Bond cleavage arsenic-carbon

The first example of biological arsenic-carbon bond cleavage was described by Challenger. Trimethylarsine is produced when S. brevicaulis and P. notatum act on C1CH2CH2AsO(OH)2. Because P. notatum does not methylate arsenate, it seems likely that loss of the (jlCH2CH2 group takes place after at least one methylation step. 

Attempts to prepare arsolyl anions by reductive cleavage of s-chloro-2,3,4,5-tetramethylarsole or reductive cleavage of the permethylated l,l -biarsole result in erratic yields of the anion (153) and are contaminated by elemental arsenic. A superior procedure calls for reduction of the. 45-phenyl derivative (Scheme 35). With this procedure, analytically pure anion (153) is prepared in near quantitative yield by extracting the byproduct PhLi with ether after the reaction has finished. Reaction of this anion with 2.0 equivalents of TMEDA allows the preparation of crystals of its TMEDA adduct (68) that are suitable for x-ray analysis. This shows the nearly planar arsole ring to be rj-5 coordinated, the arsenic-carbon bonds to be intermediate between single and double bond... 

Quinn JP, G McMullan (1995) Carbon-arsenic bond cleavage by a newly isolated Gram-negative bacterium strain ASV2. Microbiology (UK) 141 721-727. 

There are two remaining systems for enzymatic changes in arsenicals, the periplasmic reduction of arsenate to arsenite as part of an oxyanion-coupled anaerobic respiration (16,68) (Chapter 13) and the coupled cleavage of carbon-arsenic bonds with oxidation to arsenate (7). These systems appear to be of major environmental concern in arsenic-containing settings, but they have not been approached by molecular genetics as yet. 

In addition to iodonium, sulfonium and selenonium compounds, onium salts of bromine, chlorine, arsenic, and phosphoras are also stable and can act as sources of cation radicals as well as Bronsted acids, when irradiated with light. Performance of diaryl chloronium and diaryl bromonium salts was studied by Nickers and Abu. Also, aryl ammonium and aryl phosphonium, and an alkyl aryl sulfonium salt were investigated. It appears that the general behavior of these materials is similar to diphenyl iodonium and triphenyl sulfonium salts. These are formations of singlet and triplet states followed by cleavages of the carbon-onium atom bonds and in-cage and out of cage-escape reactivity. The anions of choice appear to be boron tetrafluoride, phosphorus hexafluoride, arsenic hexafluoride, and antimony hexafluoride. 

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