Oxidation of Arsines to Arsine Oxides

More limited investigations of the oxidation of triorganoarsines in the presence of transition metal complexes have been carried out but it appears that many of the same complexes which catalyze phosphine oxidation are also effective for arsines. The ruthenium complex, [Ru(NCSXN0XPPh3)2(02)], for example, has been found to be an efficient catalyst for the oxidation of triphenylarsine [79] the initial rate of oxidation being three to four times greater than the corresponding rate for triphenyl-phosphine oxidation under the same conditions. However, the rate of this oxidation was rapidly diminished by decomposition of the catalyst so that in a short time ca. 30 min) the catalyst was virtually ineffective. 

When 30 ml of a solution of [RhCl(PPh3)3] (0.3 g) and EDA (0.3 g) was refluxed for 2 hr (presumably in the presence of O2) then concentrated to 10 ml and chilled at 0 °C overnight, a new complex crystallized. This complex contained one fully oxidized ligand, EDAO2 (ethylene-1,2-fcw-diphenylarsine oxide) and one unoxidized ligand, EDA. The structure of the complex [RhCl(EDAXEDA02)] was formulated as XI, below based on magnetic, spectroscopic (UV, visible and IR) and other physical studies. 

Solutions of triphenylarsine and [Fe(nmt)2] in acetonitrile take up oxygen slowly with formation of triphenylarsine oxide [133], The rate of oxygen consumption by triphenylarsine was slow (/1/2 = 10-50hr), but the first-order rate plots were linear over more than two half-times. For [Fe(mnt)2] = 1.93 x 10 M, [ni As] = 3.3 X 10 M, t,/2 = 36hr in oxygen. 

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