Formation of Porphyrins in the Presence of Acid-Labile Metalloporphyrins:  A New Route to Mixed-Metal Multiporphyrin Arrays

Abstract

The ability to incorporate distinct metalloporphyrins at designated sites in multiporphyrin arrays is essential for diverse applications in materials and biomimetic chemistry. The synthesis of such mixed-metal arrays via acid catalyzed reactions has largely been restricted to metalloporphyrins of stability class II (e.g., Cu, Co, Ni) or I. We describe routes for the rational synthesis of mixed-metal arrays via acid-catalyzed condensations that are compatible with metalloporphyrins of stability class III (e.g., Zn) and IV (e.g., Mg). The routes are demonstrated for p-phenylene-linked arrays. The key finding is that several mild Lewis acids [InCl(3), Sc(OTf)(3), Yb(OTf)(3), and Dy(OTf)(3)], which are known to catalyze the dipyrromethane + dipyrromethane-dicarbinol condensation in CH(2)Cl(2) at room temperature without acidolysis, do not demetalate zinc or magnesium porphyrins under the same conditions. Rational routes to porphyrin dyads and triads employ reaction of a (porphyrin)-dipyrromethane and a (porphyrin)-dipyrromethane-dicarbinol. The porphyrin-forming reactions (six examples) proceed in yields of 18-28%. The metalation states of the arrays prepared in this manner include Zn-free base (ZnFb), MgFb, ZnFbMg, ZnFbZn, and ZnFbFb. Studies of the catalysis process indicate that the dipyrromethane + dipyrromethane-dicarbinol condensation is catalyzed by both the Lewis acid and a Brønsted acid derived in situ from the Lewis acid. Taken together, the ability to employ otherwise "acid-labile" metalloporphyrins as precursors in condensation procedures should broaden the scope of accessible mixed-metal multiporphyrin arrays and motivate further studies of the application of mild Lewis acid catalysts in porphyrin chemistry.

Electronic and energy level engineering of directly fused porphyrin-conjugated polymers – impact of the central metal cation

“…S11b in the ESI †) due to a less remarkable demetallation effect, consistent with the LDI-HRMS analysis. Demetallation in pZnDPP and pMgDPP is not surprising since Zn 2+ and Mg 2+ are known labile cations 29 and the demetallation of the zinc(II) porphyrin was previously reported in the oCVD reaction of ZnDMP. 20 Evidence of demetallation followed by significant remetalation of the porphyrin core was observed in the LDI-HRMS spectra of the pAgDPP film that is dominated by the peaks related to fused iron porphyrin dimers [(FeDPP) 2 -7H-Cl] + (Fig.…”

Nanorings with copper(ii) and zinc(ii) centers: forcing copper porphyrins to bind axial ligands in heterometallated oligomers

“…Heterometallated porphyrin oligomers have been widely investigated as model systems for exploring electron transfer, 18–20 energy transfer, 21–24 nonlinear optical activity 25 and molecular recognition. 26–28 The presence of an open-shell copper( ii ) ion in a porphyrin oligomer provides a local fluorescence-quenching site, due to relaxation via d–d transitions, although phosphorescence from trip-doublet states is sometimes observed.…”

Probing Ground‐state Hole Transfer Between Equivalent, Electrochemically Inaccessible States in Multiporphyrin Arrays Using Time‐resolved Optical Spectroscopy

“…The new strategy for determining hole‐transfer rates between nominally equivalent sites employs the ZnFbFb triads shown in Chart 3. The p ‐phenylene‐linked triad ZnFbFbΦ was prepared previously as part of a program to investigate new methods for synthesizing porphyrins under mild acid‐catalysis conditions (28). The triad ZnFbFbU contains diphenylethyne linkers and was prepared for the studies reported herein.…”