title: Helimeric porphyrinoids: stereostructure and chiral resolution of meso-tetraarylmorpholinochlorins.
abstract: The synthesis and chiral resolution of free-base and Ni(II) complexes of a number of derivatives of meso-tetraphenylmorpholinochlorins, with and without direct β-carbon-to-o-phenyl linkages to the flanking phenyl groups, is described. The morpholinochlorins, a class of stable chlorin analogues, were synthesized in two to three steps from meso-tetraphenylporphyrin. The conformations and the relative stereostructures of a variety of free-base and Ni(II) complexes of these morpholinochlorins were elucidated by X-ray diffractometry. Steric and stereoelectronic arguments explain the relative stereoarray of the morpholino-substituents, which differ in the free-base and Ni(II) complexes, and in the monoalkoxy, β-carbon-to-o-phenyl linked morpholinochlorins, and the dialkoxy derivatives. The Ni(II) complexes were all found to be severely ruffled whereas the free-base chromophores are more planar. As a result of the helimeric distortion of their porphyrinoid chromophores, the ruffled macrocycles possess a stable inherent element of chirality. Most significantly, resolution of the racemic mixtures was achieved, both by classical methods via diastereomers and by HPLC on a chiral phase. Full CD spectra were recorded and modeled using quantum-chemical computational methods, permitting, for the first time, an assignment of the absolute configurations of the chromophores. The report expands the range of known pyrrole-modified porphyrins. Beyond this, it introduces large chiral porphyrinoid π-systems that exist in the form of two enantiomeric, stereochemically stable helimers that can be resolved. This forms the basis for possible future applications, for example, in molecular-recognition systems or in materials with chiroptic properties.
authors.affiliation: Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060, USA. c.bruckner@uconn.edu
authors.forename: Christian
authors.initials: C
authors.lastname: Brückner
authors.forename: Daniel C G
authors.initials: DC
authors.lastname: Götz
authors.forename: Simon P
authors.initials: SP
authors.lastname: Fox
authors.forename: Claudia
authors.initials: C
authors.lastname: Ryppa
authors.forename: Jason R
authors.initials: JR
authors.lastname: McCarthy
authors.forename: Torsten
authors.initials: T
authors.lastname: Bruhn
authors.forename: Joshua
authors.initials: J
authors.lastname: Akhigbe
authors.forename: Subhadeep
authors.initials: S
authors.lastname: Banerjee
authors.forename: Pedro
authors.initials: P
authors.lastname: Daddario
authors.forename: Heather W
authors.initials: HW
authors.lastname: Daniell
authors.forename: Matthias
authors.initials: M
authors.lastname: Zeller
authors.forename: Ross W
authors.initials: RW
authors.lastname: Boyle
authors.forename: Gerhard
authors.initials: G
authors.lastname: Bringmann