Reactions of hybrid organotellurium ligands 1-(4-methoxyphenyl telluro)-2-[3-(6-methyl-2-pyridyl)propoxy]ethane (L 1) and 1-ethylthio-2-[2-thienyltelluro]ethane (L 2) with mercury (II) bromide: formation of complexes and their decomposition

Abstract

Two tellurium ligands 1-(4-methoxyphenyltelluro)-2-[3-(6-methyl-2-pyridyl)propoxy]ethane ( L 1) and 1-ethylthio-2-[2-thienyltelluro]ethane ( L 2) have been synthesized by reacting nucleophiles [4-MeO–C 6H 4Te −] and [C 4H 3S-2-Te −] with 2-[3-(6-methyl-2-pyridyl)propoxy]ethylchloride and chloroethyl ethyl sulfide, respectively. Both the ligands react with HgBr 2 resulting in complexes of stoichiometry [HgBr 2 · L 1/ L 2] ( 1/ 4), which show characteristic NMR ( 1H and 13C{ 1H}). On crystallization of 1 from acetone–hexane (2:1) mixture, the cleavage of L 1 occurs resulting in 4-MeOC 6H 4HgBr ( 2) and [RTe +→HgBr 2]Br − ( 3) (where R = –CH 2CH 2OCH 2CH 2CH 2-(2-(6-CH 3–C 5H 3N))). The 2 is characterized by X-ray diffraction on its single crystal. It is a linear molecule and is the first such system which is fully characterized structurally. The Hg–C and Hg–Br bond lengths are 2.085(6) and2.4700(7) Å. The distance of four bromine atoms (3.4041(7)–3.546(7) Å) around Hg ( cis to C) is greater than the sum of van der Waal’s radii 3.30 Å. This mercury promoted cleavage is observed for an acyclic ligand of RArTe type for the first time and is unique, as there appears to be no strong intramolecular interaction to stabilize the cleavage products. The 4 on crystallization shows the cleavage of organotellurium ligand L 2 and formation of a unique complex [(EtS(CH 2) 2SEt)HgBr(μ-Br)Hg(Br)(μ-Br) 2Hg(Br)(μ-Br)BrHg(EtS(CH 2) 2SEt)] · 2HgBr 2 ( 5), which has been characterized by single crystal structure determination and 1H and 13C{ 1H} NMR spectra. The elemental tellurium and [C 4H 3SCH 2] 2 are the other products of dissociation as identified by NMR (proton and carbon-13). The cleavage appears to be without any transmetalation and probably first of its kind. The centrosymmetric structure of 5 is unique as it has [HgBr 3] − unit, one Hg in distorted tetrahedral geometry and one in pseudo-trigonal bipyramidal one. The molecule of 5 may also be described as having [(EtSCH 2CH 2SEt)HgBr] + [HgBr 3] − units, which dimerize and co-crystallize with two HgBr 2 moieties. There are very weak Hg⋯Br interactions between co-crystallized HgBr 2 units and rest of the molecule. [Hg(3)–Br(1)/Hg(3)–Br(4) = 3.148(1)/3.216(1) Å]. The bridging Hg⋯Br distances, Hg(2)–Br(4)′, Hg(2)′–Br(4) and Hg(1)–Br(2), are from 2.914(1) to 3.008(1) Å.