Chapter 112 Organometallic 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 compounds
Chapter 113 Grignard & 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 halogen
Chapter 114 Grignard & 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 C
Chapter 115 Gilman Reagents Gilman reagents, also called organocuprates, are prepared from the reaction of an organolithium reagent with copper(I) iodide in diethyl ether or THF
Chapter 116 Gilman 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 S N 1 or S N 2 reaction Mechanism unknown, probably radical
Chapter 117 Suzuki and Heck Reactions Various palladium catalysts substitute ordinary unfunctionalized alkenes for Br, I, or triflate (OT f ) 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 118 Grubbs & Schrock Metathesis Terminal alkenes couple eliminating ethylene with rhodium catalyst (Grubbs). Terminal alkynes couple eliminating acetylene (ethyne) using molybdenum or tungsten catalyst (Schrock).
Chapter 119 Retrosynthetic 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 ROH