Navamoney Arulsamy

Catalytic and magnetic properties of a new series of binuclear copper(II) complexes

Abstract Binuclear copper(II) complexes of ligands derived from condensation of 2,6- diformyl-4-methylphenol with various aromatic mono- and diamines have been synthesized. Complexes derived from monoamines have the Cu 2 LCl 3 composition and those from diamines have the Cu 2 L′Cl 2 composition, where L and L′ represent the ligands. Analytical data, conductance and spectral studies support these formulations. Cu 2 LCl 3 complexes are chloro-bridged, as evidenced by two intense IR bands centred around 300 and 320 cm −1 . Magnetic susceptibility measurements show that Cu 2 LCl 3 complexes have low μ eff f values indicating magnetically interacting copper(II) centres and Cu 2 L′Cl 2 complexes have non-interacting copper(II) centres. Cu 2 LCl 3 complexes undergo single-step quasi-reversible reduction at - 0.62 V vs SCE. Catalysis of Cu 2 LCl 3 complexes for the oxidation of 3,5-di- t-butylcatechol (3,5-DTBC) and ascorbic acid by dioxygen is studied.

SPECTRAL AND ELECTROCHEMICAL INVESTIGATIONS OF COPPER(II) N-SALICYLIDENE-AMINO ACIDATO COMPLEXES AND THEIR IMIDAZOLE, PYRAZOLE AND PYRIDINE ADDUCTS

SummaryCopper(II) Schiff base complexes derived from salicylaldehyde and amino acids such as glycine, L-alanine, L-serine, L-threonine, and β-alanine, Cu(sal-aa)(H2O) and their imidazole, pyrazole and pyridine adducts, Cu(sal-aa)L have been prepared. Their electronic spectral and e.s.r. data in water concur with information obtained in dioxane-H2O mixtures; cyclic voltammetric (c.v.) and differential pulse voltammetric (d.p.v.) data were collected in aqueous media; based on the experimental data, a three-step electrode mechanism has been proposed. In pH 5-3.5 the presence of protonated species, [Cu(sal-aaH)(H2O)]+ is evident from c.v. profiles. The electronic spectra of Cu(sal-aa)L adducts show a shift ofca. 10–20 nm in the d-d band position to lower wavelengths. E.s.r. parameters giso, g‖ and A‖ are lower and Aiso higher for the adducts compared to the parent complexes. These changes are commensurate with increased planar covalency resulting from the replacement of H2O molecules by N-donor ligands. The electrochemical behaviour of pyridine adducts is similar to that of Cu(sal-aa)(H2O) complexes. Imidazole and pyrazole adducts show irreversible one-electron reduction, this difference in electrochemical behaviour being related to the difference in electron acceptor ability of the N-donor ligands. At low pHs, the electrochemical behaviour of the adducts is similar to that of the parent complexes.

Homoleptic Tris-Diphosphine Re(I) and Re(II) Complexes and Re(II) Photophysics and Photochemistry

The ligand-to-metal charge transfer state (LMCT) of [(dmpe)3Re](2+) (dmpe = 1,2-bis(dimethylphosphino)ethane) has been demonstrated to be a potent oxidant (E(0)(Re(2+*)/Re(+)) = 2.61 V vs standard calomel electrode). This complex has been traditionally prepared by nontrivial routes in low yields, and very little has been achieved in optimizing the ground state and emission energy properties of the general class of complexes [(PP)3Re](2+) (PP = chelating diphosphine) through phosphine modification. Improved syntheses for Re(I) tris-homoleptic diphosphine complexes [(PP)3Re](+) (PP = 1,2-bis(dimethylphosphino)ethane (dmpe), 1,2-bis(diethylphosphino)ethane (depe), bis(dimethylphosphino)methane (dmpm), bis(diphenylphosphino)methane (dppm), Me2PCH2PPh2, 1,3-bis(dimethylphosphino)propane (dmpp), or 1,2-bis(dimethyl-phosphino)benzene (dmpb)) were achieved by single-pot reactions exploiting the reducing potential of the phosphines when reacted with Re(V) oxo-complexes in 1,2-dichlorobenzene at 160-180 °C. Single-electron chemical oxidation of [(PP)3Re](+) yields luminescent Re(II) analogues; appropriate use of Ph3C(+), Cp2Fe(+), or (4-BrC6H4)3N(+) B(C6F5)4(-) salts produced [(PP)3Re](2+) complexes in good yields. Crystallographic trends for the Re(+)/Re(2+) pairs show significantly lengthened Re(2+)-P bonds for [(PP)3Re](2+) relative to the corresponding [(PP)3Re](+) system. The redox and luminescence behavior of the complexes indicates the luminescence is from a ligand P(σ)-to-metal (Re(dπ)) charge transfer ((2)LMCT) state for all the complexes. Structured luminescence at 77 K is postulated to originate from relaxation of the (2)LMCT state into two spin-orbit coupled states: the ground state and a state ∼ 3000 cm(-1) above the ground state. The excited-state reduction potential (Re(II*/I)) for [(depe)3Re](2+) was determined from the free energy dependence of luminescence quenching rate constants. Yields for formation of charge separated ions were determined for three of the complexes with a variety of electron donors. Despite favorable electrostatics, no charge separated ions were observed for radical ion pairs for which the energy of back electron transfer exceeded 1.1 V.

Unexpected formation of ruthenium(II) hydrides from a reactive dianiline precursor and 1,2-(Ph2P)2-1,2-closo-C2B10H10.

Reaction of the new precursor cis, trans-Ru(cod)(anln)2Cl2 with the diphosphine 1,2-bis(diphenylphosphino)-1,2-dicarba-closo-dodecaborane (o-dppc) unexpectedly results in two new ruthenium(II) hydrides, trans-Ru(o-dppc) 2(H)Cl and the neutral, five-coordinate complex Ru(o-dppc)(nido-dppc)(H), depending upon the reaction conditions [anln is aniline and nido-dppc is 7,8-(Ph2P)2C2B9H10(-)]. Chloride abstraction from trans-Ru(o-dppc)2(H)Cl leads to another five-coordinate hydride, [Ru(o-dppc)2(H)](+), which is isolated as either a triflate or hexafluorophosphate salt. On the basis of labeling and reactivity studies, the source of the hydride appears to be the cod ligand.

Synthesis and Characterization of Iron(II) Quinaldate Complexes

Treatment of iron(II) chloride or iron(II) bromide with 2 equiv of sodium quinaldate (qn = quinaldate or C(10)H(6)NO(2)(-)) yields the coordinatively unsaturated mononuclear iron(II) quinaldate complexes Na[Fe(II)(qn)(2)Cl].DMF and Na[Fe(II)(qn)(2)Br].DMF (DMF = N,N-dimethylformamide), respectively. When a similar synthesis is carried out using iron(II) triflate, a solvent-derived linear triiron(II) complex, [Fe(II)(3)(qn)(6)(DMF)(2)], with two five-coordinate iron(II) centers and a single six-coordinate iron(II) center is obtained. Each of these species has been characterized using X-ray diffraction. The vibrational features of these complexes are consistent with the observed solid-state structures. Each of these compounds exhibits an iron(II)-to-quinaldate (pi*) charge-transfer band between 520 and 550 nm. These metal-to-ligand charge-transfer bands are sensitive to substitution of the quinaldates as well as alteration of the first coordination sphere ligands. However, the (1)H NMR spectra of these paramagnetic high-spin iron(II) complexes are not consistent with retention of the solid-state structures in a DMF solution. The chemical shifts, longitudinal relaxation times (T(1)), relative integrations, and substitution of the quinaldate ligands provide a means to fully assign the (1)H NMR spectra of the paramagnetic materials. These spectra are consistent with coordination equilibria between five- and six-coordinate species in a DMF solution. Electrochemical studies are reported to place these oxygen-sensitive compounds in a broader context with other iron(II) compounds. Iron complexes of bidentate quinoline-2-carboxylate-derived ligands are germane to metabolic pathways, environmental remediation, and catalytic applications.

Magnetic and electrochemical studies of a series of homo- and hetero-dinuclear copper(II) nickel(II) and zinc(II) complexes

Abstract Homo- and hetero-dinuclear copper(II), nickel(II) and zinc(II) complexes of a dinucleating ligand derived from the condensation of 2 mol of 2,6-diformyl-4-methylphenol and 1 mol of 1,3-diaminopropane (L) have been prepared as their perchlorate salts, and characterized and studied for their magnetic and redox properties. The homo-dinuclear copper(II) and nickel(II) complexes and the hetero-dinuclear complexes containing copper(II) and nickel(II) exhibit antiferromagnetic coupling at room temperature. A comparison of the redox behaviour of the zinc(II) containing hetero-dinuclear complexes with that of the homo- and hetero-dinuclear complexes containing copper(II) and nickel(II) shows that in most of the cases the exchange coupling influences the redox properties of the complexes.

Spectral and electrochemical investigations on some condensation products of copper(II)-amino acid complexes

SummaryCondensation products of several copper(II) amino acid complexes with formaldehyde or acetaldehyde have been prepared together with ethene-bridged copper(II) amino acid complexes. Structures were deduced from analytical and spectral data. Electronic spectral, e.s.r. and electrochemical behaviour at neutral and various low pH conditions were examined. Spectra of the unbridged complexes indicate the formation of [CuL]+ type species at pHca. 5, whereas the bridged complexes are stable at pH 3. The electrochemical behaviour of each complex is identical except for the doubly bridged complex. These results are explained in terms of a three-step electrode mechanism. The data show that the planarity of the complexes increases from unbridged, to bridged, to doubly bridged structures.

Stereospecific reactions of copper(II) complexes of serine and threonine with formaldehyde

SummaryCondensations of Cu(L-ser)2 and Cu(L-thr)2 (where L-ser=L-serinato anion and L-thr=L-threoninato anion) with formaldehyde at pH 4.5 yield two new optically active products:bis[L-(oxazolidine-4-carboxylato)]-copper(II) monohydrate (1) andbis[L-(N-hydroxymethyl-5-methyloxazolidine-4-carboxylato)]copper(II) dihydrate (2), respectively. Cu(D-ser)2 and Cu(D-thr)2 also undergo similar reactions. The new products are different from the products obtained from Cu(DL-ser)2 and Cu(DL-thr)2, and a mechanism has been suggested to explain the stereospecificity of these conversions. Condensation of Cu(L-ser)2 with formaldehyde and ammonia at pH 4.5 yields the new product, [3N,7N-(1,3,5,7-tetraazabicyclo-[3.3.1]nonyl)di(hydroxymethyl)-acetato]copper(II), (3). The compexes have been characterized by analytical and by i.r. electronic and c.d. spectral data. Complexes (1) and (2) undergo a reversible CuII/CuI redox process in aqueous media at −0.18 Vversus s.c.e.; complex (3) exhibits irreversible CuII/CuI reduction at −0.49 V confirming the presence of a rigid pentamethylenediaza-bridged ligand system.

Sequential electron transfer in an intermolecularly interacting copper(II)-amino acid system

Abstract Ethylenediamine-N,N′-diacetatocopper(II) (Cu-EDDA) exhibits two reversible one-electron redox processes at a hanging mercury drop electrode (HMDE) at −0.28 and −0.39 V vs SCE in aqueous medium. This is attributed to the existence of the complex as a dimer in aqueous solution due to weak intermolecular metal-metal interactions.

Differential reactivity pattern for the condensation reactions of copper(II) complexes of DL- and L-amino acids

The condensation reactions of copper(II) complexes of DL and L forms of alanine, serine and threonine with aliphatic aldehydes reveal differential reactivity for the bis(amino acidato)copper(II) complexes. The reaction of [Cu(DL-ala)2](where ala = alaninato anion) with formaldehyde and ammonia, at an acidic pH of 5, yields a pentamethylenediaza group containing product, [(αR,α′S)-N3N7-(1,3,5,7-tetraazabicyclo[3.3.1]nonane)di(2-methylacetato)]copper(II)1, but at higher pH conditions (pH > 8.0), yields the known oxazolidine group containing product, diaquabis(4-methyloxazolidine-4-carboxylato)-copper(II)2. However, the reaction of [Cu(L-ala)2] with formaldehyde and ammonia at pH 8.5 is known to yield an optically active isomer of 1, viz. [(αS,α′S)-N3,N7-(1,3,5,7-tetraazabicyclo-[3.3.1]nonane)di(2-methylacetato)]copper(II)1a. Though the latter reaction also yields the oxazolidine group containing product 2 at very basic pH (> 10), the formation of 2 reveals racemization during the reaction process. Similarly, whereas the copper(II) complexes of DL-serine and DL-threonine readily undergo condensation reactions with aldehydes such as formaldehyde, propionaldehyde, butyraldehyde and valeraldehyde, yielding oxazolidine group containing products, the corresponding L-amino acidatocopper(II) complexes do not undergo condensation under the same experimental conditions except in the case of formaldehyde, demonstrating differential reactivity of DL- and L-amino acidatocopper(II) complexes. The crystal structures of the products obtained from the reactions of [Cu(DL-ser)2](ser = serinato anion) and [Cu(DL-thr)2](thr = threoninato anion) with formaldehyde, aqua[N,N′-(2-oxapropanediyl)bis(oxazolidine-4-carboxylato)]copper(II) Sesquihydrate 3 and [N,N′-(2-oxapropanediyl)bis(5-methyloxazolidine-4-carboxylato)]copper(II) monohydrate 4, respectively, have been determined. Complex 3 crystallizes in the triclinic space group P. a= 10.802(2), b= 11.039(2), c= 13.460(3)A, α= 75.14(3), β= 69.57(3), γ= 87.53(3)° and Z= 4. Complex 4 also crystallizes in the triclinic space group P, a= 7.388(2), b= 10.017(2), c= 11.485(2)A, α= 115.27(3), β= 101.89(3), γ= 91.79(3)° and Z= 2.