8Chapter 14 mod

8Chapter 14 mod - Chapter 14 Organometallic Compounds 14-1...

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Unformatted text preview: Chapter 14 Organometallic Compounds 14-1 14.1 Organometallic Nomenclature 14-2 Metal is the parent Metal is the parent Lii L H2C CHNa Cyclopropyllithium Vinylsodium CH3CH2MgCH2CH3 CH3MgI Diethylmagnesium Methylmagnesium iodide 14-3 14.2 Carbon-Metal Bonds in Organometallic Compounds 14-4 Electronegativities Electronegativities F O N C H 4.0 3.5 3.0 2.5 2.1 2.1 H Cu Zn Al Mg Mg Li Na K 2.1 1.9 1.6 1.5 1.2 1.0 0.9 0.8 14-5 Polarity of Bonds Polarity of Bonds δ+ R δ– X δ– R δ+ M organometallics are a organometallics source of nucleophilic carbon carbon 14-6 Polarity of Bonds Polarity of Bonds CH3F CH3Li 14-7 14.3 Preparation of Organolithium Compounds 14-8 Organolithium Compounds Organolithium Compounds Organolithium normally prepared by reaction of alkyl halides normally with lithium with R X + 2Li R Li + LiX same for Ar—X same Ar An oxidation-reduction reaction: An carbon is reduced 14-9 Examples Examples diethyl ether (CH3)3CCl + 2Li (CH3)3CLi + LiCl –10°C (75%) diethyl ether Br + 2Li Br Lii + LiBr L 35°C (95-99%) 14-10 Electron Bookkeeping Electron Bookkeeping R [R X] • X + Li • – • R • Li Li• R• + + Li+ • X– • 14-11 14.4 Preparation of Organomagnesium Compounds: Grignard Reagents 14-12 Grignard Reagents Grignard Reagents prepared by reaction of alkyl halides prepared with magnesium with R X + Mg RMgX same for Ar—X same Ar Diethyl ether is most often used solvent. Diethyl Tetrahydrofuran is also used. Tetrahydrofuran 14-13 Examples Examples diethyl ether Cll + Mg C MgCl MgCl –10°C (96%) diethyl ether Br + Mg Br MgBr MgBr 35°C (95%) 14-14 Electron Bookkeeping Electron Bookkeeping R • [R X] • – X + Mg • • + Mg+ • Mg+ • R • Mg+ • X– • R• + • X– • 14-15 Order of Reactivity Order of Reactivity I > Br > Cl >> F RX > ArX 14-16 Forbidden Groups Forbidden Groups certain groups cannot be present in the solvent the halide from which the Grignard reagent the is prepared is the substance with which the Grignard the reagent reacts reagent 14-17 Forbidden Groups Forbidden Groups Anything with an OH, SH, or NH group i.e. an acidic hydrogen therefore cannot use H2O, CH3OH, OH, CH3CH2OH, etc. as solvents CH cannot prepare Grignard reagent from cannot substances such as HOCH2CH2Br, etc. substances 14-18 14.5 Organolithium and Organomagnesium Compounds as Brønsted Bases 14-19 Brønsted basicity Brønsted basicity δ– R M H δ+ • OR' •• •• • R H + – •• M • OR' • •• Grignard reagents (M = MgX) and organolithium reagents (M = Li) are strong organolithium bases. bases. 14-20 Example Example CH3CH2CH2CH2Li + H2O water is a stronger water acid than butane acid CH3CH2CH2CH3 + LiOH (100%) 14-21 Example Example MgBr + CH3OH MgBr methanol is a methanol stronger acid than benzene benzene + CH3OMgBr (100%) 14-22 Table 14.2 Table 14.2 Approximate Acidities of Hydrocarbons Approximate Acidities of Hydrocarbons Hydrocarbon (CH3)3CH 71 CH3CH3 62 CH4 60 Ethylene Benzene Ammonia Acetylene Water 45 43 36 26 16 pKa Hydrocarbons are Hydrocarbons very weak acids. very Their conjugate Their bases are very strong bases. strong Grignard reagents Grignard and organolithium reagents are strong bases. bases. 14-23 Acetylenic Grignard Reagents Acetylenic Grignard Reagents are prepared by an acid-base reaction CH3CH2MgBr + CH3CH3 + HC CH stronger acid HC CMgBr weaker acid 14-24 14.6 Synthesis of Alcohols Using Synthesis Grignard Reagents Grignard 14-25 Grignard reagents act as nucleophiles Grignard reagents act as nucleophiles toward the carbonyl group toward the carbonyl group δ– R δ+ C diethyl ether R C • O •– •• •• MgX O • •• •• • two-step sequence two-step gives an alcohol as the isolated product + MgX H3O+ R C • OH •• • 14-26 Grignard reagents react with: Grignard reagents react with: formaldehyde to give primary alcohols aldehydes to give secondary alcohols aldehydes ketones to give tertiary alcohols esters to give tertiary alcohols 14-27 Grignard reagents react with: Grignard reagents react with: Grignard formaldehyde to give primary alcohols 14-28 Grignard reagents react with formaldehyde Grignard reagents react with formaldehyde H δ– R δ+ H C diethyl ether H R C • O •– •• •• MgX O • •• •• • H + MgX H3O+ product is a product primary alcohol primary H R C • OH •• H 14-29 Example Example Mg Cll C diethyl ether MgCl MgCl H C O H CH2OH (64-69%) H3O+ CH2OMgCl 14-30 Grignard reagents react with: Grignard reagents react with: formaldehyde to give primary alcohols aldehydes to give secondary alcohols aldehydes 14-31 Grignard reagents react with aldehydes Grignard reagents react with aldehydes H δ– R δ+ R' C MgX O • •• •• • diethyl ether H R C R' O • + MgX •– •• •• H3O+ product is a product secondary alcohol secondary H R C • OH •• R' 14-32 Example Example Mg CH3(CH2)4CH2Br diethyl ether CH3(CH2)4CH2MgBr H3C C O H CH3(CH2)4CH2CHCH3 OH (84%) H3O+ CH3(CH2)4CH2CHCH3 OMgBr 14-33 Grignard reagents react with: Grignard reagents react with: formaldehyde to give primary alcohols aldehydes to give secondary alcohols aldehydes ketones to give tertiary alcohols 14-34 Grignard reagents react with ketones Grignard reagents react with ketones R" δ– R δ+ R' C diethyl ether R" R C • O •– •• •• MgX O • •• •• • R' + MgX H3O+ product is a product tertiary alcohol tertiary R" R C • OH •• R' 14-35 Example Example Mg CH3Cl CH HO CH3 (62%) diethyl ether H3O+ CH3MgCl O ClMgO CH3 CH 14-36 14.7 Synthesis of Alcohols Using Organolithium Reagents Organolithium reagents react with Organolithium aldehydes and ketones in the same way that Grignard reagents do. way 14-37 Example Example H2C O CHLi + CH 1. diethyl ether 2. H3O+ CHCH CH2 CH OH (76%) 14-38 14.8 Synthesis of Acetylenic Alcohols 14-39 Using Sodium Salts of Acetylenes Using Sodium Salts of Acetylenes NaNH2 HC CH HC NH3 CNa O HC CNa + HO C CH 1. NH3 2. H3O+ (65-75%) (65-75%) 14-40 Using Acetylenic Grignard Reagents Using Acetylenic Grignard Reagents CH3(CH2)3C CH + CH3CH2MgBr diethyl ether CH3(CH2)3C CMgBr + CH3CH3 1. H2C O 2. H3O+ CH3(CH2)3C CCH2OH (82%) 14-41 14.9 Retrosynthetic Analysis Retrosynthetic analysis is the process by Retrosynthetic which we plan a synthesis by reasoning backward from the desired product (the "target molecule"). "target 14-42 Retrosynthetic Analysis of Alcohols Retrosynthetic Analysis of Alcohols C OH Step 1 Locate the carbon that bears the Step hydroxyl group. hydroxyl 14-43 Retrosynthetic Analysis of Alcohols Retrosynthetic Analysis of Alcohols C OH Step 2 Disconnect one of the groups Step attached to this carbon. attached 14-44 Retrosynthetic Analysis of Alcohols Retrosynthetic Analysis of Alcohols C OH 14-45 Retrosynthetic Analysis of Alcohols Retrosynthetic Analysis of Alcohols MgX C O What remains is the combination of Grignard What reagent and carbonyl compound that can be used to prepare the alcohol. used 14-46 Example Example CH3 C There are two There other possibilities. Can you see them? them? CH2CH3 OH CH3MgX O C CH2CH3 14-47 Synthesis Synthesis CH3Br Mg, diethyl ether CH3MgBr O 1. C CH2CH3 2. H3O+ CH3 C OH CH2CH3 14-48 Preparation of Tertiary Alcohols From Esters and Grignard Reagents (also in Chapter 19) 14-49 Grignard reagents react with esters Grignard reagents react with esters δ– R R' •• δ+ OCH3 •• C MgX O • •• •• • diethyl ether R' R C • O •– •• •• •• OCH3 •• + MgX but species formed is but unstable and dissociates under the reaction conditions to form a ketone conditions 14-50 Grignard reagents react with esters Grignard reagents react with esters δ– R R' •• δ+ OCH3 •• C R' diethyl ether R • O •– •• •• MgX O • •• •• • this ketone then goes on to react with a second mole of the Grignard reagent to give a tertiary alcohol give C •• OCH3 •• + MgX –CH3OMgX R R' C O• •• • 14-51 Example Example O 2 CH3MgBr + (CH3)2CHCOCH3 1. diethyl ether 2. H3O+ OH (CH3)2CHCCH3 CH3 Two of the groups Two attached to the tertiary carbon come from the Grignard reagent Grignard (73%) 14-52 14.10 Alkane Synthesis Using Alkane Organocopper Reagents Organocopper 14-53 Lithium Dialkylcuprates Lithium Dialkylcuprates Lithium dialkylcuprates are useful Lithium synthetic reagents. reagents. They are prepared from alkyllithiums and They a 2RLi + CuX R2CuLi + LiX 2RLi Cu copper(I) halide. copper(I) [customary solvents are diethyl ether and [customary tetrahydrofuran (THF)] tetrahydrofuran 14-54 How? How? the alkyllithium first reacts with the the copper(I) halide Li halide R R Li+ R Cu I Li Cu I– 14-55 How? How? the alkyllithium first reacts with the copper(I) halide Li halide R R Li+ R Cu I Li Cu I– then a second molecule of the alkyllithium then reacts with the alkylcopper species formed in the first step the R Li+ R Li R Cu R Cu – 14-56 Lithium diorganocuprates are used to Lithium diorganocuprates are used to form C—C bonds form C—C bonds R2CuLi + R'X R R' + RCu + LiX Ar2CuLi + R'X Ar R' + ArCu + LiX 14-57 Example: Lithium dimethylcuprate Example: Lithium dimethyl cuprate Example: dimethyl Example: dimethyl (CH3)2CuLi + CH3(CH2)8CH2I diethyl ether CH3(CH2)8CH2CH3 (90%) primary alkyl halides work best (secondary primary and tertiary alkyl halides undergo elimination) tertiary 14-58 Example: Lithium diphenylcuprate Example: Lithium diphenyl cuprate Example: diphenyl Example: diphenyl (C6H5)2CuLi + CH3(CH2)6CH2I diethyl ether CH3(CH2)6CH2C6H5 (99%) 14-59 Vinylic halides can be used Vinylic halides can be used (CH3CH2CH2CH2)2CuLi + Br Br diethyl ether CH2CH2CH2CH3 (80%) (80%) 14-60 Aryl halides can be used Aryl halides can be used (CH3CH2CH2CH2)2CuLi + I diethyl ether CH2CH2CH2CH3 (75%) 14-61 14.11 An Organozinc Reagent An for for Cyclopropane Synthesis 14-62 Iodomethylzinc iodide Iodomethylzinc iodide formed by reaction of diiodomethane with zinc that has been coated with copper (called zinc-copper couple) CH2I2 + Zn Cu ICH2ZnI reacts with alkenes to form cyclopropanes reaction with alkenes is called the Simmons-Smith reaction 14-63 Example Example CH2CH3 H2C via I C CH3 CH2 ZnI CH2I2, Zn/Cu diethyl ether CH2CH3 CH CH3 (79%) 14-64 Stereospecific syn-addition Stereospecific syn-addition CH3CH2 CH2CH3 C H CH2I2, Zn/Cu CH3CH2 CH H C H diethyl ether CH2CH3 H 14-65 Stereospecific syn-addition Stereospecific syn-addition CH3CH2 H C H CH2I2, Zn/Cu CH3CH2 CH H C CH2CH3 diethyl ether H CH2CH3 14-66 14.12 Carbenes and Carbenoids 14-67 Carbene Carbene name to give to species that contains a divalent carbon (carbon with two bonds and six electrons) •• C Br Br Dibromocarbene (same chemistry with dichlorocarbenes) Carbenes are very reactive; normally cannot be Carbenes isolated and stored. isolated Are intermediates in certain reactions. 14-68 Generation of Dibromocarbene Generation of Dibromocarbene Br Br – •• H + • OC(CH3)3 •• C • •• Br Br Br C• • – + H •• OC(CH3)3 •• Br 14-69 Generation of Dibromocarbene Generation of Dibromocarbene •• C Br Br + Br – Br Br C• – • Br 14-70 Carbenes react with alkenes Carbenes react with alkenes to give cyclopropanes to give cyclopropanes KOC(CH3)3 + CHBr3 CHBr Br (CH3)3COH Br (75%) CBr2 is an intermediate stereospecific syn addition 14-71 14.13 Transition-Metal Organic Transition-Metal Compounds Compounds 14-72 Introduction Introduction Many organometallic compounds derived from transition metals have useful properties. Typical transition metals are iron, nickel, chromium, platinum, and rhodium. 14-73 18-Electron Rule 18-Electron Rule The number of ligands attached to a metal will be such that the sum of the electrons brought by the ligands plus the valence electrons of the metal equals 18. When the electron-count is less than 18, When metal is said to be coordinatively unsaturated coordinatively and can take on additional ligands. 18-Electron rule is to transition metals as the octet rule is to second-row elements. 14-74 Example Example CO OC Ni CO CO Nickel carbonyl Ni has the electron Ni configuration [Ar]4s23d8 configuration Ni has 10 valence Ni electrons electrons Each CO uses 2 Each electrons to bond to Ni electrons 4 CO contribute 8 CO valence electrons valence 10 + 8 = 18 14-75 Example Example OC Cr (Benzene)tricarbonylchromium CO CO Cr has the electron configuration [Ar]4s23d4 Cr has 6 valence electrons Each CO uses 2 electrons to bond to Cr Each Cr 3 CO contribute 6 valence electrons benzene uses its 6 π electrons to bind to Cr. benzene Cr 14-76 Example Example Fe Ferrocene Fe2+ has the electron configuration [Ar]3d6 has Each cyclopentadienide anion contributes 6 π Each electrons electrons Total 6 + 6 + 6 = 18 Organometallic compounds with Organometallic cyclopentadienide ligands are called metallocenes. metallocenes. 14-77 14.14 14.14 Homogeneous Catalytic Homogeneous Hydrogenation Hydrogenation Wilkinson’s Catalyst Wilkinson’s Catalyst Ni, Pt, Pd, and Rh can act as a heterogeneous catalyst in the hydrogenation of alkenes. catalyst However, tris(triphenylphosphine)rhodium chloride However, was found to be soluble in organic solvents. was This catalyst was developed by Sir Geoffrey This Wilkinson, who received a Nobel Prize in 1973. Wilkinson, P(C6H5)3 (C6H5)3P Rh Cl P(C6H5)3 Wilkinson's Catalyst Mechanism of Homogeneous Hydrogenation Hydrogenation Steps 1 and 2: Catalyst is converted to the active form. + H2 Cl then - (C6H5)3P P(C6H5)3 Cl Rh (C6H5)3P (C6H5)3P P(C6H5)3 then - (C6H5)3P H Rh P(C6H5)3 H + H2 This is the active form of the catalyst. Mechanism of Homogeneous Hydrogenation Hydrogenation Step 3: Alkene bonds to rhodium through π electrons. Step Cl Cl (C6H5)3P H Rh P(C6H5)3 H (C6H5)3P H Rh P(C6H5)3 H + CH2=CHCH3 CH2=CHCH3 Rhodium-alkene complex Mechanism of Homogeneous Hydrogenation Hydrogenation Step 4: Rhodium-alkene complex rearranges. Cl (C6H5)3P H Rh P(C6H5)3 Cl H CH2=CHCH3 Rhodium-alkene complex (C6H5)3P H Rh P(C6H5)3 CH2CH2CH3 Mechanism of Homogeneous Hydrogenation Hydrogenation Step 5: Hydride migrates from Rh to carbon. Cl (C6H5)3P H Rh P(C6H5)3 CH2CH2CH3 [(C6H5)3P]2RhCl + CH3CH2CH3 Mechanism of Homogeneous Hydrogenation Hydrogenation Step 6: Active form of the catalyst is regenerated. Cl [(C6H5)3P]2RhCl + H2 (C6H5)3P H Rh P(C6H5)3 H 14.15 14.15 Olefin Metathesis Olefin Metathesis Olefin In crossed-olefin metathesis, one alkene is In converted to a mixture of two new alkenes. converted 2 CH3CH=CH2 catalyst CH2=CH2 + CH3CH=CHCH3 The reaction is reversible, and regardless of The whether we start with propene or a 1:1 mixture of ethylene and 2-butene, the same mixture is obtained. obtained. Olefin Metathesis Olefin The reaction is generally catalyzed a transition The metal complex. Typically Ru, W, or Mo are used.Shown below is Grubb’s catalyst. used.Shown Cl PCy Ru Cl PCy CH Cy = Ring-Opening Metathesis Ring-Opening Ring-opening metathesis is used as a method Ring-opening of polymerization. of Usually, it is applied most often when ring Usually, opening creates a relief of strain, as in some bicyclic alkenes. bicyclic =HC catalyst CH= -80oC n Norbornene Polynorbornene 14.16 Ziegler-Natta Catalysis of Ziegler-Natta Alkene Polymerization Alkene The catalysts used in coordination polymerization are transition-metal organic compounds. 14-78 Ethylene oligomerization Ethylene oligomerization n H2C CH2 Al(CH2CH3)3 CH3CH2(CH2CH2)n-2CH CH2 Triethylaluminum catalyzes the formation Triethylaluminum of alkenes from ethylene. of These compounds are called ethylene These ethylene oligomers and the process is called oligomers oligomerization. oligomerization 14-79 Karl Ziegler Karl Ziegler Karl n H2C CH2 Al(CH2CH3)3 CH3CH2(CH2CH2)n-2CH CH2 Ziegler found that oligomerization was Ziegler affected differently by different transition metals. Some gave oligomers with 6-18 carbons, others gave polyethylene. carbons, 14-80 Karl Ziegler Karl Ziegler n H2C CH2 Al(CH2CH3)3 CH3CH2(CH2CH2)n-2CH CH2 The ethylene oligomers formed under The Ziegler's conditions are called linear α-olefins -olefins and have become important industrial chemicals. chemicals. 14-81 Karl Ziegler Karl Ziegler Karl n H2C CH2 Al(CH2CH3)3 CH3CH2(CH2CH2)n-2CH CH2 The polyethylene formed under Ziegler's The conditions is called high-density polyethylene and has, in many ways, more desirable properties than the polyethylene formed by free-radical polymerization. free-radical 14-82 Giulio Natta Giulio Natta n H2C CHCH3 Al(CH2CH3)3 polypropylene Natta found that polymerization of propene Natta under Ziegler's conditions gave mainly isotactic polypropylene (methyl groups on same side). This discovery made it possible to produce polypropylene having useful properties. useful 14-83 Ziegler-Natta Catalysts Ziegler-Natta Catalysts A typical Ziegler-Natta catalyst is a typical combination of TiCl4 and (CH3CH2)2AlCl, combination AlCl, or TiCl3 and (CH3CH2)3Al. or Many Ziegler-Natta catalyst combinations Many include a metallocene. include 14-84 Mechanism of Coordination Polymerization Mechanism of Coordination Polymerization Al(CH2CH3)3 + TiCl4 ClAl(CH2CH3)2 + CH3CH2TiCl3 14-85 Mechanism of Coordination Polymerization Mechanism of Coordination Polymerization Al(CH2CH3)3 + TiCl4 ClAl(CH2CH3)2 + CH3CH2TiCl3 CH3CH2TiCl3 + H2C CH2 CH3CH2TiCl3 H2C CH2 14-86 Mechanism of Coordination Polymerization Mechanism of Coordination Polymerization CH3CH2TiCl3 H2C CH2 14-87 Mechanism of Coordination Polymerization Mechanism of Coordination Polymerization TiCl3 CH3CH2CH2CH2 CH3CH2TiCl3 H2C CH2 14-88 Mechanism of Coordination Polymerization Mechanism of Coordination Polymerization TiCl3 CH3CH2CH2CH2 H2C CH2 H2C CH2 TiCl3 CH3CH2CH2CH2 14-89 Mechanism of Coordination Polymerization Mechanism of Coordination Polymerization CH3CH2CH2CH2CH2CH2 TiCl3 H2C CH2 TiCl3 CH3CH2CH2CH2 14-90 Mechanism of Coordination Polymerization Mechanism of Coordination Polymerization CH3CH2CH2CH2CH2CH2 TiCl3 H2C CH2 etc. 14-91 End of Chapter 14 ...
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