3.0 Organometallic Reagents

Organometallic compounds are those compounds which have metal-carbon bond. Due to the significant difference in electronegativity between metals and carbon, they are highly polar in nature. However, this definition is not quite explicit as many reagents deemed to be organometallic in nature do not possess a metal carbon bond. Wilkinson catalyst, (RhCl₂ (PPhl₃)₂), a popular organometallic catalyst for hydrogenation reaction does not possess a metal–carbon bond. Thus, the above definition may be modified to include compounds containing metal- electronegative atom bonds in the gambit of organometallic compounds.

Fig 1: Elements commonly involved in formation of organometallic compounds. (Elements highlighted in blue are the source of most common organometallic reagents used for organic synthesis)

Fig 2 : M.O diagram of C-Li bond showing the high degree of polarization.

The high polarity of the metal-carbon bond is responsible for the high ionic nature of the organometallic compounds (Fig 2). As such these reactions mostly involve nucleophilic attack of the carbanion on the electrophillic center of an organic molecule.

TRIVIA The first organometallic compound was synthesized by French Chemist Louis Claude Cadet de Gassicourt in 1760 by the reaction of potassium acetate with arsenic trioxide. This red coloured liquid is called Cadet's Fuming Liquid in his honour.