Copper(I) coordination chemistry of (pyridylmethyl)amide ligands

Copper(I) chloro complexes were synthesized with a family of ligands, HL(R) [HL(R) = N-(2-pyridylmethyl)acetamide, R = null; 2-phenyl-N-(2-pyridylmethyl)acetamide, R = Ph; 2,2-dimethyl-N-(2-pyridylmethyl)propionamide, R = Me3; 2,2,2-triphenyl-N-(2-pyridylmethyl)acetamide, R = Ph3)]. Five complexes were synthesized from the respective ligand and cuprous chloride: [Cu(HL)Cl]n (1), [Cu2(HL)4Cl2] (2), [Cu2(HL(Ph))2(CH3CN)2Cl2] (3), [Cu2(HL(Ph)3)2Cl2] (4), and [Cu(HL(Me)3)2Cl] (5). X-ray crystal structures reveal that for all complexes the ligands coordinate to the Cu in a monodentate fashion, and inter- or intramolecular hydrogen-bonding interactions formed between the amide NH group and either amide C=O or chloro groups stabilize these complexes in the solid state and strongly influence the structures formed. Complexes 1-5 display a range of structural motifs, depending on the size of the ligand substituent groups, hydrogen bonding, and the stoichiometry of the starting materials, including a one-dimensional coordination polymer chain (1) and binuclear (2-4) or mononuclear (5) structures.     

Structural and Spectroscopic Characterization of a Mononuclear Hydroperoxo–Copper(II) Complex with Tripodal Pyridylamine Ligands

A model for the key intermediate in copper oxygenase reactions, the Cu(II )–OOH complex, was prepared with the novel tripodal pyridylamine ligand, bis(6-pivalamide-2-pyridylmethyl)(2-pyridylmethyl)amine. The HOO⁻ moiety is stabilized by hydrogen bonding to two amine H atoms (see structure on the right).     

Synthesis, characterization, and reactivity of new copper(II) complexes of 2-methylthio-N-(2-pyridylmethyl)acetamide

Copper(II) complexes were prepared with the new N(2)S(thioether) ligand 2-methylthio-N-(2-pyridylmethyl)acetamide (2-HL(N2S)). [Cu(2-L(N2S))Cl(MeOH)], which formed in the presence of excess triethylamine, is a distorted square pyramidal complex containing the ligand with the amide nitrogen deprotonated. The structurally analogous complex, [Cu(2-HL(N2S))Cl(2)], which formed in the absence of triethylamine, contains 2-HL(N2S) in the tautomeric imidic acid form. Neutral copper(II) N(2)S(thioether)S(thiolate) species were generated by addition of alkyl or aromatic thiolates to [Cu(2-L(N2S))Cl(MeOH)] and an unusual decomposition pathway was discovered.     

Synthesis and characterization of novel ferrocene-containing pyridylamine ligands and their ruthenium(II) complexes: electronic communication through hydrogen-bonded amide linkage

Tris(2-pyridylmethyl)amine (TPA) derivatives with one or two ferrocenoylamide moieties at the 6-position of one or two pyridine rings of TPA were synthesized. The compounds, N-(6-ferrocenoylamide-2-pyridylmethyl)-N,N-bis(2-pyridylmethyl)amine (Fc-TPA; L1) and N,N-bis(6-ferrocenoylamide-2-pyridylmethyl)-N-(2-pyridylmethyl)amine (Fc2-TPA; L2), were characterized by spectroscopic methods, cyclic voltammetry, and X-ray crystallography. Their Ru(II) complexes were also prepared and characterized by spectroscopic methods, cyclic voltammetry, and X-ray crystallography. [RuCl(L1)(DMSO)]PF(6) (1) that contains S-bound dimethyl sulfoxide (DMSO) as a ligand and an uncoordinated ferrocenoylamide moiety exhibited two redox waves at 0.23 and 0.77 V (vs ferrocene/ferrocenium ion as 0 V), due to Fc/Fc(+) and Ru(II)/Ru(III) redox couples, respectively. [RuCl(L2)]PF(6) (2) that contains both coordinated and uncoordinated amide moieties showed two redox waves that were observed at 0.27 V (two electrons) and 0.46 V (one electron), assignable to Ru(II)/Ru(III) redox couples overlapped with the uncoordinated Fc/Fc(+) redox couple and the coordinated Fc/Fc(+), respectively. In contrast to 2, an acetonitrile complex, [Ru(L2)(CH(3)CN)](PF(6))(2) (3), exhibited three redox couples at 0.26 and 0.37 V for two kinds of Fc/Fc(+) couples, and 0.83 V for the Ru(II)/Ru(III) couple (vs ferrocene/ferrocenium ion as 0 V). In this complex, the redox potentials of the coordinated and the uncoordinated Fc-amide moieties were discriminated in the range of 0.11 V. Chemical two-electron oxidation of 1 gave [RuIIICl(L1+)(DMSO)](3+) to generate a ferromagnetically coupled triplet state (S = 1) with J = 13.7 cm-1 (H = -JS(1)S(2)) which was estimated by its variable-temperature electron spin resonance (ESR) spectra in CH(3)CN. The electron spins at the Ru(III) center and the Fe(III) center are ferromagnetically coupled via an amide linkage. In the case of 2, its two-electron oxidation gave the same ESR spectrum, which indicates formation of a similar triplet state. Such electronic communication may occur via the amide linkage forming the intramolecular hydrogen bonding.     

Monomeric and dimeric copper(II) complexes of a novel tripodal peptide ligand: structures stabilized via hydrogen bonding or ligand sharing

The novel tripodal ligand N-(bis(2-pyridyl)methyl)-2-pyridinecarboxamide (Py3AH) affords monomeric and dimeric copper(II) complexes with coordinated carboxamido nitrogens. Although many chloro-bridged dimeric copper(II) complexes are known, [Cu(Py3A)(Cl)] (1) remains monomeric and planar with a pendant pyridine and does not form either a chloro-bridged dimer or the ligand-shared dimeric complex [Cu(Py3A)(Cl)]2 (4) in solvents such as CH3CN. When 1 is dissolved in alcohols, square pyramidal alcohol adducts [Cu(Py3A)(Cl)(CH3OH)] (2) and [Cu(Py3A)(Cl)(C2H5OH)] (3) are readily formed. In 2 and 3, the ROH molecules are bound at axial site of copper(II) and the weak axial binding of the ROH molecule is strengthened by intramolecular hydrogen bonding between ROH and the pendant pyridine nitrogen. Two ligand-shared dimeric species [Cu(Py3A)(Cl)]2 (4) and [Cu(Py3A)]2(ClO4)2 (5) have also been synthesized in which the pendant pyridine of one [Cu(Py3A)] unit completes the coordination sphere of the other [Cu(Py3A)] neighbor. These ligand-shared dimers are obtained in aqueous solutions or in complete absence of chloride in the reaction mixtures.     

Synthesis and Crystal Structure of N-Benzyl-N'-(2-pyridyl)urea and Its Mononuclear Cu(II) Complex

A new ligand of N-benzyl-N'-(2-pyridyl)urea L and its self-assembly product with CuCl2, [Cu(II)LCl2]∞ 1, have been synthesized and structurally characterized by IR, 1H NMR and single-crystal X-ray diffraction analysis. In the structure of L, the urea groups adopt Z,E conformation to form dimers through intermolecular hydrogen bonds; while in complex 1, it assumes Z,Z conformation to fit for the coordination sphere of the Cu(II) ions. The coordinated units are connected through intermolecular N-H…Cl hydrogen bonds to form an extended 2D framework. Finally, a 3D structure is obtained via π-π stacking interactions between pyridyl rings.     

Pincer-like amido complexes of platinum, palladium, and nickel

The ligands bis(8-quinolinyl)amine (BQAH, 1), (2-pyridin-2-yl-ethyl)-(8-quinolinyl)amine (2-pyridin-2-yl-ethyl-QAH, 2), o-dimethylaminophenyl(8-quinolinyl)amine (o-(NMe2)Ph-QAH, 3), and 3,5-dimethylphenyl(8-quinolinyl)amine (3,5-Me2Ph-QAH, 4) have been prepared in high yield from aryl halide and amine precursors by palladium-catalyzed coupling reactions. Deprotonation of 1 with nBuLi in toluene affords the lithium amide complex [Li][BQA] (5), whose dimeric solid-state crystal structure is presented. Lithium amide 5 was transmetalated by TlOTf to afford the thallium(I) amido complex [Tl][BQA] (6). An X-ray structural study of 6 shows it to be a 1:1 complex of the BQA ligand and Tl. Entry into the group 10 chemistry of the parent ligand 1 was effected by both protolytic and metathetical strategies. Thus, the divalent chloride complexes (BQA)PtCl (7), (BQA)PdCl (8), and (BQA)NiCl (9) were prepared and fully characterized. An X-ray structural study for each of these three complexes shows them to be well-defined, square-planar complexes in which the auxiliary BQA ligand binds in a planar, eta(3)-fashion. For comparison, the reactivity of ligands 2-4 with (COD)PtCl2 was studied. While reaction with ligand 2 afforded an ill-defined product mixture, ligands 3 and 4 reacted with (COD)PtCl2 to generate the unusual alkyl complexes (o-(NMe2)Ph-QA)Pt(1,2-eta(2)-6-sigma-cycloocta-1,4-dienyl) (10) and (3,5-Me2Ph-QA)Pt(1,2-eta(2)-6-sigma-cycloocta-1,4-dienyl) (11), both of which have been structurally characterized.     

Proton and anion control of framework complexity in copper(II) complex structures derived from 2-(hydroxymethyl)pyridine

Three copper(II) complexes derived from 2-(hydroxymethyl)pyridine (LH) have been synthesised and a comparative X-ray investigation of their respective crystal structures undertaken. In the absence of added base, LH reacts with copper(II) chloride or nitrate to yield the five-coordinate [Cu(LH)₂Cl]Cl and six-coordinate [Cu(LH)₂(NO₃)₂] species. In the chloro complex the coordination geometry is distorted trigonal bipyramidal, with the pyridyl nitrogens occupying the axial position and two hydroxyl oxygens from the bidentate ligands together with a chloro group occupying the equatorial sites. The structure of the nitrate species, published previously, has been reinvestigated at low temperature in order to specify the weak interactions in the crystal; it contains two molecules of bidentate LH bound trans in the equatorial plane while monodentate nitrato ligands occupy the axial sites. In each of these complexes the hydroxyl protons act as hydrogen bond donors, interacting with the non-coordinated chloride anion in [Cu(LH)₂Cl]Cl and the coordinated nitrato groups in [Cu(LH)₂(NO₃)₂] to form bridged, hydrogen-bonded, copper(II)-organic arrays in each case; offset face-to-face π-stacking in the latter produces a two dimensional structure. Further weak CH?Cl, CH?O interactions stabilise both arrangements. The X-ray structure of the complex [Cu(L)₂] · 4H₂O containing the deprotonated ligand is also described. The presence of the latter results in the above hydrogen bonding arrangements being ‘switched off’ and instead a new two-dimensional network involving bridging tetrameric water clusters hydrogen bound to adjacent ligand hydroxo groups to give extended sheets is generated; offset face-to-face π-stacking occurs between sheets to yield a three dimensional array.     

Synthesis and Crystal Structure of N-Benzyl-N＇-（2-pyridyl）urea and Its Mononuclear Cu（Ⅱ） Complex

A new ligand of N-benzyl-N＇-（2-pyridyl）urea L and its self-assembly product with CuCl2, [Cu（Ⅱ）LCl2]∞ 1, have been synthesized and structurally characterized by IR, 1H NMR and single-crystal X-ray diffraction analysis. In the structure of L, the urea groups adopt Z,E conformation to form dimers through intermolecular hydrogen bonds; while in complex 1, it assumes Z,Z conformation to fit for the coordination sphere of the Cu（Ⅱ） ions. The coordinated units are connected through intermolecular N-H...Cl hydrogen bonds to form an extended 2D framework. Finally, a 3D structure is obtained via π-π stacking interactions between pyridyl rings     

Synthesis of an asymmetrical tripodal tetraamine ligand and its five-coordinate copper(II) complex

A simple synthesis has been devised for the tripodal 3,3,4-tetraamine ligand N{(CH2)3NH2}2{(CH2)4NH2} (L). This ligand forms a copper(II) complex, [Cu (LH)Cl2]ClO4 (7), the structure of which has been determined by X-ray diffraction. The cation contains a five-coordinate copper atom, bonded to two chloride ions, the two propylamine groups and the tertiary nitrogen atom of the ligand; the arrangement is a distorted trigonal bipyramid, in which the two primary amine groups occupy the axial positions. The butylamine group of the ligand does not coordinate to copper but is protonated. It is involved in hydrogen bonding to the perchlorate ion. The e.p.r. spectrum of [Cu(dpt)Cl2] is very similar to that of (7), suggesting that it also has a trigonal bipyramidal structure. This revised version was published online in June 2006 with corrections to the Cover Date.     

From amine to ruthenaziridine to azaallyl: unusual transformation of di-(2-pyridylmethyl)amine on ruthenium

The complexation of di-(2-pyridylmethyl)amine to RuHCl(PPh(3))(3) affords the salt [RuH{κ(3)N-fac-1,3-di-(2-pyridylmethyl)amine}(PPh(3))(2)]Cl. Reaction with potassium tert-butoxide at room temperature yields the unusual ruthenaziridine complex RuH{κ(3)C(alk)NN(py)-1,3-di-(2-pyridylmethyl)amine}(PPh(3))(2), where the central nitrogen atom, adjacent alkyl carbon, and pyridine arm coordinate to the metal, leaving the second pyridine arm uncoordinated. Surprisingly, heating of this ruthenaziridine complex with concomitant H(2) formation affords the ruthenium azaallyl complex RuH(κ(3)N-1,3-di-(2-pyridyl)-2-azaallyl)(PPh(3))(2). This is a rare example of a 4d metal complex containing the azaallyl ligand. X-Ray crystal structures and NMR characterization of all three compounds are presented herein.     

Structural studies and anticancer activity of a novel (N6O4) macrocyclic ligand and its Cu(II) complexes

A novel (N6O4) macrocyclic ligand (L) and its Cu(II) complexes have been prepared and characterized by elemental analysis, spectral, thermal (TG/DTG), magnetic, and conductivity measurements. Quantum chemical calculations have also been carried out at B3LYP/6-31+G(d,p) to study the structure of the ligand and one of its complexes. The results show a novel macrocyclic ligand with potential amide oxygen atom, amide and amine nitrogen atoms available for coordination. Distorted square pyramidal ([Cu(L)Cl]Cl·2.5H2O (1), [Cu(L)NO3]NO(3)·3.5H2O (2), and [Cu(L)Br]Br·3H2O (4) and octahedral ([Cu(L)(OAc)2]·5H2O (3)) geometries were proposed. The EPR data of 1, 2, and 4 indicate d1x2(-y)2 ground state of Cu(II) ion with a considerable exchange interaction. The measured cytotoxicity for L and its complexes (1, 2) against three tumor cell lines showed that coordination improves the antitumor activity of the ligand; IC50 for breast cancer cells are ≈8.5, 3, and 4 μg/mL for L and complexes (1) and (2), respectively.     

Synthesis and crystal structure of an imidazolate-bridged dicopper tris(2-aminoethyl)amine complex

The [Cu(tren)(Im)Cu(tren)](ClO4)3·MeCN complex [tren=tris(2-aminoethyl)amine; Im=imidazolate anion] has been synthesized and characterized spectrally. The X-ray crystal structure analysis reveals that the imidazolate anion serves as a bridge to form a noncentrosymmetric dimeric structure in the complex. The co-ordination geometry about each copper(II) ion is a distorted trigonal bipyramid with three primary amine groups of the tren ligand forming the equatorial plane. The tertiary amine group and the imidazolate anion are in the axial positions. This revised version was published online in June 2006 with corrections to the Cover Date.     

Syntheses, structures, and properties of copper(II) complexes of bis(2-pyridylmethyl) derivatives of o-, m-, and p-phenylenediamine and aniline

Copper(II) complexes of the ligand 1,n-bis[bis(2-pyridylmethyl)amino]benzene with n = 2-4 (1,n-tpbd) and its mononuclear derivative bis(2-pyridylmethyl)aniline (phbpa) were synthesized and structurally characterized. Magnetic measurements and DFT calculations were performed on [CuCl2(phbpa)], [Cu2Cl4(1,3-tpbd)], [(Cu2Cl2(ClO4)(1,3-tpbd))Cl(Cu2Cl2(OH2)(1,3-tpbd))](ClO4)2, and [Cu2(OH2)2(S2O6)(1,3-tpbd)]S2O6, and the exchange-polarization mechanism was successfully demonstrated.     

Metal Complexes of Saccharin with the N-(2-hydroxyethyl)-ethylenediamine Ligand: Synthesis,Characterization and Spectroscopic Examination. Crystal Structures of trans- Bis(Saccharinato)Bis{N-(2-hydroxyethyl)-Ethylenediamine} copper(II) and Cadmium(II)

The novel transition metal saccharinato complexes of N-(2-hydroxyethyl)-ethylendiamine (HydEt-en) have been synthesized and characterized by elemental analyses, magnetic moments, UV-Vis and IR spectra. Coordination behaviour of HydEt-en has been studied. The Mn(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) form mononuclear complexes, while the Fe(II) and Co(II) complexes are dimeric. The crystal structures of the [Cu(sac)₂(HydEt-en)₂] and [Cd(sac)₂(HydEt-en)₂] complexes, where sac is the deprotonated form of saccharin, were determined by x-ray diffraction. The metal ions are octahedrally coordinated by these ligands. The amine ligand acts as a bidentate N-donor ligand and its ethanol group is not involved in coordination. The sac ions coordinate through the deprotonated N as a monodentate ligand. The NH and OH groups of the amine ligand are involved in intra- and intermolecular hydrogen bonding with the carbonyl and sulphonyl oxygens of the sac ions to form a three-dimensional infinite network.     

Di­chloro­bis­(glycocy­amine-O)copper(II)

The title compound, [CuCl₂(C₃H₇N₃O₂)₂], is a new copper(II) complex with glycocy­amine [(di­amino­methyl­ene­amino)­acetic acid], the first complex ever reported with this organic mol­ecule. It is composed of discrete centrosymmetric coordinated Cu^II monomers, the Cu atoms being located at inversion centers. Each metal ion is square-planar coordinated by two Cl atoms and two glycocy­amine O atoms. The coordinating glycocy­amine mol­ecule exists as a zwitterion, the H atom from the carboxyl group being transferred to the guanidinium group. A three-dimensional network of hydrogen bonds links the monomers and stabilizes the structure.     

Proton-coupled electron shuttling in a covalently linked ruthenium-copper heterodinuclear complex

A heterodinuclear complex based on a Ru(II)-TPA [TPA = tris(2-pyridylmethyl)amine] complex having a peripheral Cu(II)(bpy)(2) (bpy = 2,2'-bipyridine) group bonded through an amide linkage displayed reversible intramolecular electron transfer between the Ru and Cu complex units that can be controlled by protonation and deprotonation of the bridging amide moiety.     

Spectroscopic, thermal and voltammetric studies of crystalline complex trans-N,N'-bis(salicylidene)-1',2'-cyclohexanediamine with Cu(II)

The dimeric complex, [C20H20CuN2O2]2, has been prepared and characterized by thermal analysis, IR spectroscopy and single-crystal X-ray diffraction techniques. The Cu atom in the binuclear complex exists in a distorted square-pyramidal configuration, defined by three O atoms and two N atoms. The crystal structure is stabilized by intermolecular C-H...O hydrogen bonding interaction. The electrochemical property of the complex was investigated in CH2Cl2 by cyclic voltammetry at 100 mV s(-1) scan rate.     

Copper(II) complexes with the N,N,O-tridentate ligand 6-amino-5-formyl-1,3-dimethyluracilato-(N6)-benzoylhydrazone: synthesis, spectral and XRD studies

From reactions between different Cu(II) salts and the Schiff base 6-amino-5-formyl-1,3-dimethyluracil-benzoylhydrazone (H₂BEZDO) in alcohol, six new copper complexes with simplified formulas [Cu(HBEZDO)(H₂O)(MeOH)]NO₃ (1), [CuCl(HBEZDO)(DMF)] (2), [CuBr(HBEZDO)]·2H₂O (3), CuBr(HBEZDO) (4), Cu(ClO₄)(HBEZDO)·H₂O (5), and Cu(SO₄)_1/2(HBEZDO)·1 H₂O (6) were isolated. The structures of compounds 1, 2 and 3 have been established by means of XRD diffraction methods. In the three compounds, the Schiff base acts as a tridentate monodeprotonated ligand through the N(6), N(51) and O(52) atoms, making two five- and six-membered chelate rings. In the structure of 1 and 2, the solvent molecules are coordinated giving square-based pyramidal environments, with the basal plane completed by a MeOH (1) or Cl (2) and the apical positions occupied by the oxygen atom of a water (1) or a DMF molecule (2). The molecular unit of the complex [CuBr(HBEZDO)]·2H₂O (3) is defined by a square-plane containing the three donor atoms of the organic ligand and a bromide ligand (Cu–Br 2.384 Å), but there is a stronger tetragonally elongated pyramidal geometry around the metal, the apical position of the polyhedron being occupied by a weakly bound-to-copper bromine atom (3.086 Å) of a neighbouring molecule. This fact gives the appearance of an apparent dimer with very asymmetric bromine bridges, in which there are no exchange interactions between metal centres. Also, infrared, magnetic and EPR data of the isolated complexes are reported.     

Synthesis,characterization, and polymerization activity of [bis(4,4'-bis(neophyldimethylsilylmethyl)-2,2'-bipyridyl)copper(I)]+CuBr2- and Implications for copper(I) catalyst structures in atom transfer radical polymerization

A series of 4,4'-disilyl-substituted-2,2'-bipyridine ligands were prepared using a metathesis reaction of the dianion of 4,4'-dimethyl-2,2'-bipyridine with several trialkylsilyl chlorides: 4,4'bis(tert-butyldimethylsilylmethyl)-2,2'-bipyridine (dTBDMSbipy), 4,4'-bis(dimethylthexylsilylmethyl)-2,2'-bipyridine (dTHEXbipy), and 4,4'-bis(neophyldimethylsilylmethyl)-2-2'-bipyridine (dNEObipy). It was observed that the side chain length correlated with the ability of the ligand to form hydrocarbon soluble complexes of copper(I) bromide, with dNEObipy forming the most soluble and easily crystallized complexes. The atom transfer radical polymerization (ATRP) of styrene using dNEObipy as the ligand displayed molecular weight control equivalent to other ATRP systems in which solubilizing ligands, such as 4,4'-di-5-nonyl-2,2'-bipyridine or 4,4'-di-n-heptyl-2,2'-bipyridine, were used. The one-to-one complex of dNEObipy with CuBr was prepared and its crystal structure was determined. The resulting complex had the ionic formulation [(dNEObipy)2Cu]+[CuBr2]- and displayed similar activities in styrene ATRP as the standard 2 dNEObipy/CuBr catalyst system. These and other polymerization results in addition to NMR experiments suggest that the predominant copper(I) species formed in ATRP solutions is the 2-to-1 ligand-to-copper(I) cation, [(dNEObipy)2Cu]+, with either a dihalocuprate or halide counteranion, depending upon the conditions.