organometallic reagents carbon-metal bonds

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Organometallic Reagents Carbon-Metal Bonds. R. X. R. M. Nucleophilic carbon. +. . . +. Organometallic Reagents. R. X + 2 Li. R. Li + Li X. Organolithium Reagents. normally prepared by reaction of alkyl halides with lithium. - PowerPoint PPT Presentation

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PowerPoint Presentation - Organic Chemistry Fifth Edition

Organometallic ReagentsCarbon-Metal Bonds

1RX+RM+Nucleophilic carbon4

Organometallic Reagents

same for ArXis an oxidation-reduction reaction: carbon is reduced

Organolithium ReagentsRX + 2LiRLi + LiXnormally prepared by reaction of alkyl halides with lithium10Examples(CH3)3CCl + 2Lidiethylether10C(CH3)3CLi + LiCl(75%)Br+ 2Lidiethylether35CLi+ LiBr(95-99%)11

Preparation of Organomagnesium Reagentssame for ArXGrignard ReagentsRX + MgRMgXprepared by reaction of alkyl halides with magnesiumDiethyl ether is most often used solvent. Tetrahydrofuran is also used.10Nobel Prize 1912

Born: 6 May 1871, Cherbourg, FranceDied: 13 December 1935, Lyon, FranceAffiliation at the time of the award: Nancy University, Nancy, France10Examplesdiethylether10C(96%)Br+ Mgdiethylether35CMgBr(95%)Cl+ MgMgCl11Alkyl halides, vinyl halides, and aryl halides can all be used to form organolithium and organomagnesiumcompoundsHowever, these organometallic compounds cannot be prepared from compounds containing acidic groups (OH, NH2, NHR, SH, C=CH, CO2H)Cannot use H2O, CH3OH, CH3CH2OH, etc. as solventsCannot prepare from substances such as HOCH2CH2Br, etc.Synthesis of Alcohols Grignard or Organolithium ReagentsOrganolithium reagents react with carbonyls in the same general way that Grignard reagents do.1Direct formation of a Grignard reagent, involves an alkyl halide reacted with Mg metal.

Grignard Reagents

Indirect Grignard ReagentsGrignard Reagents can be prepared from other Grignard Reagents (trans-metallation)

26Indirect Grignard Reagents-acetylenic Grignard Reagents are prepared by an acid-base Grignard reaction CH3CH2MgBr+CH3CH3stronger acidweaker acidHCCHHCCMgBr+26QuestionSelect the best method to prepare CH3CH2CCMgI.A)CH3CH2CC-I + Mg (in diethyl ether)B)I-CH2CH2CCH + Mg(OH)2 (in diethyl ether)C)CH3CH2CCH + CH3MgI (in diethyl ether)D)CH3CH2CCH + Mg (in diethyl ether)A Grignard reagent, RMgX, is a very strong base and a good nucleophile; water/moisture MUST be avoided in its reaction.

Grignard Reactions

QuestionIf water cant be used as a solvent, can other protic solvents be used instead?

Yes (A) / No (B)

ExampleMgBr(100%)+ CH3OH+CH3OMgBr11Grignard reagents act as nucleophilestoward the carbonyl groupRMgXCO+MgX+RCOdiethyletherRCOHH3O+two-step sequence gives an alcohol as the isolated product 23formaldehyde to give primary alcohols other aldehydes to give secondary alcoholsketones to give tertiary alcoholsesters to give tertiary alcoholsGrignard reagents react with:3formaldehyde to give primary alcohols Grignard reagents react with:3Grignard reagents react with formaldehydeRMgXCOMgX++RCORCOHH3O+diethyletherproduct is a primary alcoholHHHHHH23ExamplediethyletherClMgMgClCOHHCH2OMgClH3O+CH2OH(64-69%)5formaldehyde to give primary alcohols aldehydes to give secondary alcoholsGrignard reagents react with:3QuestionThe reaction between propanal and ethylmagnesium chloride followed by H3O+ will produce

A) B)

C)D)

Grignard reagents react with aldehydesRMgXCO+RCORCOHH3O+diethyletherproduct is a secondary alcoholHR'HR'HR'MgX+23ExamplediethyletherMgCOH3CHH3O+(84%)CH3(CH2)4CH2BrCH3(CH2)4CH2MgBrCH3(CH2)4CH2CHCH3OMgBrCH3(CH2)4CH2CHCH3OH5Question What is the product of the reaction of ethylmagnesium bromide (CH3CH2MgBr) with butanal (CH3CH2CH2CH=O) followed by dilute acid?A)2-hexanolB)1-butanolC)3-hexanolD)3-pentanolExample(76%)H2CCHLi+CHO1. diethyl ether

2. H3O+CH2CHCHOH5formaldehyde to give primary alcohols aldehydes to give secondary alcoholsketones to give tertiary alcoholsGrignard reagents react with:3Grignard reagents react with ketonesRMgXCOMgX++RCORCOHH3O+diethyletherproduct is a tertiary alcoholR"R'R"R'R"R'23Question What is the product of the reaction shown at the right?

A)B)

C)D)

ExamplediethyletherMgH3O+(62%)CH3ClCH3MgClOCH3ClMgOCH3HO5QuestionTwo alcohols, each having the molecular formula C11H22O, are formed in the reaction of methyl lithium with 3-(R)-tert-butylcyclohexanone. These two alcohols areA)constitutional isomers.B)enantiomers in equal amounts.C)enantiomers in unequal amounts.D)diastereomers.

Preparation of Tertiary AlcoholsFrom Esters and Grignard Reagents

1Grignard reagents react with estersRMgXCO

MgX++RCOdiethyletherOCH3OCH3R'R'but species formed is unstable and dissociates under the reaction conditions to form a ketone23Grignard reagents react with estersRMgXCO

MgX++RCOdiethyletherOCH3OCH3R'R'CH3OMgXCORR'

this ketone then goes on to react with a second mole of the Grignard reagent to give a tertiary alcohol23Example2 CH3MgBr+(CH3)2CHCOCH3O1. diethyl ether

2. H3O+(CH3)2CHCCH3OHCH3(73%)Two of the groups attached to the tertiary carbon come from the Grignard reagent26QuestionWhich one of the compounds below will be produced when 2 moles of methylmagnesium bromide is added to 1 mole of methyl propanoate (CH3CH2CO2CH3) followed by acid?A)CH3CH2COCH3B)CH3CH2CO2-MgBrC)(CH3)2C(OH)CH2CH3D)CH3CH2CH2CH3 E) 3-methyl-2-butanol

What is the product of the following reaction?QuestionGrignard Reactions

Question Which one of the compounds below will be produced when methylmagnesium bromide is added to propanoic acid (CH3CH2CO2H)?A)CH3CH2COCH3B)CH3CH2CO2-MgBrC)CH3CH2CH(OH)CH3D)CH3CH2CH2CH3

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