Bonded Organometals

The first organometal to be reported was cacodyl [tetramethyldiarsine, (CH3)4As2]. It was prepared almost as an afterthought by Cadet de Gassicourt, a Parisian military apothecary, in 1760 (45). Cadet was working on cobalt solutions for use as invisible inks. The two common ores of cobalt, smaltite and cobaltite, both contain arsenic, and arsenic trioxide was formed as a by-product. When he pyrolyzed this oxide with potassium acetate. Cadet got a red-brown liquid that fumed in air and gave off a terrible stench. 

Cacodyl was later found to be tetramethyldiarsine (251), with the weakness of the arsenic-arsenic bond accounting for its high reactivity. But before this became known, cacodyl was believed to be a free radical hence the -yl in the name. This belief contributed both to research on the theory of radicals, and, more importantly, to the further development of organometallic chemistry. 

Cacodyl and its derivatives are now mostly of historical interest. One derivative, cacodylic acid [dimethylarsonic acid, (CH3)2As02H], and its sodium salt, are commercially available and are widely used as herbicides. 

This mobile fluid was diethylzinc, whereas the white mass of crystals contained both ethylzinc iodide and Znlg. Dimethylzinc was prepared in similar fashion (9S)  

A second description, equally graphic, further describes the hazards that Frankland and other chemists faced when working with such air-sensitive poisonous materials (98)  

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Brookhart, M. and Green, M.L.H. (1983) Carbon—hydrogen—transition metal bonds./. Organomet. Chem., 250, 395. 

Cook, M. A. Eabom, C. Walton, D. R. M. Organosilicon compounds XLVIII. Effects of a-trimethylsilyl groups on rates of reaction at carbon-halogen bonds./. Organomet. Chem. 1971, 29, 389-396. 

Three o-bonded organometals found widespread nonmedicinal commercial uses. These, and later developments, are covered in a collection of papers published by the American Chemical Society (777). First, in 1923, Thomas Midgeley and associates 106, 188) developed the use of tetraethyllead as an additive to gasoline in order to control fuel combustion. The great growth in the number of automobiles and similar vehicles since that time has likewise led to vast expansion in the use of tetraethyllead as well as tetramethyllead. In recent years, these additives have come under heavy criticism as a source of lead pollution. 

Kitching, W., Fong, C. W., Insertion of Sulfur Dioxide and Sulfur Trioxide Into Metal-Carbon-Bonds, Organometal. Chem. Rev. A 5 [1970] 281/321. 

Green, M. (1986) The road from alkynes to molybdenum-carbon multiple bonds. Organomet. Chem., 300, 93. 

Chemical shifts and spin-spin coupling data for cr-bonded organomet llic compounds are summarized in Tables I through IX. Within each table, the... 

Kitching W, Fong CW. Insertion of sulfur dioxide and sulfur trioxide into metal-carhon bonds. Organomet. Chem. Rev. Sec A. 1970 5(3) 281-321. 

G. Fritz Advances in Inorg. Chem. 31, 171-214 (1987) N. C. Ngr.man, Polyhedron 12, 2431-46 (1993) and references cited therein. M. Driess, Adx Organomet. Chem. 39. 193-229 (1996) — also deals with sila-arsenes containing Si=As bonds). 

Figure 4.46 Orbital interaction diagram for the Au6C framework in (H3PAu)6C2+showing the important bonding interactions of the carbon 2s and 2p orbitals with the MOs of the gold cluster. (Reprinted from J. Organomet. Chem., 384, 405, 1990, with kind permission from Elsevier Science S.A., P.O. Box 564, 1001 Lausanne, Switzerland.)...

This prediction has now been confirmed by the observation (R. Alexander, C. Eaborn and T. G. Traylor, /. Organometal. Chem., 21 (1970) P65) that a solvent-isotope effect is obtained in base cleavage of benzyl- and aryl-tin bonds by NaOH in MeOH-MeOD. 

Kobayashi S. Lanthanide Triflate-Catalyzed Carhon-Carhon Bond-Forming Reactions in Organic Synthesis Top. Organomet. Chem. 1999 2 63-118 Keywords lanthanide triflates, rare earth compounds... 

Eaborn, C., Cleavages of aryl-silicon and related bonds by electrophiles, <7. Organomet. Chem. 100, 43 (1975). 

For a review of compounds containing both carbon-halogen and carbon-metal bonds, see Chivers, T. Organomet Chem. Rev. Sect A, 1970, 6, 1. 

Shah S, Protasiewicz JD (1998) J Chem Soc Chem Commim 1585 Yoshifuji M, Shima 1, Inamoto N, Hirotsu K, Higuchi T (1981) J Am Chem Soc 103 4587 Smith RC, Shah S, Protasiewicz JD (2002) J Organomet Chem 646 255 Smith RC, Ren T, Protasiewicz JD (2002) Eur J Inorg Chem 2779 Shah S, Protasiewicz JD (2000) Coord Chem Rev210 181 Shah S, Yap GPA, Protasiewicz JD (2000) J Organomet Chem 608 12 Schmidpeter A (1990) In Regitz M, Scherer OJ (eds) Multiple bonds and low coordination in phosphorus chemistry. Thieme, Stuttgart... 

Organometals and metal hydrides as electron donors in addition reactions 245 Oxidative cleavage of carbon-carbon and carbon-hydrogen bonds 253 Electron-transfer activation in cycloaddition reactions 264 Osmylation of arene donors 270... 

The organic analogues of the reactions to be discussed here are the borane reductions of aldehydes and ketones and the addition of metal alkyls across ketonic carbonyls, equation 15. In contrast to the ease of these organic reactions, qualitative data which has accumulated in our laboratory over the last decade demonstrates that the carbonyl group in organometallies is fairly resistant to addition across CO. For example, many stable adducts of organometallie carbonyls with aluminum alkyls are known, eq. lc, but under similar conditions a ketone will quickly react by addition of the aluminum alkyl across the CO bond. A similar reactivity pattern is seen with boron halides. 

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