Ru/O₂‑Catalyzed Oxidative C–H Activation/Alkyne Annulation Using Quinoline-Functionalized NHC as a Directing and Functionalizable Group

The ruthenium/O2-catalyzed oxidative annulation reaction of imidazo[1,5-a]quinolin-2-ium salts with alkynes via N-heterocyclic carbene-directed C–H activation to obtain π-conjugated fused imidazo[1,5-a]quinolin-2-ium derivatives is reported. Molecular oxygen has been explored as an economic and clean oxidant and an alternative to metal oxidants. The current protocol exhibits a wide range of substrate scope including bioactive (±)-α-tocopherol derivatives. Moreover, most of the annulated products show strong fluorescence properties, indicating their potential for making new light-emitting materials

Coordination and Ligand Substitution Chemistry of Bis(cyclooctyne)copper(I)

Cationic bis­(alkyne)­copper­(I) carbonyl and bis­(alkyne)­copper­(I) isocyanide complexes have been synthesized from the precursor (cyclooctyne)₂CuBr. [Cu­(cyclo­octyne)₂(CO)]­[SbF₆] and [Cu­(cyclooctyne)₂(CN^tBu)]­[SbF₆] have trigonal-planar and three-coordinate copper centers. The copper carbonyl complex [Cu­(cyclooctyne)₂(CO)]­[SbF₆] displays its C–O stretching frequency in the “nonclassical” metal carbonyl region (2171 cm^–1), and the analogous copper­(I) isocyanide complex [Cu­(cyclooctyne)₂(CN^tBu)]­[SbF₆] also has an unusually high CN stretching band at 2230 cm^–1. The reaction of 3,5-Me₂C₆H₃NH₂ and 4-^tBuC₆H₄NH₂ with [Cu­(cyclooctyne)₂(CO)]­[SbF₆] led to CO displacement rather than addition to CO. CN^tBu reacts with [Cu­(cyclooctyne)₂(CO)]­[SbF₆] to afford [Cu­(cyclooctyne)₂(CN^tBu)]­[SbF₆]. The syntheses of [Cu­(cyclooctyne)­(CN^tBu)₂]­[SbF₆] and [Cu­(CN^tBu)₄]­[SbF₆] from the (cyclooctyne)₂CuBr precursor are also reported

Isolable, Copper(I) Dicarbonyl Complexes Supported by <i>N</i>‑Heterocyclic Carbenes

Cationic copper­(I) dicarbonyl complexes supported by <i>N</i>-heterocyclic carbene ligands, SIPr and IPr*, have been synthesized. [(SIPr)­Cu­(CO)₂]­[SbF₆] and [(IPr*)­Cu­(CO)₂]­[SbF₆] have a trigonal planar, three-coordinate copper atom with an average Cu–CO distance of 1.915 Å and display C–O stretching frequencies higher than that of the free CO (2143 cm^–1). The high CO stretching frequencies suggest that the Cu­(I)–CO interaction in these cationic adducts is dominated by electrostatic and OC → Cu σ-donor components. [(SIPr)­Cu­(CO)₂]­[SbF₆] and [(IPr*)­Cu­(CO)₂]­[SbF₆] readily form the corresponding [(SIPr)­Cu­(CO)­(H₂O)]­[SbF₆] and [(IPr*)­Cu­(CO)­(H₂O)]­[SbF₆] with loss of a CO even with traces of water, but they can be converted back to the dicarbonyl adducts using excess CO. The synthesis and structure of [(IPr*)­Cu­(H₂O)]­[SbF₆] are also reported. It is a two-coordinate copper adduct with a Cu–O distance of 1.874(2) Å. It reacts with excess CO to form [(IPr*)­Cu­(CO)₂]­[SbF₆]

Coordination and Ligand Substitution Chemistry of Bis(cyclooctyne)copper(I)

Cationic bis­(alkyne)­copper­(I) carbonyl and bis­(alkyne)­copper­(I) isocyanide complexes have been synthesized from the precursor (cyclooctyne)₂CuBr. [Cu­(cyclo­octyne)₂(CO)]­[SbF₆] and [Cu­(cyclooctyne)₂(CN^tBu)]­[SbF₆] have trigonal-planar and three-coordinate copper centers. The copper carbonyl complex [Cu­(cyclooctyne)₂(CO)]­[SbF₆] displays its C–O stretching frequency in the “nonclassical” metal carbonyl region (2171 cm^–1), and the analogous copper­(I) isocyanide complex [Cu­(cyclooctyne)₂(CN^tBu)]­[SbF₆] also has an unusually high CN stretching band at 2230 cm^–1. The reaction of 3,5-Me₂C₆H₃NH₂ and 4-^tBuC₆H₄NH₂ with [Cu­(cyclooctyne)₂(CO)]­[SbF₆] led to CO displacement rather than addition to CO. CN^tBu reacts with [Cu­(cyclooctyne)₂(CO)]­[SbF₆] to afford [Cu­(cyclooctyne)₂(CN^tBu)]­[SbF₆]. The syntheses of [Cu­(cyclooctyne)­(CN^tBu)₂]­[SbF₆] and [Cu­(CN^tBu)₄]­[SbF₆] from the (cyclooctyne)₂CuBr precursor are also reported

Inducing Single Molecule Magnetic Behavior in a [Co₄O₄] Cubane via a Pronounced Solvatomagnetic Effect

The pyrazole-based tridentate diol ligand 2-(1-(2-hydroxyethyl)-1<i>H</i>-pyrazol-3-yl)­phenol (H₂L) forms a cubane-type complex [Co₄L₄(MeOH)₄] (<b>1</b>) that features a {Co₄O₄} core and four exogenous MeOH ligands. Electrospray ionization mass spectrometry suggests that the MeOH ligands are easily lost, and thermogravimetric analysis evinces a thermally induced release of those methanol molecules from solid material in the temperature range from 380 to 440 K. Desolvation was found to give rise to a pronounced solvatomagnetic effect that causes a switching of the spin ground state of the {Co₄O₄} core from diamagnetic to magnetic. Furthermore, the desolvated “naked” [Co₄L₄] cube (<b>1</b>*) shows slow relaxation of the magnetization and butterfly-like magnetic hysteresis at 2 K. A comparatively high relaxation barrier <i>U</i>_eff/<i>k</i>_B = 64.4 K and a characteristic relaxation time τ₀ = 3.8 × 10^–9 s for <b>1</b>* have been derived from an Arrhenius plot. These findings thus demonstrate that the emergence of interesting magnetic properties in molecule-based materials can be triggered via a solvatomagnetic process, even for materials that in their solvated form have a diamagnetic (<i>S</i>_T = 0) ground state

Triple Role of Proton Sponge (DMAN) in the Palladium-Catalyzed Direct Stereoselective Synthesis of <i>C</i>‑Aryl Glycosides from Glycals

The triple role of 1,8-bis(dimethylamino)naphthalene (proton sponge) as a reductant, ligand precursor, and organic base in the palladium-catalyzed Heck-type coupling reaction of glycals with aryl iodides affords the rapid and stereoselective synthesis of 2′,3′-unsaturated α-C-aryl glycosides in excellent yields. The role of the proton sponge in reducing palladium(II) to (0) has been studied using cyclic voltammetry, UV–vis, HRMS, and other spectroscopic techniques. This is the first example of a palladium proton sponge complex utilized in coupling reactions. The method is observed to be tolerant of various functional groups, as demonstrated by the huge substrate scope. Moreover, the 2′,3′-unsaturated α-C-aryl glycosides were also converted to 3-keto-β-C-glycosides under sterically hindered pyridinium salt catalysis via a ring-opening and -closing mechanism

Reversible Solvatomagnetic Effect in Novel Tetranuclear Cubane-Type Ni₄ Complexes and Magnetostructural Correlations for the [Ni₄(μ₃‑O)₄] Core

A new family of tetranuclear nickel cube complexes [Ni₄L₄(solv)₄] (<b>1</b>, solv = MeOH; <b>2</b>, solv = H₂O; H₂L = pyrazole-based tridentate {ONO} ligand) has been studied in detail, in particular by X-ray diffraction and superconducting quantum interference device (SQUID) magnetometry. Different solvates <b>1·H</b>_<b>2</b><b>O</b>, <b>2·4C</b>_<b>3</b><b>H</b>_<b>6</b><b>O</b>, <b>2·CH</b>_<b>2</b><b>Cl</b>_<b>2</b>, and <b>2·H</b>_<b>2</b><b>O</b> were obtained in crystalline form. Only small structural variations were found for the Ni–O–Ni angles of the [Ni₄O₄] cores of those compounds, but these slight variations have dramatic consequences for the magnetic properties. [Ni₄L₄(MeOH)₄]·H₂O (<b>1·H</b>_<b>2</b><b>O</b>) and [Ni₄L₄(H₂O)₄]·H₂O (<b>2·H</b>_<b>2</b><b>O</b>) can be reversibly interconverted in the solid state by exposure to the respective solvent, MeOH or H₂O, and this goes along with a switching of the spin ground state from magnetic (<i>S</i>_T = 4) to diamagnetic (<i>S</i>_T = 0). Likewise the (irreversible) loss of lattice solvent in [Ni₄L₄(H₂O)₄]·4C₃H₆O (<b>2·4C</b>_<b>3</b><b>H</b>_<b>6</b><b>O</b>) to give <b>2·2C</b>_<b>3</b><b>H</b>_<b>6</b><b>O</b> changes the ground state from <i>S</i>_T = 4 to <i>S</i>_T = 0. In view of these dramatic solvatomagnetic effects for the present [Ni₄L₄(solv)₄] complexes, which occur upon extrusion of lattice solvent or facile exchange of coordinated solvent molecules while keeping the robust [Ni₄O₄] core intact, a note of care is issued: whenever magnetic data are obtained for powdered material or for crystals that easily loose lattice solvent molecules, the magnetic properties may not necessarily reflect the situation observed in the corresponding single crystal diffraction study. Finally, a thorough analysis of the present series of complexes as well as other {Ni₄(μ₃-OR)₄} cubes reported in the literature confirms that a correlation between the (Ni–O–Ni)_av bond angle and <i>J</i> in [Ni₄O₄] cubane complexes does indeed exist

Reversible Solvatomagnetic Effect in Novel Tetranuclear Cubane-Type Ni₄ Complexes and Magnetostructural Correlations for the [Ni₄(μ₃‑O)₄] Core

A new family of tetranuclear nickel cube complexes [Ni₄L₄(solv)₄] (<b>1</b>, solv = MeOH; <b>2</b>, solv = H₂O; H₂L = pyrazole-based tridentate {ONO} ligand) has been studied in detail, in particular by X-ray diffraction and superconducting quantum interference device (SQUID) magnetometry. Different solvates <b>1·H</b>_<b>2</b><b>O</b>, <b>2·4C</b>_<b>3</b><b>H</b>_<b>6</b><b>O</b>, <b>2·CH</b>_<b>2</b><b>Cl</b>_<b>2</b>, and <b>2·H</b>_<b>2</b><b>O</b> were obtained in crystalline form. Only small structural variations were found for the Ni–O–Ni angles of the [Ni₄O₄] cores of those compounds, but these slight variations have dramatic consequences for the magnetic properties. [Ni₄L₄(MeOH)₄]·H₂O (<b>1·H</b>_<b>2</b><b>O</b>) and [Ni₄L₄(H₂O)₄]·H₂O (<b>2·H</b>_<b>2</b><b>O</b>) can be reversibly interconverted in the solid state by exposure to the respective solvent, MeOH or H₂O, and this goes along with a switching of the spin ground state from magnetic (<i>S</i>_T = 4) to diamagnetic (<i>S</i>_T = 0). Likewise the (irreversible) loss of lattice solvent in [Ni₄L₄(H₂O)₄]·4C₃H₆O (<b>2·4C</b>_<b>3</b><b>H</b>_<b>6</b><b>O</b>) to give <b>2·2C</b>_<b>3</b><b>H</b>_<b>6</b><b>O</b> changes the ground state from <i>S</i>_T = 4 to <i>S</i>_T = 0. In view of these dramatic solvatomagnetic effects for the present [Ni₄L₄(solv)₄] complexes, which occur upon extrusion of lattice solvent or facile exchange of coordinated solvent molecules while keeping the robust [Ni₄O₄] core intact, a note of care is issued: whenever magnetic data are obtained for powdered material or for crystals that easily loose lattice solvent molecules, the magnetic properties may not necessarily reflect the situation observed in the corresponding single crystal diffraction study. Finally, a thorough analysis of the present series of complexes as well as other {Ni₄(μ₃-OR)₄} cubes reported in the literature confirms that a correlation between the (Ni–O–Ni)_av bond angle and <i>J</i> in [Ni₄O₄] cubane complexes does indeed exist

Zinc-Mediated Carbene Insertion to C–Cl Bonds of Chloromethanes and Isolable Zinc(II) Isocyanide Adducts

The zinc adduct {[HB­(3,5-(CF₃)₂Pz)₃]­Zn}⁺, which was generated from [HB­(3,5-(CF₃)₂Pz)₃]­ZnEt and [Ph₃C]­{B­[3,5-(CF₃)₂C₆H₃]₄}, catalyzes the activation of C–halogen bonds of chloromethanes via carbene insertion. Ethyl diazoacetate serves as the carbene precursor. The presence of {[HB­(3,5-(CF₃)₂Pz)₃]­Zn}⁺ in the reaction mixture was confirmed by obtaining {[HB­(3,5-(CF₃)₂Pz)₃]­Zn­(CN^tBu)₃}⁺ using CN^tBu as a trapping agent. {[HB­(3,5-(CF₃)₂Pz)₃]­Zn­(CN^tBu)₃}⁺ loses one zinc-bound CN^tBu easily to produce five-coordinate {[HB­(3,5-(CF₃)₂Pz)₃]­Zn­(CN^tBu)₂}⁺

Tris(alkyne) and Bis(alkyne) Complexes of Coinage Metals: Synthesis and Characterization of (cyclooctyne)₃M⁺ (M = Cu, Ag) and (cyclooctyne)₂Au⁺ and Coinage Metal (M = Cu, Ag, Au) Family Group Trends

The tris­(alkyne) copper complex [(cyclooctyne)₃Cu]­[SbF₆] has been synthesized using cyclooctyne and in situ generated CuSbF₆. Tris­(alkyne) silver complexes [(cyclooctyne)₃Ag]⁺ involving weakly coordinating counterions such as [SbF₆]⁻ and [PF₆]⁻ have also been isolated in good yield using cyclooctyne and commercially available AgSbF₆ and AgPF₆. These coinage metal tris­(alkyne) adducts have trigonal-planar metal sites. The alkyne carbon atoms and the metal site form distorted spoke-wheel (rather than upright trigonal-prismatic) structures in the solid state. In [(cyclooctyne)₃Cu]­[SbF₆], these distortions result in a propeller-like arrangement of alkynes. A cationic gold­(I) complex having two alkynes has been prepared by a reaction of equimolar amounts of Au­(cyclooctyne)₂Cl and AgSbF₆ in dichloromethane. The gold atom of [(cyclooctyne)₂Au]⁺ coordinates to the cyclooctynes in a linear fashion, while the carbon atoms of the alkyne groups form a tetrahedron around gold­(I). Optimized geometries of cationic [(cyclooctyne)₃M]⁺, [(cyclooctyne)₂M]⁺, and [(cyclooctyne)­M]⁺ and neutral [(cyclooctyne)₂MCl] and [(cyclooctyne)­MCl] adducts (M = Cu, Ag, Au) using density functional theory (DFT) at the BP86/def2-TZVPP level of theory and a detailed analysis of metal–alkyne bonding interactions are also presented