Inorganic Grignard analogues. Reaction of cobalt powder with triorganodiiodophosphorus compounds to form [PR3I][Co(PR3)I3]. Crystal structure of [PPh3I][Co(PPh3)I3], and isolation of the novel complexes [PPh3I][Co(PPh3)IBr2] and [SbPh3I][Co(SbPh3)I3]

Abstract

The reactions of a large number of triorganodiiododophosphorus compounds, R₃Pl₂[R₃= Et₃, Prⁿ₃, Buⁿ₃, PhMe₂, Ph₂Me, Ph₂Prⁿ, Ph₃(o-,m-or p-MeC₆H₄)Ph₂, or (m-MeC₆H₄)₃], with unactivated cobalt metal in dry diethyl ether have been studied. All reactions produce the novel ionic complexes [PR₃I][Co(PR₃)I₃] in quantitative yield, illustrated crystallographically for [PPh₃I][Co(PPh₃)I₃]. However, where R₃= PhMe₂ both the ionic complex and the cobalt(III) complex [Co(PPhMe₂)₂I₃] are produced from the same reaction. The previously reported isolation of the ‘frozen transition-state complex’[Co(PBuⁿ₃)₃I₈] from the reaction of Buⁿ₃Pl₂ with cobalt powder has been reinvestigated; when allowed to proceed to completion, the reaction produces the ionic complex described above. The compound Ph₃PlBr reacts with cobalt powder to produce the mixed-halide ionic complex [PR₃I][Co(PR₃)IBr₂]. All the complexes [PR₃I][Co(PR₃)I₃] have been studied using Raman and visible spectroscopy, the latter confirming the tetrahedral geometry of the cobalt anion. Very little reaction is observed with the corresponding dibromophosphorus compounds, R₃PBr₂, but in some cases visible spectroscopic studies on the trace of complex formed suggest a tetrahedral cobalt(II) species, perhaps similar to the iodo-complexes described above. Additionally, Ph₃SbI₂ reacts with cobalt metal in an analogous way to Ph₃Pl₂ to produce the novel complex [SbPh₃I][Co(SbPh₃)I₃].