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[(CF 3) 8T( 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[(CF 3) 8TPC] (i.e., X = H) indicates a sterically hindered, strongly saddled geometry, with numerous short F...F nonbonded contacts of 2.5-2.9 A and certain beta carbons displaced by over 1.5 A relative to the mean corrole plane. The CF 3 groups generally appear as quartets in the (19)F NMR spectra, with unexpectedly large (5) J FF coupling constants of about 14 Hz, apparently a manifestation of the highly crowded structure. The eight CF 3 groups together exert a powerful influence on the redox potentials of the copper corrole core. Thus, the E 1/2ox of Cu[(CF 3) 8TPC] (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(Br 8TPC) (1.14 V). Intriguingly, the beta CF 3 groups also greatly intensify the influence of the meso aryl substituents on the redox potentials, relative to the other Cu[Y 8T( p-XP)C] series, where Y = H, F, and Br. The Cu[(CF 3) 8T( 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[(CF 3) 8T( 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.