Anthony Schultz

Stoichiometric Self-Assembly of Isomeric, Shape-Persistent, Supramacromolecular Bowtie and Butterfly Structures

Two novel macromolecular constitutional isomers have been self-assembled from previously unreported terpyridine ligands in a three-component system. The terpyridine ligands were synthesized in high yields via a key Suzuki coupling. Restrictions of the possible outcomes for self-assembly ultimately provided optimum conditions for isolation of either a molecular bowtie or its isomeric butterfly motif. These isomers have been characterized by ESI-MS, TWIM-MS, (1)H NMR, and (13)C NMR. Notably, these structural isomers have remarkably different drift times in ion mobility separation, corresponding to different sizes and shapes at high charge states.

Self-Assembly of a Supramolecular, Three-Dimensional, Spoked, Bicycle-like Wheel†

Where theres a wheel, theres a way: The terpyridine-based title system has been synthesized through a facile self-assembly process. Two tris(terpyridine) ligands possessing angles of either 120° or 60° between adjacent tpy units were mixed with a stoichiometric amount of Zn(2+) (2:6:12) to generate the desired coordination-driven bicycle-like wheel (90 % yield).

Hexameric Palladium(II) Terpyridyl Metallomacrocycles: Assembly with 4,4′-Bipyridine and Characterization by TWIM Mass Spectrometry†

The construction of 2D or 3D materials using supramolecular chemistry principles has become an intriguing area of research. In particular, terpyridine-based building blocks have played a pivotal role in the construction of dimers, triangles, trigonal prisms, squares, 7–9] pentagons, and hexagons, based on their planar tridentate coordination mode and their facile potential for modification. Terpyridine (terpy) and its metal complexes are also of interest because of their well-known photophysical and electronic properties. Thus, the use of terpyridine for the construction of materials and molecular architectures with increasing complexity will continue to mature. However, the difficulty of obtaining single crystals suitable for X-ray structure determination means that other reliable techniques are essential for the characterization of macromolecular structures. Electrospray ionization (ESI) mass spectrometry has been applied in the identification and characterization under mild ionization conditions. In particular, the cold-spray (CSI) technique reported by Fujita and co-workers, and the Fourier transform mass spectrometry (FTMS) technique developed by Schalley and coworkers are the most prominent ESI-based methods. The work of Piguet and co-workers is also notable. Unfortunately, the signals that correspond to different charge states are superimposed and only a few isotope patterns of different charge states can be deconvoluted. Recently, traveling wave ion mobility mass spectrometry (TWIM-MS), a variant of ion mobility mass spectrometry (IM-MS), has been successfully applied to the detection and characterization of supramolecules. Ion-mobility-based separation enhances the resolving power of mass spectrometry by adding shapeand charge-dependent dispersion, which reduces isomer superposition and can deconvolute the isotope patterns of different charge states. Notably, isomeric linear and cyclic structures have been separated based on their different drift time in the ion mobility device. Herein, we report the 4,4’-bipyridine (bpy) assisted assembly of a hexagonal, dodeca Pd terpyridyl based macrocycle, and its characterization by NMR and TWIMMS. A recent example of the use of terpyridine and its Pd coordination for the formation of a metallocyclic rectangle was reported by Bosnich and co-workers, whereby two cofacially oriented, Pd terpyridine MeCN adducts were dimerized upon the addition of 4,4’-bipyridine. Our synthetic efforts began with an improved preparation of 1,3-bis(2,2’:6’,2’’-terpyridin-4’-yl)-5-tert-butylbenzene (1), which was isolated in 60% yield and exhibited identical H and C NMR spectra to that of the initially reported ligand. Ligand 1 was prepared by the reduction of commercially available 5-tert-butylbenzene-1,3-dicarboxylic acid with BH3·THF, followed by selective oxidation with pyridinium chlorochromate (PCC) and subsequent grinding with 2-acetylpyridine (4.05 equivalents) and NaOH to give an orange solid, which was then added to NH4OH and EtOH and heated at reflux for 24 hours. This ligand, which has coordination sites that are positioned 120 degrees apart, was treated with [Pd(MeCN)4](BF4)2 in dry MeCN to give [(1,3-bis(2,2’:6’,2’’-terpyridin-4’-yl)-5-tert-butylbenzene)Pd2(MeCN)2](BF4)4 2 in nearly quantitative yield (Scheme 1). Ligand 1 was initially insoluble in MeCN, but was readily solubilized when treated with [Pd(MeCN)4](BF4)2 in MeCN. The H NMR data confirmed the formation of adduct 2, with signals at d= 8.68 (s, 3’,5’-terpyH), 8.63-8.58 (m, 6,6’’-terpyH and 3,3’’-terpyH), 8.49 (t, 4,4’’-terpyH), and 7.89 ppm (t, 5,5’’terpyH); see Figure 1. A downfield shift of the tert-butyl singlet peak (from d= 1.51 to 1.57 ppm, Dd= 0.06 ppm) and the IR absorptions observed at 2334 and 2304 cm 1 assigned to the C N stretch also support the formation of a Pd adduct 2. [*] Dr. S. Perera, Dr. X. Li, Dr. M. Soler, A. Schultz, Prof. Dr. C. Wesdemiotis, Dr. C. N. Moorefield, Prof. Dr. G. R. Newkome Department of Polymer Science, Department of Chemistry, The University of Akron 302 Buchtel Common, Akron, OH 44325 (USA) Fax: (+1)330-972-2368 E-mail: wesdemiotis@uakron.edu newkome@uakron.edu Homepage: http://www.dendrimers.com [] These authors contributed equally to this work.

Stable, Trinuclear Zn(Ii)- and Cd(Ii)-Metallocycles: Twim-Ms, Photophysical Properties, and Nanofiber Formation

A series of trimeric, Zn(II)- and Cd(II)-metallocycles is reported. Structural characterization of the highly stable triangles was supported by traveling-wave ion mobility-mass spectrometry (TWIM-MS) and gradient tandem mass spectrometry (gMS(2)). Their unique photophysical properties and self-assembly to form nanofibers are also described.

Dondorff Rings: Synthesis, Isolation, and Properties of 60°‐Directed Bisterpyridine‐Based Folded Tetramers

Square feat: The synthesis, isolation, and characterization of five novel bisterpyridine-based metallomacrocycles, possessing a folded tetrameric configuration is reported (see figure). The initial dimeric building block with the stable linear {tpy-Ru(II)-tpy} connectivity circumvents the formation of the thermodynamically favored molecular triangles.

Structure and Conformation of the Medium-Sized Chlorophosphazene Rings

Medium-sized cyclic oligomeric phosphazenes [PCl2N]m (where m = 5-9) that were prepared from the reaction of PCl5 and NH4Cl in refluxing chlorobenzene have been isolated by a combination of sublimation/extraction and column chromatography from the predominant products [PCl2N]3 and [PCl2N]4. The medium-sized rings [PCl2N]m have been characterized by electrospray ionization-mass spectroscopy (ESI-MS), their (31)P chemical shifts have been reassigned, and their T1 relaxation times have been obtained. Crystallographic data has been recollected for [PCl2N]5, and the crystal structures of [PCl2N]6, and [PCl2N]8 are reported. Halogen-bonding interactions were observed in all the crystal structures of cyclic [PCl2N]m (m = 3-5, 6, 8). The crystal structures of [P(OPh)2N]7 and [P(OPh)2N]8, which are derivatives of the respective [PCl2N]m, are also reported. Comparisons of the intermolecular forces and torsion angles of [PCl2N]8 and [P(OPh)2N]8 with those of three other octameric rings are described. The comparisons show that chlorophosphazenes should not be considered prototypical, in terms of solid-state structure, because of the strong influence of halogen bonding.

From dendrimers to fractal polymers and beyond

O advento da quimica dendritica tem facilitado a pesquisa de materiais por permitir o controle preciso do posicionamento do componente funcional na arquitetura macromolecular. Os protocolos sinteticos iterativos usados para construcao dos dendrimeros foram desenvolvidos baseados no desejo de elaborar moleculas extremamente ramificadas, com alta massa molecular, massa exata e funcionalidade planejada. Arborols, inspirados em arvores e precursores de macromoleculas utilitarias, conhecidas hoje como dendrimeros, foram os primeiros exemplos a empregar blocos de construcao de ramificacao-C 1→3; Caracteristicas fisicas dos Arborols, incluindo a sua forma globular, excelente solubilidade, e agregacao, combinam-se para revelar o potencial supramolecular inerente (isto e, a micela unimolecular) destas especies unicas. A arquitetura que e caracteristica dos materiais dendriticos tambem exibe qualidades fractais com base em estruturas repetitivas, ramificadas e auto-similares. Assim, o design fractal e os aspectos supramoleculares destas construcoes sao sugestivas de um campo maior de materiais fractais que incorporam geometrias repetidas. O uso de terpiridina-M2+-terpiridina (onde, M = Ru, Zn, Fe, etc) em conjunto com algoritmos matematicos tais como as formas da base do Triângulo de Seirpinski, tem permitido o inicio da exploracao da construcao de materiais fractais. A propensao da auto-criacao de moleculas fractais para arquiteturas de ordem superior adiciona outra dimensao para essa nova arena de materiais e construcao de compostos.