Reactions of dihalogenotriorgano-phosphorus, -arsenic and -antimony compounds with [Fe2(CO)9]. Single-crystal structures of the iron(III) complexes [(Ph3PO)2H][FeBr4] and [Ph4Sb][Fel4]·Ph3Sbl2 and of [Fe(CO)3(Ph3P)2]

Abstract

The reaction of [Fe₂(CO)₉] with compounds of stoichiometry R₃EX₂[R₃E = Ph₃P, (p-MeOC₆H₄)₃P, Me₂PhP, Me₃As or Ph₃Sb, X = I; R₃E = Ph₃P, Ph₃As or Me₃As, X = Br] has been investigated and shown to yield diverse products. A series of complexes with the ionic structure [R₃EX][Fe(R₃E)X₃][E = P, R₃= Ph₃, Me₂Ph or (p-MeOC₆H₄)₃, X = I; R₃E = Me₃As; X = I or Br] has been obtained. The reaction of [Fe₂(CO)₉] with Ph₃PBr₂ and Ph₃AsBr₂, however, resulted in the formation of the iron(III) complexes [(Ph₃E)₂Br][FeBr₄]. Hydrolysis of [(Ph₃P)₂Br][FeBr₄] by trace quantities of water produces [(Ph₃PO)₂H][FeBr₄], the crystal structure of which has been determined. Triphenylantimony diiodide reacted with [Fe₂(CO)₉] yielding the surprising ionic adduct [Ph₄Sb][FeI₄]·Ph₃SbI₂, remarkable not only for the phenyl migration at the antimony atom, but also for the formation of the rare [FeI₄]^– anion from a zerovalent iron carbonyl complex. The reaction of [Fe₂(CO)₉] with the milder diphosphine tetraiodide, I₂Ph₂PCH₂CH₂PPh₂I₂, produced [Fe(CO)₃(Ph₂PCH₂CH₂PPh₂)I][I₃], a complex in which three CO ligands are retained.