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

Abstract

Treatment of NCSe(CH2)3SeCN with o-C6H4(CH2Br)2 in Na–NH3–tetrahydrofuran yielded L2 (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 L1 (1,5-diselenacyclooctane) or L2 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 1H NMR spectroscopy, mass spectrometry and microanalysis. Crystal structure determinations on [Cu(L2)2]BF4, [Ag(L1)2]BF4 and [Ag(L2)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 telluro-ethers. The preparation of the tetraselenoether macrocyclic complex [Ag([16]aneSe4)]BF4 ([16]aneSe4 = 1,5,9,13-tetraselenacyclohexadecane) has also been determined. Compounds L1 and L2 reacted with 2 molar equivalents of [AuCl(tht)] (tht = tetrahydrothiophene) to yield [(AuCl)2L1] or [(AuCl)2L2] respectively as white solids. These neutral compounds are thought to involve linear Se–Au–Cl fragments. Compound L2 reacted with 1 molar equivalent of MCl2 (M = Pd or Pt) in refluxing MeCN to give cis-[MCl2(L2)]. Unusual low-frequency co-ordination shifts [δ(free ligand) – δ(complex)] were revealed by 77Se-{1H} NMR spectroscopy in each case. This is in contrast to cis-[MCl2(L1)] which display high-frequency co-ordination shifts. The 195Pt NMR spectroscopic data on cis-[PtCl2(L2)] are consistent with an Se2Cl2 donor set at PtII. The crystal structure of cis-[PdCl2(L2)] shows a distorted square-planar arrangement, with d(Pd–Se) slightly longer than in cis-[PdCl2(L1)].