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].