Arsenic rings

Although antimony-antimony compounds tend to form as polymers rather than as cyclic structures, several cyc/o-antimony(III) compounds have recently been characterized. Eller-mann and Veit114 have synthesized the Sb3R4 analogues of the well known three-membered arsenic ring compounds (equation 41). 

Phosphorus—phosphorus bonds, addition, to alkynes, 10, 751 Phosphorus rings, chromium carbonyl link arsenic rings, 5, 226 As, Sb, Se, Te, Sn rings, 5, 226 boron rings, 5, 222 carbon rings, 5, 224 characteristics, 5, 221 oxygen rings, 5, 227... 

F. Antimony Rings That Have No Counterparts in Arsenic Ring Chemistry.. 571... 

It is of interest that the fold angle for the antimony four ring is smaller than for the arsenic ring. Stronger transannular attraction of antimony atoms compared to arsenic may be responsible for these differences. Selected structural data are given in Table 2. 

Relatively little is known of the chemistry of antimony rings compared to arsenic rings. The reactions of arsenic homocycles have been reviewed several times " . They include cleavage of the As—As bonds with halogens and insertion of chalcogens or unsaturated hydrocarbons and reductive cleavage with potassium metal. Representative examples are given in equations 15-18. 

As in the case of monocyclic 1,3-azaphospholes/arsoles (Section 3.16.4.1.4) tris(trimethyl-silyl)phosphine/arsine provides the phosphorus/arsenic ring member by replacing the oxygen atom of an oxazolium ring. 

Unlike cyclic silicon-phosphorus compounds, which occur as dimers and/or trimers, the cyclic silicon-arsenic ring of (Me2SiAsMe)4 is eight-membered. It results from MeAsHLi and Me2SiCl2 along with polymer, and occurs in solution as a mixture of conformers (equation 90)no. 

Various three-and four-membered phosphorus-arsenic ring systems, e.g., (58), have been isolated from the reactions of aryldichloroarsines with bis(trimethylsilyl)phosphido complexes of... 

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