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

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 NaBH4 reduction 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 d3 Cr(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