Chapter 13 Organometallic Chemistry

Chapter 13 Organometallic Chemistry13-1 Historical Background13-2 Organic Ligands and Nomenclature13-3 The 18-Electron Rule13-4 Ligands in Organometallic Chemistry13-5 Bonding Between Metal Atoms and Organic π Systems13-6 Complexes Containing M-C, M C, and M C Bonds13-7 Spectral Analysis and Characterization ofOrganometallic Complexes“Inorganic Chemistry” Third Ed. Gary L. Miessler, Donald A. Tarr, 2004, Pearson Prentice Hallhttp://en.wikipedia.org/wiki/Expedia

13-1 Historical BackgroundSandwich compoundsCluster compounds

13-1 Historical BackgroundOther examples of organometallic compounds

13-1 Historical BackgroundOrganometallic CompoundOrganometallic chemistry is the study of chemical compoundscontaining bonds between carbon and a metal.Organometallic chemistry combines aspects of inorganicchemistry and organic chemistry.Organometallic compounds find practical use in stoichiometricand catalytically active compounds.Electron counting is key in understanding organometallicchemistry. The 18-electron rule is helpful in predicting thestabilities of organometallic compounds. Organometalliccompounds which have 18 electrons (filled s, p, and d orbitals)are relatively stable. This suggests the compound is isolable, butit can result in the compound being inert.

13-1 Historical BackgroundIn attempt to synthesize fulvaleneProduced an orange solid (ferrocene)Discovery of ferrocene began the era of modern organometallicchemistry.Staggered ringsEclipsed ringsSkew rings

13-2 Organic Ligands and NomenclatureWrite hydrocarbon ligands before the metal.ηsuperscriptBridging ligand - μSubscript indicating the number of metal atoms bridged.

13-2 Organic Ligands and Nomenclature

13-3 The 18-Electron Rule; counting electronsIn main group chemistry, the octet ruleDonor Pair methodNeutral Ligand method

13-3 The 18-Electron Rule; counting electronsM-M single bond counts as one electron per metal

13-3 The 18-Electron Rule; why 18 electrons?s2p6 vs s2p6d10Have to considertypes of ligandStrong σ–donorability of COStrong π–acceptorability of COGood for 18electron rule

13-3 The 18-Electron Rule; why 18 electrons?[Zn(en)3]2 ; ? Electron speciesgood σ-donor not as strong as COeg orbitals are not sufficientlyantibondingTiF62- ; ? Electron speciesσ-donorπ-donorWhat happen?

Ligand field theory;Pi-Bondingmetal-to-ligand π bondingor π back-bonding-Increase stability-Low-spin configuration-Result of transfer ofnegative charge away fromthe metal ionLigand-to metal π bonding-decrease stability-high-spin configuration

13-3 The 18-Electron Rule; square-planar complexes16 electron complexesmight be stableSquare-planarcomplexes haveimportant catalyticbehaviorWhy?

13-4 Ligands in Organometallic Chemistry; carbonyl (CO) complexes

13-4 Ligands in Organometallic Chemistry; carbonyl (CO) complexes

13-4 Ligands in Organometallic Chemistry; carbonyl (CO) complexesExperimental evidenceFree CO vs M-COInfrared spectroscopy and X-ray crystallographyFree CO has a C-O stretch at 2143 cm-1Cr(CO)6 has a C-O stretch at 2000 cm-1C-O distance 112.8 pmMetal complexes 115 pm

13-4 Ligands in Organometallic Chemistry; carbonyl (CO) complexesIn general, the more negative the charge on theorganometallic species, the greater the tendencyof the metal to donate electrons to the π* orbitalsof CO and the lower the energy of the C-Ostretching vibrations.

13-4 Ligands in Organometallic Chemistry; bridging modes of CO

13-4 Ligands in Organometallic Chemistry; bridging modes of COTerminal and bridging carbonyl ligands can beconsidered 2-electron donors.

13-4 Ligands in Organometallic Chemistry; bridging modes of CO

13-4 Ligands in Organometallic Chemistry; binary carbonyl complexes17-e- too small to permit aseventh coordination siteBinary carbonyl complexesMore detailanalysis isnecessary

13-4 Ligands in Organometallic Chemistry; binary carbonyl complexesSynthesis of binary carbonyl complexes1. Direct reaction of a transition metal and CO; high T & P2. Reductive carbonylations3. Thermal or photochemical reactionExchange reaction

13-4 Ligands in Organometallic Chemistry; oxygen-bonded cabonyls

13-4 Ligands in Organometallic Chemistry; ligands similar to COCS, CSeSimilar to CO in their bonding modesIn terminal or bridgingCS usually functions as a stronger σ donor and π acceptorthan COisoelectronic; CN- and N2CN- is a stronger σ donor and a somewhat π weakeracceptor than COCN- bonds readily to metals having higher oxidation statesN2 is a weaker donor and acceptor than CONitrogen fixation

13-4 Ligands in Organometallic Chemistry; ligands similar to CO; NO complexes

13-4 Ligands in Organometallic Chemistry; hydride and dihydrogen complexesHydride complexesOrganic synthesis,catalytic reaction

13-4 Ligands in Organometallic Chemistry; hydride and dihydrogen complexesDihydrogen complexesOrganic synthesis,catalytic reactionDistance of H-Hthe metal is electron rich and donatestrongly to the π* of H2 ?with CO and NO ?

13-4 Ligands in Organometallic Chemistry; ligands having extended π systemsπ bonding within the ligands themselveslinear systems

13-4 Ligands in Organometallic Chemistry; ligands having extended π systemsπ bonding within the ligands themselveslinear systems

13-4 Ligands in Organometallic Chemistry; ligands having extended π systemsπ bonding within the ligands themselvescyclic systems

13-4 Ligands in Organometallic Chemistry; ligands having extended π systemsπ bonding within the ligands themselvescyclic systems

13-4 Bonding between Metal Atoms and Organic πSystems; linear π systemsπ –ethylene complexesTypically bent backaway from the metalπ-bonding electron pairthe empty π*-orbitalFree ethylene133.7 pm, 1623 cm-1Coordinated ethylene 137.5 pm, 1516 cm-1

13-4 Bonding between Metal Atoms and Organic πSystems; linear π systemsπ –allyl complexesacceptorDonor or acceptordonor

13-4 Bonding between Metal Atoms and Organic πSystems; linear π systemsπ –allyl complexesConversion between η1 and η3Catalytic reactionOther linear π systems

13-4 Bonding between Metal Atoms and Organic πSystems; cyclic π systemsCyclopentadienyl (Cp) complexesη1, η3 and η5C5(CH3)5 Cp*Gas phase and low-TMost stable conformation

13-4 Bonding between Metal Atoms and Organic πSystems; cyclic π systems

13-4 Bonding between Metal Atoms and Organic πSystems; cyclic π systemsMolecularorbitalenergylevels ofFerrocene

13-4 Bonding between Metal Atoms and Organic πSystems; cyclic π systems

13-4 Bonding between Metal Atoms and Organic πSystems; cyclic π systemsOther metallocenes# of electron stability reactivity

13-4 Bonding between Metal Atoms and Organic πSystems; cyclic π systems

13-4 Bonding between Metal Atoms and Organic πSystems; cyclic π systemsComplexescontainingcyclopentadienyland CO ligandHalf-sandwich

13-5 Fullerene ComplexesTypes of fullerene complexes1. Adducts to the oxygens2. As a lignd3. Encapsulated metals4. Intercalation compounds of alkali metalsAdducts to the oxygens

13-5 Fullerene ComplexesAs ligandsDihapto, pentahepto, hexahaptoDisplacement reactionMore than one metal

13-5 Fullerene ComplexesC70η2-η2-η2 and η5

13-5 Fullerene ComplexesEncapsulated metalsBy laser-induced vapor phase reactions between carbon and the metalLa@C82; La3 , C823-

13-6 Complexes Containing M-C, M C and M C Bonds

13-6 Complexes Containing M-C, M C and M C Bonds; alkyl and related complexesSynthetic routeRelatively rare: kinetically unstable and difficult to isolateEnhancing the stability; By blocking pathways to decompositionmtallacycleProposed as intermediates in a variety catalytic processes

13-6 Complexes Containing M-C, M C and M C Bonds; alkyl and related complexes

13-6 Complexes Containing M-C, M C and M C Bonds; carbene complexesd orbitalp orbital

13-6 Complexes Containing M-C, M C and M C Bonds; carbene complexes2-electron donorHighly electronegative atom can participate in the π bonding stabilize

13-6 Complexes Containing M-C, M C and M C Bonds; carbene complexesOlefin metathesisHighly nucleophilic reagentX-ray; Cr-C, C-ONMR; RT (one signal), low T (two peak)Why?C-O 143 pmC O 116pmHighly electronegative atom can participate in the π bonding stabilize

13-6 Complexes Containing M-C, M C and M C Bonds; carbyne (alkylidyne) complexes 3-electron donorLewis acidσ donorπ acceptor

13-6 Spectral Analysis and Characterization ofOrganometallic Complexes; IR spectraX-ray, Mass spectrometry, elementalanalysis, conductivity measurement etc.# of bandsProvide clues to the geometry or symmetry

13-6 Spectral Analysis and Characterization ofOrganometallic Complexes; IR spectra

13-6 Spectral Analysis and Characterization ofOrganometallic Complexes; IR spectrapositions of bandsProvide clues to the electronic environment on the metalThe greater the electronic density on the metal ?In general, the more negative the charge on theorganometallic species, the greater the tendencyof the metal to donate electrons to the π* orbitalsof CO and the lower the energy of the C-Ostretching vibrations.

13-6 Spectral Analysis and Characterization ofOrganometallic Complexes; IR spectraWhat do you get from this data?Other ligands also have similar correlation. (NO )

13-6 Spectral Analysis and Characterization ofOrganometallic Complexes; NMR spectra1H, 13C, 19F, 31P,metal nuclei etc.Chemical shifts, splitting patterns, coupling constants13CNMRChemical shift

13-6 Spectral Analysis and Characterization ofOrganometallic Complexes; NMR spectra1HNMRintegration

13-6 Spectral Analysis and Characterization ofOrganometallic Complexes; NMR spectraMolecular rearrangement processesAt RT; 2 singletsAt low TRing whizzer

HomeworkExercise 13-1 13-12Problem 1, 2, 4, 6, 13, 20, 33.

Organometallic chemistry is the study of chemical compounds . Organometallic compounds find practical use in stoichiometric and catalytically active compounds. Electron counting is key in understanding organometallic chemistry. The 18-electron rule is helpful in predicting the . Homework Exercise 13-1 13-12 Problem 1, 2, 4, 6, 13, 20, 33.