The Cluster Polyazide Complexes: Synthesis, Crystal Structures, and 14N NMR Studies of [{Re3(μ-X)3}(N3)9]3- (X = Br or I)

Azide cluster complexes [{Re₃(μ-Br)₃}(N₃)₉]^3- and [{Re₃(μ-I)₃}(N₃)₉]^3- were obtained by reaction of Re₃X₉ (X = Br or I, respectively) with sodium azide in methanol. The complexes were crystallized as cesium salts of the compositions Cs₃[{Re₃(μ-Br)₃}(N₃)₉]·H₂O (1) and Cs₃[{Re₃(μ-I)₃}(N₃)₉]·H₂O (2) and characterized by X-ray single-crystal diffraction and elemental analyses, mass spectrometry, ¹⁴N NMR spectroscopy, and DFT calculations. In the anions, each rhenium atom is coordinated by three azide ligands. To the best of our knowledge, these compounds represent the first case of metal cluster polyazide complexes (i.e., where each metal atom bears more than one azide ligand). Both complexes are stable in air but are very shock sensitive, and spontaneous explosive decomposition is also possible.

SPAAC iClick: progress towards a bioorthogonal reaction in-corporating metal ions

Combining strain-promoted azide-alkyne cycloaddition (SPAAC) and inorganic click (iClick) reactivity provides access to metal 1,2,3-triazolates. Experimental and computational insights demonstrate that iClick reactivity of the tested metal azides (LM-N₃, M = Au, W, Re, Ru and Pt) depends on the accessibility of the azide functionality rather than electronic effects imparted by the metal. SPAAC iClick reactivity with cyclooctyne is observed when the azide functionality is sterically unencumbered, e.g. [Au(N₃)(PPh₃)] (Au-N3), [W(η³-allyl)(N₃)(bpy)(CO)₂] (W-N3), and [Re(N₃)(bpy)(CO)₃] [bpy = 2,2'-bipyridine] (Re-N3). Increased steric bulk and/or preequilibria with high activation barriers prevent SPAAC iClick reactivity for the complexes [Ru(N₃)(Tp)(PPh₃)₂] [Tp = tris(pyrazolyl)borate] (Ru-N3), [Pt(N₃)(CH₃)(PⁱPr₃)₂] [ⁱPr = isopropyl] (Pt(II)-N3), and [Pt(N₃)(CH₃)₃]₄ ((PtN3)4). Based on these computational insights, the SPAAC iClick reactivity of [Pt(N₃)(CH₃)₃(P(CH₃)₃)₂] (Pt(IV)-N3) was successfully predicted.

An Application Exploiting Aurophilic Bonding and iClick to Produce White Light Emitting Materials

The paper focuses on exploiting aurophilic bonding to produce white light emitting materials. Inorganic Click (iClick) is employed to link two or four Au(I) metal ions through a triazolate bridge. Depending on the choice of phosphine ligand (PEt3 or PPh3), dinuclear Au2-FO or tetranuclear Au4-FO complexes can be controllably synthesized (FO = 2-(9,9-dioctylfluoreneyl-)). The iClick products Au2-FO and Au4-FO are characterized by combustion analysis and multinuclear NMR, TOCSY 1D, 1H-13C gHMBC, and 1H-13C gHSQC. In addition, the photophysical properties of Au2-FO and Au4-FO were examined in THF solution. Transient absorption spectroscopy was employed to elucidate the excited state features of the gold compounds. Solution processed OLEDs were fabricated and characterized, which gave white light electroluminescence with CIE coordinates (0.34, 0.36), as seen referenced to CIE standard illuminant D65 (0.31, 0.32). TDDFT computational analysis of Au2-FO and Au4-FO reveals the origin of light emission. In the case of Au4-FO, direct excitation leads to increased aurophilic bonding in the excited state, and as a result the emission profile is broadened to cover a larger region of the visible spectrum, thus giving white light emission. Designing molecules that can access or increase aurophilic bonding in the excited state provides another tool for fine-tuning the emission profiles of gold complexes.

Phosphorescent complexes of {Mo6I8}4+ with triazolates: [2+3] cycloaddition of alkynes to [Mo6I8(N3)6]2−

“Click” reaction of activated alkynes with [Mo₆I₈(N₃)₆]²⁻ produces novel emissive triazolate complexes with the {Mo₆I₈}⁴⁺ cluster core.

Water-soluble Re6-clusters with aromatic phosphine ligands – from synthesis to potential biomedical applications

New hexarhenium clusters exhibit radio- and photoluminescence, have low cytotoxicity, are capable of penetrating into cells and exhibit photodynamic toxicity.

A quantitative study of vapor diffusions for crystallizations: rates and solvent parameter changes

Vapor diffusion crystallizations are among the most versatile methods for growing X-ray quality crystals. While many experimental sections describe the successful use of various solvent combinations, the literature has been entirely lacking in quantitative data (rates, measures of solvent strength changes) that might allow more informed planning rather than simple trial-and-error approaches. We here report the diffusion-induced volume changes for 44 solvent combinations over the first 60 h under standardized conditions, plus six more combinations that exhibit little or no volume changes. Additionally, the inner and outer vial compositions at 24 h were determined, and the resulting changes in solvation parameters were quantified using Hansen solubility parameters. Some general preliminary effects of changes in volume ratios and scale are described. These results identify two dozen solvent combinations with larger changes in solvent parameters than the very commonly used diethyl ether/dichloromethane example. These results should allow a more informed approach to the execution of vapor diffusion crystallizations than has previously been possible.

Protecting-Group-Free Site-Selective Reactions in a Metal-Organic Framework Reaction Vessel

Site-selective organic transformations are commonly required in the synthesis of complex molecules. By employing a bespoke metal-organic framework (MOF, 1·[Mn(CO)₃N₃]), in which coordinated azide anions are precisely positioned within 1D channels, we present a strategy for the site-selective transformation of dialkynes into alkyne-functionalized triazoles. As an illustration of this approach, 1,7-octadiyne-3,6-dione stoichiometrically furnishes the mono-"click" product N-methyl-4-hex-5'-ynl-1',4'-dione-1,2,3-triazole with only trace bis-triazole side-product. Stepwise insights into conversions of the MOF reaction vessel were obtained by X-ray crystallography, demonstrating that the reactive sites are "isolated" from one another. Single-crystal to single-crystal transformations of the Mn(I)-metalated material 1·[Mn(CO)₃(H₂O)]Br to the corresponding azide species 1·[Mn(CO)₃N₃] with sodium azide, followed by a series of [3+2] azide-alkyne cycloaddition reactions, are reported. The final liberation of the "click" products from the porous material is achieved by N-alkylation with MeBr, which regenerates starting MOF 1·[Mn(CO)₃(H₂O)]Br and releases the organic products, as characterized by NMR spectroscopy and mass spectrometry. Once the dialkyne length exceeds the azide separation, site selectivity is lost, confirming the critical importance of isolated azide moieties for this strategy. We postulate that carefully designed MOFs can act as physical protecting groups to facilitate other site-selective and chemoselective transformations.

Small molecule activation of nitriles coordinated to the [Re6Se8]2+ core: formation of oxazine, oxazoline and carboxamide complexes

Novel oxazine, oxazoline and carboxamide cluster complexes were prepared when different nucleophilic oxygen species reacted with nitriles coordinated to the Lewis acidic [Re6Se8]2+ cluster core. Reaction of ICH2CH2O- (generated in situ) with [Re6Se8(PEt3)5(NCR)]A2 (1A2 (R = Me) and 2A2 (R = Ph) where A = BF4-), leads to the formation of [Re6Se8(PEt3)5(2-methyloxazoline)]2+ (32+) and [Re6Se8(PEt3)5(2-phenyloxazoline)]2+ (42+). Similarly, reaction of BrCH2CH2CH2O- with the same nitrile complexes, 1A2 and 2A2 (where A = BF4- or SbF6-) leads to the corresponding oxazine complexes, [Re6Se8(PEt3)5(2-methyloxazine)]2+ (52+) and [Re6Se8(PEt3)5(2-phenyloxazine)]2+ (62+). In addition, reaction of 2(BF4)2 with KOH leads to the formation of the carboxamide complex, [Re6Se8(PEt3)5(phenylcarboxamide)](BF4) (7(BF4)). The neutral oxazine and oxazoline ligands can be removed using either heat or UV irradiation; UV irradiation was found to be more efficient at ligand removal as indicated by the shorter reaction times. The relative coordination strength of the neutral N-donor ligands was determined by these reaction times. X-ray structure determinations of 5(BF4)2 and 7(BF4) are also reported.

Photophysical and photochemical studies of tricarbonyl rhenium(i) N-heterocyclic carbene complexes containing azide and triazolate ligands

Rhenium NHC complexes bound to azide anions readily react with alkynes to form the corresponding triazolate complexes, a new class of photochemically active species.

On the Critical Effect of the Metal (Mo vs. W) on the [3+2] Cycloaddition Reaction of M3 S4 Clusters with Alkynes: Insights from Experiment and Theory

Whereas the cluster [Mo3 S4 (acac)3 (py)3 ](+) ([1](+) , acac=acetylacetonate, py=pyridine) reacts with a variety of alkynes, the cluster [W3 S4 (acac)3 (py)3 ](+) ([2](+) ) remains unaffected under the same conditions. The reactions of cluster [1](+) show polyphasic kinetics, and in all cases clusters bearing a bridging dithiolene moiety are formed in the first step through the concerted [3+2] cycloaddition between the C≡C atoms of the alkyne and a Mo(μ-S)2 moiety of the cluster. A computational study has been conducted to analyze the effect of the metal on these concerted [3+2] cycloaddition reactions. The calculations suggest that the reactions of cluster [2](+) with alkynes feature ΔG(≠) values only slightly larger than its molybdenum analogue, however, the differences in the reaction free energies between both metal clusters and the same alkyne reach up to approximately 10 kcal mol(-1) , therefore indicating that the differences in the reactivity are essentially thermodynamic. The activation strain model (ASM) has been used to get more insights into the critical effect of the metal center in these cycloadditions, and the results reveal that the change in reactivity is entirely explained on the basis of the differences in the interaction energies Eint between the cluster and the alkyne. Further decomposition of the Eint values through the localized molecular orbital-energy decomposition analysis (LMO-EDA) indicates that substitution of the Mo atoms in cluster [1](+) by W induces changes in the electronic structure of the cluster that result in weaker intra- and inter-fragment orbital interactions.

Crystal structure of octa-μ3-selenido-(p-toluene-sulfonato-κO)penta-kis-(tri-ethyl-phosphane-κP)-octa-hedro-hexa-rhenium(III) p-toluene-sulfonate di-chloro-methane disolvate

The title compound, [Re6Se8{O3SC6H4(CH3)}{P(C2H5)3}5](CH3C6H4SO3)·2CH2Cl2, contains the face-capped hexa-nuclear [Re6(μ3-Se)8](2+) cluster core. The [Re6Se8](2+) cluster core displays a non-crystallographic center of symmetry and is bonded through the Re(III) atoms to five tri-ethyl-phosphane ligands and one p-toluene-sulfonate ligand. One p-toluene-sulfonate counter-ion and two di-chloro-methane solvent mol-ecules are also present in the asymmetric unit. One of the ethyl chains of one triethylphos-phane ligand and one of the CH2Cl2 solvent molecules are disordered over two sets of sites (occupancy ratios 0.65:0.35 and 0.5:0.5, respectively). The Re-O(sulfon-ate) bond length of 2.123 (5) Å is similar to other Re-O bond lengths of hexa-nuclear rhenium chalcogenide clusters containing other O-donor ligands such as dimethyl sulfoxide (DMSO), di-methyl-formamide (DMF) and hydroxide.

Organogold oligomers: exploiting iClick and aurophilic cluster formation to prepare solution stable Au4 repeating units

Cluster formation via multiple gold–gold bonds provides sufficient thermodynamic driving force to overcome entropic penalties to link multiple units and create solution stable organogold oligomers.

Au-iClick mirrors the mechanism of copper catalyzed azide–alkyne cycloaddition (CuAAC)

Isolated digold-triazolate products and first-order kinetic profiles for Au–acetylide/azide reactants in iClick provide compelling support for two copper ions in CuAAC.

The first water-soluble hexarhenium cluster complexes with a heterocyclic ligand environment: synthesis, luminescence, and biological properties

The hexarhenium cluster complexes with benzotriazolate apical ligands [{Re6(μ3-Q)8}(BTA)6](4-) (Q = S, Se; BTA = benzotriazolate ion) were obtained by the reaction of [{Re6(μ3-Q)8}(OH)6](4-) with molten 1H-BTA (1H-benzotriazole). The clusters were crystallized as potassium salts and characterized by X-ray single-crystal diffraction, elemental analyses, and UV-vis and luminescence spectroscopy. In addition, their cellular uptake and toxicity were evaluated. It was found that both clusters exhibited luminescence with high lifetimes and quantum yield values; they were taken up by the cells illuminating them under UV irradiation and, at the same time, did not exhibit acute cytotoxic effects.

First oxido-bridged cubo-octahedral hexanuclear rhenium clusters

The first discrete hexanuclear metal clusters with cores adopting the M6(μ-O)12 cubo-octahedral topology have been synthesized in the course of a simple one-pot reaction. We present a new class of rhenium clusters which are the first hexanuclear rhenium complexes with 12 bridging ligands and the first clusters with octahedrally arranged Re atoms bridged only by O atoms forming a unique cube-like Re6(μ-O)12 unit. Our synthetic strategy demonstrates a new approach to the syntheses of polynuclear rhenium complexes under mild conditions. We discovered that the [Re6(μ-O)12(3-Mepy)6]BPh4 cluster compound has the ability to undergo reversible or/and quasireversible redox reactions without changing spatial structure and overall geometry. Subsequently, a reduction reaction of [Re6(μ-O)12(3-Mepy)6]BPh4 was performed successfully and almost quantitatively resulting in the formation of the molecular [Re6(μ-O)12(3-Mepy)6] complex.