Copper β-Octakis(trifluoromethyl)corroles: New Paradigms for Ligand Substituent Effects in Transition Metal Complexes

The reaction of copper beta-octabromo-meso-triarylcorrole derivatives with methyl 2,2-difluoro-2-(fluorosulfonyl)acetate has provided four beta-octakis(trifluoromethyl)corrole complexes, Cu[(CF3)(8)T(p-XP)C] (X = F, H, Me, OMe), in moderate yields. The new complexes present a conglomeration of remarkable substituent effects, both steric and electronic. DFT (OLYP/TZP) geometry optimization of Cu[(CF3)(8)TPC] (i.e., X = H) indicates a sterically hindered, strongly saddled geometry, with numerous short F center dot center dot center dot F nonbonded contacts of 2.5-2.9 angstrom and certain beta carbons displaced by over 1.5 angstrom relative to the mean corrole plane. The CF3 groups generally appear as quartets in the F-19 NMR spectra, with unexpectedly large (5)J(FF) coupling constants of about 14 Hz, apparently a manifestation of the highly crowded structure. The eight CF3 groups together exert a powerful influence on the redox potentials of the copper corrole core. Thus, the E-1/2ox of Cu[(CF3)(8)TPC](1.4 V vs saturated calomel electrode) is a full half of a volt above that of Cu(TPC) (0.9 V) and a quarter of a volt above that of Cu(Br8TPC) (1.14 V). Intriguingly, the beta CF3 groups also greatly intensify the influence of the meso aryl substituents on the redox potentials, relative to the other Cu[Y8T(p-XP)C] series, where Y = H, F, and Br. The Cu[(CF3)(8)T(p-XP)C] complexes also exhibit the most red-shifted optical spectra of any series of metallocorroles synthesized to date. Thus, between Cu(TPC) and Cu[(CF3)(8)T(p-MeO-P)C], the Soret maximum shifts by nearly 100 nm. The observed red-shifts are attributed in part to charge-transfer transitions of the Soret region and in part to the extreme nonplanar distortions.