As—C-Containing Compounds

Many compounds of pentacoordinated arsenic(V) containing only As—C bonds are reported in the literature and are summarized in Table I. 

Although more than 100 years ago Cahours (35) claimed to have obtained pentamethylarsorane by the reaction of dimethylzinc with tetramethylarsonium iodide, subsequent attempts (55,195) to synthesize pentaalkylarsoranes by the reaction of tetraalkylarsonium salts with organometallic compounds were unsuccessful. However, Mitschke and Schmidbaur (137) have obtained pentamethylarsorane in 80% yield by the following reaction  

On the basis of spectral studies a trigonal-bipyramidal structure has been proposed for this compound. Low-temperature XH-NMR spectra in toluene indicate that all methyl protons are magnetically equivalent down to -95°C and that the exchange of methyl groups at the equatorial and axial positions in MesAs is faster than the NMR scale (137). 

The unit cell of Ph5As has been reported by Wheatley and Wittig (187). From these data it has been concluded that the molecule adopts the expected trigonal-bipyramidal conformation, very similar to that found for pentaphenylphosphorane (189). It is interesting to mention here that the unsolvated Ph5Sb crystallizes with square-pyramidal geometry (15,188) in a triclinic cell rather than in the monoclinic Cc 

Compound Melting point (°C) Physical measurements Reference 

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