Guest‐Dependent Isomer Convergence of a Permanently Fluxional Coordination Cage

Abstract

A fluxional bis‐monodentate ligand, based on the archetypal shape‐shifting molecule bullvalene, self‐assembles with M2+ (M=Pd2+ or Pt2+) to produce a highly complex ensemble of permanently fluxional coordination cages. Metal‐mediated self‐assembly selects for an M2L4 architecture while maintaining shape‐shifting ligand complexity. A second level of simplification is achieved with guest‐exchange; the binding of halides within the M2L4 cage mixture results in a convergence to a cage species with all four ligands present as the “B isomer”. Within this confine, the reaction graph of the bullvalene is greatly restricted, but gives rise to a mixture of 38 possible diastereoisomers in rapid exchange. X‐ray crystallography reveals a preference for an achiral form consisting of both ligand enantiomers. Through a combination of NMR spectroscopy and DFT calculations, we elucidate the restricted isomerisation pathway of the permanently fluxional M2L4 assembly.

Taming Shapeshifting Anions: Total Synthesis of Ocellatusone C

“…Optimized ground state geometries and thermally corrected (195 K) free energies of the corresponding isomeric anions were computed at the B3LYP-D3­(BJ)/ 6-311+G­(d,p)/PCM­(THF)//B3LYP-D3­(BJ)/6-31+G­(d,p)/ PCM­(THF) level of theory (Table ). Insightfully, computations suggest the importance of Coulombic interactions between the dynamic anions and corresponding counterion (K+) . This interaction is strengthened for electron-donating substituents (X = SPh, OMe), favoring the isomerization to a chelated bicyclo­[3.2.2]­nonane isomer by nearly 7.0 kcal/mol (for X = SPh, relative to a bicyclo­[3.3.1]­nonadienyl anion).…”

The Journey to Fluorescent Bullvalenes: Pitfalls and Prospects

“…[6] With this synthetic route, a large series of compounds has been synthesized and investigated, for example, with respect to their interconverting networks, their supramolecular association with cyclodextrins, metal ions, bacteria, and proteins. [6][7][8][9][10][11][12][13][14] Recently, bullvalene (3 a) has regained much interest because of its potential to serve as a suitable fluxional platform for the development of adaptive sensor arrays or dynamic supramolecular structures. [1,7,8,9,15,16] Specifically, Bode and coworkers have introduced several different approaches for the application of adaptive host-guest interactions of substituted bullvalones and bullvalenes for the detection of analytes, such as fullerenes, catechols, or carbohydrates by means of 13 Clabelling and NMR-spectroscopic analysis as well as by CD-and differential absorption spectroscopy (Figure 1).…”

“…[6][7][8][9][10][11][12][13][14] Recently, bullvalene (3 a) has regained much interest because of its potential to serve as a suitable fluxional platform for the development of adaptive sensor arrays or dynamic supramolecular structures. [1,7,8,9,15,16] Specifically, Bode and coworkers have introduced several different approaches for the application of adaptive host-guest interactions of substituted bullvalones and bullvalenes for the detection of analytes, such as fullerenes, catechols, or carbohydrates by means of 13 Clabelling and NMR-spectroscopic analysis as well as by CD-and differential absorption spectroscopy (Figure 1). [17][18][19][20][21][22] But although the bullvalene structure has been established successfully as dynamic, adaptive scaffold in these molecular chemosensors, none of the employed sensing approaches is based on fluorescence as an output signal, so far.…”

“…To add to that, experimental and computational studies have indicated that the required vicinal substitution at the bullvalene core is relatively high in energy and, therefore, mostly not observed. [6,8,9,10,13] Herein, we describe the synthesis and detailed structure elucidation and photophysical characterization of the novel aryl-substituted bullvalene derivative 8 in comparison with the corresponding non-fluxional isomeric lumibullvalene derivatives 7 a-c. The latter were available coincidentally as main byproducts in the bullvalene synthesis.…”

LiBF4‐Induced Rearrangement and Desymmetrization of a Palladium‐Ligand Assembly

“…The host-guest chemistry of palladium-based assemblies has been investigated extensively, [1] and these studies have led to applications in medicinal chemistry [2] and catalysis. [3] The majority of the known guest molecules are either anionic [4] or neutral, [5] and dominant factors for guest binding are electrostatic forces and solvophobic interactions. Cations appear to be less suited as guests for Pd II -based hosts, because the hosts themselves are polycationic species.…”