1,2-Bis(dimethylarsino)benzene

Coordination chemistry

Related, but non-chelating organoarsenic ligands include triphenylarsine and trimethylarsine. Work on diars preceded the development of the chelating diphosphine ligands such as dppe, which are now prevalent in homogeneous catalysis.

Diars is a bidentate ligand used in coordination chemistry. It was first described in 1939, but it was popularized by R. S. Nyholm for its ability to stabilize metal complexes with unusual oxidation states and coordination numbers, e.g. TiCl(diars). High coordination numbers arise because diars is fairly compact and the As-M bonds are long, which relieves crowding at the metal center. In terms of stabilizing unusual oxidation states, diars stabilizes Ni(III), as in [NiCl(diars)]Cl.

Of historical interest is the supposedly diamagnetic Ni(diars), obtained by heating nickel perchlorate with diars. Octahedral d complexes characteristically have triplet ground states, so the diamagnetism of this complex was puzzling. Later by X-ray crystallography, the complex was shown to be pentacoordinate with the formula Ni(triars)(diars), where triars is the tridentate ligand [CHAs(CH)]As(CH), arising from the elimination of trimethylarsine.

Preparation and handling

Diars is prepared by the reaction of ortho-dichlorobenzene and sodium dimethylarsenide: :CHCl + 2 NaAs(CH) → CH(As(CH)) + 2 NaCl It is a colorless liquid. Oxygen converts diars to the dioxide, CH(As(CH)O).

References

References

1. Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. {{ISBN. 0-12-352651-5.
2. [[Joseph Chatt. Chatt]], J.; Mann, F. G. "The Synthesis of Ditertiary Arsines. Meso- and Racemic Forms of Bis-4-Covalent-Arsenic Compounds" Journal of the Chemical Society, 1939, 610–615. {{doi. 10.1039/JR9390000610
3. B. Bosnich, R. S. Nyholm, P. J. Pauling, M. L. Tobe "A nickel(II)-catalyzed synthesis of a triarsine from a diarsine" J. Am. Chem. Soc. 1968, volume 90, pp 4741–4742. {{doi. 10.1021/ja01019a049
4. Anthony Nicholl Rail; ''Some new reactions of a ditertiary arsine ligand''; Ph.D. Thesis; University College London; 1973
5. Feltham, R. D.; Silverthorn, W. "''o''-Phenylenebis(dimethylarsine)" Inorganic Syntheses 1967, Vol. X, pp. 159–164. {{doi. 10.1002/9780470132418.ch24