Post-assembly Functionalization of Organoplatinum(II) Metallacycles via Copper-free Click Chemistry

We describe the use of a strain-promoted copper-free click reaction in the post-self-assembly functionalization of organoplatinum­(II) metallacycles. The coordination-driven self-assembly of a 120° cyclooctyne-tethered dipyridyl donor with 60° and 120° di-Pt­(II) acceptors forms molecular rhomboids and hexagons bearing cyclooctynes. These species undergo post-self-assembly [3+2] Huisgen cycloaddition with a variety of azides to give functionalized ensembles under mild conditions

Fe–Pt Twisted Heterometallic Bicyclic Supramolecules via Multicomponent Self-Assembly

Herein, we describe a novel multicomponent self-assembly approach that has the prospect of furnishing unprecedented heterometallic bicyclic architectures with a high level of constitutional control. The methodology relies on the coordination directionality, and the stoichiometry of the individual precursor units, as well as on the difference of the coordination preference of the associated metal ions. As a proof-of-concept example, two aesthetically pleasing Fe–Pt heterometallic bicyclic metallacycles <b>6a</b> and <b>6b</b>, consisting of nine communicative components from four unique species, were prepared in ca. 70% isolated yields and fully characterized by multinuclear NMR, 2D NMR, electrospray ionization time-of-flight mass, and UV–vis spectroscopies. Furthermore, density functional theory based computations suggest that each of these supramolecular constructs encompasses two twisted [organo–Pt­(II)←pyridine] coordination based irregular hexagons that are joined via a robust [terpyridine→Fe­(II)←terpyridine] hinge

Photophysical and Computational Investigations of Bis(phosphine) Organoplatinum(II) Metallacycles

A series of endohedral and exohedral amine-functionalized ligands were synthesized and used in the construction of supramolecular <i>D</i>_2<i>h</i> rhomboids and a <i>D</i>_6<i>h</i> hexagon. These supramolecular polygons were obtained via self-assembly of 120° dipyridyl donors with 180° or 120° diplatinum precursors when combined in 1:1 ratios. Steady-state absorption and emission spectra were collected for each ligand and metallacycle. Density functional theory (DFT) and time-dependent DFT calculations were employed to probe the nature of the observed optical transitions for the rhomboids. The emissive properties of these bis­(phosphine) organoplatinum metallacycles arise from ligand-centered transitions involving π-type molecular orbitals with modest contributions from metal-based atomic orbitals. The <i>D</i>_2<i>h</i> rhomboid self-assembled from 2,6-bis­(4-pyridylethynyl)­aniline and a 60° organoplatinum­(II) acceptor has a low-energy excited state in the visible region and emits above 500 nm, properties which greatly differ from those of the parent 2,6-bis­(4-pyridylethynyl)­aniline ligand

Tetra‑, Hexa‑, Dodeca-Nuclear Ir Supramolecules via Bridge-Driven Self-Assembly of Tetrazolyl Ligands

Herein, we report the formation of multinuclear Ir₄, Ir₆, and Ir₁₂ supramolecular complexes via the bridge-driven self-assembly of tetrazolyl ligands. The synthesis of dimeric half-sandwich Ir units was made by the reaction of half-sandwich Ir units and tetrazolyl ligands in a molar ratio of 1:2. The use of different ligands containing multiple tetrazolyl units resulted in the formation of different Ir supramolecular architectures. The reaction of [Cp*IrCl₂]₂, AgOTf, and 1,2- or 1,3-ditetrazolyl benzene in a molar ratio of 1:3:1 resulted in the formation of rectangular tetranuclear or truncated trigonal pyramidal hexanuclear Ir complexes, respectively. On the other hand, the reaction of [Cp*IrCl₂]₂, AgOTf, and 1,3,5-tritetrazolyl benzene in a molar ratio of 6:18:4 produced a supramolecular dodecanuclear iridium complex. The molecular structure of the complex resembled a truncated tetrahedral structure with a large inner cavity, as determined by X-ray crystallography

Near-Infrared Emissive Discrete Platinum(II) Metallacycles: Synthesis and Application in Ammonia Detection

Two novel discrete organoplatinum­(II) metallacycles are prepared by means of coordination-driven self-assembly of a 90° organoplatinum­(II) acceptor, <i>cis</i>-(PEt₃)₂Pt­(OTf)₂, with two donors, a pyridyl donor, 9,10-di­(4-pyridylvinyl)­anthracene, and one of two dicarboxylate ligands. Both metallacycles display aggregation-induced emission as well as solvatochromism. More interestingly, both metallacycles exhibit near-infrared fluorescent emission in the solid state and can be used to detect ammonia gas

Hierarchical Self-Assembly of Responsive Organoplatinum(II) Metallacycle–TMV Complexes with Turn-On Fluorescence

Here we report that the rod-like tobacco mosaic virus (TMV), having a negatively charged surface, can be assembled into three-dimensional micrometer-sized bundle-like superstructures via multiple electrostatic interactions with a positively charged molecular “glue”, namely, a tetraphenylethylene (TPE)-based discrete organoplatinum­(II) metallacycle (<b>TPE-Pt-MC</b>). Due to the nanoconfinement effect in the resultant <b>TMV/TPE-Pt-MC</b> complexes and the aggregation-induced emission (AIE) activity of the TPE units, these hierarchical architectures result in a dramatic fluorescence enhancement that not only provides evidence for the formation of novel metal–organic biohybrid materials but also represents an alternative to turn-on fluorescence. Moreover, the dissociation of these final constructs and subsequent release of individual virus have been achieved by disrupting the <b>TPE-Pt-MC</b> core using tetrabutylammonium bromide (TBAB). This strategy is also compatible with other protein-based nanoparticles such as bacteriophage M13 and ferritin, proving the generality of this approach. Hence, this research will open new routes for the fabrication of functional biohybrid materials involving metal–organic complexes and anisotropically shaped bionanoparticles

A Discrete Amphiphilic Organoplatinum(II) Metallacycle with Tunable Lower Critical Solution Temperature Behavior

Oligo­(ethylene glycol) (OEG)-decorated supra­molecular assemblies are distinguished by their neutral character and macro­scopic temperature-sensitive phase transition behavior. OEG function­alization is an emerging strategy to obtain thermo­responsive macrocyclic amphi­philes, although known methods organize the hydro­philic and hydro­phobic segments by covalent bonding. Coordination-driven self-assembly offers an alternative route for organizing OEG-function­alized precursors into nano­scopic architectures, resulting in well-defined metalla­cycle cores surrounded by hydro­philic scaffolds to impart overall amphi­philic character. Here a tri­(ethylene glycol)-function­alized thermo­sensitive amphi­philic metalla­cycle was prepared with high efficiency by means of the <i>directional-bonding approach</i>. The ensembles thus formed showed good lower critical solution temperature behavior with a highly sensitive phase separation and excellent reversibility. Moreover, the clouding point decreased with increasing metalla­cycle concentration and addition of K⁺

Saccharide-Functionalized Organoplatinum(II) Metallacycles

Coordination-driven self-assembly can be used to construct metallacycles decorated with saccharide functionalities by combining organoplatinum acceptor building blocks with glycosylated dipyridyl donors. We describe here the synthesis of a suite of donors encoded with 120° directionality. The 1,3-bis­(pyridin-4-ylethynyl)­benzene cores contain one of four pendant saccharide groups, resulting in a glucose-, galactose-, mannose-, and lactose-variant. The angularity of these donors makes them suitable for the self-assembly of [2 + 2] rhomboids and [3 + 3] hexagons containing two and three saccharide groups on combination with a 60 or 120° acceptor, respectively. The synthesis and characterization of eight such metallacycles are described, supported by multinuclear NMR and electrospray mass spectrometry data that confirm clean, highly symmetric products with the expected stoichiometries of formation. This work illustrates the use of coordination-driven self-assembly to obtain nanoscopic metallacycles with biologically relevant functionalities in high yields and facile synthetic methods

Tunable Visible Light Emission of Self-Assembled Rhomboidal Metallacycles

Supramolecular coordination complexes (SCCs) have been proposed for applications necessitating photon emitting properties; however, two critical characteristics, facile tunability and high emission quantum yields, have yet to be demonstrated on SCC platforms. Herein, a series of functionalized <i>D</i>_2<i>h</i> [D₂A₂] rhomboids (D = 2,6-bis­(4-ethynylpyridine)­aniline-based ligands; A = 2,9-bis­[<i>trans</i>-Pt­(PEt₃)₂NO₃]­phenanthrene) is described with emission wavelengths spanning the visible region (λ_max = 476–581 nm). Tuning was achieved by simple functional group modifications <i>para</i> to the aniline amine on the donor building block. Steady-state absorption and emission profiles were obtained for each system and are discussed. When the Hammett σ_<i>para</i> constants for the functional groups <i>para</i> to the aniline amine were plotted versus the wavenumber (cm^–1) for the λ_max of the emission profile, a linear relationship was observed. By utilizing this relationship, the emission wavelength of a given rhomboid can be predetermined on the basis of the Hammett constant of the functionality employed on the donor precursor. This range of visible light emission for a suite of simple rhomboids along with the predictive nature of the wavelength of emission is unprecedented for these types of systems

Engineering Functionalization in a Supramolecular Polymer: Hierarchical Self-Organization of Triply Orthogonal Non-covalent Interactions on a Supramolecular Coordination Complex Platform

Here we present a method for the construction of functionalizable supramolecular polymers by controlling three orthogonal interactions within a single system: (i) coordination-driven self-assembly; (ii) H-bonding; and (iii) host–guest interactions between crown ether and dialkylammonium substrates. Three unique molecules constitute the supramolecular construct, including a 2-ureido-4-pyrimidinone (UPy)-functionalized rigid dipyridyl donor and a complementary organo­platinum­(II) acceptor decorated with a crown ether moiety that provide the basis for self-assembly and polymerization. The final host–guest interaction is demonstrated by using one of two dialkylammonium molecules containing fluorophores that bind to the benzo-21-crown-7 (B21C7) groups of the acceptors, providing a spectroscopic handle to evaluate the functionalization. An initial coordination-driven self-assembly yields hexagonal metallacycles with alternating UPy and B21C7 groups at their vertices. The assembly does not interfere with H-bonding between the UPy groups, which link the discrete metallacycles into a supramolecular network, leaving the B21C7 groups free for functionalization via host–guest chemistry. The resultant network results in a cavity-cored metallogel at high concentrations or upon solvent swelling. The light-emitting properties of the dialkylammonium substrates were transferred to the network upon host–guest binding. This method is compatible with any dialkylammonium substrate that does not disrupt coordination nor H-bonding, and thus, the unification of these three orthogonal interactions represents a simple yet highly efficient strategy to obtain supramolecular polymeric materials with desirable functionality