Organometallic Compounds

ORGANOMETALLIC COMPOUNDS, organic compounds containing a metal in direct bond with carbon, e.g., zinc ethyl, Zn(CH₃)₂, discovered by Frankland (1849). Organometallic compounds can be pure and mixed; in the latter, the metal is bonded to carbon and a halogen, e.g., CH₃-ZnJ; mixed organometallic compounds are possible only for metals with a valence greater than one. Pure organometallic compounds are mostly liquids, while mixed ones often appear in crystalline form. All organometallic compounds, especially zinc-organic and magnesium-organic ones, possess a high reaction capacity. Mixed magnesium-organic compounds of the RMgX type (X being a halogen), in particular magnesium-iodine-organic compounds, were studied by Grignard (see Grignard reaction); in the Grignard reaction, ether plays the role of a catalyst, and it is assumed that it forms intermediate compounds with organic halo derivatives of the type R₂O<MgX_m> (R being a radical, for example C₂H₅) or of the type R₂O<MgCH₃X>, an oxonium compound with tetravalent oxygen. Ether can be replaced by a tertiary amine (Chelintsev). Magnesium-organic compounds are of great importance in synthetic organic chemistry, since with their help it is possible to synthesize substances of almost any class of organic chemistry. Magnesium-organic compounds have displaced zinc-organic compounds in synthetic practice, which are also very capable of the most diverse synthesis reactions, but represent a great hazard in handling, since, unlike magnesium-organic compounds, they very easily self-ignite in air. In addition to compounds with Zn and Mg, organometallic compounds with As, Sb, Bi, Hg, Al, Cd, Na, K, and other metals are also known; aromatic organometallic compounds have also been obtained, such as mercurydiphenyl, [(C₆H₅)₂Hg]. Organometallic compounds were of great importance for establishing the maximum valence and atomic weights of elements. Organometallic compounds are obtained by various methods, e.g.: 1) by the action of alkyl halides on metals: 2Zn + 2CH₃J = Zn₂J₂ + Zn(CH₃)₂; 2) by the action of metals on other organometallic compounds: Hg(C₂H₅)₂ + 2Na = 2Na-C₂H₅ + Hg; 3) by the action of metal halides on zinc- and magnesium-organic compounds: 2Zn(CH₃)₂ + SnCl₄ = Sn(CH₃)₄ + 2ZnCl₂, and by other methods. Many organometallic compounds are used in medicine in chemotherapy. Thus, certain mixed organometallic compounds of mercury, of the RHgX type, possessing a stronger bactericidal action than corrosive sublimate, do not exert the toxic effect on the organism (kidneys) characteristic of the latter: mercurosal, flumerin are used in the treatment of syphilis, mercurochrome, mercurophen, metaphen, novasurol, etc., for septic diseases. Organometallic compounds of arsenic include salvarsan (see) and the new preparation "Albert 102" similar to it in action, organometallic compounds of antimony include "Heyden 471", organometallic compounds of bismuth include the preparation Bi(C₆H₅)₃, which has a bactericidal effect on spirochetes and trypanosomes; a similar effect is exerted by certain organometallic compounds containing simultaneously arsenic and antimony. Organometallic compounds of arsenic (arsines) have found application as combat chemical agents (sneezing gases, lewisite). Certain lead organometallic compounds, which are extremely toxic [Pb(C₂H₅)₄], have recently become widespread in certain countries as antiknock agents in internal combustion engines, which has caused the appearance in the USA of a special law prescribing precautionary measures in the production, transportation, and use of these substances. Such biologically important substances as blood pigments (hematin) and chlorophyll are not classified as true organometallic compounds, since in them the metal is apparently bound directly not to carbon, but to nitrogen.

I. Yatsynikov.