Exploring the Metal-Centered Reactivity of Isomeric, N-Bridged Biscyclometalated Platinum(II) Complexes.

The field of platinum chemistry is ubiquitous in the research of anticancer drugs and new OLED materials. Within the vast library of existing compounds, the majority of work focuses on complexes in the +2 and +4 oxidation states, with comparatively few examples of PtIII complexes reported without bridging ligands. PtIII complexes with metal-metal bonding can be made by mild oxidation of PtII complexes having bis(phenylpyridine) ligands.

A Redox-active Cyclometalated Platinum Ring Enables Synthetic Post-processing of a [2]Rotaxane.

Post-synthetic modification of mechanically interlocked molecules (MIMs) is an attractive avenue to add complexity to already intricate systems. This remains an important, challenging topic that is under-developed. In this paper, we report the synthesis and characterization of a [2]rotaxane molecule featuring a ring appended to an emissive cyclometalated Pt unit.

π-Extended ligands with dual-binding behavior: hindered rotation unlocks unexpected reactivity in cyclometalated Pt complexes.

Cyclometalated platinum complexes play a crucial role in catalysis, bioimaging, and optoelectronics. Phenylpyridines are widespread cyclometalating ligands that generate stable and highly emissive Pt complexes. While it is common practice to modify these ligands to fine-tune their photophysical properties, the incorporation of polycyclic aromatic hydrocarbons into the ligand's structure has been largely overlooked.

Photoisomerisation of Exo-Imine Complexes and the Role of MECP in the Reverse Thermal Equilibrium: An Experimental and DFT Computational Investigation.

Complexes [MCl Cp*] (M=Ir, Rh), [RuCl (p-cymene)] and [Ir(C^N) Cl] (HC^N=a, phenylpyridine ; b, phenylpyrazole,) react with imine ligands derived from ο-aminophenol to yield complexes with an exocyclic C=N bond which has a cis or trans configuration. The trans isomer is favoured except for sterically crowded complexes Cp*M (M=Ir, Rh) when the imine has a mesityl substituent, for which the cis isomer is favoured. The complexes undergo photoisomerisation in visible light but revert back to the original isomer over time or when heated.

Molecular Flytraps Held Together by Platinum-Platinum Intermetallic Bonds.

Metal-metal bonds have rarely been explored as active elements in supramolecular assemblies despite their unique potential to introduce responsive behavior. In this report, a dynamic molecular container composed of two cyclometalated Pt units is constructed using Pt-Pt bonds. This molecule-the flytrap-has a flexible jaw composed of two [18]crown-6 ethers that can adapt their shape to bind large inorganic cations with sub-micromolar affinity.

Cycling a Tether into Multiple Rings: Pt-Bridged Macrocycles for Differentiated Guest Recognition, Pseudorotaxane Transformations, and Guest Capture and Release.

Macrocycle engineering is a key topic in supramolecular chemistry. When synthesizing a ring, one can obtain either complex mixtures of macrocycles of different sizes or a single ring if a template is utilized. Here, we unite these approaches along with post-synthetic modifications to transform a single tether into multiple rings-up to five per tether.

Synergistic Properties of Arabinogalactan (AG) and Hyaluronic Acid (HA) Sodium Salt Mixtures.

The properties of mixtures of two polysaccharides, arabinogalactan (AG) and hyaluronic acid (HA), were investigated in solution by the measurement of diffusion coefficients of water protons by DOSY (Diffusion Ordered SpectroscopY), by the determination of viscosity and by the investigation of the affinity of a small molecule molecular probe versus AG/HA mixtures in the presence of bovine submaxillary mucin (BSM) by HNMR spectroscopy. Enhanced mucoadhesive properties, decreased mobility of water and decreased viscosity were observed at the increase of AG/HA ratio and of total concentration of AG. This unusual combination of properties can lead to more effective and long-lasting hydration of certain tissues (inflamed skin, dry eye corneal surface, etc.

Breathing Room: Restoring Free Rotation in a Schiff-Base Macrocycle through Endoperoxide Formation.

Macrocyclization is a popular method for preparing hosts, but it can have unintended effects, like limiting molecular free rotation to yield mixtures of inseparable isomers. We report a [3 + 3] Schiff-base macrocycle () with anthracene bridges. Restricted rotation about the phenyl-anthracene bonds leads to exist as a mixture of conformations ( and ).

Photoconductive Properties and Electronic Structure in 3,5-Disubstituted 2-(2'-Pyridyl)Pyrroles Coordinated to a Pd(II) Salicylideneiminate Synthon.

The synthesis and the electrochemical, photophysical, structural, and photoconductive properties of three new heteroleptic Pd(II) complexes with various 3',5'- disubstituted-2-(2'-pyridil) pyrroles H(N^N) as coordinated ligands are reported. The coordination of the metal center was completed by a functionalized Schiff base H(O^N) used as an ancillary ligand. The [(N^N)Pd(O^N)] complexes showed highly interesting photoconductive properties which have been correlated to their electronic and molecular structures.

Influence and Substituent Effects on the HOMO-LUMO Energy Gap and Stokes Shift in Ru Mono-Diimine Derivatives.

The ground (S) and excited triplet (T) electronic states and corresponding optical spectra of a series of cationic complexes [RuH(CO)L(PPh)] (L=2,2´-bipyridyl) (Rubpy), 4,4´-dicarboxylic-2,2´-bipyridyl (Rudcbpy), bis-4,4'-(N-methylamide)-2,2´-bipyridyl (Rudamidebpy), bis-4,4'-(methyl)-2,2´-bipyridyl (RudMebpy), [Ru(CO)dcbpy(PPh)] (Ru(2CO)dcbpy), and [Ru(H)dcbpy(PPh)] (Ru(2H)dcbpy) have been studied by combined Density Functional/Time-Dependent Density Functional (DFT/TDDFT) techniques using different combinations of DFT exchange-correlation functionals and basis sets. PBE0/LANL2DZ provided more accurate geometries to describe S whereas B3LYP/LANL2DZ predicted spectral energies that correlated better with the available experiment data. The Ru (II) complexes with different substituents emit photons ranging from 560-610 nm in the series RudMebpy, Rubpy, Rudamidebpy, Rudcbpy.

Programming permanent and transient molecular protection mechanical stoppering.

Chemical protection is an essential tool in synthetic chemistry, which involves blocking reactive sites on a molecule through covalent bonds. Physical approaches, such as encapsulation and host-mediated protection, have emerged as interesting alternatives that use steric bulk to inhibit reactivity. Here, we report the protection of a redox-active viologen through its incorporation into mechanically interlocked molecules (MIMs), namely hetero[4]rotaxanes.

Expanded campestarene hosts for tetra- and dinuclear uranyl(vi) complexes.

The first expanded campestarenes based on a keto-enamine scaffold have been constructed using uranyl acetate as a template. Macrocycles with six and eight aryl rings in their backbone host dinuclear and tetranuclear uranium(vi) species, respectively. The complexes were characterized by SCXRD, FT-IR, UV-vis, and NMR spectroscopy, and DFT calculations corroborated their structures.

The Rich Tautomeric Behavior of Campestarenes.

Campestarenes are a new family of Schiff-base macrocycles that form selectively in a one-step synthesis. These macrocycles with five-fold symmetry show solvent-dependent tautomerization and dimerization or aggregation. In this paper, we have prepared new soluble campestarenes that do not aggregate.

Linkage Isomerism in Silver Acylpyrazolonato Complexes and Correlation with Their Antibacterial Activity.

Novel silver(I) acylpyrazolonato coordination polymers of formula [Ag(Q(R))]n (1-3) have been synthesized by interaction of silver nitrate with HQ(R) in methanol in the presence of an equivalent quantity of KOH (in general HQ(R) = 1-phenyl-3-methyl-4-RC(═O)-5-pyrazolone, in detail HQ(fb), R = -CF2CF2CF3; HQ(cy), R = -cyclo-C6H11; HQ(be), R = -C(H)═C(CH3)2). [Ag(Q(R))]n react with 2-ethylimidazole (2EtimH), 1-methylimidazole (Meim), and triphenylphosphine (PPh3), affording the mononuclear Ag(Q(fb))(EtimH) (4), Ag(Q(cy))(Meim)2 (5), Ag(Q(be))(Meim) (6), and Ag(Q(R))(PPh3)2 (7-9). All complexes have been analytically and spectroscopically characterized, and for some of them the X-ray crystal structure has been resolved.

Emissive Ir(III) complexes bearing thienylamido groups on a 1,10-phenanthroline scaffold.

The synthesis, structures and photophysical properties of a series of bis-cyclometallated Ir(iii) complexes bearing phenylpyrazole (ppz) cyclometallating ligands and phenanthroline-based ancillary ligands containing thienyl- and bithienylamido groups are reported. All complexes are emissive in solution, while in PMMA films strong emission is observed from the thienylamido substituted complex with no emission from the bithienylamido complex. The bithienylamido substituted complex has an excited state lifetime which is significantly longer than the emission lifetime, attributed to the population of non-equilibrated (3)MLCT and (3)LC states in this complex.

Deuteration of Aromatic Rings under Very Mild Conditions through Keto-Enamine Tautomeric Amplification.

We have discovered a surprising, mild method for deuteration of select aromatic compounds that is facilitated by a keto-enamine tautomeric intermediate. The mechanism of the reaction has been studied using kinetics experiments and detailed computational analysis. It was found that a chain of water molecules has a substantial role in lowering the activation barrier to the tautomerization-enhanced deuteration reaction.

Non-symmetrical aryl- and arylethynyl-substituted thioalkyl-porphyrazines for optoelectronic materials: synthesis, properties, and computational studies.

A series of novel non-symmetrically substituted mono β-aryl and β-arylethynyl (alkylsulfanyl)porphyrazines and the corresponding Ni(ii) complexes have been prepared by the Suzuki-Miyaura and Sonogashira cross-coupling reactions with the aim to investigate substituent effects on their electronic and aggregation properties. Spectroscopic, electrochemical and computational investigations show that in both aryl and arylethynyl compounds efficient electron transfer between the aryl and macrocycle moieties occurs. The highest perturbation of the porphyrazine π-electron core is provided by strong electron-donating (NMe2) and electron withdrawing (NO2) aryl substituents, which increase and decrease the macrocycle electron density, respectively.

Tuning the emission lifetime in bis-cyclometalated iridium(III) complexes bearing iminopyrene ligands.

Bis-cyclometalated Ir(III) complexes with the general formula Ir(ppz)2(X^NPyrene), where ppz = 1-phenylpyrazole and X^NPyrene is a bidentate chelate with X = N or O, are reported. Modifications on the ancillary ligand containing pyrene drastically affect the emission lifetimes observed (0.329 to 104 μs).

Pyridine imines as ligands in luminescent iridium complexes.

Biscyclometallated iridium complexes [Ir(ppz)2(X^Y)][PF6] (X^Y = pyridine imine) have been synthesised. The pyridineimine ligands are prepared in situ during the complexation. The complexes show room temperature emission between 640 and 780 nm in CH2Cl2 solution.

An interplay between infrared multiphoton dissociation Fourier-transform ion cyclotron resonance mass spectrometry and density functional theory computations in the characterization of a tripodal quinolin-8-olate Gd(III) complex.

A new hexadentate, tripodal 8-hydroxyquinoline based ligand (QH3) and its gadolinium(III) tris-chelated (GdQ) complex with hemicage structure was investigated by using high resolution Fourier-transform ion cyclotron resonance mass spectrometry (FTICRMS). The protonated adduct of the free ligand and its hemicage tripodal Gd(III) complex, [GdQ + H](+), were first observed in experiments of electrospray ionization (ESI) with a linear ion trap (LTQ) mass spectrometer and further investigated by using high resolution FTICRMS. Gas-phase dissociation of the protonated Gd(III) complex, by infrared multiphoton dissociation (IRMPD) FTICR MS, demonstrated a fragmentation pattern with six main product cluster ions labeled as [Fn](+) (n = 1 up to 6).

Atropisomerism in a thermally switchable, cyclometallated iridium complex.

Two stable diastereomeric atropisomers of a cyclometallated iridium complex containing a pyrene functionalized pyridine imine ligand have been isolated. These are the first fully characterized examples of metal containing atropisomers in which the rotational axis is not between two chelating atoms. The atropisomers can be converted thermally via a rocking motion of the pyrene moiety.

Role of entropy and autosolvation in dimerization and complexation of C60 by Zn7 metallocavitands.

The supramolecular chemistry of bowl-shaped heptazinc metallocavitands templated by Schiff base macrocycles has been investigated. Dimerization thermodynamics were probed by (1)H NMR spectroscopy in benzene-d(6), toluene-d(8), and p-xylene-d(10) and revealed the process to be entropy-driven and enthalpy-opposed in each solvent. Trends in the experimentally determined enthalpy and entropy values are related to the thermodynamics of solvent autosolvation, solvent molecules being released from the monomeric metallocavitand cavity into the bulk solvent upon dimerization.

Cyclometalated Pt(IV) trans-diiodo adducts: experimental and computational studies within an homologous series of compounds.

Four cyclometalated Pt(IV) compounds, 1a,b and 2a,b, were successfully obtained by oxidative addition of I(2) to 2-phenylpyridinate (PhPy) and Nile Red (NR) derived Pt(II) complexes with acetylacetonate (acac) or hexafluoroacetylacetonate (hacac) ancillary ligands. Single crystal X-ray diffraction, electrochemical, photophysical and computational studies have been performed in comparison with the analogues Pt(II) compounds, shedding new light on the role of the oxidation state of the metal centre towards both the luminescence properties and the dioxygen quenching.

Regioselectivity in the nitration of dialkoxybenzenes.

Dinitrodialkoxybenzene derivatives are important precursors for Schiff base macrocycles and a variety of other molecules. During our investigations, we have found that the dinitration reaction of 1,2-dialkoxybenzenes proceeds with unusual regioselectivity, giving exclusively the desired 1,2-dialkoxy-4,5-dinitrobenzene product, but we have been unable to find a good explanation for this result. The dinitration of 1,4-dialkoxybenzene derivatives also exhibits surprising regioselectivity that has hitherto been left unexplained.

Capsule formation, carboxylate exchange, and DFT exploration of cadmium cluster metallocavitands: highly dynamic supramolecules.

A family of molecular heptacadmium carboxylate clusters templated inside [3 + 3] Schiff base macrocycles has been isolated and studied by variable temperature solution and solid-state NMR spectroscopy, single-crystal X-ray diffraction (SCXRD), and density functional theory (DFT) calculations. These metallocavitand cluster complexes adopt bowl-shaped structures, induced by metal coordination, giving rise to interesting host-guest and supramolecular phenomena. Specifically, dimerization of these metallocavitands yields capsules with vacant coordination and hydrogen-bonding sites accessible to encapsulated guests.