Synthesis And Properties Of The Metal Complexes Of Sandwich Porphyrin And Phthalocyanine

Phthalocyanines and porphyrins are two important classes of pigments which have found their applications in various disciplines. Both series belong to a cyclic tetrapyrrole family in which the four isoindole or pyrrole nitrogen atoms are able to complex with a range of metal ions. With large metal centers which favor octa-coordination (e.g. rare earths, actinides, group 4 transition metals, and main group elements such as In, Sn, As, Sb, and Bi), sandwich-type complexes in the form of double- and triple-deckers can be formed. Due to the intramolecular π-π interactions and the intrinsic nature of the metal centers, these novel complexes display characteristic features, which cannot be found in their non-sandwich counterparts, enabling them to be used in different areas. They are versatile materials for electrochromic displays, field effect transistors, gas sensors and as structural and spectroscopic models for the special pair found in the bacterial photosynthetic reaction centers.1. Synthesis, Structure, Spectroscopic Properties, and Electrochemistry of Rare Earth Sandwich Compounds with Mixed 2,3-Naphthalocyaninato and Octaethylporphyrinato LigandsFor sandwich complexes with an unpaired electron in one of the tetrapyrrole ligands, one of the fundamental questions is related to the extent of hole delocalization. To have a better understanding on this issue, there is a need of more examples of heteroleptic complexes in which the individual chromophoric ligands exhibit very different optical and redox properties. 2,3-Naphthalocyanine is a phthalocyanine derivative having a more extended π system. As shown by experiments and theoretical calculations, the linear benzoannulation destabilizes the HOMO level leading to a smaller HOMO-LUMO gap. As a result, 2,3-naphthalocyanine has a lower ionization energy and oxidation potential than the phthalocyanine analogue, and its characteristic Q band is also significantly red-shifted.Although naphthalocyaninate-containing sandwich compounds have been known for some time, studies have been focused on the homoleptic complexes, mainly of lutetium(III). Heteroleptic naphthalocyaninato complexes remain extremely rare. We have developed a straightforward and simple methodology to prepare a new series of complexes Mm(Nc)(OEP) (M = Y, La-Lu except Ce and Pm) and Min2(Nc)(OEP)2 (M = Nd, Eu). These rare heteroleptic complexes have been fully characterized by elemental analyses and a wide range of spectroscopic methods, including Mass, EPR, UV-Vis, NIR, NMR, IR and Raman. The molecular structures of all of double-deckers and one triple-decker have also been determined, and the structural parameters have been systematically analyzed and compared. According to the spectroscopic, electrochemical and structural studies, all the complexes exhibit significant jt-jt interactions, for the double-deckers, the hole or the unpaired electron is delocalized over both macrocyclic ligands.2. Tuning the Valence of the Cerium Center in (Na)phthalocyaninato and Porphyrinato Cerium Double-Deckers by Changing the Nature of the Tetrapyrrole LigandsAmong the whole rare earth series, cerium is the only exception. Having an electronic configuration of [Xe]4f15d16s2, this lanthanide may also utilize the electron in the extended 4f orbital in reactions leading to an additional +4 oxidation state. For all the bis(porphyrinato) complexes [Ce(Por)2] and the mixed double-deckers [Ce(Pc)(Por)j reported so far, it is believed that the cerium center is tetravalent and both tetrapyrrole rings are dianionic. Compared with the porphyrin analogues, bis(phthalocyaninato) cerium complexes have been little studied and the exact valence of the metal center remains elusive. While the spectroscopic properties of cerium double-decker [Ce{Nc(fBu)4}2] suggests the presence of a trivalent cerium center. To resolve and clarify this controversial issue, we have prepared a series of cerium double-deckers using a range of tetrapyrrole ligands with very different electronic properties, and systematically examined their structural, electrochemical and spectroscopic properties, including the X-ray absorption near-edge structure(XANES) of the cerium center. The results demonstrate that the valent state of the cerium center varies from III to IV depending on the electronic nature of the two tetrapyrrole ligands.3. Design, synthesis and characterization of chiral sandwich-typephthalocyaninato metal complexesThere has been a growing interest in optically active tetrapyrrole derivatives because of their biological relevance and various potential applications. While chiral porphyrins, ranging from synthetic to naturally occurring analogues, have been extensively studied over the past few decades, the phthalocyanine counterparts have only been reported recently. Because of the unique structure, sandwich-like rare earth complexes with certain tetrapyrrole ligands can exhibit chirality. We have designed and synthesized three series of chiral sandwich-type phthalocyaninato metal complexes as follows: Pb[Pc(a-OR)4] [R = C5Hn, C7H15, Q0H7], [Mm(Pc){Pc(a-OC5Hn)4}] (M = Y, Sm-Lu) and (Pc)M(Pc)M[Pc(a-OC5Hn)4] (M = Sm, Gd, Lu). These new complexes have been fully characterized by elemental analyses and a wide range of spectroscopic methods, their electrochemical properties have been studied systematically. The molecular structures of Pb[Pc(a-0 CsHnM, [Mul(Pc){Pc(a-OC5Hii)4}] (M = Sm, Eu and Er) and (Pc)M(Pc)M[Pc(a-OC5Hn)4] (M = Gd, Lu) have been determined by single-crystal X-ray diffraction analysis. According to the spectroscopic, electrochemical and structural studies, all these molecules are intrinsically chiral possessing a C4 or Cs symmetry.