2-Pyridyl- and quinolin-2-yl-functionalised organyltellurium ligands. The stabilisation of diorganyl tritellurides. The crystal and molecular structures of 2-(2-pyridyl)phenyltellurium(IV) tribromide, dimethyldithiocarbamato[2-(2-pyridyl)phenyl]tellurium(II), and p-ethoxyphenyl 2-(2-pyridyl)phenyl telluride

Abstract

The syntheses and spectroscopic data (¹³C n.m.r.) for some new organyltellurium ligands are described. Thus trans metallation of 2-(2-pyridyl)phenyl-(R) or 2-(quinolin-2-yl)phenyl-(R′) mercury(II) chloride with TeBr₄ gives the organyltellurium tribromides RTeBr₃ and R′TeBr₃, which may be reduced to the organyltellurium bromides RTeBr and R′TeBr, some metathesis reactions of which are described; or, in the presence of excess hydrazine, to diorganyl ditellurides, R₂Te₂ and R′₂Te₂. Reduction of RTeBr₃X with NaBH₄ gave a novel tritelluride, R₂Te₃; a method of preparation for R′₂Te₃ was also devised. Syntheses of the tellurides R₂Te, R′₂Te, and RTe(C₆H₄OEt-p) were developed and the intermediacy of ionic compounds [R₂TeBr][HgClBr₂] and [R₂TeCl][HgCl₃] noted. The crystal structures of 2-(2-pyridyl)phenyltellurium(IV) tribromide, (1), dimethyldithiocarbamato [2-(2-pyridyl)phenyl]tellurium(II), (2), and p-ethoxyphenyl 2-(2-pyridyl)phenyltelluride, (3), have been determined from three-dimensional X-ray counter data. Complex (1) is triclinic, space group P with a= 6.953(6), b= 8.382(1), c= 12.133(2)Å, α= 78.68(1), β= 82.87(4), γ= 87.14(4)°, and Z= 2; R= 0.0735 for 1 963 observed reflections. The co-ordination about Te is octahedral with a vacant equatorial position, two Br atoms apical, the third Br and the organic group equatorial [Te–C, 2.110(19); Te–N, 2.244(14)Å]. The compound is essentially monomeric, with a weak association between Te and Br [3.596(3)Å] in a neighbouring molecule. Complex (2) is triclinic, space group P with a= 8.809(3), b= 9.032(5), c= 10.727(4)Å, α= 83.06(4), β= 86.49(3), γ= 63.68(4), and Z= 2; R= 0.0417 for 2 502 observed reflections. The co-ordination about Te is trigonal bipyramidal, C(1) and two lone pairs of Te comprising the equatorial co-ordination and the S(1) atom together with the pyridyl-N atom axial [Te–C, 2.111(5); Te–N, 2.354(4)Å]. No significant intermolecular contacts occur. Complex (3) is monoclinic, space group P2₁/c with a= 13.422(2), b= 16.469(3), c= 7.711(3)Å, β= 91.01(2)°, and Z= 4; R= 0.0415 for 2 014 observed reflections. The Te atom is bonded to two C atoms. The N atom of the pyridyl ring is twisted away from Te [Te–N, 2.695(4)Å] by rotation of the pyridyl ring about the pyridyl–phenyl bond by 23.2(3)°, a manifestation of the trans effect of the Te–C(ethoxyphenyl) covalent bond.