Dinitrogen Complexes of Sulfur-Ligated Iron

We report a unique class of dinitrogen complexes of iron featuring sulfur donors in the ancillary ligand. The ligands utilized are related to the recently studied tris(phosphino)silyl ligands (2-R_2PC_6H_4)_3Si (R = Ph, iPr) but have one or two phosphine arms replaced with thioether donors. Depending on the number of phosphine arms replaced, both mononuclear and dinuclear iron complexes with dinitrogen are accessible. These complexes contribute to a desirable class of model complexes that possess both dinitrogen and sulfur ligands in the immediate iron coordination sphere

Dual mutualistic associations in sainfoin (Onobrychis viciifolia Scop.) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Agronomy at Massey University

Recent studies established that many legumes, when infected with the appropriate Rhizobium spp. and arbuscular fungi, nodulated better and exhibited greater dinitrogen fixation than plants infected with only the rhizobia. A similar study, therefore, was carried out in a glasshouse using sainfoin (Onobrychis viciifolia Scop.), a legume that is rapidly gaining recognition as a potential forage crop in New Zealand and other parts of the world. Pre-germinated seeds (cv. Fakir) were planted in sterilized soils and incubated with an effective Rhizobium spp. (strain NZP 5301), a mixture of endophytes (Gigaspora magarita Becker & Hall, Glomus fasciculata (Thax. sensu Gerd.) Gerdemann & Trappe and Glomus tenuis (Greenall) Hall), or both eht rhizobia and endophytes. The experiment also included a control, without any inoculation. Endophyte infection, nodulation and dinitrogen fixation, total nitrogen and phosphorus concentrations, and plant growth and development were determined on eleven sequential samplings over about twenty weeks, up to the stage of green inflorescence. Arbuscular mycorrhiza formation did not occur with the first endophyte inoculation, containing Gigaspora magarita Becker & Hall, even after 93 days of growth. This is probably because the inoculum used consisted of a low quantity of viable spores and mycelia. The second inoculation, containing the three endophyte species, produced only a low degree of infection between day 115 and 137, possibly because the extensive root lignification and relatively higher root phosphorus concentration (0.50%) restricted fungal invasion and establishment within the root cortex. Mycorrhiza formation did not increase phosphate uptake, improve nodulation and dinitrogen fixation, or increase plant growth. This is due probably to the already well-developed root systems that were efficiently exploiting the small soil volume within the bags. Rhizobia-inoculated plants produced more nodules, larger nodules and consequently, a greater nodule dry weight than the uninoculated plants. The nodules produced in the inoculated plants were red instead of green as in the uninoculated plants, and exhibited a greater dinitrogen fixation. As a result, these inoculated plants contained a higher concentration of shoot, root and nodule nitrogen, and a greater dry weight accumulation in the shoots and nodules. The shoot and nodule phosphorus concentrations, however, were lower in the rhizobia-inoculated than in the uninoculated plants due to the greater amount of shoot and nodule tissues which caused a dilution effect. These rhizobia effects on nodulation and dinitrogen fixation, nitrogen and phosphorus concentrations, and plant growth and development became more prominent with time. The relatively higher nodule phosphorus concentration when compared with the shoot and root phosphorus concentrations suggests that phosphorus was presumably required in large quantities by the dinitrogen-fixing system

Fundamental organometallic reactions: Applications on the CYBER 205

Two of the most challenging problems of Organometallic chemistry (loosely defined) are pollution control with the large space velocities needed and nitrogen fixation, a process so capably done by nature and so relatively poorly done by man (industry). For a computational chemist these problems are on the fringe of what is possible with conventional computers (large models needed and accurate energetics required). A summary of the algorithmic modification needed to address these problems on a vector processor such as the CYBER 205 and a sketch of findings to date on deNOx catalysis and nitrogen fixation are presented

A catalytic cycle for oxidation of tert-butyl methyl ether by a double C−H activation-group transfer process

A square-planar, iridium(I) carbene complex is shown to effect atom and group transfer from nitrous oxide and organic azides, releasing the corresponding formate or formimidate and an iridium(I)−dinitrogen adduct. The dinitrogen complex performs C−H activation upon photolysis or thermolysis, regenerating the carbene from tert-butyl methyl ether with loss of H_2. Taken together, these reactions represent a net catalytic cycle for C−H functionalization by double C−H activation to generate metal−carbon multiple bonds. Additionally, the unusual group transfer from diazo reagents underscores the unique nature of the reactivity observed for nucleophilic-at-metal carbene complexes

The synthesis and characterization of new higher nuclearity arene-ruthenium-sulfur clusters : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Chemistry at Massey University, New Zealand

This thesis describes a project investigating the synthesis and characterization of new higher nuclearity arene-ruthenium-sulfur clusters and arene-ruthenium-nitrogen complexes. The thesis is divided into four chapters, with the introduction in Chapter One. The synthesis and characterization of new higher nuclearity arene-ruthenium-sulfur clusters are described in Chapter Two. These include two novel clusters, [Ru₅S₄(cymene)₄](PF₆)₂, [Ru₄(S₂)(SO)(cymene)₄](PF₆)₂ and one known cluster, [Ru₃S₂(cymene)₃](PF₆)₂. The X-ray crystallographic structures of these three arene-ruthenium-sulfur clusters are discussed in detail including how the number of valence electrons influences the structure, how the solid state structure and single crystal structure effect each other and how the structures determine the chemical shifts and other characters of the clusters. The unusual signals of these three clusters on ¹H NMR spectra are discussed carefully. The mechanisms of formation of arene-ruthenium-sulfur clusters are described in detail. Some electrochemistry and calculations (quantum chemistry) are also involved. The synthesis and characterization of arene-ruthenium-nitrogen complexes are described in Chapter Three. These include two new mono-nuclear complexes, [RuCl₂(NH₃)(cymene)], [Ru(NH₃)₃(cymene)](PF₆)₂, one novel amide dimer [RuCl(NH₂)(cymene)]₂ and one known complex, [RuCl(NH₃)₂(cymene)]PF₆. The mechanisms of reactions in which they are formed are also discussed. In Chapter Four, the experimental data is presented. The X ray crystallography of [Ru₅S₄(cymene)₄](PF₆)₂, [Ru₄(S₂)(SO)(cymene)₄](PF₆)₂, [RuCl₂(NH₃)(cymene)] and [RuCl(NH₂)(cymene)]₂ is described in detail

Gradient-Driven Molecule Construction: An Inverse Approach Applied to the Design of Small-Molecule Fixating Catalysts

Rational design of molecules and materials usually requires extensive screening of molecular structures for the desired property. The inverse approach to deduce a structure for a predefined property would be highly desirable, but is, unfortunately, not well-defined. However, feasible strategies for such an inverse design process may be successfully developed for specific purposes. We discuss options for calculating 'jacket' potentials that fulfill a predefined target requirement - a concept that we recently introduced [T. Weymuth, M. Reiher, MRS Proceediungs, 2013, 1524, DOI:10.1557/opl.2012.1764]. We consider the case of small-molecule activating transition metal catalysts. As a target requirement we choose the vanishing geometry gradients on all atoms of a subsystem consisting of a metal center binding the small molecule to be activated. The jacket potential can be represented within a full quantum model or by a sequence of approximations of which a field of electrostatic point charges is the simplest. In a second step, the jacket potential needs to be replaced by a chemically viable chelate-ligand structure for which the geometry gradients on all of its atoms are also required to vanish. In order to analyze the feasibility of this approach, we dissect a known dinitrogen-fixating catalyst to study possible design strategies that must eventually produce the known catalyst.Comment: 40 pages, 6 tables, 5 figure

Synthesis of Alkaline Earth Diazenides MAEN2 (MAE = Ca, Sr, Ba) by Controlled Thermal Decomposition of Azides under High Pressure

The alkaline earth diazenides MAEN2 with MAE = Ca, Sr and Ba were synthesized by a novel synthetic approach, namely, a controlled decomposition of the corresponding azides in a multianvil press at highpressure/ high-temperature conditions. The crystal structure of hitherto unknown calcium diazenide (space group I4/mmm (no. 139), a = 3.5747(6) Å, c = 5.9844(9) Å, Z = 2, wRp = 0.078) was solved and refined on the basis of powder X-ray diffraction data as well as that of SrN2 and BaN2. Accordingly, CaN2 is isotypic with SrN2 (space group I4/mmm (no. 139), a = 3.8054(2) Å, c = 6.8961(4) Å, Z = 2, wRp = 0.057) and the corresponding alkaline earth acetylenides (MAEC2) crystallizing in a tetragonally distorted NaCl structure type. In accordance with literature data, BaN2 adopts a more distorted structure in space group C2/c (no. 15) with a = 7.1608(4) Å, b = 4.3776(3) Å, c = 7.2188(4) Å, β = 104.9679(33)°, Z = 4 and wRp = 0.049). The N−N bond lengths of 1.202(4) Å in CaN2 (SrN2 1.239(4) Å, BaN2 1.23(2) Å) correspond well with a double-bonded dinitrogen unit confirming a diazenide ion [N2]2−. Temperature-dependent in situ powder X-ray diffractometry of the three alkaline earth diazenides resulted in formation of the corresponding subnitrides MAE2N (MAE = Ca, Sr, Ba) at higher temperatures. FTIR spectroscopy revealed a band at about 1380 cm−1 assigned to the N−N stretching vibration of the diazenide unit. Electronic structure calculations support the metallic character of alkaline earth diazenides

Cu-Mg-Fe-O-(Ce) complex oxides as catalysts of selective catalytic oxidation of ammonia to dinitrogen (NH3-SCO)

Multicomponent oxide systems 800-Cu-Mg-Fe-O and 800-Cu-Mg-Fe-O-Ce were tested as catalysts of selective catalytic oxidation of ammonia to dinitrogen (NH3-SCO) process. Materials were obtained by calcination of hydrotalcite-like compounds at temperature 800 degrees C. Some catalysts were doped with cerium by the wet impregnation method. Not only simple oxides, but also complex spinel-like phases were formed during calcination. The influence of chemical composition, especially the occurrence of spinel phases, copper loading and impregnation by cerium, were investigated. Materials were characterized by several techniques: X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), low-temperature nitrogen adsorption (BET), cyclic voltammetry (CV), temperature programmed reduction (H-2-TPR), UV-vis diffuse reflectance spectroscopy and scanning electron microscopy (SEM). Examined oxides were found to be active as catalysts of selective catalytic oxidation of ammonia with high selectivity to N-2 at temperatures above 300 degrees C. Catalysts with low copper amounts (up to 12 wt %) impregnated by Ce were slightly more active at lower temperatures (up to 350 degrees C) than non-impregnated samples. However, when an optimal amount of copper (12 wt %) was used, the presence of cerium did not affect catalytic properties. Copper overloading caused a rearrangement of present phases accompanied by the steep changes in reducibility, specific surface area, direct band gap, crystallinity, dispersion of CuO active phase and Cu2+ accessibility leading to the decrease in catalytic activity.Web of Science102art. no. 15

On the feasibility of N2 fixation via a single-site FeI/FeIV cycle: Spectroscopic studies of FeI(N2)FeI, FeIV=N, and related species

The electronic properties of an unusually redox-rich iron system, [PhBPR 3]FeNx (where [PhBPR 3] is [PhB(CH2PR2)3]−), are explored by Mössbauer, EPR, magnetization, and density-functional methods to gain a detailed picture regarding their oxidation states and electronic structures. The complexes of primary interest in this article are the two terminal iron(IV) nitride species, [PhBPiPr 3]FeN (3a) and [PhBPCH2Cy 3]FeN (3b), and the formally diiron(I) bridged-Fe(μ-N2)Fe species, {[PhBPiPr 3]Fe}2(μ-N2) (4). Complex 4 is chemically related to 3a via a spontaneous nitride coupling reaction. The diamagnetic iron(IV) nitrides 3a and 3b exhibit unique electronic environments that are reflected in their unusual Mössbauer parameters, including quadrupole-splitting values of 6.01(1) mm/s and isomer shift values of −0.34(1) mm/s. The data for 4 suggest that this complex can be described by a weak ferromagnetic interaction (J/D < 1) between two iron(I) centers. For comparison, four other relevant complexes also are characterized: a diamagnetic iron(IV) trihydride [PhBPiPr 3]Fe(H)3(PMe3) (5), an S = 3/2 iron(I) phosphine adduct [PhBPiPr 3]FePMe3 (6), and the S = 2 iron(II) precursors to 3a, [PhBPiPr 3]FeCl and [PhBPiPr 3]Fe-2,3:5,6-dibenzo-7-aza bicyclo[2.2.1]hepta-2,5-diene (dbabh). The electronic properties of these respective complexes also have been explored by density-functional methods to help corroborate our spectral assignments and to probe their electronic structures further