Iron(II), cobalt(II) and nickel(II) complexes with the tripod ligand tris(2-dicyclohexylphosphinoethyl)amine

Abstract

The tripod ligand tris(2-dicyclohexylphosphinoethyl)amine Cynp3), sterically hindered on the three phosphorus atoms, forms iron(II), cobalt(II) and nickel(II) complexes of general formula [MX(Cynp3)] Y, (M = Co, Ni; X = Cl, Br, I, NCS; Y = BPh4. M = Fe; X = Cl, Br, I; Y = BPh4. M = Co; X = Y = Cl, Br, I, NCS and M = Fe; X = Y = NCS). The iron complexes are five-coordinated with a trigonal bipyramidal structure. The nickel complexes are four-coordinate (donor set NP2X) with a square planar geometry and a non-bonded phosphine group. The cobalt complexes [CoX(Cynp3)]BPh4 are high-spin five-coordinate with a distorted trigonal bipyramidal geometry both in the solid state and in solution. In the [CoX(Cynp3)] X complexes the ligand acts as tetradentate in the solid state, whereas in solution tetrahedral species in which the ligand acts as bidentate (donor set P2X2) are also formed. Two isomeric bis-thiocyanate derivatives have been obtained, one blue and one brown. The former is high-spin with a pseudotetrahedral geometry, whereas the latter is low-spin with a trigonal bipyramidal geometry and donor set Np2(NCS)2. In solution, both complexes give rise to the same trigonal bipyramidal species.