Bromination and iodination of diphosphane dichalcogenides

Abstract

The diphosphane dichalcogenides dppmSe₂, dppeSe₂, dⁱprpmSe₂, dⁱprpeSe₂, dppmS₂ and dppeS₂, [dppm = bis(diphenylphosphano)methane, dppe = bis(diphenylphosphano)ethane, dⁱprpm = bis(diisopropylphosphano)methane, dⁱprpe = bis(diisopropylphosphano)ethane] have been treated with elemental bromine or iodine and the products 1–15 characterized by single crystal X-ray diffraction. DppeSe₂ with bromine or iodine gives the simple (and previously known) adducts dppe(SeBr₂)₂1 or dppe(SeI₂)₂2 respectively; dⁱprpeSe₂ reacts similarly to give dⁱprpe(SeBr₂)₂3 (at 0 °C) or dⁱprpe(SeI₂)₂4. The bromine derivatives display a T-shaped geometry at selenium, whereas the iodine derivatives involve linear Se–I–I groups. With dppmSe₂ and bromine, a product was formed at −50 °C, but could not be isolated; at room temperature the reaction leads to a mixture of products, from which only [dppmBr₂]²⁺ [Se₂Br₁₀]^2–5 (the anion involving a dibromine molecule coordinating to a Se centre) could be isolated. Reaction of dppeSe₂ with excess bromine at room temperature leads to [dppeBr₂]²⁺·½[SeBr₆]^2–·[SeBr₂·Br₂·Br₃]⁻6. The reaction of dppmSe₂ with iodine gives the 1 : 2 adduct [dppmSe₂I]⁺ [I₃]⁻7, the cation of which contains a novel five-membered CP₂Se₂ heterocycle. In a 1 : 1 ratio the same reaction gives another 1 : 2 adduct, [I₂Se(dppm)Se–I–Se(dppm)SeI₂]⁺ [I₃]⁻8. DⁱprpmSe₂ with iodine gives [dⁱprpmSe₂I]⁺ [I₃]⁻9, analogous to 7, and with bromine at 0 °C the corresponding product [dⁱprpmSe₂Br]⁺ [Br₃]⁻10. At room temperature, dⁱprpeSe₂ reacts with bromine to give a mixture of [dⁱprpe(SeBr₂)Br]⁺ Br⁻11 and [dⁱprpeBr₂]²⁺ [SeBr₄]^2–12, whereas dⁱprpmSe₂ forms [dⁱprpmBr₂]²⁺ [SeBr₄]^2–13, analogous to 12. The disulfides dppmS₂ and dppeS₂ react with bromine to give [dppmSBr]⁺ [Br₃]⁻14 and [dppeSBr]⁺ [Br₃]⁻15.