Acyclic arsines

The (-h)-enantiomer of the arsino-acetic acid 51 was isolated with use of ( —)-a-methylbenzylamine as resolving agent (Table 2) The racemic arsine was prepared by permanganate oxidation of allylethylphenylarsine, followed by SO2/HCI reduction of the intermediate arsine oxide. 

TABLES. Direct resolutions of acyclic arsino-anilines with ( + )-tartaric acid 

Sodium ethylphenylarsenide with carbon dioxide yields crystalline ethylphenylarsino-formic acid (52) after treatment with dilute sulphuric acid. The arsinoformic acid was resolved with ( —)-quinine. The less-soluble diastereomer, after three recrystallizations from chloroform, was decomposed with dilute sulphuric acid into ( —)-52, which required purification by extraction into benzene to separate it from arsine oxide (Table 2). 

The arsino-anilines 53-61 were resolved by the fractional crystallization of (-h)-hydrogentartrate salts (Table A handicap in evaluating the work relating to the 

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Acyclic arsines are superior to phosphines in their ability to retain chirality, with the R3AS inversion barrier, being ca 40kcalmol" compared to that of RjP, ca 30kcalmoP . Where the thermal degradation of P-chiral transition metal catalyst is significant, the substitution of arsenic for phosphorus may lead to an acceptable stability. 

Acyclic arsines have been obtained in enantiomerically pure form and, on account of their high inversion barrier, these compounds hold configuration indefinitely. We illustrate two methods for their formation from enantiomerically pure arsonium salts, and these are shown for 41 and 43. Salt 41 is converted into 42 by cathodic reduction, and 43 is transformed into 44 by reaction with aqueous cyanide ion also formed in the latter case is 45, which accounts for the allyl (prop-2-enyl) group (see Wild9). 

The gas-phase dipole moment of arsabenzene was found to be 1.10D 45). In cyclohexane solution it was measured as 1.02D27). These values are typical of those found for tertiary arsines for trimethylarsine p = 0.86D76), for triethylarsine p = 1.04D77) and for triphenylarsine p = 1.23D78). No dipole moment data are available for stibabenzene and bismabenzene. However, based on trends shown in acyclic compounds 79), it is expected that they have smaller moments. 

The arsines, AsRs, are among the most numerous and widely studied organo-arsenic compounds. They include both acyclic (e.g. Mc3As) and heterocyclic (e.g. cyclo-C5H10ASCH3) structures. Arsines are classified as derivatives of the parent compound ASH3 by successive substitutions to form the family of compounds R3 AsH (n = 0-3). Thus we include in this section arsine itself, ASH3, together with the primary, secondary and tertiary arsines. 

Tellurium coordination is seen in a series of acyclic bidentate ligands that coordinate through Te-N donor atoms or Te-0 donor atoms. An interesting series of adamantane-like cage complex cations that contain mercury(II) have been prepared and have the general formula [ j,-ER2(HgL)4] + (E = S,Se,orTe L = phosphine or arsine). These cations contain a variety of Hg-L bonds and have been characterized using heteronuclear NMR ( P, Te, Hg). 

Both the diastereoisomers (70) and (71) react with Fe(CO)s to give complexes (72), best by u.v. irradiation, and (73), brat by heating the components. In (73) the acyclic ditertiary arsine shows the triligate behaviour more commonly associated with cyclic vinylic ditertiary arsines such as f4fars. Complexes (72) show only singlets in their i F n.m.r. spectra, and probably undergo positional exchange in... 

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