Dicopper(I) Oxalate Complexes Stabilized by Lewis Bases: Potential Precursors for Copper Deposition

Elucidating the role of temperature and water on the π-complexation strength of copper(I) ion-containing ionic liquids using inverse gas chromatography

BACKGROUND

The π-complexation capability of copper(I) ion has been exploited in olefin/paraffin separations, but its propensity of undergoing disproportionation to copper(II) ion and copper metal has limited its use. Imidazolium-based ionic liquids (ILs) can serve as solvents for copper(I) ions as they facilitate copper(I) ion-olefin complexation and can enhance its stability. To precisely monitor how copper(I) ions complex with olefins in ILs and evaluate the effects of environmental factors, it is necessary to construct an experimental platform capable of quantitatively measuring their molecular-level interactions.

RESULTS

This study employs an innovative inverse chromatography platform to measure changes in molecular-level interactions between copper(I) ions and olefins when the temperature and water content in the system are carefully controlled. Gas chromatographic stationary phases comprised of the 1-decyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([C10MIM+][NTf2-]) IL containing 0.5 M [Cu+][NTf2-] were pre-heated to 140 °C maximizing copper(I) ion's π-complexation capability. The chromatographic retention of alkenes, dienes, and alkynes on the copper(I) ion/IL stationary phase was observed to be predominantly influenced by their partitioning between the carrier gas and copper(I) ion as well as between the IL and copper(I) ion. Upon introducing water to the system, the Gibbs free energy of solvation for olefins showed less favorable solvation into the stationary phase. In contrast, their solvation was significantly enhanced when the [Cu+][NTf2-]/[C10MIM+][NTf2-] stationary phase was heated to an elevated temperature, indicating that the π-complexation capability of copper(I) ion can be regenerated as needed.

SIGNIFICANCE

This study demonstrates that the stability of copper(I) ions can be improved by dissolving them into appropriate IL solvents. Moreover, the olefin separation performance of the copper(I) ion/IL stationary phase was found to be adjustable by the application of different column treatment conditions (i.e., heating and water introduction), opening the possibility of devising more stable, reliable, and efficient olefin separation systems based on copper(I) ion and IL solvents.

Terminal and Internal Alkyne Complexes and Azide-Alkyne Cycloaddition Chemistry of Copper(I) Supported by a Fluorinated Bis(pyrazolyl)borate

Copper plays an important role in alkyne coordination chemistry and transformations. This report describes the isolation and full characterization of a thermally stable, copper(I) acetylene complex using a highly fluorinated bis(pyrazolyl)borate ligand support. Details of the related copper(I) complex of HC≡CSiMe₃ are also reported. They are three-coordinate copper complexes featuring η²-bound alkynes. Raman data show significant red-shifts in C≡C stretch of [H₂B(3,5-(CF₃)₂Pz)₂]Cu(HC≡CH) and [H₂B(3,5-(CF₃)₂Pz)₂]Cu(HC≡CSiMe₃) relative to those of the corresponding alkynes. Computational analysis using DFT indicates that the Cu(I) alkyne interaction in these molecules is primarily of the electrostatic character. The π-backbonding is the larger component of the orbital contribution to the interaction. The dinuclear complexes such as Cu₂(μ-[3,5-(CF₃)₂Pz])₂(HC≡CH)₂ display similar Cu-alkyne bonding features. The mononuclear [H₂B(3,5-(CF₃)₂Pz)₂]Cu(NCMe) complex catalyzes [3 + 2] cycloadditions between tolyl azide and a variety of alkynes including acetylene. It is comparatively less effective than the related trinuclear copper catalyst {μ-[3,5-(CF₃)₂Pz]Cu}₃ involving bridging pyrazolates.

On the Hydrogen Oxalate Binding Motifs onto Dinuclear Cu and Ag Metal Phosphine Complexes

We report the binding geometries of the isomers that are formed when the hydrogen oxalate ((CO₂)₂H=HOx) anion attaches to dinuclear coinage metal phosphine complexes of the form [M₁M₂dcpm₂(HOx)]⁺ with M=Cu, Ag and dcpm=bis(dicyclohexylphosphino)methane, abbreviated [MM]⁺. These structures are established by comparison of isomer‐selective experimental vibrational band patterns displayed by the cryogenically cooled and N₂‐tagged cations with DFT calculations of the predicted spectra for various local minima. Two isomeric classes are identified that feature either attachment of the carboxylate oxygen atoms to the two metal centers (end‐on docking) or attachment of oxygen atoms on different carbon atoms asymmetrically to the metal ions (side‐on docking). Within each class, there are additional isomeric variations according to the orientation of the OH group. This behavior indicates that HOx undergoes strong and directional coordination to [CuCu]⁺ but adopts a more flexible coordination to [AgAg]⁺. Infrared spectra of the bare ions, fragmentation thresholds and ion mobility measurements are reported to explore the behaviors of the complexes at ambient temperature.

Acetylene and terminal alkyne complexes of copper(i) supported by fluorinated pyrazolates: syntheses, structures, and transformations

A variety of isolable, 2 : 1 and 1 : 1 copper(i)–alkyne complexes of containing pyrazolate ligand supports are presented as well as the copper pyrazolate mediated acetylenic C–H and alkyne CC bond functionalizations.

From bis(silylene) and bis(germylene) pincer-type nickel(II) complexes to isolable intermediates of the nickel-catalyzed Sonogashira cross-coupling reaction

The first [ECE]Ni(II) pincer complexes with E = Si(II) and E = Ge(II) metallylene donor arms were synthesized via C-X (X = H, Br) oxidative addition, starting from the corresponding [EC(X)E] ligands. These novel complexes were fully characterized (NMR, MS, and XRD) and used as catalyst for Ni-catalyzed Sonogashira reactions. These catalysts allowed detailed information on the elementary steps of this catalytic reaction (transmetalation → oxidative addition → reductive elimination), resulting in the isolation and characterization of an unexpected intermediate in the transmetalation step. This complex, {[ECE]Ni acetylide → CuBr} contains both nickel and copper, with the copper bound to the alkyne π-system. Consistent with these unusual structural features, DFT calculations of the {[ECE]Ni acetylide → CuBr} intermediates revealed an unusual E-Cu-Ni three-center-two-electron bonding scheme. The results reveal a general reaction mechanism for the Ni-based Sonogashira coupling and broaden the application of metallylenes as strong σ-donor ligands for catalytic transformations.

Monomeric copper(I), silver(I), and gold(I) alkyne complexes and the coinage metal family group trends

A series of thermally stable, easily isolable, monomeric, and isoleptic coinage metal alkyne complexes have been reported. Treatment of [N{(C(3)F(7))C(Dipp)N}(2)]Li (the lithium salt of the 1,3,5-triazapentadiene [N{(C(3)F(7))C(Dipp)N}(2)]H) with AuCl, CF(3)SO(3)Ag or CF(3)SO(3)Cu in the presence of 3-hexyne led to the corresponding coinage metal alkyne complex [N{(C(3)F(7))C(Dipp)N}(2)]M(EtC[triple bond]CEt) in good yield (M = Au, Ag, Cu; Dipp = 2,6-diisopropylphenyl). X-ray crystal structures of the three coinage metal alkynes are remarkably similar, and show the presence of trigonal-planar metal sites with eta(2)-bonded 3-hexyne. The M-C and M-N bond distances vary in the order Cu < Au < Ag. The bending of the C-C[triple bond]C bond angle is largest for the gold, followed by Cu and Ag adducts. The gold adduct also shows the largest decrease in C[triple bond]C stretching frequency in Raman, while the Ag adduct shows the smallest change compared to that of the uncoordinated alkyne. DFT calculations on [N{(CF(3))C(Ph)N}(2)]M(EtC[triple bond]CEt) and the related ClM(EtC[triple bond]CEt) predict that the M-alkyne bond energy varies in the order Ag < Cu < Au. The gold adducts are also predicted to have the longest C[triple bond]C, largest deviation of C-C[triple bond]C bond angle from linearity, and smallest C[triple bond]C stretching frequency, followed by the Cu and Ag adducts. In these triazapentadienyl coinage metal adducts, the sigma-donation from alkyne --> M dominates over the M --> alkyne pi-back-donation.