Complexes of Bi- and ter-valent cobalt with olefinic ditertiary arsines

Abstract

Cobalt(II) salts react with 1,2-bis(dimethylarsino)ethylene (edas)(ca. 90%trans, 10%cis) under u.v. irradiation to give complexes of cis-edas in good yield. The intermediate complexes of trans-edas are generally unstable, but a black compound Col₂(trans-edas)₂ with one unpaired electron can be isolated; this probably contains bridging ligand groups in a polymeric structure. The cobalt(II) complexes CoX₂(cis-edas)₂(X = Cl, Br, I, or NO₃), which have one unpaired electron, are probably five-co-ordinate in solution and tetragonally distorted octahedral in the solid state. The complex CoCl₂(cis-edas) appears to consist of the planar cation [Co(cis-edas)₂]²⁺ and the tetrahedral anion [CoCl₄]^2– in the solid state, but attempts to prepare [Co(cis-edas)₃]²⁺ give only the tervalent derivative [Co(cis-edas)₃]³⁺. The cobalt(II) halogeno-complexes of cis-edas are readily oxidised to cobalt(III) complexes of the type [CoX₂(cis-edas)₂]Y [X = Cl or Br; Y = Cl, Br, or PF₆; X = NCS, Y = PF₆ or Co(SCN)₄] The chemical and physical properties of the cobalt–cis-edas complexes are generally very like those of the analogous complexes of o-phenylenebis(dimethylarsine).