Synthesis and characterisation of transition-metal complexes involving cyclic diselenoether ligands

Treatment of NCSe(CH2)(3)SeCN with o-C6H4(CH2Br)(2) in Na-NH3-tetrahydrofuran yielded L-2 (3H-1,4,5,7-tetrahydro-2,6-benzodiselenonine) in greater than 80% yield. This cyclic diselenoether has been fully characterised spectroscopically and structurally. Reaction of [Cu(MeCN)(4)]Y (Y = BF4 or PF6) or AgBF4 with 2 molar equivalents of L-1 (1,5-diselenacyclooctane) or L-2 afforded the mononuclear species [M(L)(2)]Y (M = Cu, Y BF4 or PF6; M = Ag, Y = BF4). These compounds have been characterised by IR and H-1 NMR spectroscopy, mass spectrometry and microanalysis Crystal structure determinations on [Cu(L-2)(2)]BF4, [Ag(L-1)(2)]BF4 and [Ag(L-2)(2)]BF4 confirmed the discrete molecular nature of these products, giving distorted tetrahedral cations in each case. These structures are compared to the structures of related species involving acyclic bidentate thio-, seleno- and telluroethers. The preparation of the tetraselenoether macrocyclic complex [Ag([16]aneSe(4))]BF4([16]aneSe(4) = 1,5,9,13-tetraselenacyclohexadecane) has also been determined. Compounds L-1 and L-2 reacted with 2 molar equivalents of [AuCl(tht)] (tht = tetrahydrothiophene) to yield [(AuCl)(2)L-1] or [(AuCl)(2)L-2] respectively as white solids. These neutral compounds are thought to involve linear Se-Au-Cl fragments. Compound L-2 reacted with 1 molar equivalent of MCl2 (M = Pd or Pt) in refluxing MeCN to give cis-[MCl2(L-2)]. Unusual low-frequency coordination shifts [delta(free ligand) - delta(complex)] were revealed by Se-77-{H-1} NMR spectroscopy in each case. This is in contrast to cis-[MCl2(L-1)] which display high-frequency co-ordination shifts. The Pt-195 NMR spectroscopic data on cis-[PtCl2(L-2)] are consistent with an Se2Cl2 donor set at Pt-II. The crystal structure of cis-[PdCl2(L-2)] shows a distorted square-planar arrangement, with d(Pd-Se) slightly longer than in cis-[PdCl2(L-1)].