Halogenation reactions of electron-rich diphosphazane ligand-bridged derivatives of dicobalt octacarbonyl: crystal structures of [Co2(µ-I)(µ-CO)(CO)2{µ-(MeO)2PN(Et)P(OMe)2}2]BPh4 and [Co(CO)2{P(OMe)3}2{(MeO)2PN(Et)P(OMe)2-χP}]BPh4

Abstract

Halogenation of [Co₂(CO)₄{µ-(RO)₂PN(Et)P(OR)₂}₂](R = Me or Prⁱ) by I₂, Br₂, or freshly distilled CCl₄ affords the cations [Co₂(µ-X)(µ-CO)(CO)₂{µ-(RO)₂PN(Et)P(OR)₂}₂]⁺(X = I, Br, or Cl respectively). A single-crystal X-ray diffraction study on [Co₂(µ-I)(µ-CO)(CO)₂{µ-(MeO)₂PN(Et)P(OMe)₂}₂] BPh₄ confirms that these cations have A-frame structures with a neutral ligand, CO, occupying a bridging site additional to the bridging halogen atom. For R = Me (only) the cations slowly undergo a Michaelis–Arbusov type rearrangement initiated by attack of halide ions at a co-ordinated phosphorus atom, to give the neutral complexes [Co₂(µ-X)(µ-CO)(CO)₂{µ-(MeO)₂PN(Et)P(OMe)₂}{µ-(MeO)₂PN(Et)P(O)(OMe)}]. The latter could not be isolated but [Co₂(µ-I)(µ-CO)(CO)₂{µ-(PrⁱO)₂PN(Et)P(OPrⁱ)₂}{µ-(PrⁱO)₂PN(Et)P(O)(OPrⁱ)}] is readily isolated from the reaction of [Co₂(µ-I)(µ-CO)(CO)₂{µ-(PrⁱO)₂PN(Et)P(OPrⁱ)₂}₂]⁺ with hydride ions. When undistilled (Analar grade) rather than freshly distilled CCl₄ is used to chlorinate [Co₂(CO)₄{µ-(MeO)₂PN(Et)P(OMe)₂}₂] an unexpected product, viz.[Co(CO)₂{P(OMe)₃}₂{(MeO)₂-PN(Et)P(OMe)₂-κP}]⁺ is formed; this cation contains one cobalt atom bonded to two trimethyl phosphite ligands, two carbonyl ligands, and a pendant diphosphazane ligand, as confirmed X-ray crystallographically.