Organoarsenic compounds structures

The most common structures of arsenic compounds are tetrahedral and pyramidal, which are similar when the sterically active lone pair is counted. Tetrahedral symmetry holds the potential for chirality and indeed many chiral organoarsenic compounds have been prepared. Arsenic may also use d orbitals for (d-d)n bonding and for hybridization with s2 and p3 orbitals, resulting in trigonal bipyramidal or octahedral structures. In the former the more electronegative substituents occupy the apical position. 

Is tetramethyldiarsine an organometallic compound By definition, arsenic is a so-called metalloid or semi-metal , not a metal, and thus organoarsenic compounds like the organic compounds of boron or silicon are not per se organometallics. There is no doubt that the preparation of tetramethyldiarsine and the elucidation of its structure may in retrospect be linked to the development of organometallic chemistry, but it would be far beyond the scope of this book, if the chemistry of the organic compounds of the metalloids in its entirety was discussed. 

The physical, structural, and spectroscopic properties of organoarsenic compounds have been summarized in a... 

The pyrolysis of organoarsenic compounds containing the arsenyl moiety has some limited preparative applications [arsenyl (As=0) by analogy with phosphoryl (P=0)]. The compounds are based on the arsonic acid RAs(0)(0H)2, the arsinic acid R2As(0)0H and the arsine oxide R3As=0 structures. The acids are in interesting contrast with the phosphorus series. The phosphonic and phosphinic esters are prepared from the phosphorus(III) precursors via the Arbuzov synthesis. This synthetic route fails with the arsenic analogues, and further, if an alkyl halide or a salt is added in the pyrolysis of arsonic or arsinic acid esters a retro-Arbuzov reaction takes place . ... 

Examination of the molecular structures and boiling points of the organoarsenic compounds lead Gudzinowicz and Driscoll to the conclusion that the introduction of either a perfluoromethyl or... 

FIGURE 4.11 Structural formulas of some common herbicides. Organoarsenic compounds such as MSMA are no longer registered for herbicidal use. 

Catenation. Metal-metal bonds are a feature of many organoarsenic compounds. For example, the first to be prepared (by Cadet de Gassi-court in 1760) was the spontaneously air-inflammable liquid cacodyl which was later shown to be tetramethyldiarsine, Me2As-AsMe2, and several of the compounds found by Ehrlich to be useful chemotherapeutic agents were derivatives of arsenobenzene, (PhAs). The structure of the parent compound has recently been shown to be based on a chair-shaped Asg ring (4.18). Arsenomethane (MeAs)5 is a pentamer with a puckered Asj ring (4.19). 

There is a comprehensive review of this area2 so only a few recent developments will be mentioned here. Organoarsenic intramolecular coordination compounds, e.g. (1), have also recently been reviewed,3 and organoarsenic chemistry is reviewed annually.4 There is a review containing 102 references on arsonium ylides.5 The canonical structures of the arsenic ylides are... 

Hydrolysis of C(CH2Asl2)4 (95) with aqueous NaOH earried out in THF in sealed glass ampoules under vacuum gave the arsonous acid-organoarsenic oxide compound 94-H (equation 67) in 55.5% yield (m.p. > 300 °C, decomp.). 94 heated with a large excess of DjO at 150 °C in a sealed ampoule produced (DO)2AsCH2C(CH2AsO)3 (94-D) in 75.4% yield (equation 68) The crystal structure 94-D has been determined by X-ray diffraction... 

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