Diphosphaarsirane I, phosphadiarsirane II, and diphosphadiarsetane III [R = 2,4,6-(Me3C)3C6H2, [Fe] = (C5Me5)Fe(CO)2; C5H5 = h5-cyclopentadienyl] were prepd. by treating [Fe]P(SiMe3)2 with RAsCl2. The structure of I was detd. by x-ray crystallog. [Fe]P:AsR was also identified as a product in this reaction by 31P NMR and derivatized by Z-(C8H14)Cr(CO)5 (C8H14 = cyclooctadiene) to give (OC)5CrP[Fe]:AsR in 32% yield.