Axial, Helical, and Planar Chirality in Directly Linked Basket-Handle Porphyrin Arrays

Abstract

The single-electron oxidative dimerization of basket-handle porphyrins (BHPs) with different coordinated metal ions [Cu(II), Ni(II), Pd(II), Zn(II)] yielded directly meso-meso linked dimers in excellent yields. The synthetic protocol is suited for coupling substrates with different meso-substituents (H, Br, aryl, alkyl) opposite to the coupling site. Experimental findings concerning reactivities and selectivities were in good agreement with theoretical investigations using ALIE calculations. The dimers, which all are axially chiral, were resolved into their enantiomers by HPLC on a chiral phase. ECD spectra were measured in the stopped-flow mode and compared with results from quantum-chemical ECD calculations to assign the absolute configuration. One directly linked dimer was further oxidized to a fused system, which possessed a stable helical chirality. Its absolute configuration was again assigned by ECD investigations. Furthermore, functionalized BHPs and tetraarylporphyrins were coupled under Suzuki conditions to give dimers and trimers with either β-meso or β-β linkages. Because of the steric shielding of one of the BHP hemispheres, the products were formed with full diastereoselectivity regarding all porphyrin-porphyrin axes. The stereostructures of these arrays were investigated by quantum-chemical calculations (DFT-D3, TD DFT, and sTD DFT), and the absolute configurations were assigned for all chiral representatives.

Synthesis of Porphyrinquinone and Doubly‐Fused Diporphyrin Quinone Through Oxidation of Diarylporphyrins Using a Hypervalent Iodine Compound

“…In fact, 4 could be recovered, although it underwent minor decomposition. Similar behaviors were reported for the highly bent nickel complexes of 7 . Compound 4 should be more flexible than the metallated analogues.…”

“…The molecular structure of 4 elucidated by X‐ray diffraction at 93 K (Figure ) shows a helical conformation with C2 symmetry due to the steric repulsion between two β‐protons, similar to that observed with analogous compounds . The crystal contains both P and M enantiomers, and thus, the space group is achiral ( C 2/c).…”

“…To date, only quinoid compounds derived from meso ‐ meso ‐linked and meso ‐ meso‐ , β – β‐, β′ – β′‐ triply‐linked diporphyrins ( 5 and 6 , Figure ) have been reported. Quinoids derived from doubly‐linked diporphyrin have not been reported to date, although Osuka's group and others have reported a similar type of porphyrin analogue 7 as well as related diporphyrins 8 and 9 (Figure ) . Herein, we also report the structure and properties of 4 .…”

Cryptochirality in 2,2′‐Coupled BODIPY DYEmers

“…HPLC‐ECD measurements, which were the first obvious choice, are known to be hampered for compounds with strong absorptions and relatively weak ECD effects, as exhibited by the current compounds. In fact, the HPLC‐ECD measurements were partially successful for compounds 5 and 7 .…”

Self-Assembly of Covalently Linked Porphyrin Dimers at the Solid–Liquid Interface

“…Intrigued by the cooperative reactivity of manganese porphyrins adsorbed at adjacent locations at the solid–liquid interface, we decided to design and synthesize covalently connected metal-porphyrins, with the ultimate aim to investigate with STM the possible cooperativity between two metal centers in the same molecule. Several examples of covalently linked porphyrin dimers have been described [28,29,30,31,32] and some have been imaged with STM in an ultra-high vacuum environment or at a solid–liquid interface [33,34,35,36,37]. Our intention to adsorb porphyrin dimers as immobilized assemblies at a solid–liquid interface required the attachment of long aliphatic chains, which are known to aid assembly as a result of van der Waals interactions with the surface and intermolecular alkane chain interdigitation [38].…”