An investigation of halide abstraction by arsenic(III): reactions of AsCl3 with MCl2(M = Mg or Zn) and TiCl4 in donor solvents (MeCn or POCl3). Formation and crystal structure of the dimeric titanium(IV) compound [Ti2Cl6(POCl3)2(PO2Cl2)2]

Abstract

Reactions of TiCl₄, MgCl₂, and ZnCl₂ with AsCl₃ in acetonitrile as solvent (L) have been studied. Rather than the expected halide abstraction by As^III to provide anionic chIoroarsenic(III) and cationic chlorometal species, the simple adducts TiCl₄L₂, MgCl₂L₂, and ZnCl₂L₂ were isolated. Treatment of TiCl₄ and AsCl₃ with L = POCl₃ provides the yellow complex [Ti₂Cl₆(POCl₃)₂(PO₂Cl₂)₂](1) whose structure has been determined by X-ray crystallography. Crystals are monoclinic, space group P2₁/n, with a= 8.612(8), b= 15.339(13), c= 10.232(11)Å, β= 98.0(1)°, and Z= 2. 1 899 Independent reflections were measured on a diffractometer of which 1 341 were used in the final refinement. The structure was refined to R′ 0.075. The crystal contains discrete centrosymmetric dimeric molecules involving O,O′-dichlorophosphate bridging ligands. The titanium centres are octahedrally co-ordinated to three chlorine atoms and three oxygen atoms each in the fac arrangement. Two of these oxygens belong to separate bridging dichlorophosphate groups and the third is provided by a co-ordinated POCl₃ molecule. Possible reaction pathways leading to the formation of the eight-membered bimetallocycle (1) are discussed.