Synthesis and structural characterization of monomeric zinc(II), cadmium(II), and mercury(II) arenethiolates with a chelating oxazoline ligand

Abstract

The synthesis and characterization of homoleptic zinc(II), cadmium(II), and mercury(II) thiolates derived from 4,4-dimethyl-2-phenyloxazoline (1) are described. The disulfide [Ox₂S₂ (3), Ox=2-(4,4-dimethyl-2-oxazolinyl)phenyl] is prepared by the oxidation of lithium arenethiolate OxS⁻Li⁺ (2), and structurally characterized. The disulfide 3 is chiral and enantiomerically pure in the solid state. The thiolate derivatives, M[S(Ox)]₂ [M=Zn (4), or Cd (5)], are prepared in good yield by the metathesis reactions of MCl₂ with lithium arenethiolate 2. The mercury complex 6 is synthesized by treating 3 with elemental mercury. The complexes are quite stable and highly soluble in common nonpolar organic solvents. X-ray diffraction results show that the zinc thiolate 4 and cadmium thiolate 5 are monomeric in the solid state. The geometry around the metal ion in these two complexes is found to be distorted tetrahedral. The zinc complex is chiral and has crystallized in two different crystalline modifications. The single crystal structures have been determined for both the crystalline modifications, a monoclinic modification (4a) and an orthorhombic one (4b). The crystal structure of 4a shows that the complex is "helically" chiral and enantiomerically pure whereas the crystal structure of 4b shows the modification to be racemic. The spontaneous splitting of the racemates, which is responsible for the isolation of optically active compound, indicates that there should be some solubility differences between the racemates and pure enantiomers. ¹H- and ¹³C-NMR measurements indicate that the complex 4 retains its "helical" structure in solution.