Fine-tuning the electronic properties of highly stable organometallic Cu(III) complexes containing monoanionic macrocyclic ligands

A family of highly stable organometallic Cu(III) complexes with monoanionic triazamacrocyclic ligands (L(i)) with general formula [CuL(i)]+ have been prepared and isolated, and their structural, spectroscopic, and redox properties thoroughly investigated. The HL(i) ligands have been designed in order to understand and quantify the electronic effects exerted by electron donor and electron-withdrawing groups on either the aromatic ring or the central secondary amine or on both. In the solid state the Cu(III) complexes were mainly characterized by single-crystal X-ray diffraction analysis, whereas in solution their structural characterization was mainly based on 1H NMR spectroscopy given the diamagnetic nature of the d(8) square-planar Cu(III) complexes. Cyclic voltammetry together with 1H NMR and UV/Vis spectroscopy have allowed us to quantify the electronic effects exerted by the ligands on the Cu(III) metal center. A theoretical analysis of this family of Cu(III) complexes has also been undertaken by DFT calculations to gain a deeper insight into the electronic structure of these complexes, which has in turn allowed a greater understanding of the nature of the UV/Vis transitions as well as the molecular orbitals involved.     

Dibenzothiophenesulfilimines: A Convenient Approach to Intermolecular Rhodium-Catalysed C−H Amidation

A sulfilimine-based Group 9 transition-metal-catalysed C−H amidation procedure is reported. Dibenzothiophene-based sulfilimines were shown to constitute a class of novel amidation reagents which enable the transfer of a wide range of N-sulfonyl and N-acyl moieties. It was demonstrated that sulfilimines, which are easily accessible from cheap reagents, are safe-to-handle and represent broadly applicable amidation reagents. The dibenzothiophene can be recycled after use. The C−H amidation was shown to proceed with high selectivity and gave the mono-amidated products, mostly in good to excellent yields.     

Effects of long‐term exposure to elevated CO2 conditions in slow‐growing plants using a 12C‐enriched CO2‐labelling technique

Despite their relevancy, long‐term studies analyzing elevated CO₂ effect in plant production and carbon (C) management on slow‐growing plants are scarce. A special chamber was designed to perform whole‐plant above‐ground gas‐exchange measurements in two slow‐growing plants (Chamaerops humilis and Cycas revoluta) exposed to ambient (ca. 400 µmol mol^?1) and elevated (ca. 800 µmol mol^?1) CO₂ conditions over a long‐term period (20 months). The ambient isotopic ¹³C/¹²C composition (δ¹³C) of plants exposed to elevated CO₂ conditions was modified (from ca. ?12.8‰ to ca. ?19.2‰) in order to study carbon allocation in leaf, shoot and root tissues. Elevated CO₂ increased plant growth by ca. 45% and 60% in Chamaerops and Cycas, respectively. The whole‐plant above‐ground gas‐exchange determinations revealed that, in the case of Chamaerops, elevated CO₂ decreased the photosynthetic activity (determined on leaf area basis) as a consequence of the limited ability to increase C sink strength. On the other hand, the larger C sink strength (reflected by their larger CO₂ stimulatory effect on dry mass) in Cycas plants exposed to elevated CO₂ enabled the enhancement of their photosynthetic capacity. The δ¹³C values determined in the different plant tissues (leaf, shoot and root) suggest that Cycas plants grown under elevated CO₂ had a larger ability to export the excess leaf C, probably to the main root. The results obtained highlighted the different C management strategies of both plants and offered relevant information about the potential response of two slow‐growing plants under global climate change conditions. Copyright © 2008 John Wiley & Sons, Ltd.     

Covering point sets with two disjoint disks or squares

We study the following problem: Given a set of red points and a set of blue points on the plane, find two unit disks C_R and C_B with disjoint interiors such that the number of red points covered by C_R plus the number of blue points covered by C_B is maximized. We give an algorithm to solve this problem in O(n^8/3log²n) time, where n denotes the total number of points. We also show that the analogous problem of finding two axis-aligned unit squares S_R and S_B instead of unit disks can be solved in O(nlogn) time, which is optimal. If we do not restrict ourselves to axis-aligned squares, but require that both squares have a common orientation, we give a solution using O(n³logn) time.     

MPI+X: task-based parallelisation and dynamic load balance of finite element assembly

The main computing phases of numerical methods for solving partial differential equations are the algebraic system assembly and the iterative solver. This work focuses on the first task, in the context of a hybrid MPI+X paradigm. The matrix assembly consists of a loop over the elements, faces, edges or nodes of the MPI partitions to compute element matrices and vectors and then of their assemblies. In a MPI+X hybrid parallelism context, X has consisted traditionally of loop parallelism using OpenMP, with different techniques to avoid the race condition, but presenting efficiency or implementation drawbacks. We propose an alternative, based on task parallelism using some extensions to the OpenMP programming model. In addition, dynamic load balance will be applied, especially efficient in the presence of hybrid meshes. This paper presents the proposed methodology, its implementation and its validation through the solution of large computational mechanics problems up to 16k cores.     

Coexistence stability in a four-member hypercycle with error tail through center manifold analysis

Nonlinear Dynamics - Establishing the conditions allowing for the stable coexistence in hypercycles has been a subject of intensive research in the past decades. Deterministic, time-continuous...     

Phosphine–Alkene Ligands as Mechanistic Probes in the Pauson–Khand Reaction

An alkyne tetracarbonyl dicobalt complex with a chelated phosphine–alkene ligand, in which the phosphorus atom and the alkene from the ligand are attached to the same cobalt atom has been prepared, isolated, and characterized by X‐ray crystallography. The complex serves as a mechanistic model for an intermediate of the Pauson–Khand (PK) reaction. Although the alkene fragment is located in an equatorial coordination site with an appropriate orientation, and, therefore, should undergo insertion, it failed to give the PK product upon either thermal or N‐methylmorpholine N‐oxide activation. However, a phosphine–alkene complex that contains a terminal alkene readily provided the corresponding PK product. We attribute this change in reactivity to the different ability of each olefin to undergo 1,2‐insertion. These results provide further insights into the factors that govern a crucial step in the PK reaction, the olefin insertion.