Organometallic Compounds: Chapter 11Organometallic CompoundsGrignard & Lithium ReagentsGrignard & Lithium ReagentsGilman ReagentsSlide 6Suzuki and Heck ReactionsGrubbs & Schrock MetathesisRetrosynthetic Analysis: Using Ethylene Oxide (EO)Chapter 11 1Organometallic Compounds:Organometallic Compounds:Chapter 11Chapter 11Chapter 11 2Organometallic CompoundsMost metals are less electronegative than carbonIn general a carbon bonded to a metal is nucleophilic and carbanion-like (C–)Four major classes of organometallic compounds are:Organolithium compoundsGrignard reagentsCupratesOrganopalladium compoundsChapter 11 3Grignard & Lithium ReagentsGrignard and lithium Organometallic reagents made by reacting a halide with elemental metalMg essentially slides into C-halogen bondLi simply replaces halogenChapter 11 4Grignard & Lithium ReagentsAlthough the carbon–metal bonds are not completely ionic, organolithium compounds and Grignard reagents react as if the carbon portion were a carbanionConsider the reaction of a Grignard reagent with an ethylene oxideEthylene oxide is a good way to extend a carbon chain by two carbons via use of halide to make organometallic cpd with negative charge on CCH2CH2OCH3CH2CH2CH2CH2CH2OCH3CH2CH2CH2MgBr ++ Mg2+ + Br-CH3CH2CH2CH2CH2CH2OHCH3CH2CH2CH2CH2CH2OHChapter 11 5Gilman ReagentsGilman reagents, also called organocuprates, are prepared from the reaction of an organolithium reagent with copper(I) iodide in diethyl ether or THFChapter 11 6Gilman ReagentsWhen a Gilman reagent reacts with an alkyl halide (except F-) one of the alkyl groups replaces the halideAlkyl groups can substitute halogens attached to alkene or aromatic C with Gilman reagent; impossible with SN1 or SN2 reactionMechanism unknown, probably radicalChapter 11 7Suzuki and Heck ReactionsVarious palladium catalysts substitute ordinary unfunctionalized alkenes for Br, I, or triflate (OTf) leaving group attached to benzene or alkene (Heck).Reagent can even be made to substitute alkyl groups if a dialkoxyalkylborane reagent is used with it (Suzuki).Chapter 11 8Grubbs & Schrock MetathesisTerminal alkenes couple eliminating ethylene with rhodium catalyst (Grubbs).Terminal alkynes couple eliminating acetylene (ethyne) using molybdenum or tungsten catalyst (Schrock).Chapter 11 9Retrosynthetic Analysis: Using Ethylene Oxide (EO)Product has 2 extra C’s plus CN2 extra C’s mean use EOAlways work back to an ROH for EO analysisRetro EO addn removes 2 C’s and an OHHere CN has sub’d for an ROH-derived LG (leav grp)Make OTs the LG & derive the ROTs from ROHCyclohexyl C attacks EO to make this