Structural studies of diaminocyclohexane-containing aza-crown ether macrocycles and their Zn(II) complexes

Atwood, Phillip D.; Aykanat, Aylin; Shalumova, Tamila; Tanski, Joseph M.; Folmer-Andersen, J. Frantz

doi:10.1016/j.poly.2013.08.062

Cited by 2 publications

(1 citation statement)

References 43 publications

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“…Similar time scales are indicated for the two structures, but it is suggested that the cis -conformer coexists in the form of two structural groups that do not equilibrate on the time scale for EET. Both cis - and trans -isomers are anticipated to undergo fast equilibration between axial and equatorial species, but such exchange is unlikely to compete with EET across the spacer group. There are several possible sites for internal rotation, and the amide bonds can themselves alternate between cis - and trans -geometries .…”

Section: Results and Discussionmentioning

confidence: 99%

Ultrafast Through-Space Electronic Energy Transfer in Molecular Dyads Built around Dynamic Spacer Units

et al. 2018

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A pair of complementary molecular dyads have been synthesized around a 1,2-diaminocyclohexyl spacer that itself undergoes ring inversion. Despite these conformational exchange processes, the donor and acceptor occupy quite restricted spatial regions, and they are not interchangeable. The donor and acceptor pair comprise disparate boron dipyrromethene dyes selected to display favorable electronic energy transfer (EET). Steady-state emission spectroscopy confirms that through-space EET from donor to acceptor is almost quantitative, aided by the relatively short separations. Ultrafast time-resolved fluorescence spectroscopy has allowed determination of the rates of EET for both dyads. Surprisingly, in view of the close proximity of donor and acceptor (center-to-center separations less than 20 Å), the EET dynamics are well-accounted for in terms of the computed molecular conformations and conventional Förster theory. One dyad appears as a single family of conformations, but EET for the second dyad corresponds to dual-exponential kinetics. In this latter case, an intramolecular hydrogen bond helps stabilize an open geometry, wherein EET is relatively slow.

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Section: Results and Discussionmentioning

confidence: 99%

Ultrafast Through-Space Electronic Energy Transfer in Molecular Dyads Built around Dynamic Spacer Units

et al. 2018

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Group 4 Lanthanide and Actinide Organometallic Inclusion Complexes

et al. 2015

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with an excess of catecholborane (HBCat) yields macrocyclic complexes where the metal is encapsulated inside a 15-membered, hexaoxo, trianionic macrocycle built from alternating catechol and catecholborate fragments. With ThCl 4 (THF) 3 as the starting material, the reaction produced a macrocyclic complex with one chloride ligand and three solvent molecules in the apical positions; however, for the zirconium and uranium complexes the apical positions are occupied by one C 5 Me 5 ligand and a THF solvent molecule. In the samarium and neodymium complexes, only solvent molecules occupy the apical positions. Transmetalation of the ligand among different complexes in refluxing THF were performed. When the zirconium macrocycle was treated with a slight excess of ThCl 4 or NdCl 3 , the corresponding (η 2 -catechol-μ-catecholborate) 3 ThCl(C 4 H 8 O) 3 ·C 4 H 8 O (2) and (η 2 -catechol-μ-catecholborate) 3 Nd(C 4 H 8 O) 3 ·C 4 H 8 O (4) macrocycles were obtained in 87% and 79% yields, respectively. In addition, the reaction of the samarium macrocycle complex (η 2 -catechol-μ-catecholborate) 3 Sm(C 4 H 8 O) 3 ·C 4 H 8 O (3) with a slight excess of ThCl 4 allowed the formation of complex 2 in 76% yield. While some of the pentamethylcyclopentadienyl (Cp*)-containing inclusion complexes were found to be catalytically inactive in the polymerization of ε-caprolactone, the lanthanides and thorium complexes were found to be active, yielding only short chains of polycaprolactone. The X-ray molecular structures for all of the complexes are presented and discussed. Experiments performed with Cp* 2 ThMe 2 and catecholborane allowed us to trap the intermediate Cp*(H)BH 2 BH 2 complex, which was trapped in situ and characterized by 11 B NMR, allowing us to propose a possible mechanism for the formation of the macrocycle. ■ INTRODUCTIONInclusion complexes bearing a metallic ionic center and a macrocyclic ligation present an important field in modern organometallic chemistry. This spectacular supramolecular chemistry is an escalating research area, crossing boundaries between chemistry, physics, materials science, and biology. 1 The insertion of the metal ion into a macrocyclic system can be performed by building the macrocycle motif around the metal center following a template effect or by the reaction of the metal ion with an already constructed macrocycle (such as crown ethers, phorphyrins, etc.). 2 During the past few years, many inclusion complexes of the transition metals and especially the rare-earth metals have been reported. In most cases, the second method was employed: i.e. first synthesizing the macrocyclic ligation followed by introduction of the metal moiety. 3 Specifically for zirconium and the rare-earth metals, many macrocyclic inclusion complexes, mostly for crown ethers and analogous macrocycles, are known. 4 Among the actinide inclusion complexes expanded porphyrin systems, and related macrocycles with pyrrole base donor atoms, including recently developed "Pac-man" polypyrroles, 5 calixarenes, 6 crown ethers, and a...

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Structural studies of diaminocyclohexane-containing aza-crown ether macrocycles and their Zn(II) complexes

Cited by 2 publications

References 43 publications

Ultrafast Through-Space Electronic Energy Transfer in Molecular Dyads Built around Dynamic Spacer Units

Ultrafast Through-Space Electronic Energy Transfer in Molecular Dyads Built around Dynamic Spacer Units

Group 4 Lanthanide and Actinide Organometallic Inclusion Complexes

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