Macrocyclic polyphosphane ligands. Iron(II), cobalt(II), and nickel(II) complexes of (4RS,7RS,13SR,16SR)-tetraphenyl-1,10-dipropyl-1,10-diaza-4,7,13,16-tetraphosphacyclo-octadecane: crystal structures of their tetraphenylborate derivatives

Abstract

The chiral configuration of the title ligand, β-L¹, and its co-ordinative behaviour towards iron(II), cobalt(II), and nickel(II) have been ascertained by determining the X-ray crystal structures of the low-spin complexes [Fe(β-L¹)][BPh₄]₂·Me₂NCHO (1), [Co(β-L¹)][BPh₄]₂·Me₂NCHO (2), and [Ni(β-L¹)][BPh₄]₂(3). Complex (1) crystallises in the triclinic space group P, with a= 15.156(3), b= 12.649(2), c= 13.333(3)Å, α= 63.37(1), β= 61.44(2), γ= 68.01(1)°, and Z= 1. The iron atom is pseudo-octahedrally co-ordinated by the two nitrogen and four phosphorus atoms of the macrocycle. Complex (2) crystallises in the monoclinic space group C2/c, with a= 23.616(5), b= 13.078(4), c= 27.358(7)Å, β= 110.64(3)°, and Z= 4. The cobalt atom is co-ordinated by the four phosphorus atoms at normal bond distances of 2.265 Å(av.), whereas the nitrogen atoms are further (2.63 Å) from the metal. Complex (3) crystallises in the triclinic space group P, with a= 13.581(2), b= 13.110(3), c= 13.483(2), α= 118.45(2), β= 116.09(2), γ= 80.22(2)°, and Z= 1. The nickel atom is square planar, being co-ordinated by the four phosphorus atoms, whilst the two nitrogen atoms are definitely unto-ordinated at 3.27 Å. The structural rearrangement in the series of d⁶, d⁷, and d⁸ compounds is interpreted in terms of progressively larger metal–axial ligand electronic repulsions.