A Synthetic Strategy for Cofacial Porphyrin‐Based Homo‐ and Heterobimetallic Complexes

Abstract

We present a straightforward and generally applicable synthesis route for cofacially linked homo‐ and heterobimetallic porphyrin complexes. The protocol allows the synthesis of unsymmetrical aryl‐based meso‐meso as well as β‐meso‐linked porphyrins. Our method significantly increases the overall yield for the published compound known as o‐phenylene‐bisporphyrin (OBBP) by a factor of 6.8. Besides the synthesis of 16 novel homobimetallic complexes containing MnIII, FeIII, NiII, CuII, ZnII, and PdII, we achieved the first single‐crystal X‐ray structure of an unsymmetrical cofacial benzene‐linked porphyrin dimer containing both planar‐chiral enantiomers of a NiII2 complex. Additionally, this new methodology allows access to heterobimetallic complexes such as the FeIII‐NiII containing carbon monoxide dehydrogenase active site analogue. The isolated species were investigated by various techniques, including ion mobility spectrometry, DFT calculations, and UV/Vis spectroscopy. This allowed us to probe the influence of interplane distance on Soret band splitting.

Novel Cofacial Porphyrin‐Based Homo‐ and Heterotrimetallic Complexes of Transition Metals

“…Next, the as‐synthesised free‐base ligand with the trans/cis ratio of 98 : 2 was triply metallated with six different transition metals (Scheme 5), and the resulting metal complexes, bearing the same trans/cis ratio were systematically analysed with UV‐Vis, IR‐spectroscopy, MS and IMS. For the metal coordination, we observed that reaction times needed to be only slightly extended relative to our previous dimer work to obtain complete three‐fold complexation [17] . Exceptionally this does not hold for the 3Ni‐OBTP 13 complex since we observed degradation while stirring in DMF at 100 °C.…”

“…We have developed a facile synthetic route towards the novel o ‐phenylene‐trisporphyrin (free base OBTP, 6H‐OBTP) 3 as a cofacial ligand system (Scheme 1) using pyrrole and benzaldehyde as starting materials. As previously reported by us for bisporphyrins, we have used the well‐established condensation of two pyrroles 1 with paraformaldehyde to yield dipyrromethane 4 in 65 % yield to begin the seven‐step reaction procedure [17,18] . 4 can be used to build up trans‐substituted porphyrin cores like 5,15‐diphenylporphyrin ( 5 ) if benzaldehyde is employed as the corresponding aldehyde [19] .…”

“…and the following monobromination with NBS, yielded the bromo‐porphyrin precursor 7 in an overall yield of 38 % (Scheme 2). [19,20] After introducing the bromo‐substitution, the linker moiety can be incorporated without a second mixed‐condensation reaction, as is normally the case in literature [17] . Instead, we use a standard Suzuki–Miyaura cross‐coupling reaction with 2‐formylphenyl‐boronic acid as the coupling counterpart (Scheme 3).…”

“…uses rather expensive bis(3‐ethyl‐4‐methyl‐1H‐pyrrol‐2‐yl)methane as the basis for all condensation reactions [14] . Additionally, this synthetic approach constrains the fine‐tuning of distances because it only allows meso‐connected porphyrin subunits and restricts the incorporation of residues [17] . Similarly, the synthesis route developed by Therien et al.…”

Metal‐to‐Metal Distance Modulation by Ligand Design: A Case Study of Structure‐Property Correlation in Planar Chiral Cyclophanyl Metal Complexes

“…[11] Tuning multinuclear metal complexes, among various contributing factors based on the nature of the metal type, oxidation state, and coordination capabilities, M-to-M distance modulation has been a promising approach for identifying and optimizing structureproperty relationship from the perspective of cooperative effects. [12] Ligand design is of utmost relevance in investigating structure-property relationships and stands at the center from the application perspectives of metalloarenes. [13] Structural features of the bridging ligand such as flexibility or rigidity, steric, electronic effects, spatial orientation, and systematic variation of M-to-M distances to comprise novel functionalities are crucial contributing factors.…”