Chromium complexes arsenic ligands

Although trialkyl- and triarylbismuthines are much weaker donors than the corresponding phosphoms, arsenic, and antimony compounds, they have nevertheless been employed to a considerable extent as ligands in transition metal complexes. The metals coordinated to the bismuth in these complexes include chromium (72—77), cobalt (78,79), iridium (80), iron (77,81,82), manganese (83,84), molybdenum (72,75—77,85—89), nickel (75,79,90,91), niobium (92), rhodium (93,94), silver (95—97), tungsten (72,75—77,87,89), uranium (98), and vanadium (99). The coordination compounds formed from tertiary bismuthines are less stable than those formed from tertiary phosphines, arsines, or stibines. 

Like the related diphosphenes, diarsenes are potential donors towards low oxidation state transition metals via either the arsenic lone pairs of electrons or through the n bond itself. In two chromium pentacarbonyl complexes investigated, one of the arsenic atoms donates a lone pair of electrons and the double bond remains essentially intact, increasing marginally from 2.224 A in the uncomplexed ligand to 2.246 A after coordination - . 

Chromium(IV) is stabilized in the reduction of [HCr04] by H3ASO3 in the presence of the ligand (CH3CH2)2C(0H)C02" (L"). The mechanism of the redox process involves formation of a complex between chromium(IV) and the arsenic(III) species followed by two pathways in which and L are required. The chromium(IV) product, formulated as [CrOL2], comproportionates with excess [HCr04] to give the more stable chromium(V) derivate. A number of reactions of chromium(V) derivates have been reported. ... 

---