title: Axially chiral beta,beta'-bisporphyrins: synthesis and configurational stability tuned by the central metals.
abstract: In this paper, the synthesis of a new type of intrinsically chiral, directly beta,beta'-linked, octa-meso-aryl-substituted bisporphyrins is described, by using an optimized Suzuki-Miyaura coupling procedure. This strategy leads to a broad variety of such axially chiral 'superbiaryls', differing in their metalation states and substitution patterns. On the basis of an efficient route to as-yet-unknown beta-boronic acid esters of various meso-tetraarylporphyrins (TAPs) by a two-step bromination-borylation protocol, 18 axially chiral bisporphyrin derivatives were prepared in good to excellent yields. As compared to all other directly linked dimeric porphyrin systems, the joint presence of eight bulky meso substituents and the peripheral position of the porphyrin-porphyrin linkage is unprecedented. The axial configurations and rotational barriers of the pure atropo-enantiomers were investigated by HPLC-CD experiments on a chiral phase in combination with quantum chemical CD calculations. According to the HPLC experiments and in agreement with quantum chemical calculations by applying the dispersion-corrected BLYP method, the configurational stability of the central porphyrin-porphyrin axis strongly depends on the nature of the central metals. Cyclovoltammetric studies proved the systematic influence of the meso substituents and of the metal ions on the oxidation potentials of the bisporphyrins. The novel axially chiral bis(tetrapyrrole) compounds described here are potentially useful as substrates for asymmetric catalysis, biomimetic studies on directed electron-transfer processes, for photodynamic therapy (PDT), and for chiral recognition.
authors.affiliation: Institute of Organic Chemistry and Röntgen Research Center for Complex Material Systems, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Bringmann
authors.forename: Daniel C G
authors.initials: DC
authors.lastname: Götz
authors.forename: Tobias A M
authors.initials: TA
authors.lastname: Gulder
authors.forename: Tim H
authors.initials: TH
authors.lastname: Gehrke
authors.forename: Torsten
authors.initials: T
authors.lastname: Bruhn
authors.forename: Thomas
authors.initials: T
authors.lastname: Kupfer
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Radacki
authors.forename: Holger
authors.initials: H
authors.lastname: Braunschweig
authors.forename: Alexander
authors.initials: A
authors.lastname: Heckmann
authors.forename: Christoph
authors.initials: C
authors.lastname: Lambert
mesh_terms: D001897:Boronic Acids / Q000737:chemistry; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D004952:Esters / Q000737:chemistry; D008665:Metalloporphyrins / Q000138:chemical synthesis / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D011166:Porphyrins / Q000138:chemical synthesis / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013237:Stereoisomerism; D013816:Thermodynamics
chemical_list: D001897:Boronic Acids; D004952:Esters; D008665:Metalloporphyrins; D011166:Porphyrins