Rhodium assisted C-H activation of N-(2 '-hydroxyphenyl)benzaldimines. Synthesis, structure and electrochemical properties of a group of organorhodium complexes

Reaction of a group of N-(2'-hydroxyphenyl)benzaldimines, derived from 2-aminophenol and five para-substituted benzaldehydes (the para substituents are OCH3, CH3, H, Cl and NO2), with [Rh(PPh3)(3)Cl] in refluxing toluene in the presence of a base (NEW afforded a family of organometallic complexes of rhodium(III). The crystal structure of one complex has been determined by X-ray crystallography. In these complexes the benzaldimine ligands are coordinated to the metal center, via dissociation of the phenolic proton and the phenyl proton at the ortho position of the phenyl ring in the imine fragment, as dianionic tridentate C,N,O-donors, and the two PPh3 ligands are trans. The complexes are diamagnetic (low-spin d(6), S = 0) and show intense MLCT transitions in the visible region. Cyclic voltammetry shows a Rh(III)-Rh(IV) oxidation within 0.63-0.93 V vs SCE followed by an oxidation of the coordinated benzaldimine ligand. A reduction of the coordinated benzaldimine is also observed within -0.96 to -1.04 V vs SCE. Potential of the Rh(Ill)-Rh(IV) oxidation is found to be sensitive to the nature of the para-substituent. (c) 2006 Elsevier B.V. All rights reserved.

Synthesis, structure, and electrochemical properties of a family of 2-(arylazo)phenolate complexes of ruthenium with unusual C-C coupling and N=Ncleavage

Reaction of 2-(4'-R-phenylazo)-4-methylphenols (R = OCH3, CH3, H, Cl, and NO2) with [Ru(dmso)(4)Cl-2] affords a family of five ruthenium(III) complexes, containing a 2-(arylazo)phenolate ligand forming a six-membered chelate ring and a tetradentate ligand formed from two 2-(arylazo) phenols via an unusual C-C coupling linki.ng the two ortho carbons of the phenyl rings in the arylazo fragment. A similar reaction with 2-(2'-methylphenylazo)-4-methylphenol with [Ru(dmso)(4)Cl-2] has afforded a similar complex, in which one 2-(2'-methylphenylazo)-4-methylphenolate ligand is coordinated forming a six-membered chelate ring, and the other two ligands have undergone the C-C coupling reaction, and the coupled species is coordinated as a tetradentate ligand forming a five-membered N,O-chelate ring, a nine-membered N,N-chelate ring, and another five-membered chelate ring. Reaction of 2-(2',6'-dimethylphenylazo)-4-methylphenol with [Ru(dmso)(4)Cl-2] has afforded a complex in which two 2-(2',6'-dimethylphenylazo)-4-methylphenols are coordinated as bidentate N,O-donors forming five- and six-membered chelate rings, while the third one has undergone cleavage across the N=N bond, and the phenolate fragment, thus generated, remains coordinated to the metal center in the iminosemiquinonate form. Structures of four selected complexes have been determined by X-ray crystallography. The first six complexes are one-electron paramagnetic and show rhombic ESR spectra. The last complex is diamagnetic and shows characteristic H-1 NMR signals. All the complexes show intense charge-transfer transitions in the visible region and a Ru(III)-Ru(IV) oxidation on the positive side of SCE and a Ru(III)-Ru(II) reduction on the negative side.

Chemical, physical and electrical properties of aged dodecylbenzene 3: thermal ageing of mixed isomers in nitrogen and under sealed conditions

Commercial dodecylbenzene cable fluid was aged at temperatures of 105 and 135 degrees C in dry oxygen-free nitrogen. In addition, selected samples were aged at 135 degrees C under sealed conditions where air was excluded from the headspace above the oil. A variety of analytical techniques, such as ultra-violet visible and infra-red spectroscopy, acid number and water content measurements, were then used to characterize the aged oils. In addition, their electrical properties were assessed by dielectric spectroscopy. Compared with ageing in air, the ageing rate was reduced significantly and, as expected, no major oxidation peaks were detected in the infrared spectrometer. Significantly, very little absorbance at 680 nm ("red absorbers") was detected in samples aged with copper and, consequentially, no large increases in dielectric loss were recorded within the ageing times considered here. This study compliments previous investigations on cable fluid and 1-phenyldodecane aged in air and show that the same ageing indicators are valid in oils aged under conditions which more closely resemble those found in high voltage plant.

Chemical, physical and electrical properties of aged dodecylbenzene: thermal ageing of mixed isomers in air

A commercial dodecylbenzene (DDB) cable oil was aged at temperatures between 90 and 135 degrees C in air and was analyzed using various analytical techniques including optical and infra-red spectroscopy and dielectric analysis. On ageing, the oil darkened, significant oxidation features were found by infra-red spectroscopy and the acid number, water content and dielectric loss all increased. Ageing in the presence of paper or aluminum did not affect the ageing process, whereas ageing was significantly modified by the presence of copper. An absorption at 680 nm ("red absorbers") was detected by ultra-violet/visible spectroscopy followed by the production of an opaque precipitate. A reaction between copper and the acid generated on ageing is thought to produce copper carboxylates, and X-ray fluorescence confirmed that copper was indeed present in both the aged oil and the precipitate. Significantly, once red absorbers were detected, the dielectric loss increased to catastrophically high values and, therefore, the appearance of these compounds may serve as a useful diagnostic indicator. The development of acidity on ageing appears to be key in initiating the destructive copper conversion reaction and hence the control of oil acidity may be key to prolonging the life of DDB cable oils.

Chemical, physical and electrical properties of aged dodecylbenzene 2: thermal ageing of single isomers in air

The linear isomer of dodecylbenzene (DDB), 1-phenyldodecane, was aged at temperatures of 105 and 135 degrees C in air and the resultant products were analyzed using a range of analytical techniques. On ageing, the 1-phenyldodecane darkened, the acid number, dielectric loss and water content increased and significant oxidation peaks were detected in the infrared spectrum. When aged in the presence of copper, a characteristic peak at 680 nm was also detected by UV/visible spectroscopy but, compared with previous studies of a cable-grade DDB, the strength of this peak was much increased and no appreciable precipitate formation occurred. At the same time, very high values of dielectric loss were recorded. On ageing in the absence of copper, an unusually strong infrared carbonyl band was seen, which correlates well with the detection of dodecanophenone by gas chromatography / mass spectrometry and nuclear magnetic resonance spectroscopy. It was therefore concluded that the ageing process proceeds via the initial production of aromatic ketones, which may then be further oxidized to carboxylic acids. In the presence of copper, these oxidation products are present in lower quantities, most of these oxidation products being combined with the copper present in the oil to give copper carboxylates. The behavior is described in terms of a complex autoxidation mechanism, in which copper acts as both an oxidizing and a reducing agent, depending on its oxidation state and, in particular, promotes elimination via the oxidation of intermediate alkyl radical species to carbocations.

The synthesis, structure, and electrochemical properties of Fe(C CC N)(dppe)Cp and related compounds

The cyanoacetylide complex Fe(CCCN)(dppe)Cp (3) is readily obtained from sequential reaction of Fe(CCSiMe3)(dppe)Cp with methyllithium and phenyl cyanate. Complex 3 is a good metalloligand, and coordination to the metal fragments [RhCl(CO)(2)], [Ru(PPh3)(2)Cp](+), and [Ru(dppe)Cp*](+) affords the corresponding cyanoaceylide-bridged heterobimetallic complexes. In the case of the 36-electron complexes [Cp(dppe)Fe-CCCN-MLn](n+), spectroscopic and structural data are consistent with a degree of charge transfer from the iron centre to the rhodium or ruthenium centre via the C3N bridge, giving rise to a polarized ground state. Electrochemical and spectroelectrochemical methods reveal significant interactions between the metal centres in the oxidized (35 electron) derivatives, [Cp(dppe)Fe-CCCN-MLn]((n+1)+).

Synthesis, structure and magnetic properties of mono- and di-nuclear nickel(II) thiocyanate complexes with tridentate N3 donor Schiff bases

The 1:1 condensation of N-methyl-1,3-diaminopropane and N,N-diethyl-1,2-diminoethane with 2-acetylpyridine, respectively at high dilution gives the tridentate mono-condensed Schiff bases N-methyl-N'-(1-pyridin-2-yl-ethylidene)-propane-1,3-diamine (L-1) and N,N-diethyl-N'-(1-pyridin-2-yl-ethylidene)-ethane-1,2-diamine (L-2). The tridentate ligands were allowed to react with methanol solutions of nickel(II) thiocyanate to prepare the complexes [Ni(L-1)(SCN)(2)(OH2) (1) and [{Ni(L-2)(SCN)}(2)] (2). Single crystal X-ray diffraction was used to confirm the structures of the complexes. The nickel(II) in complex 1 is bonded to three nitrogen donor atoms of the ligand L-1 in a mer orientation, together with two thiocyanates bonded through nitrogen and a water molecule, and it is the first Schiff base complex of nickel(II) containing both thiocyanate and coordinated water. The coordinated water initiates a hydrogen bonded 2D network. In complex 2, the nickel ion occupies a slightly distorted octahedral coordination sphere, being bonded to three nitrogen atoms from the ligand L-2, also in a mer orientation, and two thiocyanate anions through nitrogen. In contrast to 1, the sixth coordination site is occupied by a sulfur atom from a thiocyanate anion in an adjacent molecule, thus creating a centrosymmetric dimer. A variable temperature magnetic study of complex 2 indicates the simultaneous presence of zero-field splitting, weak intramolecular ferromagnetic coupling and intermolecular antiferromagnetic interactions between the nickel(II) centers.

Synthesis, crystal structure and magnetic properties of three unprecedented tri-nuclear and one very rare tetra-nuclear copper(II) Schiff-base complexes supported by mixed azido/phenoxo/nitrato or acetato bridges

Three novel mixed bridged trinuclear and one tetranuclear copper(II) complexes of tridentate NNO donor Schiff base ligands [Cu-3(L-1)(2)(mu(LI)-N-3)(2)(CH3OH)(2)(BF2)(2)] (1), [Cu-3(L-1)(2)(mu(LI)-NO3-I kappa O.2 kappa O')(2)] (2), [Cu-3(L-2)(2)(mu(LI)-N-3)(2)(mu-NOI-I kappa O 2 kappa O')(2)] (3) and [Cu-4(L-3)(2)(mu(LI)-N-3)(4)(mu-CH3COO-I kappa O 2 kappa O')(2)] (4) have been synthesized by reaction of the respective tridentate ligands (L-1 = 2[1-(2-dimethylamino-ethylimino)-ethyl]-phenol, L-2 = 2[1-(2-diethylamino-ethylimino)-ethyl]-phenol, L-3 = 2-[1-(2-dimethylamino-ethylimino)-methyl]-phenol) with the corresponding copper(II) salts in the presence of NaN3 The complexes are characterized by single-crystal X-ray diffraction analyses and variable-temperature magnetic measurements Complex 1 is composed of two terminal [Cu(L-1)(mu(LI)-N-3)] units connected by a central [Cu(BF4)(2)] unit through nitrogen atoms of end-on azido ligands and a phenoxo oxygen atom of the tridentate ligand The structures of 2 and 3 are very similar, the only difference is that the central unit is [Cu(NO1)(2)] and the nitrate group forms an additional mu-NO3-I kappa O 2 kappa O' bridge between the terminal and central copper atoms In complex 4, the central unit is a di-mu(L1)-N-3 bridged dicopper entity, [Cu-2(mu(L1)-N-3)(2)(CH3COO)(2)] that connects two terminal [Cu(L-3)(mu(L1)-N-3)] units through end-on azido; phenoxo oxygen and mu-CH3COO-1 kappa O center dot 2 kappa O' triple bridges to result in a tetranuclear unit Analyses of variable-temperature magnetic susceptibility data indicates that there is a global weak antiferromagnetic interaction between the copper(II) ions in complexes 1-3, with the exchange parameter J of -9 86, -11 6 and -19 98 cm(-1) for 1-3, respectively In complex 4 theoretical calculations show the presence of an antiferromagnetic coupling in the triple bridging ligands (acetato, phenoxo and azido) while the interaction through the double end-on azido bridging ligand is strongly ferromagnetic.

Synthesis, crystal structure, and magnetic properties of a very rare double μ-1,1-azido- and a μ-1,1-(OMe)-bridged FeIII dimer containing a N,N,O-donor tridentate Schiff base ligand

Two new Fe-III complexes, [Fe2L2(mu-OMe)(2)(NCS)(2)] (1) and [Fe2L2(mu-N-3)(2)(N-3)(2)] (2), have been synthesized using a N,N,O-donor tridentate Schiff base ligand HL {2-[(2-dimethylaminoethylimino)methyl]phenol}, the condensation product of salicylaldehyde and N,N-dimethyl-1,2-diaminoethane. The complexes were characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. Both crystal structures are centrosymmetric dimers containing two Fe-III atoms, which are bridged in compound 1 by two methoxy anions and in compound 2 by two mu-1,1-azides. The chelating tridentate Schiff base and a terminal thiocyanato (for 1) or azido (for 2) group complete the hexacoordination of the distorted octahedral environment of each iron center. The magnetic properties of compound 1 show the presence of antiferromagnetic exchange interactions mediated by double methoxy bridges (J = -29.45 cm(-1)). Compound 2 shows the presence of very weak ferromagnetic exchange interactions mediated by double mu-1,1-N-3 bridges (J = 1.08 cm(-1)).

Synthesis, structure and electrochemical properties of some thiosemicarbazone complexes of ruthenium

Reaction of salicylaldehyde thiosemicarbazone (L-1), 2-hydroxyacetophenone thiosemicarbazone (L-2) and 2-hydroxynapthaldehyde thiosemicarbazone (L-3) with [Ru(dmso)(4)Cl-2] affords a family of three dimeric complexes (1), (2) and (3) respectively. Crystal structure of the complex (3) has been determined. In these complexes, each monomeric unit consists of one ruthenium center and two thiosemicarbazone ligands, one of which is coordinated to ruthenium as O,N,S-donor and the other as N,S-donor forming a five-membered chelate ring. Two such monomeric units remain bridged by the sulfur atoms of the O,N,S-coordinated thiosemicarbazones. Due to this sulfur bridging, the two ruthenium centers become so close to each other, that a ruthenium-ruthenium single bond is also formed. All the complexes are diamagnetic in the solid state and in dimethylsulfoxide solution show intense absorptions in the visible and ultraviolet region. Origin of these spectral transitions has been established from DFT calculations. Cyclic voltammetry on the complexes shows two irreversible ligand oxidations on the positive side of SCE and two irreversible ligand reductions on the negative side.

Structure and magnetic properties of an unprecedented syn-antiμ-nitrito-1κO:2κO′ bridged Mn(iii)-salen complex and its isoelectronic and isostructural formate analogue

The preparation, crystal structures and magnetic properties of two new isoelectronic and isomorphous formate-and nitrite-bridged 1D chains of Mn(III)-salen complexes, [Mn(salen)(HCOO)](n) (1) and [Mn(salen)(NO2)](n) (2), where salen is the dianion of N,N'-bis(salicylidene)-1,2-diaminoethane, are presented. The structures show that the salen ligand coordinates to the four equatorial sites of the metal ion and the formate or nitrite ions coordinate to the axial positions to bridge the Mn(III)-salen units through a syn-anti mu-1 kappa O:2 kappa O' coordination mode. Such a bridging mode is unprecedented in Mn(III) for formate and in any transition metal ion for nitrite. Variable-temperature magnetic susceptibility measurements of complexes 1 and 2 indicate the presence of ferromagnetic exchange interactions with J values of 0.0607 cm(-1) (for 1) and 0.0883 cm(-1) (for 2). The ac measurements indicate negligible frequency dependence for 1 whereas compound 2 exhibits a decrease of chi(ac)' and a concomitant increase of chi(ac)'' on elevating frequency around 2 K. This finding is an indication of slow magnetization reversal characteristic of single-chain magnets or spin-glasses. The mu-nitrito-1 kappa O:2 kappa O' bridge seems to be a potentially superior magnetic coupler to the formate bridge for the construction of single-molecule/-chain magnets as its coupling constant is greater and the chi(ac)' and chi(ac)'' show frequency dependence.

Structure and magnetic properties of a tetranuclear Cu(II) complex containing the 2-(pyridine-2-yliminomethyl)-phenol ligand

A tetranuclear Cu(II) complex [Cu4L4(H2O)4](ClO4)4 has been synthesized using the terdentate Schiff base 2-(pyridine-2-yliminomethyl)-phenol (HL) (the condensation product of salicylaldehyde and 2-aminopyridine) and copper perchlorate. Chemical characterizations such as IR and UV/Vis of the complex have been carried out. A single-crystal diffraction study shows that the complex contains a nearly planar tetranuclear core containing four copper atoms, which occupy four equivalent five-coordinate sites with a square pyramidal environment. Magnetic measurements have been carried out over the temperature range 2–300K and with 100Oe field strengths. Analysis of magnetic susceptibility data indicates a strong antiferromagnetic (J1=−638cm−1) exchange interaction between diphenoxo-bridged Cu(II) centers and a moderate antiferromagnetic (J2=−34cm−1) interaction between N–C–N bridged Cu(II) centers. Magnetic exchange interactions (J’s) are also discussed on the basis of a computational study using DFT methodology. The spin density distribution (singlet ground state) is calculated to visualize the effect of delocalization of spin density through bridging groups.

Structure and magnetic properties of mono- and bi-dispersed ferrofluids as revealed by simulations

Using a Langevin molecular dynamics simulation, we show that the magnetic properties of a mono- and bi-dispersed ferrofluid system depend on the volume fraction and the dipolar coupling parameter. For the bi-dispersed system, most of the chains are formed by the large particles, but the aggregation behavior of the large particles is hindered by the presence of the small particles, which are predominantly attached to the end of the particle chain. To further elucidate the microscopic fluid structure, anisotropic structure factors are calculated.