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

Understanding Cu(i) local environments in MOFs via63/65Cu NMR spectroscopy

The field of metal-organic frameworks (MOFs) includes a vast number of hybrid organic and inorganic porous materials with wide-ranging applications. In particular, the Cu(i) ion exhibits rich coordination chemistry in MOFs and can exist in two-, three-, and four-coordinate environments, which gives rise to many structural motifs and potential applications. Direct characterization of the structurally and chemically important Cu(i) local environments is essential for understanding the sources of specific MOF properties. For the first time, 63/65Cu solid-state NMR has been used to investigate a variety of Cu(i) sites and local coordination geometries in Cu MOFs. This approach is a sensitive probe of the local Cu environment, particularly when combined with density functional theory calculations. A wide range of structurally-dependent 63/65Cu NMR parameters have been observed, including 65Cu quadrupolar coupling constants ranging from 18.8 to 74.8 MHz. Using the data from this and prior studies, a correlation between Cu quadrupolar coupling constants, Cu coordination number, and local Cu coordination geometry has been established. Links between DFT-calculated and experimental Cu NMR parameters are also presented. Several case studies illustrate the feasibility of 63/65Cu NMR for investigating and resolving inequivalent Cu sites, monitoring MOF phase changes, interrogating the Cu oxidation number, and characterizing the product of a MOF chemical reaction involving Cu(ii) reduction to Cu(i). A convenient avenue to acquire accurate 65Cu NMR spectra and NMR parameters from Cu(i) MOFs at a widely accessible magnetic field of 9.4 T is described, with a demonstrated practical application for tracking Cu(i) coordination evolution during MOF anion exchange. This work showcases the power of 63/65Cu solid-state NMR spectroscopy and DFT calculations for molecular-level characterization of Cu(i) centers in MOFs, along with the potential of this protocol for investigating a wide variety of MOF structural changes and processes important for practical applications. This approach has broad applications for examining Cu(i) centers in other weight-dilute systems.

Noncovalent Chelation by Halogen Bonding in the Design of Metal-Containing Arrays: Assembly of Double σ-Hole Donating Halolium with CuI-Containing O,O-Donors

Five new copper(I) complexes─composed of the paired dibenzohalolium and [CuL₂]^- (L = 1,2,4-oxadiazolate) counterions in which O,O-atoms of the anion are simultaneously linked to the halogen atom─were generated and isolated as the solid via the three-component reaction between [Cu(MeCN)₄](BF₄), sodium 1,2,4-oxadiazolates, and dibenzohalolium triflates (or trifluoroacetates). This reaction is different from the previously reported Cu^I-catalyzed arylation of 1,2,4-oxadiazolones by diaryliodonium salts. Inspection of the solid-state X-ray structures of the complexes revealed the strong three-center X···O,O (X = Br, I) halogen bonding occurred between the oxadiazolate moieties and dibenzohalolium cation. According to performed theoretical calculations, this noncovalent interaction (or noncovalent chelation) was recognized as the main force in the stabilization of the copper(I) complexes. An explanation for the different behavior of complexes, which provide either chelate or nonchelate binding, is based on the occurrence of additional -CH₃···π interactions, which were also quantified.

Distinct Reactivity Modes of a Copper Hydride Enabled by an Intramolecular Lewis Acid

We disclose a 1,4,7-triazacyclononane (TACN) ligand featuring an appended boron Lewis acid. Metalation with Cu(I) affords a series of tetrahedral complexes including a boron-capped cuprous hydride. We demonstrate distinct reactivity modes as a function of chemical oxidation: hydride transfer to CO2 in the copper(I) state and oxidant-induced H2 evolution as well as alkyne reduction.

An investigation on catalytic nitrite reduction reaction by bioinspired CuII complexes

Catalytic nitrite reductions by Cu^II complexes containing anionic ^Me2Tp, neutral ^Me2Tpm, or neutral ^iPrTIC ligands in the presence of L-ascorbic acid, which served as an electron donor and proton source, were investigated. The results showed that auxiliary ligands are important for copper-mediated catalytic nitrite reduction. Furthermore, the electronic effects of the ligand govern the nitrite reduction efficiency, which should be considered at two control points: one is the susceptibility of the LCu^I-nitrite species to protonation and the other is the susceptibility of LCu^II to reduction giving LCu^I. In addition, an external strong acid leads to the production of nitrous acid, which may suggest that the reactivity of nitrous acid toward the LCu^I species is a third control point.

Structural Elucidation, Aggregation, and Dynamic Behaviour of N,N,N,N-Copper(I) Schiff Base Complexes in Solid and in Solution: A Combined NMR, X-ray Spectroscopic and Crystallographic Investigation

A series of Cu(I) complexes of bidentate or tetradentate Schiff base ligands bearing either 1-H-imidazole or pyridine moieties were synthesized. The complexes were studied by a combination of NMR and X-ray spectroscopic techniques. The differences between the imidazole- and pyridine-based ligands were examined by 1H, 13C and 15N NMR spectroscopy. The magnitude of the 15Nimine coordination shifts was found to be strongly affected by the nature of the heterocycle in the complexes. These trends showed good correlation with the obtained Cu-Nimine bond lengths from single-crystal X-ray diffraction measurements. Variable-temperature NMR experiments, in combination with diffusion ordered spectroscopy (DOSY) revealed that one of the complexes underwent a temperature-dependent interconversion between a monomer, a dimer and a higher aggregate. The complexes bearing tetradentate imidazole ligands were further studied using Cu K-edge XAS and VtC XES, where DFT-assisted assignment of spectral features suggested that these complexes may form polynuclear oligomers in solid state. Additionally, the Cu(II) analogue of one of the complexes was incorporated into a metal-organic framework (MOF) as a way to obtain discrete, mononuclear complexes in the solid state.

Coordination Chemistry and Methylation of Mixed-Substituted Tetraphosphetanes (RP-PtBu)2 (R=Ph, Py)

Synthesis of mixed-substituted tetraphosphetanes (RP-PtBu)2 (R=Ph (4), Py (5); Py=2-pyridyl) is achieved from the condensation of dipyrazolylphosphanes RPpyr2 (R=Py (1), Ph (3); pyr=3,5-dimethylpyrazolyl) as P1 -building block (R-P) and tBuPH2 in an equimolar ratio. Compound 5 is of special interest since the presence of two pyridyl-substituents as well as the P4 -core allows for a rich coordination chemistry with coinage metal salts [Cu(MeCN)4 ][OTf], Ag[OTf] and in situ formed [Au(tht)][OTf] (tht=tetrahydrothiophene). Both tetraphosphetanes undergo alkylation reaction with MeOTf to give a series of tetraphosphetanium and tetraphosphetanediium triflate salts with additional methylation of the pyridyl-moiety in case of 5 resulting in interesting novel cyclic trications. Harsh reaction condition and an excess of MeOTf converts 5 into the cyclic trication [-P(Me Py)PMe2 P(Me Py)PtBu-]3+ (133+ ; Me Py=1-methylpyridiniumyl) through the elimination of isobutene. This salt undergoes a complicated rearrangement reaction involving a P-P/P-P bond metathesis to form trication [-P(MePy)3 PtBu-]3+ (173+ ) when reacted with Me2 PPMe2 .

Controlled scrambling reactions to polyphosphanes via bond metathesis reactions

Triphosphanes R'₂PP(R)PR'₂ (9a,c: R = Py; 9b R = BTz), 1,3-diphenyl-2-pyridyl-triphospholane 9d and pentaphospholanes (RP)₅ (13: R = Py; 18: R = BTz) are obtained in high yield of up to 98% from the reaction of dipyrazolylphosphanes RPpyr₂ (5: R = Py; 6: R = BTz; pyr = 1,3-dimethylpyrazolyl) and the respective secondary phosphane (R'₂PH, R' = Cy (9a,b), ^t Bu (9c); PhPH(CH₂)₂PHPh (9d)). The formation of derivatives 9a-d proceeds via a condensation reaction while the formation of 13 and 18 can only be explained by a selective scrambling reaction. We realized that the reaction outcome is strongly solvent dependent as outlined by the controlled scrambling reaction pathway towards pentaphospholane 13. In our further investigations to apply these compounds as ligands we first confined ourselves to the coordination chemistry of triphosphane 9a with respect to coinage metal salts and discussed the observation of different syn- and anti-isomeric metal complexes based on NMR and X-ray analyses as well as quantum chemical calculations. Methylation reactions of 9a with MeOTf yield triphosphan-1-ium Cy₂MePP(Py)PCy₂ ⁺ (10 ⁺) and triphosphane-1,3-diium Cy₂MePP(Py)PMeCy₂ ²⁺ (11 ²⁺) cations as triflate salts. Salt 11[OTf]₂ reacts with pentaphospholane 13 in an unprecedented chain growth reaction to give the tetraphosphane-1,4-diium triflate salt Cy₂MePP(Py)P(Py)PMeCy₂ ²⁺ (19[OTf]₂) via a P-P/P-P bond metathesis reaction. The latter salt is unstable in solution and rearranges via a rare [1,2]-migration of the Cy₂MeP-group followed by the elimination of the triphosph-2-en-1-ium cation [Cy₂MePPPMeCy₂]⁺ (20 ⁺) to yield a novel 1,4,2-diazaphospholium salt (21[OTf]).

Carbonyl complexes of copper(i) stabilized by bridging fluorinated pyrazolates and halide ions

Halide ions provide a promising tool to stabilize – through bridging interactions – copper carbonyl clusters of fluorinated pyrazolates.

Monoanionic, Bis(pyrazolyl)methylborate [(Ph3B)CH(3,5-(CH3)2Pz)2)]- as a Supporting Ligand for Copper(I)-ethylene, cis-2-Butene, and Carbonyl Complexes

The monoanionic bidentate ligand [(Ph₃B)CH(3,5-(CH₃)₂Pz)₂)]^- has been prepared from lithium bis(pyrazolyl)methanide and triphenylborane. This useful new ligand is closely related to the well-established bis(pyrazolyl)borate and bis(pyrazolyl)methane ligands but has key differences to both analogues as well. The ethylene, cis-2-butene, and carbon monoxide adducts [(Ph₃B)CH(3,5-(CH₃)₂Pz)₂]Cu(L) (where L = C₂H₄, cis-CH₃HC═CHCH₃, and CO) have been prepared from [(Ph₃B)CH(3,5-(CH₃)₂Pz)₂)]Li(THF), copper(I) triflate, and the corresponding coligand. These complexes have been characterized by NMR spectroscopy and X-ray crystallography. In all cases the bis(pyrazolyl) moiety is bound in κ²N fashion with the BPh₃ group rotated to sit over the metal center, sometimes coordinating to the metal via phenyl carbons as in [(Ph₃B)CH(3,5-(CH₃)₂Pz)₂)]Li(THF) and [(Ph₃B)CH(3,5-(CH₃)₂Pz)₂]Cu(CO) or simply hovering above the metal site as in [(Ph₃B)CH(3,5-(CH₃)₂Pz)₂)]Cu(C₂H₄) and [(Ph₃B)CH(3,5-(CH₃)₂Pz)₂)]Cu(cis-CH₃HC═CHCH₃). The ¹³C and ¹H resonances of the ethylene carbon and protons of [(Ph₃B)CH(3,5-(CH₃)₂Pz)₂)]Cu(C₂H₄) appear at δ 81.0 and 3.71 ppm in CD₂Cl₂, respectively. The characteristic CO frequency for [(Ph₃B)CH(3,5-(CH₃)₂Pz)₂]Cu(CO) has been observed at υ̅ 2092 cm^-1 by infrared spectroscopy and is lower than that of free CO suggesting moderate M → CO π-back-donation. A detailed analysis of these complexes has been presented herein.

Highly tunable fluorinated trispyrazolylborates [HB(3-CF3-5-{4-RPh}pz)3]− (R = NO2, CF3, Cl, F, H, OMe and NMe2) and their copper(i) complexes

A spectroscopic series of fluorinated trispyrazolylborate ligands was used to make copper(i) complexes with carbon monoxide and ethene. The tunable ligands induce clear trends in infrared and NMR spectra of the copper compounds.

Isolable, copper(I) dicarbonyl complexes supported by N-heterocyclic carbenes

Cationic copper(I) dicarbonyl complexes supported by N-heterocyclic carbene ligands, SIPr and IPr*, have been synthesized. [(SIPr)Cu(CO)(2)][SbF(6)] and [(IPr*)Cu(CO)(2)][SbF(6)] 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)][SbF(6)] and [(IPr*)Cu(CO)(2)][SbF(6)] readily form the corresponding [(SIPr)Cu(CO)(H(2)O)][SbF(6)] and [(IPr*)Cu(CO)(H(2)O)][SbF(6)] 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(H(2)O)][SbF(6)] 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)][SbF(6)].

Copper(I) and silver(I) complexes supported by the tridentate [{Ti(η(5)-C5Me5)(μ-NH)}3(μ3-N)] metalloligand

Copper(I) and silver(I) ionic compounds [(L)M{(μ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-N)}][O(3)SCF(3)] containing [MTi(3)N(4)] cube-type cations have been prepared by reaction of [(CF(3)SO(2)O)M{(μ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-N)}] (M = Cu (2), Ag (3)) with a variety of donor molecules L. Treatment of complexes 2 and 3 with NH(3) in toluene at room temperature gives the ammonia adducts [(H(3)N)M{(μ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-N)}][O(3)SCF(3)] (M = Cu (4), Ag (5)), whose X-ray crystal structures reveal two cube-type cations associated through hydrogen bonding interactions between the ammine ligands and one oxygen atom of each trifluoromethanesulfonate anion. Analogous treatment of 2 and 3 with 1 equiv of pyridine, 2,6-dimethylphenylisocyanide, tert-butylisocyanide, or triphenylphosphane gives the ionic compounds [(L)M{(μ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-N)}][O(3)SCF(3)] (L = py, M = Cu (6), Ag (7); L = CNAr, M = Cu (8), Ag (9); L = CNtBu, M = Cu (10), Ag (11); L = PPh(3), M = Cu (12), Ag (13)). The reactions of 2 and 3 with methylenebis(diphenylphosphane) (dppm) in a 1:1 ratio lead to the single-cube complexes [(dppm)M{(μ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-N)}][O(3)SCF(3)] (M = Cu (14), Ag (15)), whereas in a 2:1 ratio give the bisphosphane-bridged double-cube compounds [{M(μ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-N)}(2)(μ-dppm)][O(3)SCF(3)](2) (M = Cu (16), Ag (17)). Similarly, treatment of 2 or 3 with a half equivalent of ethane-1,2-diylbis(diphenylphosphane) (dppe) affords double-cube derivatives [{M(μ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-N)}(2)(μ-dppe)][O(3)SCF(3)](2) (M = Cu (18), Ag (19)). The X-ray crystal structures of 4, 5, 10, 14, 15, and 18 have been determined.

Carbon-yl[tris-(3,5-diphenyl-pyrazol-1-yl-κN)methane]copper(I) hexa-fluorido-phosphate-dichloro-methane-diethyl ether (4/3/1)

In the title compound, [Cu(C(46)H(34)N(6))(CO)]PF(6)·0.75CH(2)Cl(2)·0.25C(4)H(10)O, the Cu(I) atom is coordinated by three N atoms from the tridentate chelating tris-(3,5-diphenyl-pyrazol-1-yl)methane ligand (average Cu-N distance = 2.055 Å) and the C atom from a carbon monoxide ligand in a distorted tetra-hedral coordination geometry. The average N-Cu-N angle between adjacent pyrazole-ring-coordinated N atoms is 88.6°, while the average N-Cu-C angle between the pyrazole-bound N atom and the C atom of carbon monoxide is 126.3°. One of the 3-phenyl rings of the tris-(pyrazol-yl)methane ligand is disordered over two sites each with an occupancy factor of 0.50. The structure also exhibits disorder of the monosolvate that has been modeled with 0.75 CH(2)Cl(2) and 0.25 Et(2)O occupancy.

Applications of heteronuclear NMR spectroscopy in biological and medicinal inorganic chemistry

There is a wide range of potential applications of inorganic compounds, and metal coordination complexes in particular, in medicine but progress is hampered by a lack of methods to study their speciation. The biological activity of metal complexes is determined by the metal itself, its oxidation state, the types and number of coordinated ligands and their strength of binding, the geometry of the complex, redox potential and ligand exchange rates. For organic drugs a variety of readily observed spin I = 1/2 nuclei can be used (1H, 13C, 15N, 19F, 31P), but only a few metals fall into this category. Most are quadrupolar nuclei giving rise to broad lines with low detection sensitivity (for biological systems). However we show that, in some cases, heteronuclear NMR studies can provide new insights into the biological and medicinal chemistry of a range of elements and these data will stimulate further advances in this area.