General methods of synthesis of organometallic compound

---

Organometallic chemistry is the study of chemical compounds containing at least one bond between a carbon atom of an organic compound and a metal, including alkaline, alkaline earth, transition metal, and other cases. The formation of novel organometallic compounds by the reaction of organic substrates with finely divided metal powders represents a powerful tool for the synthetic chemist. The direct reaction with a zerovalent metal is the only viable method of synthesis for many of these compounds.

Depending on the reduction potential of the metal, the reactivity of organometallic compounds varies markedly, the most reactive requiring low to moderate temperatures and inert conditions (atmosphere and solvents) for preparation and use.

% Ionic Character of H₃C – Metal (CH₃)₂Hg < (CH₃)₂Cd < (CH₃)₂Zn < (CH₃)2Mg < CH₃Li

There is two general methods for synthesis of organometallic compound as follows:

1. Reactions using elemental metals

The organometallic compounds are synthesized from elemental metals as follows:

Preparation of grignard reagent, alkyl lithiums
      ( M + RX → RMX)

Metal-hydrocarban rection such as the synthesis of cyclopentadienyle sodium, NaCp
       2M + 2RX → 2RM + H₂

Direct reaction of metals with CO producing metal carbonyles.
       M + CO → M(CO)_n

Metal vapor synthesis uing high vacuum and high temperature.
       M(vapor) + Substrate → RM

2. Synthesis by reactions

These following methods are used to prepare organometallic compound:

Exchange recations such as the metathesis of metal halides with alkylating reagents.
      MX + RM' → RM + M'X

Metal halogen (hydrogen exchange processes)
      RM + R'H → R'M + RH
      RM + R'X → R'M + RX

Addition reacation such as insertation reactions.
      RM + A → R-A-M

Oxidative additions
      ML_n + AB → M(A)(B)L_m

Decarbonylation.
      RCOM → RM + CO

β−hydrogen elimination
      CH₃CH₂M → HM(C₂H₄)

Anionic ate complex formation with carbanions.
       MR_n + M'R' → M' + [MR_nR]

Reductive carbonylation of metal oxides with CO
       MO_n + mCO → M(CO) _x + nCO₂

Electrochemical methods for preparing organometallic compounds in unusual oxidation states.
       RMⁿ⁺ + e → RM^(n-1)+
       RMⁿ⁺ - e → RM⁽ⁿ⁺¹⁾⁺

Preparation of Organomagnesium Reagents

RX + Mg ---->RM_gX

oxidation – reduction

Organomagnesiums are formed by the reaction of alkyl halides with magnesium metal.

Typical solvents are normally anhydrous diethyl ether or tetrahydrofuran.

The alkyl group can be primary, secondary or tertiary.

Halide reactivity : I > Br > Cl

Preparation of Organocopper Reagents

2RLi + CuX ------->2CuLi +Li⁺X^-

---

Go to index page

---