Fischer dinuclear and mononuclear bis-carbene complexes of thiophene and thiophene derivatives

The reaction of dilithiated thiophene and thiophene derivatives with group 6 transition metal carbonyl precursors and subsequent alkylation afforded linearly arranged Fischer 2,5-bis-carbene and the rare unsymmetrical 2,3-bis-carbene chelated complexes. The latter requires a second lithiation to occur at an adjacent, less reactive site on the thiophene ring. The control of reactivity sites was investigated and achieved by either blocking more reactive positions with substituents or activating less reactive positions by lithium−halogen exchange reactions. A series of Fischer bis-carbene chelates were synthesized by manipulating the above variables. Structural features of Fischer mono-carbene, mononuclear bis-carbene, and bis-carbene chelated complexes were studied by IR, NMR, and single-crystal X-ray diffractionThe National Research Foundation of South Africa under Grant No. 73679 (S.L.)http://pubs.acs.org/journal/orgnd7hb2017ChemistryChurch History and Church PolicyCivil EngineeringClinical Epidemiolog

Cobalt silicide formation on a Si(1 0 0) substrate in the presence of an interfacial (Fe90Zr10) interlayer

The reaction between a thin film (126 nm) of Co and Si has been studied at 450 C for 24 h under high vacuum conditions, in the presence of a FeZr barrier layer. Without a diffusion barrier layer between Co and Si, Co2Si forms at 350 C as the initial phase while CoSi2 forms at 550 C. The FeZr barrier layer changed the flux of atoms arriving at the reaction interface. Co reacted with the Si from the substrate and formed a mixed layer of CoSi and CoSi2 in the interlayer region. The use of the FeZr diffusion barrier has been demonstrated to lower the temperature formation of CoSi2 to 450 C. The reactions were characterised by Rutherford backscattering spectrometry, Auger electron spectroscopy depth profiling, X-ray diffraction using CoKa radiation and scanning electron microscopy.http://www.elsevier.com/locate/nimb2016-09-30hb201

How sustainable is road transport in Gauteng, South Africa? An analysis of the R59 from the perspective of traffic volumes and vehicle loading

Abstract: The transport of freight or goods by truck (heavy vehicles) is a worldwide phenomenon. In South Africa an increase in the number of heavy vehicles, the number of axles the trucks have, as well as, an increase in the mass of goods carried by trucks has taken place. During the 1930’s until the 1980’s, the transport of freight by government owned railways was favoured over road freight transport, until transport deregulation started in the 1980’s. Deregulation focussed only on the technical and safety aspects of trucking, ignoring critical issues such the impact of trucking on freight costs; road infrastructure and negative environmental impacts. Excessive growth of road transport begs the question: how sustainable is road transport in South Africa? This study sought to determine this by undertaking an in-depth study of one important road in Gauteng, namely the R59, which links Vanderbijlpark/Vereeniging, Meyersdal, Alberton and Johannesburg. The study documents the current traffic characteristics and road usage for the R59 for the years 2004 - 2013, creating, for the first time, a traffic baseline data against which future increases or impacts can be measured. The study made use of data supplied by Gautrans and was collected by seven traffic counting stations along the Gauteng stretch of road. Six of these are secondary stations (which are operational for one week only during a year), and one is a permanent station (operated all year). The study posits that the pavement of this road is an asphalt mix, with an original design life of 20 years. The road was partly rehabilitated and resurfaced in 1996 – 1997 and in 2005 – 2006. The study shows a steady increase in traffic volumes overtime with some vehicles consistently speeding. There is a surprisingly large urban commute of people travelling from Vanderbijlpark/Vereeniging north to work and back each day. The proposed future tolling of the route will have a serious negative impact on these commuters. The R59 is also a key trucking route, carrying a significant number of long heavy trucks, and overloading is a chronic problem. This overloading is leading to visible pavement damage, in the form of cracking, formation of potholes and bleeding. The study demonstrates that the road was under-designed for the current traffic type; it is under-maintained and under-managed. The study calls for better and more consistent rehabilitation, alongside active traffic management - controlling overloading by having a manned weighbridge and imposing hefty fines on those breaking the law - if the road is to be sustainably managed into the future.M.Sc. (Environmental Management

Thiophene bimetallic carbene complexes

The syntheses of σ,σ-bimetallic biscarbene- and a, σ π -bimetallic monocarbene complexes, as well as the reactivity of the former, were investigated. The metal carbonyls Cr(C0)6, W(C0)6, Mn ( n5-C5H4Me)(C0)3 and Mn(n5-C5H5)(C0)3 were reacted with dilithiated thiophene to synthesize the novel σ,σ -bimetallic biscarbene complexes: (C0)2L3M{C(OEt)C4H2SC(OEt)}MLlC0)2, where M = Cr, W, Mn; L =CO; = n5-C5H4Me, n5-C5H5. With dilithiated 2,2'-methylene dithiophene; (C0)2L3M{C(OEt)C4H2SCH2C4H2SC( OEt)} ML3 CO )2, were obtained. These complexes were fully characterized and formulations were confirmed by ctystal structure determinations for the former. Spectroscopic data indicate the thiophene rings to act as sources of electron density which stabilize the electrophilic carbene carbons. Treatment ofmonolithiated (n5-thiophene)Cr(C0)3 with hexacarbonyls afforded in addition to the expected a,1t-bimetallic monocarbene complexes, (n1:n5-C4H3SC(OEt)M(C0)5)Cr(C0)3, the complexes (n5 : n5-C4H3SC( O(CH2}40Et)M(C0)5)Cr(C0)3 and M { C(O(CH2)40Et)C4H3S }(C0)5, where M = Cr, W. The formation of the latter two types is most unexpected and indicates that -rt-coordination of Cr(C0)3 to thiophene plays an important electronic and steric role which leads to an unique pathway in which a THF-ring is opened and incorporated into the carbene functionality. The a,1t-bimetallic monocarbene complex of (n6-benzo[b]thiophene) Cr(C0)3 was synthesized to enable a comparison with the former. Monolithiation of (n6-benzo[b]thiophene)Cr(C0)3 occured in the 2-position of the thiophene ring and (n1 : n6 C8H5SC(OEt)Cr(C0)5)Cr( C0)3 was afforded in a quantitative yield, thereby proving that -rt-coordination to the benzene ring is stronger and more distant from the a-bonded metal fragment. Related THF-incorporated complexes were not formed in this reaction. The stability of the thienylene biscarbene complexes at various temperatures, in different solvents and under two different inert atmospheres, led to the characterization of the following classes of complexes: I: (C0)2L3M{C(OEt)C4H2SC(O)OEt}; II: W{C(OEt)C4H2SC(OEt)C4H2SC(OEt)C4H2SC(O)OEt}(C0)5; III: (C0)2L3M{C(OEt)C4H2SC(S)OEt}; IV: M{C(OEt)C4H2S-3-[2,5-{C(S)OEt}2C4HS}(C0)2; V: Cr{C( OEt)C4H2SC(O)C(O)C4H2SC(O)OEt}(C0)5 . I was obtained from the decomposition in acetone under nitrogen and was presumably formed in the reaction between the carbene moiety and oxygen which had diffused into the system, as no proof of an oxygen transfer from acetone could be found. II was isolated from the analogous decomposition under argon, thus indicating that the complete elimination of oxygen from a better equiped system would lead to the formation of new and different types of oligomeric products. III was afforded by the reaction in CS2, with the exception of IV, which was yielded, for the chromium biscarbene in CS2, as well as, hexane. V was isolated from the decomposition in hexane. The result of these studies indicates that as opposed to monocarbene complexes, biscarbene complexes displayed enhanced reactivity and the reaction conditions control conversion. The reaction of the thienylene chromium and tungsten biscarbenes with hex-3-yne yielded analogous monocarbene products, M{C(OEt)CCHCC(OH)C(Et)C(Et)C(OEt)CS}(C0)5, lacking a TI-coordinated Cr(CO)3. This is a surprising result for tungsten as the expected product should be the cyclopentathienyl complex. The result suggests an alternative mechanism for the Dotz reaction and a possible reaction route is proposed. The reaction of biphenyl acetylene, however, afforded the expected cyclopentathienyl complex, M{C(OEt)CCHCC(Ph)C(Ph)CH(OEt)CS}(CO)5, in two isomeric forms. The analogous chromium reaction gave the related cyclopentathienyl product, as well as, the expected benzothienyl complex, as two isomers, with Cr(CO)3 TI-coordinated to either the benzene- or thiophene ring , and the end product lacking the Cr(CO)3-fragment. The isolation of the alkyne inserted intermediate, (CO)5Cr{C(OEt)C4H2SC(OEt)C(Ph)C(Ph) }Cr(CO)5, emphasises that the stabilization of intermediates by coordination to more than one metal fragment, highlights the value of bimetallic systems in studying reaction mechanisms.Thesis (DPhil)--University of Pretoria, 1996.ChemistryDPhilUnrestricte

C-language package for standalone embedded atom method molecular dynamics simulations of fcc structures

AbstractAb-initio molecular dynamics (MD) employs Newtonian mechanics to model and simulate the time evolution of particle trajectories in material science ensembles using a differentiable potential function. Although commercial and free packages exist for MD, their heuristic nature prevents dissection. This open-source C-language package arose out of the interest to study effects of embedded atoms in metallic face-centered cubic structures (fcc) on a standalone computer. The algorithms use velocity–time integration to output instantaneous particle parameters for up to several thousands of particles in the NVT ensemble. The functions are coded in a reusable and redistributable standalone header library file

Microstructure engineering of Pt-Al alloy thin films through Monte Carlo simulations

A kinetic algorithm, based on the regular solution model, was used in conjunction with the Monte Carlo method to simulate the evolution of a micro-scaled thin film system during exposure to a high temperature environment. Pt-Al thin films were prepared via electron beam physical vapor deposition (EB-PVD) with an atomic concentration ratio of Pt63:Al37. These films were heat treated at an annealing temperature of 400 °C for 16 and 49 minutes. Scanning Auger Microscopy (SAM) (PHI 700) was used to obtain elemental maps while sputtering through the thin films. Simulations were run for the same annealing temperatures and thin-film composition. From these simulations theoretical depth profiles and simulated microstructures were obtained. These were compared to the experimentally measured depth profiles and elemental maps

Electronic sample-and-hold circuit to minimize artifacts during high-temperature Auger electron spectroscopy measurements

An electronic sample-and-hold circuit to minimize artifacts during high-temperature Auger electron spectroscopy measurements was presented. The accurate control of sample temperature was achieved during Auger electron spectroscopy by pulsed heater current. Results showed that the output of the lock-in-amplifier responded to the pulsed current as a differentiation circuit