirstutene Conjugate addition / Michael reaction strychnine Stork enamine additions Aldol-type reactions (incl. Mukaiyama aldol) various (aldol / Claisen / Knoevenagel / Mannich / Henry etc.) Asymmetric aldol reactions: Evans / Carreira etc. saframycin A Organocatalytic asymmetric aldol saframycin A Pseudoephedrine glycinamide alkylation saframycin A Prins reaction Prins-pinacol reaction problem set # 2 Morita-Baylis-Hillman reaction McMurry condensation Gabriel synthesis problem set #3 Double-bond forming reactions Wittig reaction prostaglandin Horner-Wadsworth-Emmons reaction prostaglandin Still-Gennari olefination general discussion Julia olefination and heteroaryl variants within the Corey-Winter olefination prostaglandin Peterson olefination synthesis Barton extrusion reaction Tebbe olefination / other methylene-forming reactions tetrodotoxin hirstutene / Selenoxide elimination tetrodotoxin Burgess dehydration problem set # 3 Electrocyclic reactions and related transformations Diels-Alder reaction problem set # 1 Asymmetric Diels-Alder reaction prostaglandin Ene reaction problem set # 3 1,3-dipolar cycloadditions various [2,3] sigmatropic rearrangement various Cope rearrangement periplanone Claisen rearrangement hirstutene Oxidations – Also See Handout # 1 Swern-type oxidations (Swern / Moffatt / Parikh-Doering etc. N1999A2 Jones oxidation
    [Show full text]
  • Ruthenium Olefin Metathesis Catalysts
    Ruthenium Olefin Metathesis Catalysts: Tuning of the Ligand Environment Ruthenium olefine metathese katalysatoren: Optimalisatie van de ligandsfeer Nele Ledoux Promotor: Prof. Dr. F. Verpoort Proefschrift ingediend tot het behalen van de graad van Doctor in de Wetenschappen: Scheikunde Vakgroep Anorganische en Fysische Chemie Vakgroepvoorzitter: Prof. Dr. S. Hoste Faculteit Wetenschappen 2007 ii Members of the Dissertation Committee: Prof. Dr. F. Verpoort Prof. Dr. Ir. C. Stevens Dr. V. Dragutan Dr. R. Drozdzak Dr. R. Winde Prof. Dr. Ir. D. Devos Prof. Dr. J. Van der Eycken Prof. Dr. P. Van Der Voort Prof. Dr. K. Strubbe This research was funded by the Fund for Scien- tific Research - Flanders (F.W.O.-Vlaanderen). Acknowledgments This dissertation is the final product of an educative and fascinating journey, which involved many contributors. First of all, I wish to express my gratitude to the people with whom I learned how to do research. There is my promotor Prof. Dr. Francis Verpoort who gave me the opportunity to join his ’Catalysis group’ and ensured the necessary funding. I’m especially grateful for his confidence and indulgence. In addition, I have been extremely lucky to work with several nice colleagues. Thank you, Thank you (= double thank you ♥) to Bart who helped me conquer many small and big difficulties, and by doing so, contributed a lot to the results reported here. Special thanks to Hans for many funny moments and support over the years. Of course, my acknowledgments also go to the other boys: Carl, Stijn, David, Jeroen, Prof. Dr. Pascal Van Der Voort and not to forget Siegfried, Steven, and Mike for the pleasant working atmosphere and supportive chats.
    [Show full text]
  • Lecture 2--2016
    Chem 462 Lecture 2--2016 z [MLnXm] Classification of Ligands Metal Oxidation States Electron Counting Overview of Transition Metal Complexes 1.The coordinate covalent or dative bond applies in L:M 2.Lewis bases are called LIGANDS—all serve as σ-donors some are π-donors as well, and some are π-acceptors 3. Specific coordination number and geometries depend on metal and number of d-electrons 4. HSAB theory useful z [MLnXm] a) Hard bases stabilize high oxidation states b) Soft bases stabilize low oxidation states Classification of Ligands: The L, X, Z Approach Malcolm Green : The CBC Method (or Covalent Bond Classification) used extensively in organometallic chemistry. L ligands are derived from charge-neutral precursors: NH3, amines, N-heterocycles such as pyridine, PR3, CO, alkenes etc. X ligands are derived from anionic precursors: halides, hydroxide, alkoxide alkyls—species that are one-electron neutral ligands, but two electron 4- donors as anionic ligands. EDTA is classified as an L2X4 ligand, features four anions and two neutral donor sites. C5H5 is classified an L2X ligand. Z ligands are RARE. They accept two electrons from the metal center. They donate none. The “ligand” is a Lewis Acid that accepts electrons rather than the Lewis Bases of the X and L ligands that donate electrons. Here, z = charge on the complex unit. z [MLnXm] octahedral Square pyramidal Trigonal bi- pyramidal Tetrahedral Range of Oxidation States in 3d Transition Metals Summary: Classification of Ligands, II: type of donor orbitals involved: σ; σ + π; σ + π*; π+ π* Ligands, Classification I, continued Electron Counting and the famous Sidgewick epiphany Two methods: 1) Neutral ligand (no ligand carries a charge—therefore X ligands are one electron donors, L ligands are 2 electron donors.) 2) Both L and X are 2-electron donor ligand (ionic method) Applying the Ionic or 2-electron donor method: Oxidative addition of H2 to chloro carbonyl bis triphenylphosphine Iridium(I) yields Chloro-dihydrido-carbonyl bis-triphenylphosphine Iridium(III).
    [Show full text]
  • Steam Cracking: Chemical Engineering
    Steam Cracking: Kinetics and Feed Characterisation João Pedro Vilhena de Freitas Moreira Thesis to obtain the Master of Science Degree in Chemical Engineering Supervisors: Professor Doctor Henrique Aníbal Santos de Matos Doctor Štepánˇ Špatenka Examination Committee Chairperson: Professor Doctor Carlos Manuel Faria de Barros Henriques Supervisor: Professor Doctor Henrique Aníbal Santos de Matos Member of the Committee: Specialist Engineer André Alexandre Bravo Ferreira Vilelas November 2015 ii The roots of education are bitter, but the fruit is sweet. – Aristotle All I am I owe to my mother. – George Washington iii iv Acknowledgments To begin with, my deepest thanks to Professor Carla Pinheiro, Professor Henrique Matos and Pro- fessor Costas Pantelides for allowing me to take this internship at Process Systems Enterprise Ltd., London, a seven-month truly worthy experience for both my professional and personal life which I will certainly never forget. I would also like to thank my PSE and IST supervisors, who help me to go through this final journey as a Chemical Engineering student. To Stˇ epˇ an´ and Sreekumar from PSE, thank you so much for your patience, for helping and encouraging me to always keep a positive attitude, even when harder problems arose. To Prof. Henrique who always showed availability to answer my questions and to meet in person whenever possible. Gostaria tambem´ de agradecer aos meus colegas de casa e de curso Andre,´ Frederico, Joana e Miguel, com quem partilhei casa. Foi uma experienciaˆ inesquec´ıvel que atravessamos´ juntos e cer- tamente que a vossa presenc¸a diaria´ apos´ cada dia de trabalho ajudou imenso a aliviar as saudades de casa.
    [Show full text]
  • Carbometallation Chemistry
    Carbometallation chemistry Edited by Ilan Marek Generated on 01 October 2021, 10:03 Imprint Beilstein Journal of Organic Chemistry www.bjoc.org ISSN 1860-5397 Email: journals-support@beilstein-institut.de The Beilstein Journal of Organic Chemistry is published by the Beilstein-Institut zur Förderung der Chemischen Wissenschaften. This thematic issue, published in the Beilstein Beilstein-Institut zur Förderung der Journal of Organic Chemistry, is copyright the Chemischen Wissenschaften Beilstein-Institut zur Förderung der Chemischen Trakehner Straße 7–9 Wissenschaften. The copyright of the individual 60487 Frankfurt am Main articles in this document is the property of their Germany respective authors, subject to a Creative www.beilstein-institut.de Commons Attribution (CC-BY) license. Carbometallation chemistry Ilan Marek Editorial Open Access Address: Beilstein J. Org. Chem. 2013, 9, 234–235. Schulich Faculty of Chemistry, Technion-Israel Institute of doi:10.3762/bjoc.9.27 Technology, Haifa 32000, Israel Received: 24 January 2013 Email: Accepted: 29 January 2013 Ilan Marek - chilanm@tx.technion.ac.il Published: 04 February 2013 This article is part of the Thematic Series "Carbometallation chemistry". Keywords: carbometallation Guest Editor: I. Marek © 2013 Marek; licensee Beilstein-Institut. License and terms: see end of document. Following the pioneering Ziegler addition of nucleophiles to in the 1,2-bisalkylation of nonactivated alkenes! In this nonactivated unsaturated carbon–carbon bonds, the controlled Thematic Series, you will find
    [Show full text]
  • Some Problems in the Oxidative Addition and Binding of an Ethylene to a Transition-Metal Center
    Organometallics 1986,5, 1841-1851 1841 Some Problems in the Oxidative Addition and Binding of an Ethylene to a Transition-Metal Center JBr8me Silvestre,laqbMaria Jos6 Calhorda,'a*CRoald Hoffmann, laPage 0. Stoutland,ld and Robert G. Bergmanld Department of Chemistry and MaterriaL Sciences Center, Cornel1 University, Zthaca. New York 14853, Department of Chemistry, University of California, Berkeley, California 94720, and Materials and Molecular Research Division, Lawrence Berkeley Laboratoty, Berkeley, California 94720 Received January 9, 1986 Molecular orbital calculations have been carried out on the potential energy surface of the system CpIrL(C2H4)(L = phosphine). The geometrical and electronic characteristics of the $-olefin and vinyl hydride complexes are examined in some detail. The olefin complex is found to have a slightly lower energy than the vinyl hydride, in agreement with experiment. Different routes are studied which lead to the oxidative addition product from the 16-electron fragment and an ethylene. It is found that an M-H-C linear approach is favored, coupled with a very specific orientation of the ethylenic T system. This results from both electronic and steric requirements. A relatively small barrier is computed for the process,-and the experimentally observed competition between vinyl hydride formation and direct ethylene addition is discussed. Calculations have been performed to ascertain the existence of a separate transition state taking the v2-bound olefin into the vinyl hydride. The computations suggest the existence of two distinct transition states. The influence of substituents and particularly steric effects is analyzed. It is shown how an increase in the size of the ligand affects the shape of the surface and more specifically narrows the energy channels governing conformational changes as well as product formation.
    [Show full text]