Aspects of the transition metal coordination chemistry of phenylphosphine

This thesis describes the synthesis and reactions of phosphido complexes of both the early and late transition-metals. The thermal reaction of dodecacarbonyltriruthenium with phenylphosphine (and its cyclohexyl analogue) was investigated and new trinuclear clusters with combinations of terminal phosphine, bridging phosphido and μ3-phosphinidene ligands were isolated. These have been characterised by n.m.r. methods and the single-crystal structures of [Ru3 (μ-H)2(μ3-PPh)(PPhH2)(CO)8] and [Ru3(μ-H)(μ-PPhH)3(CO)7] have been deduced. The pyrolysis of [Ru3(m-PPh)2(CO)9] was investigated and was found to yield new hexanuclear clusters of which the fluxional trigonal prismatic structures [Ru6(μ3-H)2(μ3-PPh)2(μ4-PPh)2(CO)12] and [Ru6(μ3-PPh)2(μ4-PPh)2(CO)12] have been crystallographically determined. Their metal frameworks were found to have interesting features and are compared with the known structure [Ru6(μ3-PPh)2(μ4-PPh)3(CO)12]. We have synthesised the terminal phosphine complexes [IrCl2(PMe2Ph)3(PHR1R2)][ClO4] (R1 = R2 = H, R1 = H R2 = Ph, R1 = R2 = Ph) and these were found to deprotonate readily in the presence of base to afford the corresponding neutral phosphido complexes. Reactions of these phosphido complexes with both organic and metallic electrophiles was investigated and the crystal structure of [{IrCl2(PMe2Ph)3(PH2)}2Au][ClO4] was determined. Investigating the origin of the broad n.m.r. spectrum of [IrCl2(PMe2Ph)4][ClO4] (formed from the reaction of the phosphido complex [IrCl2(PMe2Ph)3(PPhMe)] with MeI) afforded evidence for at least three isomers in solution at low-temperature. The low temperature 31P-{1H} n.m.r. spectrum and its 31P-31P DQCOSY spectrum recorded at -75 °C have been analyzed in terms of these conformational isomers. Further investigations of the tetrakis-phosphine complexes [IrCl2(PMe3)3(PMe2Ph)][ClO4] and [IrCl2(PMe3)3(PMePh2)][ClO4] also showed the presence of rotational isomers. A controlled synthesis of the cluster [Os3(μ-H)(μ-PPhMe)(CO)10] is reported and the reactions of the anionic phosphinidene cluster [Os3(μ-H)(μ-PPh)(CO)10] with electrophiles are included. Reaction of the anion with methyliodide gave [Os3(μ-H)(μ- PPhMe)(CO)10] characterised crystallographically and found to contain an endo phenyl group indicating inversion of stereochemistry at phosphorus. The crystal structure of [{Os3(μ3-PPh)(CO)10}2Hg] is described. Reaction of the anionic phosphido complex [Mo(CO)5(PPhH)] with the metal electrophiles [PtCl2(dppe)] and [PtCl2(Pet3)2] was seen to be simple nucleophilic substitution at the platinum(II) centres. A single major product isolated from the reaction of the [Mo(CO)5(PPhH)]- with [PtCl2(dppe)] was isolated. The single-crystal X- ray structure of this compound revealed it to be [Pt(μ-PPhH)2{Mo(CO)5}2(dppe)]. 31P{1H) n.m.r. studies of this complex confirmed the existence of two diastereoisomers and these have been separated using preparative HPLC techniques. We have also shown that these complexes exist as several rotameric isomers in solution giving rise to broad n.m.r. signals in the 31P{1H} n.m.r. spectrum. The synthesis of [Pt(μ-PPhH)2{Mo(CO)5)2(PPh2C2H2PPh2)] and [Pt(μ-PPh)2{Mo(CO)4}(dppe)] reinforced the above proposal regarding rotamers in solution and these compounds are observed to occur in both possible diastereoisomeric forms. Three products have been identified from the reaction of [Mo(CO)5(PPhH)]- with [PtCl2(PEt3)2] and extensive 31P{1H} n.m.r. investigations carried out. The single-crystal X-ray structures of the two products [Pt(μ- PPhH){Mo(CO)5}Cl(PEt3)2] and trans-[Pt(μ-PPhH)2{Mo(CO)5}2(PEt3)2] have been determined. Variable-temperature 31P{1H} n.m.r. studies have shown the former complex to exist in three rotameric forms in solution and these are rapidly exchanging at room temperature. The trinuclear complex [Pt(μ-PPhH)2{Mo(CO)5)2}(PEt3)2] was identified in both cis and trans forms, the former isomer was identified by n.m.r. methods whilst the single-crystal X-ray structure of the trans isomer was determined. The 31P{1H} n.m.r. spectrum of trans-[Pt(μ-PPhH)2{Mo(CO)5}2(PEt3)2] revealed the existence of two diastereiosomeric forms

Spatio-temporal bivariate statistical models for atmospheric trace-gas inversion

Atmospheric trace-gas inversion refers to any technique used to predict spatial and temporal fluxes using mole-fraction measurements and atmospheric simulations obtained from computer models. Studies to date are most often of a data-assimilation flavour, which implicitly consider univariate statistical models with the flux as the variate of interest. This univariate approach typically assumes that the flux field is either a spatially correlated Gaussian process or a spatially uncorrelated non-Gaussian process with prior expectation fixed using flux inventories (e.g., NAEI or EDGAR in Europe). Here, we extend this approach in three ways. First, we develop a bivariate model for the mole-fraction field and the flux field. The bivariate approach allows optimal prediction of both the flux field and the mole-fraction field, and it leads to significant computational savings over the univariate approach. Second, we employ a lognormal spatial process for the flux field that captures both the lognormal characteristics of the flux field (when appropriate) and its spatial dependence. Third, we propose a new, geostatistical approach to incorporate the flux inventories in our updates, such that the posterior spatial distribution of the flux field is predominantly data-driven. The approach is illustrated on a case study of methane (CH$_4$) emissions in the United Kingdom and Ireland.Comment: 39 pages, 8 figure

Brief Announcement: Generalising Concurrent Correctness to Weak Memory

Correctness conditions like linearizability and opacity describe some form of atomicity imposed on concurrent objects. In this paper, we propose a correctness condition (called causal atomicity) for concurrent objects executing in a weak memory model, where the histories of the objects in question are partially ordered. We establish compositionality and abstraction results for causal atomicity and develop an associated refinement-based proof technique

Low Gain Avalanche Detectors (LGAD) for particle physics and synchrotron applications

A new avalanche silicon detector concept is introduced with a low gain in the region of ten, known as a Low Gain Avalanche Detector, LGAD. The detector's characteristics are simulated via a full process simulation to obtain the required doping profiles which demonstrate the desired operational characteristics of high breakdown voltage (500 V) and a gain of 10 at 200 V reverse bias for X-ray detection. The first low gain avalanche detectors fabricated by Micron Semiconductor Ltd are presented. The doping profiles of the multiplication junctions were measured with SIMS and reproduced by simulating the full fabrication process which enabled further development of the manufacturing process. The detectors are 300 μm thick p-type silicon with a resistivity of 8.5 kΩcm, which fully depletes at 116 V. The current characteristics are presented and demonstrate breakdown voltages in excess of 500 V and a current density of 40 to 100 nAcm−2 before breakdown measured at 20oC. The gain of the LGAD has been measured with a red laser (660 nm) and shown to be between 9 and 12 for an external bias voltage range from 150 V to 300 V

Owicki-Gries Reasoning for C11 RAR (Artifact)

The paper "Owicki-Gries Reasoning for C11 RAR" introduces a new proof calculus for the C11 RAR memory model that allows Owicki-Gries proof rules for compound statements, including non-interference, to remain unchanged. The proof method features novel assertions specifying thread-specific views on the state of programs. This is combined with a set of Hoare logic rules that describe how these assertions are affected by atomic program steps. The artifact includes the Isabelle formalisation of the proof method introduced in the paper. It also contains the formalisation and proof of all case studies presented in the paper. All of the theorems are accompanied with their respective proofs

Gametocyte carriage in Plasmodium falciparum-infected travellers.

BACKGROUND: Gametocytes are the sexual stage of Plasmodium parasites. The determinants of gametocyte carriage have been studied extensively in endemic areas, but have rarely been explored in travellers with malaria. The incidence of gametocytaemia, and factors associated with gametocyte emergence in adult travellers with Plasmodium falciparum malaria was investigated at the Hospital for Tropical Diseases in London. METHODS: Clinical, parasitological and demographic data for all patients presenting with P. falciparum malaria between January 2001 and December 2011 were extracted from a prospective database. These data were supplemented by manual searches of laboratory records and patient case notes. RESULTS: Seven hundred and seventy three adult patients with laboratory-confirmed P. falciparum malaria were identified. Four hundred and sixty five (60%) were born in a country where malaria is endemic. Patients presented to hospital a median of four days into their illness. The median maximum parasite count was 0.4%. One hundred and ninety six patients (25%) had gametocytes; 94 (12%) on admission, and 102 (13%) developing during treatment. Gametocytaemia on admission was associated with anaemia and a lower maximum parasitaemia. Patients with gametocytes at presentation were less likely to have thrombocytopenia or severe malaria. Patients who developed gametocytes during treatment were more likely to have had parasitaemia of long duration, a high maximum parasitaemia and to have had severe malaria. There was no apparent association between the appearance of gametocytes and treatment regimen. CONCLUSIONS: The development of gametocytaemia in travellers with P. falciparum is associated with factors similar to those reported among populations in endemic areas. These data suggest that acquired immunity to malaria is not the only determinant of patterns of gametocyte carriage among patients with the disease

Owicki-Gries Reasoning for C11 RAR

Owicki-Gries reasoning for concurrent programs uses Hoare logic together with an interference freedom rule for concurrency. In this paper, we develop a new proof calculus for the C11 RAR memory model (a fragment of C11 with both relaxed and release-acquire accesses) that allows all Owicki-Gries proof rules for compound statements, including non-interference, to remain unchanged. Our proof method features novel assertions specifying thread-specific views on the state of programs. This is combined with a set of Hoare logic rules that describe how these assertions are affected by atomic program steps. We demonstrate the utility of our proof calculus by verifying a number of standard C11 litmus tests and Peterson’s algorithm adapted for C11. Our proof calculus and its application to program verification have been fully mechanised in the theorem prove