Reactions of Thiocarbamoyl compounds with vaska complexes: mechanism and stereochemistry

Bis(dimethylthiocarbamoyl)sulfide, (Me₂NCS)₂S, reacts with (PH₃P)₂MCOCl complexes giving ionic species [Ph₃PM(η²-CSNMe₂)(S₂CNMe₂)CO]X (M = Rh, Ir; X = Cl, PF₆) as kinetic products. On standing solution, [Ph₃PRh(η²-CSNMe₂)(S₂CNMe₂)CO]Cl is slowly transformed into the thermodynamic product Ph₃PRh(η²-CSNMe₂)S₂CNMe₂)Cl. The known reactions of Vaska-type complexes with Me₂NCSCl to give [trans-(Ph₃P)₂Ir(η²-CSNMe₂)COCl]Cl and trans-(Ph₃P)₂Rh(η²-CSNMe₂)Cl₂ probably follow a similar course. (PH₃P)RuNOCl reacts with (Me₂NCS)₂S and Me₂NCSCl in the same way as (Ph₃P)₂IrCOCl, but reacts with (Me₂NCS)₂NPh to give [trans-(Ph₃P)₂Ru(η²-CSNMe₂)NOCl]PF₆. The mechanism and stereochemistry of these reactions are discussed. Reactions were monitored by NMR spectroscopy in an attempt to identify intermediate η¹-thiocarboxamido complexes, but no such species could be detected.     

Syntheses of seven-membered rings: ruthenium-catalyzed intramolecular [5+2] cycloadditions

The Ru-catalyzed intramolecular [5+2] cycloaddition of cyclopropylenynes is investigated with respect to the regio- and diastereoselectivity as well as the functional group compatibility of the reaction. Evidence for the mechanism as occurring through a ruthenacyclopentene intermediate is elucidated from 1) the study of the diastereoselectivity of the cycloaddition; 2) the effect of variation of substituents on the regioselectivity of cyclopropyl bond cleavage in 1,2-trans- and 1,2-cis-disubstituted cyclopropanes and 3) examples that clearly do not involve ruthenacyclohexene as intermediates as products still incorporate the cyclopropyl moiety. The scope and limitations of the Ru-catalyzed cycloaddition are discussed and compared with the Rh-catalyzed reaction. The potential power of this methodology towards natural product total synthesis is demonstrated by the formation of several polycyclic systems with the chosen reaction conditions and readily available cyclopropylenyne substrates.     

Reactions of a carbene stabilised indium trihydride complex, [InH3{CN(Mes)C2H2N(Mes)}] Mes = mesityl,with transition metal complexes

The reactivity of the carbene stabilised indium trihydride complex, [InH₃(IMes)] IMes = 1,3-dimesitylimidazol-2-ylidene, toward a variety of transition metal complexes has been investigated. The study has shown that the InH₃ complex can act as a carbene and/or hydride transfer reagent to transition metal centres but does not yield heterobimetallic materials. Two new complexes, [Cp₂Ti(-Cl)₂Zn(IMes)Cl] and [CpNi(H)(IMes)], have resulted from this work, both of which have been spectroscopically and structurally characterised.     

Single-ion magnetism in the extended solid-state: insights from X-ray absorption and emission spectroscopy

Large single-ion magnetic anisotropy is observed in lithium nitride doped with iron. The iron sites are two-coordinate, putting iron doped lithium nitride amongst a growing number of two coordinate transition metal single-ion magnets (SIMs). Uniquely, the relaxation times to magnetisation reversal are over two orders of magnitude longer in iron doped lithium nitride than other 3d-metal SIMs, and comparable with high-performance lanthanide-based SIMs. To understand the origin of these enhanced magnetic properties a detailed characterisation of electronic structure is presented. Access to dopant electronic structure calls for atomic specific techniques, hence a combination of detailed single-crystal X-ray absorption and emission spectroscopies are applied. Together K-edge, L_2,3-edge and Kβ X-ray spectroscopies probe local geometry and electronic structure, identifying iron doped lithium nitride to be a prototype, solid-state SIM, clean of stoichiometric vacancies where Fe lattice sites are geometrically equivalent. Extended X-ray absorption fine structure and angular dependent single-crystal X-ray absorption near edge spectroscopy measurements determine Fe^I dopant ions to be linearly coordinated, occupying a D_6h symmetry pocket. The dopant engages in strong 3dπ-bonding, resulting in an exceptionally short Fe–N bond length (1.873(7) Å) and rigorous linearity. It is proposed that this structure protects dopant sites from Renner–Teller vibronic coupling and pseudo Jahn–Teller distortions, enhancing magnetic properties with respect to molecular-based linear complexes. The Fe ligand field is quantified by L_2,3-edge XAS from which the energy reduction of 3d_z² due to strong 4s mixing is deduced. Quantification of magnetic anisotropy barriers in low concentration dopant sites is inhibited by many established methods, including far-infrared and neutron scattering. We deduce variable temperature L₃-edge XAS can be applied to quantify the J = 7/2 magnetic anisotropy barrier, 34.80 meV (∼280 cm⁻¹), that corresponds with Orbach relaxation via the first excited, M_J = ±5/2 doublet. The results demonstrate that dopant sites within solid-state host lattices could offer a viable alternative to rare-earth bulk magnets and high-performance SIMs, where the host matrix can be tailored to impose high symmetry and control lattice induced relaxation effects.

Taking advantage of synchrotron light source methods, we present the geometric and electronic structure of iron doped in lithium nitride.     

“东北水三七”中化学元素的分析

用原子吸收光谱法测下了“东北水三七”根、茎、叶的21种化学元素,结果表明,不同部位的元素含量有一定差别。     

Elliptic Genera of Level N and Elliptic Cohomology

Elliptic genera of level N have been defined by F. Hirzebruch,generalising the earlier notion of elliptic genus due to S.Ochanine. We show that there are corresponding elliptic cohomologytheories which are naturally associated to such genera and thatthese are obtained from the level 1 case by algebraic extensionof the coefficient rings from level 1 to level N modular forms.     

Functional Equations and Weierstrass Transforms

The purpose of this article is to illustrate the utility of the Weierstrass transform in the study of functional equations (and systems) of the form 1 $${\mathop \sum^N\limits_{k=0}}\alpha_{k}f(x+r_{k})=f_{0}(x)\ \ \ \, x\in\ {\rm R}.$$ One may think of α₀, α₁,…, α_N as given complex numbers, r₀, r₁,…, r_N as given real numbers, ?₀: ? → C as a given function and ? as the unknown.     

A Bruen chain forq=19

The one-to-one correspondence between the class of two-dimensional translation planes of orderq ² and the collection of spreads ofPG(3,q) has long provided a natural context for describing new planes. The method often used for constructing interesting spreads is to start with a regular spread, corresponding to a desarguesian plane, and then replace some nice subset of lines by another partial spread covering the same set of points. Indeed the first approach was replacing the lines of a regulus by the lines of its opposite regulus, or doing this process for a set of disjoint reguli. Nontrivial generalizations of this idea include thechains of Bruen and thenests of Baker and Ebert. In this paper we construct a replaceable subset of a regular spread ofPG (3, 19) which is the union of 11 reguli double covering the lines in their union, hence is a chain in the terminology of Bruen or a 11-nest in the Baker-Ebert terminology.     

On nonnegative solvability of linear operator equations

LetE be a Banach lattice having order continuous norm. Suppose, moreover,T is a nonnegative reducible operator having a compact iterate and which mapsE into itself. The purpose of this work is to extend the previous results of the authors, concerning nonnegative solvability of (kernel) operator equations on generalL ^p-spaces. In particular, we provide necessary and sufficient conditions for the operator equation x=T x+y to possess a nonnegative solutionxE wherey is a given nonnegative and nontrivial element ofE and is any given positive parameter.