Just like many other scientific discoveries, the discovery of organometallic compounds was an accident and it has proved to be one of the very significant discoveries in the scientific world. Organometallics constitute a class of compounds which contain at least one metal to carbon bond in which the carbon is a part of an organic group. In 1757, Louis Claude Cadet de Gassicourt, a French chemist, was experimenting with invisible inks by combining arsenic containing cobalt ore with potassium acetate. He observed fumes with afoul smell which was the result of the mixture containing an organometallic compound called tetramethyldiarsine. Tetramethyldiarsine (As(CH3)2- As(CH3)2) also known as cacodyl was the first synthesized organometallic compound.

Sixty-seven years later, a Danish organic chemist William Christopher Zeise placed platinum tetrachloride in boiling ethanol which resulted in the formation of trichloro-(ethene)- platinate (II) anion. This ion, when combined with a potassium counter-ion, formed a salt named Zeise salt which was the first organometallic compound containing a transition metal and also the first π complex. The structure of Zeise salt was not identified until X-ray crystallography became available in the 20th century. A great interest in organometallic compounds kicked in amongst the 19^th century chemists after the discovery of Zeise salt, although the chemists did not have an exact idea about the formation of organometallic compounds.

In the early 1860s, James Crafts and Charles Friedel became colleagues in Paris. They both shared the same interest and became lifelong co-workers and closest friends. To establish and identify a link between their interests in organic compounds and minerals they immediately set up their first joint enterprise. The standard atomic weight of silicon wasn’t known at that time and was a point of debate. Mineral analyses supported a formula of SiO₃ for silicates, whereas SiO₂ was consistent with the weight and valency of silicon in SiCl₄, whose formula was calculated from its vapour density. Crafts and Friedel treated SiCl₄ with dry ethanol and carefully separated the products by fractional distillation and each product was identified and confirmed by combustion analysis. The weight of silicon was confirmed to be 28amu and in 1863, the first organo-silicon compound SiEt₄ was formed by using diethylzinc instead of ethanol.

An entire new class of compounds called metal carbonyls was initiated by British chemist Ludwig Mond who synthesised a lot of compounds belonging to this class in the late 19th century.

In 1910, Paul Ehrlich developed a drug called Salvarsan also known as Arsphenamine, an early arsenic based organometallic compound, for treatment of syphilis. Ehrlich chose a known organic arsenic compound as a chemical starting point and synthesized hundreds of related organoarsenic compounds with Bertheim’s help. Each of these compounds were tested for biological activity, toxicity, and distribution in rabbits infected with the syphilis-causing bacteria and number 606 (Salvarsan) proved to be the best candidate as a single dose of that compound cured the rabbits. Soon Salvarsan was widely used and prescribed for the treatment of syphilis.

In early 20th century French chemist Victor Grignard who was a student of Barbier discovered a new method of coupling carbon to the carbonyl group of a ketone or an aldehyde by nucleophilic addition using an alkyl/aryl halide coupled to magnesium metal. This discovery had an enormous impact on organic chemistry and proved to be of great importance in transition-metal organometallic chemistry. This trailblazing organometallic reagent (RMgX) sailed through chemistry labs of the early twentieth century and was named after Grignard. Paul Sabatier, also a French chemist (one of Berthelot’s students) worked on the heterogeneous hydrogenation of olefins to saturated hydrocarbons using nickel, along with Senderens. Hydrogenation of fats kicked off and food industries started using this process extensively. In 1912, the Nobel Prize of Chemistry was shared by Grignard and Paul Sabatier. Even after hundreds of years, Grignard’s reagent is still used extensively as a coupling reagent to a variety of carbonyl derivatives.

Alfred Werner, who is considered the father of coordination chemistry, was a Swiss inorganic chemist who worked on the coordination theory that extended throughout the whole range of systematic inorganic chemistry and into organic chemistry as well. He defined the basics of coordination chemistry, and in 1913,he was awarded the Nobel Prize in Chemistry for his work. Werner’s work in coordination chemistry proved to be vital in the understanding of organometallic coordination and chemical reactions of compounds and contributed greatly to opening up the organometallic discipline. Various organometallic compounds were being created and used during this period.

In the 1930s, Henry Gilman an American chemist worked on organocopper compounds, also known as Gilman reagents, which are used for carbon-carbon bond formation in organic synthesis. The most extensively used organocopper compounds are the lithium diorganocuprates, which are prepared by the reaction between organolithium reagents (RLi) and copper(I) halides (CuX).

The discovery of metallocene led to the recognition of organometallic chemistry as a sub-discipline of chemistry. In 1963, Karl Ziegler and Giulio Natta were awarded the Nobel Prize in Chemistry for the joint creation of one early catalytic organometallic compound, dicyclopentadiene zircon (IV) dichloride, also known as Ziegler-Natta catalysts, to polymerize terminal olefins. Organometallic compounds were extensively used as catalysts and the chemists of the late 20th century designed new ways to couple carbon with these. Moreover, new applications for organometallics were found, and the field started expanding. The Sharpless epoxidation which allows the enantioselective epoxidation of prochiral allylic alcohols is catalysed by Ti(OiPr)4, earned the Nobel Prize in Chemistry in 2001. In 2005, Yves Chauvin, Robert H. Grubbs, and Richard R. Schrock shared the Nobel Prize for their work on metal-catalyzed olefin metathesis. The famed Heck reaction which uses palladium catalyst was awarded the Nobel Prize in 2010.

Organometallic compounds have gained great momentum over the years and are being used extensively in a broad range of applications in research and industry, as catalysts and reagents in a diverse spectrum of chemical reactions and synthesis of organic compounds. They find use in bulk hydrogenation processes. Moreover, these compounds are invaluable in the manufacture of some semiconductors, which require the use of compounds such as trimethylgallium, trimethylaluminum, trimethylindium, and trimethyl antimony. They are also used in the production of light-emitting diodes (LEDs). The medical field provides a platform for these compounds in the synthesis of numerous novel drugs. Indeed, organometallic compounds are of immense significance in the modern scenario. However, in recent times, the environmental sustainability of these have been put to question, thus paving the scope and need for much research, keeping in mind the needs of the human race and our mother planet.

REFERENCES

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