Chapter 15 PDF - Chapter 15 Organometallic Compounds Ch-15-...

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Unformatted text preview: Chapter 15 Organometallic Compounds Ch-15- Organometallic Compounds Organometallic compound: A compound with c arbon m etal bond: CM. In this chapter: M = Mg, Li, and Cu. Historically important reagents with continued usefulness for synthetic chemistry. Organometallics can bring about transformations that cannot be accomplished otherwise. Very useful reagents for synthetic chemistry, particularly for CC-bond formation . More modern reactions with organometallics in Chapter 24. Ch-15- 1 Grignard Reagents Grignard Reagent: An organomagnesium compound. RMgX, ArMgX, C=CMgX. Readily available, easily prepared, relatively easy to handle. Ph Br + Mg Et 2 O Ph MgBr Bromobenzene Phenylmagnesium bromide Preparation : Addition of alkyl (R), aryl (Ar), alkenyl (vinylic) (C=C) halide ( X = I , Br , Cl) to Mg metal in ether (Et 2 O) or THF as solvent. Alkyl Grignard reagents are in equilibrium between monoalkyl and dialkyl magnesium complexes. R MgX 2 R 2 Mg + MgX 2 Ch-15- 2 Grignard Reagents Grignard reagents (Mg = Lewis acid) dissolve in diethyl ether (Lewis base) as solvated coordination compounds . Ch-15- 3 Organolithium Reagents Prepared by reaction of an alkyl, aryl, or alkenyl halide with lithium metal. Ch-15- 4 Cl + 2 Li pentane Li + LiCl 1-Chlorobutane Butyl lithium 10 C Like Grignard reagents, organolithium compounds are (1) very reactive nucleophiles , (2) and powerful bases . Organolithium compounds react with atmospheric oxygen and with moisture; must be kept under N 2 or Ar . RMgX and RLi Carbonmetal bond (RM): Polar covalent (when the difference in electronegativity is 0.5 to 1.9, Tables 1.5, 1.6). The electronegativity E (cf. Pauling scale of electronegativity) of metals (M) is lower than that of carbon (C: E = 2.5)....
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Chapter 15 PDF - Chapter 15 Organometallic Compounds Ch-15-...

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