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

Abstract

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.

A Metallocorrole with Orthogonal Pyrrole Rings

“…As noted before, [16] the CF 3 fluorine atoms appear as quartets with high 5 J FF coupling constants (≈10-15 Hz) in the 19 F NMR spectra at room temperature and above. This was interpreted as reflecting fast rotation (on the NMR timescale) of the congested, but dynamically geared CF 3 groups; thus, each CF 3 fluorine is only split by the three fluorines on the neighboring CF 3 group.…”

“…Thus, between X = H and X = OCH 3 , the Soret maximum of Cu[(CF 3 ) 8 T(p-X-P)C] is redshifted by 48 nm. [16] The corresponding shifts are only 20 nm and 29 nm for the Cu[T(p-X-P)C] and Cu[Br 8 T(p-X-P)C] series, [25] respectively. In our synthetic paper on the subject, [16] we suggested that the large meso shifts for the β-(CF 3 Kohn-Sham MO energy levels ( Figure 5) are in qualitative accord with differences in electrochemical redox potentials.…”

“…groups, Cu[(CF 3 ) 8 T(p-X-P)C]. [16] These complexes exhibit very high reduction potentials and exceedingly strong meso substituent effects on the position of the Soret maximum. Unfortunately, none of these complexes has lent itself to an X-ray structure determination.…”

Ligand Noninnocence in Coinage Metal Corroles: A Silver Knife‐Edge

“…[20,23] Thus, copper triarylcorroles exhibit strongly meso-substituent-sensitive Soret maxima, [21,22] while goldt riarylcorroles do not.…”

Recent developments in out-of-plane metallocorrole chemistry across the periodic table

“…Subsequent study was hampered by synthetic inaccessibility of corroles until 1999, when two new routes to the preparation of free base corrole were published by Paolesse 11 and Gross. 12,13 Over the next decade, a wealth of synthetic methodologies and variants were developed for synthesis of corroles, 14 with mesosubstituents, [15][16][17][18][19][20][21] various beta-substituents, [22][23][24][25][26] and eventually including both charged 27,28 and chiral 29 free-base corroles. The development of these organic syntheses is beyond the scope of this review, but the range of properties imparted by these synthetic options has greatly broadened the scope of applications of corroles.…”