Selenoether macrocyclic chemistry–syntheses and ligand properties of new small-ring Se3- and Se2N-donor macrocycles

Abstract

Simultaneous dropwise addition of thf/EtOH solutions of Se{(CH₂)₃OTs}₂ and o-C₆H₄(CH₂SeCN)₂ or NCSe(CH₂)₃SeCN to a suspension of NaBH₄ in thf/EtOH at room temperature yields gram quantities of the 13- and 12-membered triselenoether macrocycles L¹ and L² respectively in high yield. The 11-membered ring L³ is obtained similarly by simultaneous dropwise addition of thf/EtOH solutions of Na₂[o-C₆H₄Se₂] (itself prepared by NaBH₄reduction of the polymeric [o-C₆H₄Se₂]_n) and Se{(CH₂)₃OTs}₂ to a suspension of NaBH₄ in thf/EtOH. The small-ring, potentially tridentate Se₂N(pyridyl)-donor macrocycles L⁴ and L⁵ were obtained in essentially quantitative yield by simultaneous dropwise addition of thf/EtOH solutions of 2,6-bis(bromomethyl)pyridine and either o-C₆H₄(CH₂SeCN)₂ or NCSe(CH₂)₃SeCN to a suspension of NaBH₄ in thf/EtOH at room temperature. L¹–L⁵ have been characterised by ¹H, ¹³C{¹H} and ⁷⁷Se{¹H} NMR spectroscopy, EI MS, and for L¹ and L⁴, by X-ray crystal structures. Reaction of PtMe₃I with one mol. equiv. of L (L = L¹–L⁵) in refluxing CHCl₃ gives the ionic complexes [PtMe₃(L)]I cleanly and in good yield. These were characterised by ¹H, ¹³C{¹H}, ⁷⁷Se{¹H} and ¹⁹⁵Pt NMR spectroscopy, electrospray MS, microanalyses and by crystal structures of [PtMe₃(L¹)]I and [PtMe₃(L⁴)]I, which confirm distorted octahedral coordination at Pt(IV), with fac-tridentate coordination of the macrocycle in all cases, with anionic iodide. The complexes [PtCl₂(L)] (L = L¹–L³) were obtained as poorly soluble yellow-orange solids by reaction of PtCl₂ with L in MeCN solution. The d³Cr(III) complexes of L (L = L¹–L⁵) were obtained by reaction with [CrCl₃(thf)₃] in anhydrous CH₂Cl₂ as distorted octahedral fac-[CrCl₃(L)], as poorly soluble blue-purple through to green powdered solids, which have been characterised by microanalysis, UV-visible and IR spectroscopy and by their magnetic moments. The properties of these complexes are compared with related chalcogenoether complexes from the literature involving thioether and acyclic selenoether coordination.