Ruthenium(ii) and rhodium(iii) porphyrin phosphine complexes: influence of substitution pattern on structure and electronic properties

Abstract

A series of ruthenium(II) and rhodium(III) porphyrin complexes with diphenyl phenylacetylene phosphine (dpap) was synthesised and fully characterised by UV-vis, ¹H NMR and ³¹P{¹H} NMR spectroscopy, and in most cases also by single-crystal X-ray diffraction. The substitution pattern of the porphyrin was varied with increasing meso-phenyl substitution, from octa-ethyl porphyrin (OEP), through diphenyl di-ethyl porphyrin (DPP), to tetraphenyl porphyrin (TPP) and 3,5-di-^tbutyl tetraphenyl porphyrin (tbTPP). The dpap readily displaces the CO ligand from the parent Ru(CO)(porphyrin) and the iodide from the Rh(I)(porphyrin) to give bis-phosphine complexes M(dpap)₂(porphyrin). The UV-vis spectra reveal that some of the complexes are partially dissociated at concentrations of 10⁻⁶ M, and the association constants were estimated to be in the range of 10⁶ to 10⁷ M⁻¹ for the first, and 10⁴ to 10⁶ M⁻¹ for the second binding event. The ¹H NMR chemical shifts of the complexes vary greatly despite the fact that they display very similar geometries in the solid state, and no correlation could be discerned between the crystal structures and the spectroscopic parameters in solution.