1,2-Bis(dimethylarsino)benzene

1,2-Bis(dimethylarsino)benzene is the chemical compound with the formula C₆H₄(As(CH₃)₂)₂. The molecule consists of two dimethylarsino groups attached to adjacent carbon centers of a benzene ring. It is a chelating ligand in coordination chemistry. This colourless oil is popularly abbreviated "diars."^[1]

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This organoarsenic compound is a bidentate ligand used in coordination chemistry. It was first described in 1939,^[2] but was popularlized by R. S. Nyholm for its ability to stabilize metal complexes with unusual oxidation states and coordination numbers, e.g. TiCl₄(diars)₂. High coordination numbers arise because diars is fairly compact and the As-M bonds are long, which relieves crowding at the metal center.

Diars is prepared by the reaction of ortho-dichlorobenzene and sodium dimethylarsenide:^[3]

C₆H₄Cl₂ + 2 NaAs(CH₃)₂ → C₆H₄(As(CH₃)₂)₂ + 2 NaCl

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

Oxygen quickly converts diars to the dioxide, C₆H₄(As(CH₃)₂O)₂, thus samples must be handled with the exclusion of air.

References

1. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
2. ^ 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. ^ Feltham, R. D.; Silverthorn, W. "o-Phenylenebis(dimethylarsine)" Inorganic Syntheses 1967, volume X, 159-164.