Molecular Recognition Using Ruthenium(II) Porphyrin Thiol Complexes as Probes

In situ 1H NMR data are reported for 106 Ru(porp)(RSH)2 species, where porp is the dianion of β-octaethylporphyrin (OEP), meso-tetraphenylporphyrin (TPP), and its para-substituted tetraphenyl analogues (T-p-XPP; X = OMe, Me, F, Cl, CO2Me, CF3), meso-tetrakis(3,5-dimethylphenyl)porphyrin (T-m,m′-Me2PP), and meso-tetramesitylporphyrin (TMP), and R = Me, Et, n Pr, i Pr, n Bu, t Bu, n Hex, Bn (benzyl), Ph, and p-MeOC6H4. The upfield shifts in the SH resonances upon coordination of the thiol reflect changes in the porphyrin ring current and are analyzed using an empirical model that depicts quantitatively the nonbonding, electronic, and steric interactions between the thiol ligands, where steric factors dominate, and the porphyrin plane, where electronic factors dominate; such interactions are typically involved in small-molecule recognition within metalloporphyrin systems. Implications of the findings to hemethiolate proteins and surface coordination chemistry are also briefly presented.