Synthesis, Structural and Optical Properties of Tetrabenzoporphyrin Complexes Bearing Four or Eight Peripheral Phenyl Groups

A series of free-base and phosphorus(V) complexes of tetrabenzoporphyrin (TBP) and some phosphorus(V) porphyrins containing four or eight phenyl groups on the periphery have been synthesized and characterized by X-ray crystallography, electronic absorption, and magnetic circular dichroism (MCD) spectroscopy, together with quantum chemical calculations. All phosphorus TBP and meso-tetraphenyl porphyrin complexes adapted ruffled conformations due to the small P(V) ion, although the Zn(II)TBPs containing eight phenyl (Φ) groups at the so-called β and α positions showed planar and saddled structures in the solid state, due to, respectively, marginal or severe steric hindrance between the neighboring Φ groups. All P(V)TBPs showed the Soret and Q bands beyond 450 and 700 nm, respectively, which are some of the longest wavelengths exhibited by metallated TBPs reported to date. Of the eight Φ group-substituted P(V)TBPs, those substituted at α positions always showed absorption bands at longer wavelengths than those at β positions, which was reproduced by calculated absorption spectra. The Soret band positions of meso-tetraphenylated P(V) species without fused benzo-groups (ca. 430–440 nm) were also some of the longest among metalloporphyrins of this type.