Search

X-ray crystallographic, Mossabauer, EPR Raman, and magnetic susceptibility analyses demonstrate that [(THF)(TPP)Mn-N-FePc(H(sub)2O)](I(sub)5).2THF is isostructural with the iron-iron complex whereas in [(TPP)Mn(sup)IV-N-Fe(sup)IIIPc, oxidation occurs at one of the two macrocycles. Data indicate that the former compound represents a heteroleptic and heterobimetallic mu-nitrido bridged species.

Research was conducted to examine the reduction chemistry of the parent compound (cis-Cl2W(p-Bu(super t)-calix(4)-(O)4)) to generate reactive fragments such as neutral 2-W(IV)- and monoanionic d3-W(III)-tetraoxo species. The stepwise reductive coupling resulted to the formation of metal-metal-bonded metalla-calix(4)arene dimers containing double, triple and quadruple W-W bonds. To demonstrate the electronic configuration of the metal-metal functionalities when sandwiched by two calix(4)arene tetraanions, extended Huckel calculations were carried out.

The reduction-oxidation behavior of the meso-octaethyl mono(pyridine)-tris(pyrrole) macrocycle leading to C-C bonds was investigated. Lithium and the nickelII-lithium derivatives were used as model compounds to analyze the intra- and intermolecular oxidative coupling of nickel(II)-meso-octaethyl mono(pyridine)-tris(pyrrole) complex. Experimental results showed that the oxidative transformation of oligomeric porphyrinogen derivatives causes either inter- or intramolecular C-C bonding in the absence of protons.

The synthesis, characterization, and redox properties of bis(phthalocyaninato)niobium(IV) and the X-ray crystal structure of the monoelectronically oxidized species (Pc2Nb)(I2)(I2)0.5(CINP)3.5 (CINP = 1-chloronaphthalene) are presented. Bis(phthalocyaninato)niobium(IV) has been prepared and isolated as a monosolvate. It is a stable-to-air Nb(IV) (d1) paramagnetic sandwich-like species, which, upon oxidation by I2 under mild conditions, undergoes a metal-centered monoelectronic oxidation to yield a diamagnetic Nb(V) (d0) (Pc2Nb)+ fragment.

The bis(amino) ligands omicron-methylene-bridged bis(aniline) are capable of acting as a spectroscopic 1H nuclear magnetic resonance probe, given their sensitivity to the coordination environment of the metal and even subtle changes therein. Omicron-methylene-bridged bis(aniline) derivatives serve as bidentate ligands and form rigid eight-membered metallacycles when bound to platinum(II) or palladium(II).

Electrochemical, theoretical and magnetic investigation of a dinitrogen molecule bridging two vanadium centers through a controlled stepwise chemical and electrochemical reduction found that the metal center of the parent compound reacts with N2 by either oligomerizing or binding. Adding a single electron to the fourth compound induces the dimettalic unit to promote a multielectric reduction of dinitrogen in subsequent compounds. Magnetic and theoretical data indicate coupling in compounds 4,7 and 8 and the effective reduction of the dinitrogen molecule.

The role of calix(4)arene as a supporting ligand compared to cyclopentadienyl and phenoxo anion is emphasized through the micratory insertion reaction of carbon monoxide and isocyanides, in the Zr-C bond. A kinetically and structurally defined stewise insertion process is reported. The reactions occur via metal-assisted C-C bond formation, resulting in a variety of carbon-metal-bonded fragmenets. Extended Huckel calculations were also performed.

The full synthesis and chemical behaviour of the Zr-C bond functionalities bonded to the Osub4 skeleton is reported. The approach is based on the synthesis and organometallic functionalization of (calix(4)-(OMe)(O)sub3ZrC1)sub2 and (calix(4)-(OMe)sub2(O)sub2ZrC1sub2), giving rise to two classes of derivatives linked by the based-induced demethylation of a methoxy group. The main differences between the (Osub4ZR)super2+, (Osub4Zr)+ and (Cpsub2Zr)super2 fragements are emphasized.

Chemical research shows that copper(I) complexes containing pi-delocalized bidentate N-O monoanionic ligands can be designed as efficient photosensitizers in the transformation of norbornadiene into quadricyclene. Evidence suggests that the complexes are effective because they contain metal-to-ligand charge-transfer bands.

The structural, chemical, and spectroscopic relations within the organometallic fragments of a diphosphine ligand Ph2P(omicron-C6H4CH2C6H4-omicron)PPh2, were probed using the bridging methylene compound. The bridging methylene of the bis-phenolatoanion precursor of the ligand was utilized as a probe. Data indicated the mediating role of the bridging methylene in protection of the unsaturated metal centers, induction of intermolecular activation among the hydrocarbons, and differentiation of the endo and exoprotons.

A study was conducted on the storage of electrons in the formation of the most common C-C bonds as well as the generation of electron-rich manganese(II)-Schiff base complexes and their redox chemistry. The findings led to the discovery of a novel mode of storing and releasing electrons based on reductive coupling and oxidative decoupling of C-C bonds across two Schiff base ligands.

Synthesis of the parent compound [Mn(acac-L-en)]2 [L = CH2CH2], was performed via a metathesis reaction from MnCl2 under anhydrous and anaerobic conditions. High yield was produced through the organometallic pathway. Analysis of selected bond distances and angles for the complexes showed that the planarity of the N2O2 core in [Mn(acac-L-en)]2 [L = CH2CH2] disappeared. The coordination polyhedron possessed more similarities with a trigonal bipyramid.

The complexation of transition metal ions by both the p-tert-butylcalix[4]arene tetrakis(diphenylphosphinite) and tetrakis(dimethylphosphinite) was reported. These complexes serve as phosphorus binding surfaces for two metal ions into a close geometrical proximity. Pd monometallic complex undergoes a ligand disproportionation reaction whereas its Pt analogue does not exist under similar conditions. Homonuclear bimetallic complexes are formed by the use of the more basic and less sterically demanding ligand 2.

Formation of carbon-carbon bonds which function as electron shuttles for the metal in the complex (Co2(MeOsalophen)2Na2(THF)4), as shown by its reaction with electrophiles such as alkyl halides and carbon dioxide, was the result of the reduction of substituted (Co(salophen)) with sodium at the metal. For salophen derivatives, the reductive coupling of imino groups was noted. These results affirm that reduction of cobalt(II)-Schiff base complexes occur at the metal, not at the ligand, even if the metal reacts as if it was in a reduced form.

The thermally- and solvent-assisted intra- and intermolecular migrations of Zr-C functionalities in dialkyl(dibenzotetramethyltetraazannulene)zirconium(IV) were investigated through experimental procedures and by means an extended Huckel analysis. It was found that Cr and the Z has different levels of reactivity, resulting in significant differences in their orbital structures.

Zirconium-catalyzed electrophilic activation of aliphatic C-H bonds followed by alkali hydrides-assisted beta-proton removal enables the functionalization of meso-octa-ethyl porphyrinogen periphery. Conformations of the porphyrinogen and the bifunctional nature of metal-porphyrinogen complexes control this functionalization reaction. Formation of eta2-iminoacyl involves the insertion of Bu(t)Nc into the Zr-C bond of the corresponding monometalated form.

Early oxophilic transition metals facilitate the homologation of a pyrrole to a pyridine ring within the porphyrinogen skeleton by assisting the insertion of CO into metal-carbon and metal-hydrogen bonds, producing eta2-formyl or eta2-acyl carbenium ion. The bonding mode of the pyrrolyl anion to the metal determines the regiochemistry of the reaction. Electronic and geometric characteristics of a tetrapyrrolic macrocycle can be modified by introducing one or two pyridines.

Insertion reactions use Fe2Mes4, where Mes = 2,4,6-Me3C6H2, to prepare iron-aryl complexes with doubly functionalized or differentially functionalized iron-carbon bonds. Experimental studies reveal different reactivities for bridging and terminal mesityl with respect to migratory aptitude, enabling stepwise insertion reactions. Magnetic susceptibility studies of these dimeric iron(II) complexes at different temperatures help differentiate between antiferromagnetic couplings and the presence of a metal-metal bond and X-ray studies help characterize the various products.

Two alkyl groups occupy the meso position of the porphyrinogen skeleton to produce a new oxidized form of porphyrinogen in oxidation reactions. This novel oxidation reaction involves cleavage of a cyclopropane unit formed in the reaction process. Two monoelectronic redox steps are observed in the cleavage of cyclopropane associated with the oxidation of a copper complex. An intermolecular metal-ligand redox relationship is observed in the formation of meso-octaethyl porphyrinogen-Cu(III) complex.

Redox chemistry analysis of meso-octaethylporphyrinogen-iron(II) and -cobalt(II) complexes reveals the involvement of a four-electron oxidation of porphyrinogen, leading to a novel oxidized complex form. A number of intermediates are isolated which imply a step-wise oxidation mechanism. All these oxidation processes involve the formation and subsequent cleavage of two cyclopropane units.

Titanium tetrachloride reacts with hexamethyl benzene in chlorinated solvents to give a d0-arene complex. But-2-yne is cyclotrimerized by TiCl4-promoted (eta6-C6Me6)(TiCl3)(+) complex, exhibiting the stability of the complex. A charge transfer intermediate is observed by 1H nuclear magnetic resonance spectroscopy. X-ray analysis shows these complexes to have a metallic fragment (TiCl3)(+)eta6 binding the arene moiety.

Dimesityliron(II)1,10-phenanthroline is synthesized and the complex readily reacts with alpha-amino acids to form (Fe(II)(A)2(phen)) complexes with the liberation of mesitylene in THF solution. These complexes exhibit a diversity in solubility due to amino acid residue. Optical rotation and X-ray analysis are used to characterize these complexes. The angle of rotation are compared with uncomplexed amino acids.

Pc2Ti and PC2 are oxidized by I2 and nitric acid, and the resultant compounds are analyzed for their electrical and structural properties using X-ray and spectroscopy techniques. The X-ray structure of PC2TiI2, formed by PC3Ti oxidation by I3, shows anisotropic Ti and I variations while the P2 molecule is isotropically refined. New PC complexes have better electrical conductivity than their precursors.

The preparation in tetrahydrofuran of a series of tris(amino acidato)vanadium(III) complexes and the crystal structures of tris(L-prolinato)vanadium-dimethyl sulfoxide and tris(D-prolinato)vanadium-dimethyl sulfoxide were reported. The optical rotations of all complexes are very high when compared with the values for uncomplexed alpha-amino acids.

The reaction of lithiated meso-octaethylporphyrinogen with zirconium tetrachloride in tetrahydrofuran yields a bifunctional complex that, in hydrocarbon solvents, can carry alkali/organometallic ion pairs. The complex, (eta5-eta1-eta5-eta1-Et8N4)Zr(THF), is shown by the study to bind sodium hydride in toluene by interaction of the Lewis acid Zr with the hydride and eta5-complexation of Na with the pyrrolyl anions. The porphyrinogen adapts its binding behavior to the metal's electronic demands and to the steric nature of the substrate.

The deprotonation of tmtaaH2 through LiBu(super n) or LiMe yielded the lithium derivative (tmtaa)2Li4(DME)3. The structure of the lithium derivative consists of asymmetric units with two independent (tmtaa)Li2(DME) units linked by a third DME molecule resulting in a square pyramidal coordination. The derivative is also the starting material for the synthesis of tmtaa complexes of transition metals in inorganic solvents. The complexes (tmtaa Ti Cl2).C6H6, (tmtaa Zr Cl2).2THF and (tmtaa Hf Cl2).2THF exhibit the cis arrangement of the two functionalizable M-Cl bonds.

The first of the two methods of preparing (V acac Cl2 THF 2) involves the reductive deoxochlorination of (VO acac 2) using TiCl3(THF)3. This procedure is applicable in cases wherein the oxovanadium complex can be obtained from air-aqueous solutions. Otherwise, the second method, which involves the addition of acacNa to a solution of VCl3(THF)3, can be used. Moreover, metallic zinc can be utilized to reduce the vanadium(III) chloride intermediate to (V acac Cl THF 3).

The addition of lithiated tmtaaH2 to a solution of VCl3(THF)3 results in the synthesis of (V tmtaa Cl) which serves as a source for vanadium complexes with lower oxidation states. Subsequent introduction of Grignard reagents leads to the alkylation of the vanadium derivative to (V tmtaa R) compounds, wherein R represents Me, Ch2Ph, Ph and 2,4,6-Me3C6H2. Similarly, the metal-oxo (VO tmtaa) can also act as starting material for the preparation of organometallic derivatives. The structural conformations of (V tmtaa Cl), (V tmtaa Ph) and (V tmtaa 2,4,6-Me3C6H2) are examined using X-ray analysis and H NMR spectroscopy.

The metallation of protic dinucleating ligands, acacenH2(N,N'-ethylenebis (acetylacetone imine)), salophenH2(N,N'-o-phenylenebis(salicylaldimine)), and o-pthalic acid with homoleptic copper(I)-aryl(Cu5Mes5) compound gives dinuclear copper(I) complexes. The tetradentate ligands form a trans geometry around the copper atom. The use of toluene as a solvent and CO, PPh3, and t-BuNC as auxiliary ligands stabilise the Cu(I) ion and enhances the solubility of the resulting complexes. Thus the disproportionation of copper(I) is prevented.

The meso-octaethylporphyrinogen tetraanion undergoes redox reaction with the addition of transition metals such as palladium(II). This process explains the formation of a cyclopropane reduction product which reverts back to the original tetraanion with the introduction of lithium metal. Moreover, the cobalt(II) complex of the tetraanion can be oxidized using dioxygen. Both reduction and oxidation reactions form a complex that contain a cyclopropane unit which undergo cleavage upon the occurrence of a two-electron exchange process.

The meso-octaalkylporphyrinogens represent an interesting ligand class for metal complexation. Their tetraanionic form allows stable high oxidation states, with each pyrrolyl anion serving as a sigma or a pi donor. The meso position offers flexible substitution while the absence of conjugation between the pyrroles induces special metal-hydrocarbon interactions. The octaethyl form reacts with butyllithium in THF to yield the lithiated form, Li4L(THF)4. This in turn reacts with dry or THF-solvated Fe-, Co- or CuCl2 to give the corresponding Li2ML(THF)4. As excess halide leads to further metalation, this should be avoided if the purpose is simply to prepare the lithium-metal complex.

Research has been conducted on monosolvated bis(phthalocyaninato)niobium(IV) complex. The authors report that the recrystallization of the complex has led to the isolation of a solvated form's single crystal.