Tertiary phosphine complexes of iron porphyrins: synthesis, molecular stereochemistry, and crystal structure of bis(dimethylphenylphosphine)-(meso-5,10,15,20-tetraphenylporphyrinato)iron(II)

Abstract

The bonding properties of phosphines (PR₃= PMe₃, PMe₂Ph, PMePh₂, and PH₂Ph) in iron(II) porphyrin complexes have been studied. The six-co-ordinate complexes [Fe^II(tpp)(PR₃)₂] and [Fe^II(tpp)(PMe₃)(mim)](tpp =meso-5,10,15,20-tetraphenylporphyrinate, mim =N-methylimidazole) have been prepared. The ¹H and ³¹P n.m.r. properties of these compounds are discussed in comparison with previous studies on the binding of phosphines to haemoglobins. Carbon monoxide binding to [Fe(tpp)(PR₃)₂] has also been studied and followed by i.r. spectroscopy. The crystal structure of [Fe(tpp)(PMe₂Ph)₂] has been determined by three-dimensional, single-crystal X-ray diffraction methods. The complex crystallizes in the triclinic space group P in a cell of dimensions a= 10.305(5), b= 11.149(7), c= 12.839(5)Å, α= 65.67(4), β= 63.34(3), γ= 79.25(4)°, and Z= 1. Refinement based on 3 968 observed [I > σ(I)] diffractometer data converged at R= 0.030 and R′= 0.032. The Fe–P distance is 2.284(1)Å and the average Fe–N distance 2.000(1)Å. The porphyrin core is planar and all bond parameters in the core are consistent with a low-spin iron(II) complex.