Macrocyclic polyphosphane ligands : synthesis and characterisation of three diastereoisomers of 5,8,16,19-tetraphenyl-1,12-dithia-5,8,16,19-tetraphosphacyclodocosane and the X-ray crystal structure of a dinuclear nickel(II) complex of the β isomer

Abstract

The macrocycle 5,8,16,19-tetraphenyl-1,12-dithia-5,8,16,19-tetraphosphacyclodocosane, L³, has been synthesised in 13% yield. Three of the five possible diastereoisomers are isolated and one of them (β) is used to form cobalt(II) and nickel(II) complexes with 1 : 1 and 2 : 1 metal–ligand ratios. The compound [Ni₂Br₂(β-L³)][BPh₄]₂·MeOH crystallises in the orthorhombic space group Pbca with a= 17.791 (4), b= 20.993(4), c= 22.758(5)Å, and Z= 4. Least-squares refinement gave R= 0.092, for the 917 observed reflections. The cation [Ni₂Br₂(β-L³)]²⁺ contains two nickel atoms in a slightly distorted square-planar environment related by a crystallographic centre of symmetry. Each nickel atom is co-ordinated by two phosphorus and one sulphur atoms of the macrocycle and by one bromide ion. The Ni ⋯ Ni separation within the cation is 5.13 Å. The stereochemistries of some cobalt(II) and nickel(II) complexes of β-L³ have been investigated in solution and in the solid state by electronic and ³¹P n.m.r. spectroscopy, and by magnetic measurements.