Preparation of a copper ion complex of sterically congested diphenyldiazomethanes having a pyridine ligand and characterization of their photoproducts

To show that persistent high-spin polycarbenes can be realized by utilizing hetero spin systems, two diphenyldiazomethanes having pyridyl groups, i.e., bis{4-(4-pyridyl)-2,6-dimethylphenyl}diazomethane (4,4'-DPy-1-N(2)) and {2,4-di(4-pyridyl)-6-bromophenyl}(2,6-dimethyl-4-tert-butylphenyl)diazomethane (2,4-DPy-1-N(2)), were prepared. Triplet carbenes, 4,4'-DPy-1 and 2,4-DPy-1, generated by photolysis of the corresponding diazomethanes were characterized by spectroscopic means (ESR and UV/vis in matrix at low temperatures and laser flash photolysis in solution at room temperature). The results showed that they were fairly persistent. Magnetic properties of the photoproducts from a 1:1 complex between DPy-1-N(2) and Cu(hfac)(2) (hfac = hexafluoroacetylacetonate) were characterized by ESR and a superconducting quantum interference device (SQUID) magneto/susceptometer. The field dependences of magnetization for the complexes, expressed by using M versus H/T plots, were analyzed in terms of the Brillouin function to be S = 6.80 (F = 0.60) for the 1:1 complex of 4,4'-DPy-1 and Cu(hfac)(2) and S = 3.71 (F = 0.73) for the 1:1 complex of 2,4-DPy-1 and Cu(hfac)(2) at 2.0 K. Thus, it has been demonstrated that a high-spin species is actually generated in the photoproducts and that the complexed carbenes showed significant stability.     

Preparation of copper ion complexes of sterically congested diaryldiazomethanes having a pyridine ligand and characterization of their photoproducts

To realize fairly stable high-spin polycarbenes by utilizing heterospin systems comprising 2p spins of organic radicals and 3d spins of magnetic metal ions, we prepared dianthryldiazomethanes having two pyridyl groups at the 2,2'- or 2,7-positions, that is, bis[10-(4-tert-butyl-2,6-dimethylphenyl)-2-(4-pyridyl)-9-anthryl]diazomethane (2,2'-DPy-1-N(2)) and [10-(4-tert-butyl-2,6-dimethylphenyl)-9-anthryl][(10-(4-tert-butyl-2,6-dimethylphenyl)-2,7-di(4-pyridyl)-9-anthryl]diazomethane (2,7-DPy-1-N(2)). The triplet carbene DPy-(3)1 generated by photolysis of DPy-1-N(2) was characterized by ESR and UV-vis spectroscopy in a matrix at low temperature as well as by time-resolved UV-vis in solution at room temperature. The results showed that the triplet carbene DPy-(3)1 was destabilized to some extent as opposed to the parent triplet carbene before pyridination, but it was still fairly persistent, having a half-life of more than 30 min in solution at room temperature. Photoproducts from the complex between DPy-1-N(2) and Cu(hfac)(2) were characterized in a similar manner, and the results suggested that the generated carbene centers interacted magnetically with the Cu(II) ion to form a high-spin species with significant thermal stability. The fact that no significant signals due to the isolated triplet carbene DPy-(3)1 were observed suggested that the pyridine moiety binds with Cu(hfac)(2) in a nearly quantitative manner under these cryogenic conditions. Magnetic measurements of the photoproduct using a superconducting quantum interference device (SQUID) magneto/susceptometer were performed to determine the spin state of the complex. The temperature dependence of the molar paramagnetic susceptibility indicated the presence of ferromagnetic interaction. The field dependences of magnetization for the complexes, expressed using M versus H/T plots, were analyzed in terms of the two-component Brillouin function to be S = 3.18 (F = 0.66) and S = 0.02 (F = 0.23) for the 1:1 complex of 2,7-DPy-1 and Cu(hfac)(2) and S = 2.70 (F = 0.33) and S = 0.49 (F = 0.11) for the 1:1 complex of 2,2'-DPy-1 and Cu(hfac)(2).     

Bi- and trinuclear copper(II) complexes of a sterically constrained phenol-based tetradentate ligand: syntheses, structures, and magnetic studies

Copper(II) complexes (1-3) of a sterically constrained phenol-based tetradentate N(2)O(2) ligand 1,4-bis(2-hydroxy-3,5-dimethylbenzyl)piperazine (H(2)L) have been reported. The associated anions of the copper(II) ion precursors have profound influence on the stoichiometry of the products. Thus, with perchlorate ion, the product is a binuclear compound [Cu(2)L(2)] (1), while with coordinating anions viz. Cl(-) and N(3)(-), the products [Cu(3)L(2)Cl(2)(H(2)O)].1/2H(2)L (2) and [Cu(3)L(2)(N(3))(2)(CH(3)OH)].4H(2)O (3) have triangulo trinuclear composition. The syntheses, X-ray structures, and spectroscopic and magnetic properties of these complexes are described. Compound 1 has a noncentrosymmetric structure with a rectangular Cu(2)(OPh)(2) core. It appears to be a rare example of a phenolato-bridged Cu(II) dimer exhibiting ferromagnetic interactions (J = 0.93 cm(-)(1)), a behavior in agreement with the theoretical predictions but seldom observed experimentally. In compounds 2 and 3, the copper centers are triangularly disposed, and the molecules have a shape much like that of a butterfly. The terminal copper centers Cu(1) and Cu(2) in 2 and 3 have distorted square pyramidal geometry, connected to each other by a bridging chloro- (in 2) or azido ligand (in 3) in "end to end" fashion. The central copper center (Cu(3) in 2 and Cu in 3) in both the compounds has distorted square planar geometry. The separations between the metal centers, viz. Cu(1)...Cu(2), Cu(2)...Cu(3), and Cu(3)...Cu(1), are 4.826, 3.214, and 3.244 A, respectively, in 2. The corresponding distances in 3 are 5.590, 3.178, and 3.485 A, respectively. The overall magnetic behaviors in 2 and 3 are consistent with antiferromagnetic interactions between the spin centers. In 3, the exchange couplings between the terminal and central copper centers J(Cu(1))(-)(Cu) and J(Cu(2))(-)(Cu) appear to be equal (-234 cm(-)(1)), resulting in an S = (1)/(2) ground state at temperatures near or below 77 K.     

Synthesis, structural characterization, and magnetic studies of polynuclear iron complexes with a new disubstituted pyridine ligand

A series of novel polyiron species have been prepared from the reaction of iron chloride with the 2,5-disubstituted pyridines H2L(n) (H2L1) = N,N'-bis(n-butylcarbamoyl)pyridine-2,6-dicarboxamide; H2L2 = N,N'-bis(n-ethylcarbamoyl)pyridine-2,6-dicarboxamide). By small modifications of the experimental conditions under which the reactions are carried out, it has been possible to prepare the quadruply stranded diiron(II) complex [Fe2(mu-H2L1)4(mu-Cl)2][FeCl4]2 (1), the metallamacrocycle [Fe2(mu-H2L1)2(THF)4Cl2][FeCl4]2 (2), the hexairon(III) compound [Fe6(L1)2(mu-OMe)6(mu4-O)2Cl4] (3), and the mixed-valence trinuclear iron complexes [Fe3(L(n))3(mu3-O)] (n = 1, 4; n = 2, 5). The X-ray crystal structures of 3 and 5 and magnetic studies for all the compounds are herein presented. Interestingly, the structural analysis of 5 at room temperature indicates that one of the iron centers is Fe(III) while the other two have an average valence state between Fe(II) and Fe(III). The five complexes herein presented demonstrate the great versatility that the new ligand has as a building block for the formation of supramolecular coordination assemblies.     

Synthesis and structural characterization of tris(2-mercapto-1-adamantylimidazolyl)hydroborato complexes: a sterically demanding tripodal [S3] donor ligand

The tris(2-mercapto-1-adamantylimidazolyl)hydroborato ligand, [Tm(Ad)], has been synthesized via the reaction of 1-adamantyl-2-mercaptoimidazole with MBH(4) (M = Li, K). [Tm(Ad)]M has been used to synthesize a variety of compounds of the main-group and transition elements, including [Tm(Ad)]ZnI, {[Tm(Ad)]GaI}[GaI(4)], {[Tm(Ad)]GaCl}[GaCl(4)], {[Tm(Ad)]GaGa[Tm(Ad)]}[GaCl(4)](2), {[Tm(Ad)](2)In}[InI(4)], [Tm(Ad)]In(κ(2)-mim(Ad))Cl, [Tm(Ad)]Ga→B(C(6)F(5))(3), [Tm(Ad)]In→B(C(6)F(5))(3), and [Tm(Ad)]Re(CO)(3). Structural characterization of [Tm(Ad)]Re(CO)(3) demonstrates that the [Tm(Ad)] ligand is more encapsulating than other [Tm(R)] ligands, including [Tm(Bu(t))], while IR spectroscopic studies indicate that the [Tm(Ad)] and [Tm(Bu(t))] ligands have very similar electron-donating properties.     

Preparation of sterically congested di(4-pyridyl)diazomethanes and characterization of triplet carbenes from them

Di(4-pyridyl)diazomethanes having two and four ortho chlorine groups were prepared, and the triplet carbenes generated from them were characterized by ESR and UV/vis at low temperature and time-resolved UV/vis at room temperature. An appreciable increase in the stability of triplet carbenes is achieved by introducing ortho chlorine groups. [structure: see text]     

Neutral and cationic aluminium complexes of a sterically demanding N-imidoylamidine ligand

The N-imidoylamidine ligand i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2 2 was prepared. Direct reactions with AlI3 or AlMe3 afforded [(i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2)AlI2][AlI4] 3 and [i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2)AlMe2][AlMe4].AlMe3, 4 respectively. Thermolysis of 4 gave (i-Pr2C6H3NC(=CH2)(NC6H3i-Pr2)(C(Me)NC6H3i-Pr2)AlMe2 6. Subsequent reaction with B(C6F5)3 gave the zwitterionic species [(i-Pr2C6H3)N(C(=CH2)NC6H3i-Pr2)(C(Me)NC6H3i-Pr2)AlMe(mu-MeB(C6F5)3)] 7. In a related reactions of 2, [Ph3C][B(C6F5)4] and AlMe3, AlH3.NEtMe2 or AlD3.NMe3, the complexes [(i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2)AlR2][B(C6F5)4] (R = Me 5, H 8, D 9) and [(i-Pr2C6H3)N(C(=CH2)NC6H3i-Pr2)(C(Me)NC6H3i-Pr2)AlH][B(C6F5)4] 10 are formed. Single-crystal X-ray data for 2, 3, 5 and 10 are reported.     

Preparation and characterization of mononuclear nickel(II) and copper(II) complexes of a hexaazamacrobicyclic ligand

Summary The structure of the hexaazamacrobicycle, sarcophagine, (diAMMEsar)·2H₂O, formed by extracting Co ion from the [Co(diAMMEsar H₂)]Cl₅·-H₂O cage with 8-hydroxyquinoline, has been determined by elemental analysis, and i.r., u.v.-vis., ¹H-n.m.r. and mass spectroscopies. Two octahedral complexes, [M(diAMM-EsarH₂)]Cl₄·2H₂O (M = Ni^II or Cu^II), have been prepared and characterized. The e.s.r. spectrum of the Cu^II complex in the solid state indicates spin-exchange interaction between the Cu^II ions. However, in CD₃OD-D₂O (10%) at 77K, the spectrum is characteristic of a compound having axial symmetry (d _x ²−y ²).     

Structural characterization and catalytic activities of copper complexes with pyridine-amine-phosphine-oxide ligand

A new tetradentate containing pyridine, amine and phosphine oxide donor systems (1) was synthesized by the condensation of o-diphenylphosphinoaniline with 2-pyridinecarbaldehyde. Reaction of 1 with equal molar amount of CuCl₂ and Cu(ClO₄)₂ provided the formation of [CuCl₂(1)] (4) and [[Cu(1)(H₂O)](ClO₄)₂] (5), respectively. The ligand 1 behaves as a tridentate in 4, while as a tetradentate in 5. Both complexes were characterized by EPR, UV-Vis spectroscopy and X-ray diffraction. Both copper(II) complexes are in a square-pyramidal geometry. Single crystal structure of the copper complex reveals that the copper center is surrounded by three nitrogen donors and two chloride for 4; three nitrogen donors, water and oxygen donor from the moiety of phosphine oxide for 5. Complexation of 1 with CuCl in dichloromethane resulted in the formation of the corresponding copper(I) species, which catalyzed the oxidation of benzylic alcohols under aerobic conditions.     

Synthesis,and characterization of some Cu(I) complexes having propionitrile and pyridine moieties: An investigation on their antibacterial properties

The aim of producing new biologically active compounds lead to the synthesis of some Cu(I) complexes of general formula [Cu(C₂H₅CN)₄][A] and [Cu(C₅H₅N)₄][A] (1–4) {where A: counter anion = B(C₆F₅)₄⁻ and B{C₆H₃(m-CF₃)₂}₄⁻} from the reaction of CuCl and silver salt of the corresponding counter anion. The complexes were characterized using elemental analysis, ¹H NMR, ¹¹B NMR, FT-IR Spectroscopy, UV–visible spectroscopy and thermo-gravimetric analysis (TGA). The antibacterial activities of all complexes are evaluated by the minimal inhibitory concentration (MIC), using the micro-broth dilution method, against eight bacteria (Gram-negative and Gram-positive), each with fresh clinical isolates. The MIC results were compared with those of Oxytetracycline agent as a positive control. In most cases, the compounds show broad-spectrum activities that were either, more active, or equipotent to, the antibiotic agent in the comparison tests. Complex 4 showed the greatest activity against Proteus mirabilis (Gram- negative) with a minimum inhibitory concentration (MIC) of 8 µg/mL, while complexes 2 and 3 showed the lowest activity against Pseudomonas aeruginosa (Gram-negative) and against Staphylococcus aureus (Gram-positive) with a concentration of 512 µg/mL.     

Generation and thermal bond relocation of a sterically congested cyclononatetraenyl anion

The sterically strained anion 4 was found to be thermally labile to subzero workup, readily undergoing temperature-dependent electrocyclization to a variety of tetracyclic frames.     

Synthesis,spectroscopic and magnetic properties of copper complexes with a ligand containing the pyridoxal moiety

Summary Seven new copper(II)pyridoxal salicyloylhydrazone complexes have been prepared and characterized by vibrational and electronic spectra and magnetic measurements. The u.v. absorption band maxima are compared with those of metal chelates of Schiff bases obtained from condensation of pyridoxal with amines or amino acids.     

Preparation of oligodiazo compounds by using the suzuki coupling reaction and characterization of their photoproducts

[9-[10-(4-tert-Butyl-2,6-dimethyl)phenyl]anthryl](4-bromo-2,6-dimethylphenyl)diazomethane was found to be stable enough to survive under Suzuki coupling conditions and underwent mono-, di-, and trisubstitution with benzene mono-, di-, and triboronic acids to afford benzene derivatives having one, two, and three diazo units, respectively. The products from irradiation of those diazo compounds were characterized by ESR and SQUID measurements, which revealed that triplet, quintet, and septet ground states were formed from mono-, bis-, and tris(diazo) compounds, respectively. The stability of those high-spin species was estimated by temperature-dependent ESR and UV/vis measurements as well as laser flash photolysis, which indicated that all three species are stable up to 160 K and have a half-life of a few seconds in solution at room temperature. The finding unequivocally shows that a precursor diazo unit can basically be handled as a building block to construct ploydiazo compounds and that persistent triplet carbenes, even though they greatly lose typical reactivity as a triplet carbene, still retain electronic properties and act as a spin source when aligned properly in the pi-electron frameworks to generate a high-spin molecule with remarkable thermal stability.     

Structural and functional mimic of galactose oxidase by a copper complex of a sterically demanding [N2O2] ligand

A structural and functional mimic of the galactose oxidase (GOase) enzyme active-site by a copper complex supported over a sterically demanding ligand having [N2O2] donor sites is reported. Specifically, the binding of the histidine (496 and 581) and tyrosine (272 and 495) residues to the copper center in a square-pyramidal fashion in the active-site of galactose oxidase (GOase) enzyme has been modeled in a copper complex, ([(3-tert-butyl-5-methyl-2-hydoxybenzyl)(3'-tert-butyl-5'-methyl-2'-oxobenzyl)(2-pyridylmethyl)]amine)Cu(OAc)) (1b), stabilized over a sterically demanding ligand in which the two phenolate-O atoms mimicked the tyrosine binding while an amine-N and pyridyl-N atoms emulated the histidine binding to the metal center, similar to that in the enzyme active-site. Furthermore, the copper complex 1b is found to be an effective functional model of the enzyme as it efficiently catalyzed the chemoselective oxidation of primary alcohols to aldehydes in high turnover numbers under ambient conditions. An insight into the nature of the active-species was obtained by EPR and CV studies, which in conjunction with the DFT studies, revealed that the active-species is an anti-ferromagnetically coupled diamagnetic radical cation, (1)1b+, obtained by one electron oxidation at the equatorial phenolate-O atom of the ligand in the 1b complex.     

Synthesis, characterization, and polarized luminescence properties of platinum(II) complexes having a rod-like ligand

We have synthesized a series of platinum (Pt) complexes having a rod-like ligand: 'Pt(F(2)PPy)acac', 'Pt(12F(2)PPy)acac', and 'Pt(12F(2)PPyO4)acac'. The crystal form of Pt(12F(2)PPy)acac was successfully determined to be triclinic by single-crystal X-ray structural analysis. The molecules were parallelly aligned in the unit cell. Monomer and excimer emissions of Pt(12F(2)PPy)acac were observed in hexane solution, poly(methyl methacrylate) film, and various nematic LCs. Homogeneous LC cells with the Pt complex/LC mixtures exhibited polarized optical emission resulting from monomer and excimer states. The PL intensity perpendicular to the orientation direction was higher than the parallel one in the whole wavelength region of the Pt complex and the polarization ratio of the excimer was higher than that of the monomer. The polarization ratios of the excimers were estimated to be 1.4-2.5 in nematic LC at room temperature, and decreased gradually with increasing temperature. The polarization ratios of Pt(12F(2)PPyO4)acac were higher than those of Pt(F(2)PPy)acac and Pt(12F(2)PPy)acac in all the LCs.     

A three-dimensional copper(II) coordination polymer featuring the 2,3-dioxyquinoxalinate(-2) ligand: Preparation,structural characterization and magnetic study

The synthesis, single-crystal X-ray structure and magnetic properties of [Cu₃L₂Cl₂(DMF)₄]_n (1), where L^2? is the 2,3-dioxyquinoxalinate(-2) ligand, are reported. The complex was prepared by the reaction of CuCl₂ and 1,4-dihydro-2,3-quinoxalinedione (H₂L′) under basic conditions using either solvothermal or normal laboratory techniques. Compound 1 is a 3D coordination polymer with an (8².10)-a, lig (LiGe) topology, containing the ligand in a novel 3.1111 (Harris notation) coordination mode. Variable-temperature and variable-field magnetic studies reveal that the ligand L^2? propagates weak antiferromagnetic exchange interactions through its “quinoxaline” part. IR data are discussed in terms of the structural features of 1 and the coordination mode of L^2?.