Copper Carbonyl Complexes Research Articles

Electronic effect of a perfluorinated β-diketiminate ligand on the bonding nature of copper carbonyl complexes

Two copper complexes 17Fnac2Cu(C6H6) (3) and 17Fnac2CuCO (4) containing the monoanionic, perfluorinated β-diketiminate 17Fnac2- ligand (1) (17Fnac2 = FC[C(CF3)N(C6F5)]2) were synthesized and characterized by IR and NMR spectroscopy (1H, 13C, 19F), cyclovaltammometry (CV), elemental analysis and single crystal X-ray diffraction. The perfluorinated 17Fnac2- ligand marginally reduces the π-back-bonding capacity of the copper centre to the carbonyl group in 4 when compared with the corresponding 16Fnac2- substituted complexes but substantially when compared with the fluorine free substituted derivatives. Quantum chemical calculations gave deeper insight into the bonding situation of this carbonyl complex, while CV studies were performed to determine the oxidation potential of 3 in solution. Based on these data, the influence of the degree of fluorination in different β-diketimine ligands on the electronic nature of the corresponding copper complexes is discussed.

Extremely bulky copper(i) complexes of [HB(3,5-{1-naphthyl}2pz)3]- and [HB(3,5-{2-naphthyl}2pz)3]- and their self-assembly on graphene.

The synthesis and characterization, using NMR (1H and 13C), infrared spectroscopy, and X-ray crystallography, of the ethene and carbon monoxide copper(i) complexes of hydridotris(3,5-diphenylpyrazol-1-yl)borate ([TpPh2]-) and the two new ligands hydridotris(3,5-bis(1-naphthyl)pyrazol-1-yl)borate ([Tp(1Nt)2]-) and hydridotris(3,5-bis-(2-naphthyl)pyrazol-1-yl)borate ([Tp(2Nt)2]-) are described. X-ray crystal structures are presented of [Cu(TpPh2)(C2H4)] and [Cu(Tp(2Nt)2)(C2H4)]. The compound [Cu(TpPh2)(C2H4)] features interactions between the protons of the ethene ligand and the π-electron clouds of the phenyl substituents that make up the binding pocket surrounding the copper(i) center. These dipolar interactions result in strongly upfield shifted signals of the ethene protons in 1H-NMR. [Cu(Tp(1Nt)2)(CO)] and [Cu(Tp(2Nt)2)(CO)] were examined using infrared spectroscopy and were found to have CO stretching vibrations at 2076 and 2080 cm-1 respectively. The copper(i) carbonyl complexes form self-assembled monolayers when drop cast onto HOPG and thin multilayers of a few nanometers thickness when dip coated onto graphene. General macroscopic trends such as the different tendencies to crystallize observed in the complexes of the two naphthyl-substituted ligands appear to extend well to the nanoscale where a well-organized monolayer could be observed of [Cu(Tp(2Nt)2)(CO)].

Infrared spectroscopic study of absorption and separation of CO using copper(i)-containing ionic liquids.

Absorption of carbon monoxide by copper(i)-containing ionic liquids, [Cnmim][CuX2] (Cnmim = 1-alkyl-3-methylimidazolium, n = 2, 4, 6, X = Cl, Br, I) has been investigated using in situ high pressure infrared spectroscopy. For each liquid, observation of a ν(CO) band in the region 2075-2090 cm-1 indicates the formation of copper(i) monocarbonyl complexes, assigned as [Cu(CO)X2]-. The rate of growth and equilibrium intensity of the ν(CO) absorption is dependent on applied CO pressure. Binding of CO is reversible such that complete desorption occurs rapidly on heating above 100 °C and the liquids are robust over multiple gas absorption/desorption cycles. For the series of [C6mim][CuX2] salts the CO absorption ability follows the order Cl ≥ Br ≫ I. Selective absorption of CO from CO/H2 and CO/N2 gas mixtures is demonstrated by measuring the changes in headspace CO content upon absorption and desorption of gas. For [C6mim][CuCl2], a single absorb-vent-desorb cycle yields product gas containing ∼95% CO starting from a 1 : 1 CO/N2 mixture, increasing to ∼98% CO starting from a 4 : 1 CO/N2 mixture. This is particularly promising in view of the similar boiling points of CO and N2 that hinders their separation by cryogenic distillation.

High‐Pressure‐Induced Pseudo‐oxidation of Copper Surfaces by Carbon Monoxide

AbstractInstantaneous electronic and structural modifications of Cu surfaces by high‐pressure CO were explored. At pressures over a millibar range the coverage of CO on the Cu(1 1 1) surface reached approximately one monolayer, and we observed several shake‐up peaks in the Cu 2p photoemission spectra for the first time by using ambient pressure X‐ray photoelectron spectroscopy. These shake‐up peaks resembled those obtained for oxidized surface Cu atoms. We propose that these changes are related to the generation of a copper–carbonyl complex and subsequent Cu surface restructuring owing to lateral CO–CO repulsions. The generality of this finding was investigated in two model reactions, the water‐gas shift and CO oxidation, on a Cu(1 1 1) surface, and we clearly identified the pseudo‐oxidation of Cu. These reversible changes were found to be independent of the orientation of the Cu surface and are of general importance for Cu‐based heterogeneous catalysis.

The copper carbonyl complexes revisited: Why are the infrared spectra and structures of copper mono and dicarbonyl so different?

New infrared absorption data have been obtained using isolation in solid argon and neon on copper carbonyl molecules, CuCO and Cu(CO)2, two very reactive molecules. For CuCO, all three fundamentals are now observed and it presents an unusually large matrix effect, in line with former results indicating a weak metal carbon interaction and a large total dipole moment. With help of isotopic effects, new data indicates unambiguously that Cu(CO)2 is linear and presents a notably stronger metal–carbon interaction than CuCO. Quantum chemical calculation have been carried out at the CCSD(T) level for determining energies and structural properties, as well as spectroscopic observables. The results enable an assessment of the high stability of the Cu(CO)2 molecule (first bond dissociation energy of 66kJ/mol) which suggest that observation at room temperature is possible and give a first evidence of Renner effect on a penta-atomic molecule.

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(CNtBu)][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(CNtBu)][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. CNtBu reacts with [Cu(cyclooctyne)2(CO)][SbF6] to afford [Cu(cyclooctyne)2(CNtBu)][SbF6]. The syntheses of [Cu(cyclooctyne)(CNtBu)2][SbF6] and [Cu(CNtBu)4][SbF6] from the (cyclooctyne)2CuBr precursor are also reported.

Formation of ionic complexes in cryogenic matrices: A case study using co-deposition of Cu− with rare gas cations in solid argon

Matrix isolation spectra have been obtained for ionic species formed from a beam of mass-selected ions, with a coincident beam of externally generated counter-ions used to provide charge balance. Infrared spectra were obtained for copper carbonyl complexes formed following deposition of Cu(-) ions with rare-gas counter-cations into CO-doped argon matrices. Both anionic and neutral copper carbonyl complexes Cu(CO)(n)(q) (n = 1-3; q = 0, -1) were observed in the spectra, with peak positions corresponding to previously reported assignments; new partially resolved bands appearing in the range 1830-1845 cm(-1) are assigned to larger [Cu(CO)3●(CO)n](-) aggregates, having additional CO ligands in the second solvation shell. The experimental geometry ensures that all Cu-centers initially arrive at the matrix as anions, so the relative abundance of anionic relative to neutral complexes is much higher than in previous studies employing alternative methods for ion deposition; this allows for monitoring of electron-transfer processes between anions and cations in the matrix. Comparison of time-dependent vs. temperature-dependent trends reveals that there are two distinct mechanisms by which the population of anionic complexes is converted into neutral complexes: short-range electron transfer between a cation-anion pair following diffusion, and long-range electron transfer involving photodetachment of an electron from the anion into the conduction band of solid argon, resulting in eventual recombination of the electron with a cation in a remote matrix site. The spectra also show a marked dependence on the deposition temperature and dopant concentration, in that 100-fold higher CO concentrations were required during deposition with the sample window at 10 K compared to that used at 20 K, in order to obtain a similar distribution of copper carbonyl complexes. Furthermore, although no carbonyl complexes are observed initially when low concentrations of CO are used at 10 K, upon warming the matrix to 15 K, the neutral di- and tricarbonyl peaks appear abruptly, which is attributed to fast diffusion of CO stimulated by the energy released upon short-range electron-transfer between Cu(-):counter-cation pairs.

ChemInform Abstract: Structure and Bonding in Copper(I) Carbonyl and Cyanide Complexes

AbstractReview: 285 refs.

Structure and Bonding in Copper(I) Carbonyl and Cyanide Complexes

The coordination chemistry of copper(I) carbonyls and cyano complexes is reviewed. Primary attention is focused on structural chemistry, including coordination behavior, bridging modes, network formation, flexible coordination number, and reversible ligand binding. Additional coverage of infrared spectroscopy and orbital interactions in carbonyl and cyanide bonding and the photophysical behavior of metal cyano complexes is also included.

Sandwiched sodium and half-sandwiched copper carbonyl complexes featuring polyfluorinated tris(triazolyl)borate [HB(3,5-(CF3)2Tz)3]−

Fluorinated tris(triazolyl)borate [HB(3,5-(CF(3))(2)Tz)(3)](-) (Tz = triazolyl) affords the isolation of [Na(THF)(6)]{[HB(3,5-(CF(3))(2)Tz)(3)](2)Na} with a ligand sandwiched sodium ion and a copper carbonyl complex [HB(3,5-(CF(3))(2)Tz)(3)]CuCO with a high C-O stretching frequency.

63Cu NMR Spectroscopy of Copper(I) Complexes with Various Tridentate Ligands: CO as a Useful 63Cu NMR Probe for Sharpening 63Cu NMR Signals and Analyzing the Electronic Donor Effect of a Ligand

63Cu NMR spectroscopic studies of copper(I) complexes with various N-donor tridentate ligands are reported. As has been previously reported for most copper(I) complexes, 63Cu NMR signals, when acetonitrile is coordinated to copper(I) complexes of these tridentate ligands, are broad or undetectable. However, when CO is bound to tridentate copper(I) complexes, the 63Cu NMR signals become much sharper and show a large downfield shift compared to those for the corresponding acetonitrile complexes. Temperature dependence of 63Cu NMR signals for these copper(I) complexes show that a quadrupole relaxation process is much more significant to their 63Cu NMR line widths than a ligand exchange process. Therefore, an electronic effect of the copper bound CO makes the 63Cu NMR signal sharp and easily detected. The large downfield shift for the copper(I) carbonyl complex can be explained by a paramagnetic shielding effect induced by the copper bound CO, which amplifies small structural and electronic changes that occur around the copper ion to be easily detected in their 63Cu NMR shifts. This is evidenced by the correlation between the 63Cu NMR shifts for the copper(I) carbonyl complexes and their nu(C[triple bond]O) values. Furthermore, the 63Cu NMR shifts for copper(I) carbonyl complexes with imino-type tridentate ligands show a different correlation line with those for amino-type tridentate ligands. On the other hand, 13C NMR shifts for the copper bound 13CO for these copper(I) carbonyl complexes do not correlate with the nu(C[triple bond]O) values. The X-ray crystal structures of these copper(I) carbonyl complexes do not show any evidence of a significant structural change around the Cu-CO moiety. The findings herein indicate that CO complexation makes 63Cu NMR spectroscopy much more useful for Cu(I) chemistry.

Mononuclear and Dinuclear Copper(I) Complexes of Bis(3,5-dimethylpyrazol-1-yl)methane: Synthesis, Structure, and Reactivity

The synthesis and structures of a mononuclear copper(I) carbonyl complex [Cu(OClO3)(CO)(H2CPz2')] (3) and a dinuclear copper(I) carbonyl complex [{Cu(CO)(H2CPz2')}2(mu-pyrazine)](ClO4)2 (4), where H2CPz2' = bis(3,5-dimethylpyrazol-1-yl)methane, are described. These two compounds were generated by the carbonylation of the corresponding copper(I)-acetonitrile complexes, [Cu(H2CPz2')(MeCN)](ClO4) (1) and [{Cu(H2CPz2')(MeCN)}2(mu-pyrazine)](ClO4)2 (2). Alternatively, treatment of mononuclear 1 and 3, respectively, with pyrazine in a molar ratio of 2:1 produces the pyrazine-bridged dinuclear Cu(I) complexes 2 and 4. Each of the complexes 1-4 can react with PPh3 to generate a common three-coordinated copper(I) complex [Cu(PPh3)(H2CPz2')](ClO4) (5). The structures of complexes 1-5 were all confirmed by X-ray crystallography. Comparison of the Cu(I)-C(CO) bond distances and the CO stretching frequencies of 3 and 4 indicates the back-donating properties of d pi(Cu)-pi*(pyrazine) bonds in 4, and accordingly, stabilizes the mixed-valence species generated from 2. Complex 3, stabilized by the strong interaction between copper(I) ion and perchlorate counteranion (Cu(I)-O(ClO4) = 2.240(3) A), is a potential precursor for polynuclear copper(I) carbonyl complexes.

Copper(I) Complexes of a Heavily Fluorinated β-Diketiminate Ligand: Synthesis, Electronic Properties, and Intramolecular Aerobic Hydroxylation

The aza-Wittig reaction between Ar(f)()-N=PPh(3) [Ar(f)() = 3,5-(CF(3))(2)C(6)H(3)] and 1,1,1,5,5,5-hexafluoro-2,4-pentanedione affords a new, highly fluorinated beta-diketimine, 1. Metalation by mesitylcopper(I) in benzene gives rise to the Cu(I) beta-diketiminate as its eta(2)-benzene adduct, 2a. Copper(I) carbonyl complexes of 1, and of three less-fluorinated analogues, have been generated in situ and compared by IR spectroscopy; the two backbone CF(3) groups exert a stronger electronic influence than the four N-aryl CF(3) groups. Dinuclear adduct 2b reacts readily with O(2), leading to ortho-hydroxylation of a ligand N-Ar(f)() group.

Density functional investigation on copper carbonyl complexes

The structure and bonding of copper carbonyl complexes, [Cu(CO) n] 0/+/−, have been investigated at density functional levels of theory. It was found that the bond parameters and CO bond dissociation energy are very sensitive to the size of the employed basis set. The best agreement between theory and the available experimental data has been achieved at the B3LYP level with the cc-pVTZ/TZV2P basis set.

Tris(pyrazolyl)methanesulfonates: More Than Just Analogues of Tris(pyrazolyl)borate Ligands; N,N,N‐, N,N,O‐, and Other Coordination Modes

AbstractThe thallium(I) salts of tris(pyrazolyl)methanesulfonate (Tpms) and tris(3‐tert‐butylpyrazolyl)methanesulfonate (TpmstBu) have been used to prepare the following complexes: [(TpmstBu)ZnX] [X = Cl (1a), Br (1b), I (1c), Et (3), OAc (5a)], [(TpmstBu)NiX] [X = Cl (2a), Br (2b)], [(TpmstBu)CoCl(HpztBu)] (3), [(TpmstBu)Zn(μ‐OAc)(μ‐OH)Zn(TpmstBu)] (5b), [(TpmstBu)Cu(CO)] (6a), and [(Tpms)Cu(CO)] (6b). The solid‐state structures of 1b, 2a, 3, and 5b have been determined by X‐ray analysis. The optical spectra of 2a and 3 were investigated by means of the angular overlap model to elucidate their electronic structures in view of the underlying molecular geometries. Variable‐temperature NMR and IR spectroscopic studies show that Tpms and TpmstBu can act as N,N,N and N,N,O ligands. Both coordination modes are present in solution for the zinc complexes 1a,b and the copper carbonyl complexes 6a,b. The N,N,O bonding mode is entropically favoured in solution. For the nickel complexes 2a,b, the TpmstBu ligand acts as a tripodal nitrogen ligand in the solid state and in solution. For the dinuclear zinc complex 5b, one of the TpmstBu ligands acts as an N,N,O ligand and one as an N,O ligand. Complex 5b is one of the very few structural models of the dinuclear zinc enzymes phospholipase C and phosphotriesterase. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Infrared spectra and density functional calculations of the copper thiocarbonyls: CuCS, Cu(CS)2, and Cu2CS in solid argon

Microwave discharge through CS2 vapor yielded CS which was cocondensed with laser-ablated copper atoms at 12 K in an argon matrix. Binary copper thiocarbonyl complexes: CuCS, Cu(CS)2, and Cu2CS were formed via the reactions of ground state copper atoms or dimers with CS in solid argon. On the basis of isotopic shifts and splittings as well as density functional calculations, absorptions at 1187.2, 1291.3, and 1353.9 cm−1 are assigned to the C–S stretching vibrations of the bent CuCS, linear Cu(CS)2, and end-on bonded Cu2CS molecules, respectively. The calculation results show that these copper thiocarbonyl complexes are more strongly bonded than the corresponding copper carbonyl complexes.

(η5-C5HR4)CuCO] (R = CHMe2) - A Remarkably Stable Copper Carbonyl Complex and its Reaction with P4

Carbonyl(tetraisopropylcyclopentadienyl)copper has been synthesized and isolated and can be stored at room temperature for several days. [(C5HR4)Cu(CO)] (R = CHMe2) has been characterized by 1H and 13C NMR, C,H analysis, mass spectrometry, and IR spectroscopy. Its reaction with white phosphorus yields a mixture of [(C5HR4)Cu(η2-P4)] with edge-opened P4 coordinated to a CuIII atom and [(C5HR4)Cu(μ,η2:1-P4)Cu(C5HR4)] with an additional Cu(C5HR4) fragment coordinated to one atom of the P4 ligand (R = CHMe2).

63Cu NMR Study of Copper(I) Carbonyl Complexes with Various Hydrotris(pyrazolyl)borates: Correlation between63Cu Chemical Shifts and CO Stretching Vibrations

Copper(I) carbonyl complexes with a series of hindered LR1,R2 ligands (L: hydrotris(pyrazolyl)borate, R1 and R2 are substituents at the 3- and 5-positions of the pyrazole ring, respectively), LR1,R2CuCO [R1, R2 = Me, Me (1), i-Pr, i-Pr (2), t-Bu, Me (3), t-Bu, i-Pr (4), Ph, i-Pr (5), Ph, Ph (6)] have been synthesized and characterized by 1H NMR and IR spectroscopy and elemental analysis. The molecular structures of 3 and 6 have been determined by X-ray crystallography. The electronic structures of copper(I) sites are characterized by means of 63Cu NMR spectroscopy and by the C⋮O stretching vibration. The sharp 63Cu NMR signals are observed for LR1,R2CuCO complexes in toluene at room temperature. The 63Cu NMR signals of copper(I) complexes with alkyl-substituted ligands (1−4) are observed in lower field than those of the phenyl derivatives (5, 6) correlating with the electron-density at the copper center. This argument is supported by the good correlation between the δ(63Cu) value and C⋮O stretching vibration which is a sensitive indicator of the extent of back-donation of the Cu d electrons to the antibonding C⋮O orbitals.

Copper(I) carbonyl and copper(II) acetato complexes with 2,2′-dipyridylamine and halide anions. Crystal and molecular structures of carbonylchloro(2,2′-dipyridylamine)copper(I) and acetatochloro(2,2′-dipyridylamine)copper(II)

Series of [Cu Idipyam(CO)X], [Cu IIdipyam(CH 3CO 2)X] and [Cu II(dipyam) 2(CH 3CO 2)]X complexes (dipyam=2,2′-dipyridylamine; X=Cl −, Br −, I −) were synthesized and the structures of the title compounds were determined by X-ray diffraction methods. Crystallographic details for complexes [Cu Idipyam(CO)Cl] ( 1) and [Cu IIdipyam(CH 3CO 2)Cl] ( 2) are as follows: complex 1, triclinic, space group P 1 ̄ with a=9.944(3), b=9.450(3), c=7.053(3) Å, α=69.50(2), ß=91.81(2), γ=76.33(2)°, Z=2; complex 2, triclinic, space group P 1 ̄ with a=10.093(3), b=9.098(3), c=7.444(2) Å, α=106.24(2), β=96.91(2), γ=78.87(2)°, Z=2. The dry carbonyl complexes are thermostable at 100°C or more, but their formation was reversible in solution even at room temperature. Thermal and chemical stabilities increase from the chloro to the iodo species. Among the acetato derivatives the chloro and bromo mono-dipyam complexes were easily formed, while the iodide gave preferentially the bis-dipyam complex. Each series of the complexes gave very similar IR spectra in the range 3800–250 cm −1. For the carbonyl derivatives the patterns of the far-IR 250–60 cm −1 regions were shown and the ν(Cu–X) frequencies assigned.

Synthesis and Characterization of Cationic [Tris(pyrazolyl)methane]copper(I) Carbonyl and Acetonitrile Complexes

The reaction of [Cu(NCMe)4]PF6 with equimolar amounts of the tris(substituted-pyrazolyl)methane ligands HC(3,5-Me2pz)3, HC(3-Phpz)3, and HC(3-Butpz)3 yields the respective salts {[HC(3,5-Me2pz)3]Cu(NCMe)}PF6, {[HC(3-Phpz)3]Cu(NCMe)}PF6, and {[HC(3-Butpz)3]Cu(NCMe)}PF6. These complexes are unusually resistant toward reaction with dioxygen. These acetonitrile complexes react with carbon monoxide to yield the stable complexes {[HC(3,5-Me2pz)3]Cu(CO)}PF6, {[HC(3-Phpz)3]Cu(CO)}PF6, and {[HC(3-Butpz)3]Cu(CO)}PF6, respectively. The solid-state structures of {[HC(3-Butpz)3)]Cu(NCMe)}PF6·CH2Cl2 and {[HC(3-Butpz)3]Cu(CO)}PF6 have been determined by X-ray crystallography. The structures are very similar, with the Cu−N distances to the donor atoms of the HC(3-Butpz)3 ligand 0.03 Å shorter in the carbonyl complex.