Monomeric Copper Research Articles

Spectroscopic, electrochemical and DNA binding studies of some monomeric copper(II) complexes containing N2S(thiolate)Cu core and N4S(disulfide)Cu core

We report the synthesis, characterization and spectroscopic results of the Cu(II) complexes [Cu(pabt)(OH2)](ClO4) (1), [Cu(pabt)(Imz)](ClO4) (2), [Cu(pabt)(N-MeImz)](ClO4) (3), [Cu(pabt)Cl] (4), [Cu(pma)Cl] (5), [Cu(pdta)Cl]Cl (6) and [Cu(reduced-pdta)Cl]Cl (7), (Hpabt=N-(2-mercaptophenyl)-2′-pyridylmethylenimine, Hpma=N-(2-pyridylmethyl)-2-mercaptoaniline, pdta=2,2′-di(pyridyl-2-methyleneimine)diphenyl disulfide, reduced-pdta=2,2′-di(pyridyl-2-methylamine)diphenyl disulfide, Imz=imidazole, N-MeImz=N-methylimidazole). Electronic spectra of all these compounds display strong LMCT bands in the visible region mainly associated with S→Cu(II), and consistent with TDDFT results. A four-line EPR pattern originating from the interaction of the unpaired electron with the central 63/65Cu nucleus (I=3/2, natural abundances: 63Cu, 69.17%; 65Cu, 30.83%) with the isotropic coupling constant (Aiso) values of 80±1.5G at RT for all these complexes suggests monomeric nature in solution. The redox behavior of these compounds show either nearly reversible or quasi-reversible Cu(II)/Cu(I) couple with redox potentials within the range −0.08 to −0.20V versus Ag/AgCl. Some of these compounds show strong intercalative DNA binding and its complete cleavage. 1–3 exhibit remarkable cytotoxicity against C6 glioma cell line and human cervical cancer HeLa cell line. IC50 values of 2 and 3 for the cervical cancer HeLa cell line reveal that they exhibit higher cytotoxicity than many reported Cu(II) compounds.

Spectroscopic and molecular docking studies on the interaction of human serum albumin with copper(II) complexes

Two osazone based ligands, butane-2,3-dione bis(2′-pyridylhydrazone) (BDBPH) and hexane-3,4-dione bis(2′-pyridylhydrazone) (HDBPH), were synthesized out of the 2:1M Schiff base condensation of 2-hydrazino pyridine respectively with 2,3-butanedione and 3,4-hexanedione. The X-ray crystal structures of both the ligands have been determined. The copper(II) complex of HDBPH has also been synthesized and structurally characterized. HDBPH and its copper(II) complex have thoroughly been characterized through various spectroscopic and analytical techniques. The X-ray crystal structure of the copper complex of HDBPH shows that it is a monomeric Cu(II) complex having ‘N4O2’ co-ordination chromophore. Interaction of human serum albumin (HSA) with these ligands and their monomeric copper(II) complexes have been studied by various spectroscopic means. The experimental findings show that the ligands as well as their copper complexes are good HSA binders. Molecular docking investigations have also been done to unravel the mode of binding of the species with HSA.

Polymeric and monomeric copper(II) thiophene- and furancarboxylato complexes. Bridging and terminal coordination of 3-pyridylmethanol

The synthesis and characterization of eight new coordination compounds [Cu(2-tpc)2(μ-3-pyme)2]n (1), [Cu(3-Me-2-tpc)2(μ-3-pyme)2]n (2), [Cu(5-Me-2-tpc)2(μ-3-pyme)2]n (3), [Cu(5-Cl-2-tpc)2(3-pyme)2] (4), [Cu(2-fuc)2(μ-3-pyme)2]n (5), [Cu(3-fuc)2(μ-3-pyme)2]n (6), [Cu(2,5-Me2-3-fuc)2(μ-3-pyme)2]n (7), and [Cu(5-NO2-2-fuc)2(μ-3-pyme)2]n (8) (where 2-tpc is 2-thiophenecarboxylato, 3-Me-2-tpc is 3-methyl-2-thiophenecarboxylato, 5-Me-2-tpc is 5-methyl-2-thiophenecarboxylato, 5-Cl-2-tpc is 5-chloro-2-thiophenecarboxylato, 2-fuc is 2-furancarboxylato, 3-fuc is 3-furancarboxylato, 2,5-Me2-3-fuc is 2,5-dimethyl-3-furancarboxylato, 5-NO2-2-fuc is 5-nitro-2-furancarboxylato and 3-pyme is 3-pyridylmethanol) is reported and their X-ray structures were determined. X-ray analysis revealed that samples 1–3 and 5–8 are coordination polymers, whereas the complex 4 is monomeric. The polymeric extension is achieved through bridging N,O-3-pyridylmethanol molecules, resulting in the observation of 2-D (1–3, 5–7) or 1-D polymeric chains (8). In addition, the coordination polymers are also stabilized by strong intramolecular hydrogen bonds. On the other hand, the monomeric compound 4 with monodentate N-coordinated 3-pyridylmethanol ligands forms 1-D supramolecular chain due to strong intermolecular hydrogen bonds. Electronic, IR, EPR spectra and magnetic susceptibility measurements over the temperature range 1.8–300K are discussed in terms of known crystal and molecular structure. Based on the IR spectra it can be concluded that the type of coordination of 3-pyridylmethanol as well as hydrogen bonds strongly influence the position and the shape of the stretch vibrations bands assigned to hydroxyl group.

Salicylaldimine Copper(II) complex catalyst: Pioneer for ring opening Polymerization of Lactide

Salicylaldimine copper complex has been synthesized and its reactivity for the ring-opening polymerization (ROP) of lactide has been studied. This monomeric copper complex was prepared by the reaction of copper(II) solution with one molar equivalent of salicylaldimine Schiff-base ligand in methanol under nitrogen atmosphere. This copper complex has been characterized by different spectroscopic methods, which showed square planar geometry. The molecular structure of the salicylaldimine Schiff-base has been determined by X-ray diffraction studies. The complex was tested as the initiator for the ring-opening polymerization of lactide, with variation in diamine group in ligand. The rate of polymerization is dependent on the diamine group in the following order: ethylene > propylene > phenyl. The salicylaldimine copper complex allows controlled ring-opening polymerization as indicated by the linear relationship between the percentage conversion and the number-average molecular weight. On the basis of literature reports, a mechanism for ROP of lactide has been proposed.

Coordinative versatility of 3,5-bis(4-pyridyl)-1,2,4-triazole in the construction of monomeric copper(II) and polymeric copper(I) complexes

Three complexes, namely [Cu(dpt)2(H2O)4]·2H2O (1), [Cu3I2(dpt)] n (2) and [Cu6Br3(dpt)3] n (3), have been obtained from the reactions of different copper salts with 1H-3,5-bis(4-pyridyl)-1,2,4-triazole (Hdpt). Complex 1 is mononuclear such that the CuII atom exhibits an octahedral coordination geometry involving monodentate dpt ligands, being synthesized from CuII nitrate and Hdpt at ambient temperature, while the cuprous halide cluster-based coordination polymers 2 and 3 were prepared by solvothermal reactions of CuI or CuBr with Hdpt. Complex 2 consists of [Cu3I2] n chains, which are further connected by the μ 4-dpt bridges to form a 4,6-connected three-dimensional coordination polymer. Complex 3 is a 3,3,9-connected net based on [Cu6Br3] building blocks, linked by μ 3-dpt bridges. The photoluminescence properties of complex 2 in the solid state at ambient temperature have been investigated. Syntheses and structures of three complexes [Cu(dpt)2(H2O)4]·2H2O (1), [Cu3I2(dpt)] n (2) and [Cu6Br3(dpt)3] n (3) (Hdpt = 1H-3,5-bis(4-pyridyl)-1,2,4-triazole) are described, in which the effect of the rich connectivity of the cuprous halide clusters, supported by the changeable coordination modes of dpt ligand, is revealed.

Synthesis and Immortal ROP of L-Lactide Using Copper Complex

In the present work, the -ONNO- tetradentate Schiff base ligand N, N′-bis (2-hydroxy-3-methoxybenzaldehyde) propylenediamine, [HMBPD] was synthesized. Further, complexation of this ligand with copper [HMBPD-Cu] was carried out and their reactivity for the ring-opening polymerization (ROP) of lactide (LA) has been studied. This monomeric copper complex is prepared by the reactions of copper solution with one molar equivalent of HMBPD Schiff-base ligand in ethanol under nitrogen atmosphere. This copper complex has been characterized by different spectroscopic methods, which showed square planner geometry. The copper complex is highly active towards ROP of LA. The rate of polymerization is heavily dependent on the initiator used. The copper complex allows controlled ring-opening polymerization as shown by the linear relationship between the percentage conversion and the number-average molecular weight. On the basis of literature reports, a mechanism for ROP of lactide has been proposed.

Versatile coordination chemistry of a bis(methyliminophosphoranyl)pyridine ligand on copper centres.

The coordination of a bis(methyliminophosphoranyl)pyridine ligand (L) to copper centres was studied. The use of copper(I) bromide precursors gave access to [LCuBr] (2) in which only one iminophosphorane arm is coordinated to the metal, as observed by X-ray crystallography and MAS (31)P NMR. Its fluxional behaviour in solution was demonstrated by VT-(31)P NMR, and investigated by DFT calculations. On the other hand, coordination of L to [Cu(CH3CN)4]PF6 gave a dimer [L2Cu2](PF6)2 (3) in which the two copper centres do not have the same coordination sphere as shown by X-ray crystallography. Addition of a strong ligand such as PEt3 allows the preparation of a cationic monomeric copper complex (4) in which L has a behaviour similar to that observed for 2. Synthesis of copper(II) complexes was also achieved by chemical oxidation of 2, which shows an irreversible oxidation at -0.36 vs. Fc(+)/Fc, or directly via the coordination of L to CuBr2. In [LCuBr2] (5), L adopts a pincer coordination. Finally, the catalytic behaviour of copper(I) complexes 2 and 3 was investigated in cyclopropanation reactions and [3 + 2] cycloadditions.

ChemInform Abstract: Copper(I) Trifluoromethylthiolate Complex Bearing Triphenylphosphine Ligand for Nucleophilic Trifluoromethylthiolation of Allylic Bromides.

Abstract Copper(I) trifluoromethylthiolate complex (PPh3)2Cu(SCF3) (1) has been synthesized from a convenient reaction of CuF2 with CF3SiMe3 and S8 in the presence of triphenylphosphine. The crystal structure of complex 1 has been determined by X-ray crystallography. In the solid state, complex 1 exists as a monomeric copper(I) species with a three-coordinated trigonal planar geometry. Complex 1 reacted with a wide range of allylic bromides to afford corresponding allylic trifluoromethyl thioethers in moderate to good yields. Several functional groups, including alkyl, alkoxy, nitro, halides and geranyl groups, are tolerated.

P-Quinoneimine as an intermediate in the oxidative coupling of 2-amino-5-methylphenol to 4a,7-dimethyldihydro-2-aminophenoxazinone catalyzed by a monomeric copper(II) complex

Copper(II) complex of a tetradentate N-picolatedbisbenzimidazolyl ligand is synthesized and characterized. XRD study reveals that copper(II) is in a distorted square plane comprising of two imine nitrogen, one oxygen atom from nitrate and another from a water molecule. This complex carries out the oxidative coupling of aminomethylphenol to phenoxazinone through an intermediate p-quinoneimine. The reaction is pseudo first order with respect to the catalyst and is self-inhibiting with increasing substrate concentration. Anion like acetate is found to increase the rate of reaction by nine times. EPR monitoring indicates the formation of a Cu(I) species which is the likely cause of inhibition of the catalytic reaction.

Candida albicans SOD5 represents the prototype of an unprecedented class of Cu-only superoxide dismutases required for pathogen defense.

The human fungal pathogens Candida albicans and Histoplasma capsulatum have been reported to protect against the oxidative burst of host innate immune cells using a family of extracellular proteins with similarity to Cu/Zn superoxide dismutase 1 (SOD1). We report here that these molecules are widespread throughout fungi and deviate from canonical SOD1 at the primary, tertiary, and quaternary levels. The structure of C. albicans SOD5 reveals that although the β-barrel of Cu/Zn SODs is largely preserved, SOD5 is a monomeric copper protein that lacks a zinc-binding site and is missing the electrostatic loop element proposed to promote catalysis through superoxide guidance. Without an electrostatic loop, the copper site of SOD5 is not recessed and is readily accessible to bulk solvent. Despite these structural deviations, SOD5 has the capacity to disproportionate superoxide with kinetics that approach diffusion limits, similar to those of canonical SOD1. In cultures of C. albicans, SOD5 is secreted in a disulfide-oxidized form and apo-pools of secreted SOD5 can readily capture extracellular copper for rapid induction of enzyme activity. We suggest that the unusual attributes of SOD5-like fungal proteins, including the absence of zinc and an open active site that readily captures extracellular copper, make these SODs well suited to meet challenges in zinc and copper availability at the host-pathogen interface.

Mechanistic analysis of water oxidation catalyzed by mononuclear copper in aqueous bicarbonate solutions

We characterize a mechanism for a monomeric copper catalyst reported to oxidize water in bicarbonate solution when subject to sufficiently high external potentials at near neutral pH values.

Structures and Magnetic Properties of Monomeric Copper(II) Bromide Complexes with a Pyridine-Containing Tridentate Schiff Base

Two novel copper(II) bromide complexes with pyridine containing Schiff base ligands, Cu(pmed)Br2 and Cu(dpmed)Br2 where pmed = N'-((pyridin-2-yl)methylene)ethane-1,2-diamine (pmed) and dpmed = N,Ndiethyl-N'-((pyridin-2-yl)methylene)ethane-1,2-diamine (dpmed) were synthesized and characterized using Xray single crystal structure analysis, optical and magnetic susceptibility measurements. Crystal structural analysis of Cu(pmed)Br2 showed that the copper(II) ion has a distorted square-pyramidal geometry with the trigonality index of τ = 0.35 and two intermolecular hydrogen bonds, which result in the formation of two dimensional networks in the ab plane. On the other hand, Cu(dpmed)Br2 displayed a near square-pyramidal geometry with the value of τ = 0.06. In both compounds, the NNN Schiff base and one Br atom occupy the basal plane, whereas the fifth apical position is occupied by the other Br atom at a greater Cu-Br apical distance. The reported complexes show g ⎟⎜ > g⊥ > 2.0023 with a dx2-y2 ground state and a penta-coordinated square pyramidal geometry. Variable temperature magnetic susceptibility measurements showed that the developed copper(II) complexes follow the Curie-Weiss law, that is there are no magnetic interactions between the copper(II) ions since the Cu--Cu distance is too far for magnetic contact.

Copper(I) trifluoromethylthiolate complex bearing triphenylphosphine ligand for nucleophilic trifluoromethylthiolation of allylic bromides

Copper(I) trifluoromethylthiolate complex (PPh3)2Cu(SCF3) (1) has been synthesized from a convenient reaction of CuF2 with CF3SiMe3 and S8 in the presence of triphenylphosphine. The crystal structure of complex 1 has been determined by X-ray crystallography. In the solid state, complex 1 exists as a monomeric copper(I) species with a three-coordinated trigonal planar geometry. Complex 1 reacted with a wide range of allylic bromides to afford corresponding allylic trifluoromethyl thioethers in moderate to good yields. Several functional groups, including alkyl, alkoxy, nitro, halides and geranyl groups, are tolerated.

Design of a bio-inspired copper (II) Schiff base complex grafted in mesoporous silica for catalytic oxidation

Controlled grafting of a copper (II) complex with a Schiff base ligand (LA=N-(salicylaldimine)-(N′-propyltrimethoxysilane)-diethylenetriamine) on a mesoporous MCM-41 type of silica (LUS) was accomplished using a pattering technique to allow a homogeneous distribution of isolated copper sites on the solid using trimethylsilyl groups as dispersing function. XRD patterns suggest that the final material LUS-CuLA exhibits a well-ordered 2D hexagonal structure. Elemental analysis, solid UV–Vis and EPR spectroscopies indicate that the copper (II) coordination sphere is most likely of a 3N1O type with an additional acetate ion as a ligand. Almost all the Cu(II) species grafted on the solid were EPR active (2.6wt% active species for 2.8wt% total copper measured from ICP-MS analysis) confirming the presence of monomeric copper species. Preliminary catalytic tests for phenol hydroxylation show that the supported system presents similar activity as the molecular analogue.

Air‐stable copper derivatives as efficient catalysts for controlled lactide polymerization: Facile synthesis and characterization of well‐defined benzotriazole phenoxide copper complexes

ABSTRACTAir‐stable copper catalysts supported by bis‐BTP ligands (BTP = N,O‐bidentate benzotriazole phenoxide) were synthesized and structurally characterized. The reactions of Cu(OAc)2·H2O with 2.0 molar equivalents of sterically bulky 2‐(2H‐benzotriazol‐2‐yl)‐4,6‐bis(1‐methyl‐1‐phenylethyl)phenol (CMe2PhBTP‐H) and 2‐(2H‐benzotriazol‐2‐yl)‐4,6‐di‐tert‐butylphenol (t‐BuBTP‐H) in refluxing ethanol solution afforded monomeric copper complexes [(CMe2PhBTP)2Cu] (1) and [(t‐BuBTP)2Cu] (2), respectively. The four‐coordinated copper analogue [(TMClBTP)2Cu] (3) resulted from treatment of 2‐tert‐butyl‐6‐(5‐chloro‐2H‐benzotriazol‐2‐yl)‐4‐methylphenol (TMClBTP‐H) as the ligand under the same synthetic method with ligand to metal precursor ratio of 2:1, but treatment of complex 3 in acetone gave five‐coordinated monomeric complex [(TMClBTP)2Cu(Me2CO)] (4). X‐ray diffraction of single crystals indicates that Cu complex 4 assumes a distorted square pyramidal geometry, penta‐coordinated by two BTP ligands, and one Me2CO molecule. Catalysis for lactide (LA) polymerization of BTP‐containing Cu complexes in the presence of various alcohol initiators was investigated. Complex 3 initiated by 9‐anthracenemethanol catalyzes the ring‐opening polymerization effectively not only in a “living” fashion but also in an “immortal” manner, yielding polymers with the predictable molecular weights and narrow molecular weight distributions. Initiations from multifunctional alcohols were able to produce PLLAs with two‐arm linear and three‐arm star‐shaped molecular architectures. The controlled character of Cu complex 3 also enabled us to synthesize the PEG‐b‐PLLA copolymer. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3840–3849

Synthesis and Characterization of Heteronuclear Copper(II)-Lanthanide(III) Complexes of N,N′-1,3-Propylenebis(Salicylaldiminato) Where Lanthanide(III) = Gd or Eu

Three complexes, namely, [Cu(salbn)] (1), [Cu(salbn)Gd(NO3)3·H2O] (2), and [Cu(salbn)Eu(NO3)3·H2O] (3) where salbn = N,N′-1,3-propylenebis (salicylaldiminato) have been synthesized and characterized by elemental analyses, ICP-AES, IR, UV, NMR, MS, EDX, powder XRD, and EPR spectroscopies. The EDX results suggest the presence of two different metal ions in heteronuclear complexes (2) and (3). The ligand(salbn), complex (1), and complex (3) crystallize in triclinic system while complex (2) crystallizes in monoclinic system. The EPR studies suggest that [Cu(salbn)] complex is tetragonally coordinated monomeric copper(II) complex with unpaired electron in the dx2-y2 orbital and spectral features that are the characteristics of axial symmetry while complex (2) in DMF solution at liquid nitrogen temperature exhibits an anisotropic broad signal around g ~ 2.03 which may suggest a weak magnetic spin-exchange interaction between Gd(III) and Cu(II) ions. The fluorescence intensity of Eu(III) decreased markedly in the complex (3).

Synthesis, structure, interaction with DNA and cytotoxicity of a luminescent copper(II) complex with a hydrazone ligand

A luminescent copper(II) complex [CuII(L)H2O]2SO4,1a was synthesized with the acyclic tridentate 2-hydroxy naphthaldehyde-2-pyridylhydrazone ligand, HL, 1. The molecular structure of 1a clearly shows that it is a monomeric copper(II) complex with CuN2OOW coordination with slightly distorted square planar geometry. The asymmetric unit of 1a contains two independent complex molecules and a sulfate anion. DNA binding interactions of 1a have been investigated by absorption, emission, viscosity and thermal denaturation studies. The cytotoxic activity of 1a was measured in vitro against the HeLa cells. The LD50 value was calculated as 4.97μM. There was no nuclear fragmentation observed after treatment with 1a, which revealed that the copper(II) complex 1a was not capable of inducing apoptosis. The cell cycle analysis of 1a indicated a dose dependent decrease of G0/G1 and S-phase cell population and dose-dependent increase of G2/M population compared with untreated control cell.

Mixed-ligand copper(ii)–sulfonamide complexes: effect of the sulfonamide derivative on DNA binding, DNA cleavage, genotoxicity and anticancer activity

Four ternary complexes, [Cu(L1)2(bipy)] (1) [HL1 = N-(6-chlorobenzo[d]thiazol-2-yl)-4-methylbenzenesulfonamide], [Cu(L2)2(bipy)] (2) [HL2 = N-(benzo[d]thiazol-2-yl)-4-methylbenzenesulfonamide], [Cu(L3)2(bipy)]·1/2H2O (3) [HL3 = N-(5,6-dimethylbenzo[d]thiazol-2-yl)-4-methylbenzenesulfonamide] and [Cu(L4)2(bipy)] (4) [HL4 = N-(5,6-dimethylbenzo[d]thiazol-2-yl)benzenesulfonamide], were prepared and then characterized by X-ray crystallography, spectroscopy and magnetic measurements. Whereas the molecular structure of 1 and 2 consists of a discrete monomeric copper(II) species with a distorted square planar geometry, that of 3 and 4 consists of two independent molecules. In 3, both molecules present a different coordination geometry (distorted square planar and distorted square pyramidal) while in 4 they have an identical coordination environment (distorted square planar). The propensity for binding of 1-4 to calf thymus DNA was studied by thermal denaturation, viscosimetry, and fluorescence measurements. Results indicated that the N-sulfonamide derivative plays an important role in governing the type of interaction with DNA. The ability of the complexes to cleave DNA was studied in vitro with ascorbate activation and was tested by monitoring the expression of the yEGFP gene containing the RAD54 reporter. Moreover, their antiproliferative activity was verified in two cellular models: yeast and human tumor cells in culture. Their DNA cleavage efficiency at the cellular level was found to be: 1 < 3 ~ 4 < 2. The higher propensity of 2 for inflicting DNA damage was related with its higher binding affinity to DNA. The biological studies carried out with human tumor cells, colon adenocarcinoma Caco-2 cells and leukemia Jurkat T lymphocytes confirmed that the compounds produce cell death mainly by apoptosis, the complex 2 being the most effective.

Synthesis and structure of amide oxygen-bridged polymeric and monomeric copper(II) complexes with aroylhydrazones

The synthesis and structure of two Cu(II) complexes, {[Cu2(L1)2] · DMF} n (1) and [CuL2(phen)] (2), are described. The dinegative hydrazones are obtained by deprotonation of both phenolic and amide moieties of N′-(5-bromo-2-hydroxybenzylidene)-3,5-dimethoxybenzohydrazide (H2L1) and N′-(2-hydroxybenzylidene)pyrazine-2-carbohydrazide (H2L2). In each complex the planar ligand binds the metal ion via phenolate-O, imine-N, and amide-O. Complex 1 is a polymer in which phenoxo-bridged binuclear Cu(II) units are further joined by equatorial–apical amide-O bridges. The Cu···Cu separations are 3.0306 and 3.8217 Å for the phenolate-O bridged pair and the amide-O bridged pair, respectively. Complex 2 is a monomer where chelating phen displays axial–equatorial bonding, with square-pyramidal Cu(II).

Copper Complexes with a Hybrid Scorpionate Ligand Containing Pyridazine‐3‐thione

AbstractA new scorpionate ligand, Na[HB(mim)2(PntBu)] (Na[PnBm]), with one pyridazinyl‐3‐thione and two methimazolyl (mim) substituents was prepared by mixing 6‐tert‐butylpyridazine‐3‐thione (HPntBu) and sodium dihydridobis(methimazolyl)borate (Na[Bm]) in boiling xylene. Addition of CuCl to a solution of Na[PnBm] in methanol in the presence of PR3 gave the monomeric copper(I) complexes [Cu{PnBm}(PR3)] (R = cyclohexyl 1, phenyl 2) in good yields. They were characterized by NMR spectroscopy and in the case of 2 also by single‐crystal X‐ray diffraction analysis. The latter revealed a compound in which the ligand is coordinated in a κ3‐S,S,H fashion, exhibiting a 3‐center‐2‐electron B–H···Cu interaction. Reaction of the ligand Na[PnBm] with CuCl in the absence of phosphane yielded a copper(I) complex, which was determined to be [Cu{PnBm}] (3). Variable‐temperature 1H NMR spectroscopy points to the occurrence of two dimeric isomers in solution, which interconvert in a fluxional behavior at room temperature. DFT calculations show that two isomers with a κ3‐Smim,Smim,H or a κ3‐Hmim,SPn,H coordination mode have very similar energies with a low energy barrier (25.4 kJ/mol) for their interconversion.