Synthesis, Characterization And Photochemical Research Of Planar Chiral [2.2] Paracyclophane Derivatives

The structure of the chiral ligands is an important factor in asymmetric catalysis, and the synthesis of new ligands according to the characteristics of the asymmetric catalysis reaction has been the key point of the research. Central chirality, axial chirality, planar chiral and helical chiral are the basic factors for the construction of chiral ligands. Compounds derived from [2.2]paracyclophane (PCP) are typical representatives of planar chiral ligand, and these compounds had been widely used in asymmetric catalysis as a new class of chiral ligands since 1990s. Planar chiral has been playing more and more important roles in homogeneous catalysis in modern chemistry.[2.2]paracyclophane (PCP) is a three-dimensional aromatic molecule with rigid arrangement of parallel, eclipsed benzene rings connected by the ethylene. Due to its special structural features, molecules based on PCP have been designed to mimic through-space delocalization of excited energy, probe intramolecular charge transfer across the transannular gap and understand the global transannularπ-πinteractions. In recent years, molecules based on PCP are often used to build artificial photosynthesis system as a special spacer different from many other groups such as acetylene, benzene, etc.For these reasons, and our interest in cyclophane chemistry, we designed and synthesized a series of helical compounds based on PCP, and try to apply it to asymmetric catalysis. We also studied Suzuki reaction conditions between the two kinds of particular aromatic compounds PCP bromides and porphyrin boronate. Then Novel bisporphyrin-perylene triad dyes composed of a perylene tetracarboxylic diimide (PDI) and tetraphenylporphyrin (free-base porphyrin (H2TPP) or zinc porphyrin (ZnTPP)) linked by a [2.2]paracyclophane moiety have been prepared. Structurally related compounds bearing a biphenyl or a p-terphenyl spacer have also been prepared. Photoinduced electron and energy transfer in porphyrin-perylene diimide triads were determined.The main content of the thesis was shown as follows: 1. Synthesis of cyclophanes with planar and helical chirality derived from [2.2]paracyclophane.Macrocyclic imines based on PCP were synthesized and characterized, and the absolute helicity of the imines were determined. In our synthetic pathway to the helical macrocyclic imines, the compounds 4-amino-12-bromo[2.2]paracyclophane and 4,12-diamino[2.2] paracyclophane are the key structural elements. We adopted our own methods discovered by our lab for the synthesis and resolution of the two compounds. One of the important characteristics of the two compounds is the fact that they are easily tunable in their steric profile. Suzuki-Miyaura coupling with arylboronic acids under PdCl2(dppf) catalysis gave the sterically hindered amino[2.2]paracyclophanes in good to excellent yields (85-99%). The acetamides preparedby the reaction of amino group with acetic anhydride can further diazotization to get variety of phenols and then ether. Treatment of the substituted amino[2.2] paracyclophanes with aqueous glyoxal in THF at room temperature gave corresponding imines in essentially quantitative yield. The absolute helicity of the tetraimine prepared from 4,12-diamino[2.2] paracyclophane was determined according to the X-ray single crystal diffraction. Then the absolute helicity of the other imines were also determined by the specific rotation and CD spectra.2. Preparation of [2.2]paracyclophanyl porphyrins.A facile synthetic approach for the preparation of planar chiral porphyrins derived from [2.2]paracyclophane was described. The conditions of Suzuki reaction between the two special aromatic compounds PCP and porphyrins were studied. Traditional method to the porphyrin includes condensation of pyrroles and aldehydes in refluxing propionic acid, and some unusually elaborated unsymmetrical porphyrins couldn't be prepared in this way. Palladium-catalyzed cross-coupling reactions that employ halogenated porphyrins and arylboronates have provided a facile synthetic approach for the modular preparation of porphyrin macrocyles. K3PO4·3H2O was found to be a mild and effective base with the catalyst of PdCl2(dppf) acted as effective catalytic system for the cross-coupling reaction between PCP bromides and porphyrin boronate. The method reported here may be used as a novel alternative for preparation of chiral porphyrin derivatives.3. Photoinduced energy and electron transfer in porphyrin-perylene diimide symmetric triads linked by [2.2]paracyclophane.Novel bisporphyrin-perylene triad dyes composed of a perylene tetracarboxylic diimide (PDI) and tetraphenylporphyrin (free-base porphyrin (H2TPP) or zinc porphyrin (ZnTPP)) linked by a [2.2]paracyclophane moiety have been prepared based on the above Suzuki reaction. Structurally related compounds bearing a biphenyl or a p-terphenyl spacer have also been prepared as references. The photophysical properties of these compounds are investigated by steady state electronic absorption and fluorescence spectra. The ground state absorption spectra reveal no significant interactions between the porphyrin moieties and PDI in the ground state. The fluorescence spectra suggest high efficient energy transfer from PDI to porphyrin. The energy transfer is not affected by the spacer between the porphyrin and PDI.