Mechanistic studies on iron phosphine complexes. Part 1. Protonation and substitution of trans-[FeH(X)(diphosphine)2](X = Cl or Br, diphosphine = Et2PCH2CH2PEt2 or Ph2PCH2CH2PPh2)

Abstract

The mechanisms of protonation and substitution of trans-[FeH(X)(diphosphine)₂][X = Cl or Br, diphosphine = Et₂PCH₂CH₂PEt₂(depe) or Ph₂PCH₂CH₂PPh₂(dppe)] have been investigated in tetrahydrofuran at I= 0.1 mol dm^–3([NBuⁿ₄][BF₄]) and 25 °C. In the presence of acid, HX, loss of phosphine and formation of [FeX₂(diphosphine)] occurs by a variety of pathways dependent upon the nature of the phosphine. When diphosphine = dppe rapid ring opening of the chelate from trans-[FeH(X)(diphosphine)₂] allows protonation of the pendant phosphorus atom. Subsequent dissociation of the phosphine ligand, and protonation of the metal, with release of dihydrogen, results in the formation of [FeCl₂(dppe)]. When diphosphine = depe a further pathway involving initial protonation of the metal is identifiable. In contrast, substitution of trans-[FeH(X)(diphosphine)₂] by L = CO, MeCN, or PhCN to yield trans-[FeH(L)(diphosphine)₂]⁺ has to await the slow dissociation of halide.