Creating novel ligand libraries from air-stable, chiral primary phosphines

PhD ThesisThe fearsome reputation of primary phosphines, many of which are toxic and highly reactive towards atmospheric oxygen, has constrained the use of these versatile compounds in synthetic chemistry. However, a few examples of user-friendly stable primary phosphines have been reported which owe their stability to high steric encumbrance or is as yet unexplained. Recently an electronic stabilisation has allowed for the synthesis of novel MOPtype phosphorus ligands with previously inaccessible architectures that have potential applications in homogeneous asymmetric catalysis; an introduction into the topic is given in Chapter 1. The first air-stable chiral primary phosphines 1a,b were developed in our labs. We subsequently simplified and improved the synthetic approach to afford these and previously unreported synthons on a multigram scale, which is described in Chapter 2. Phosphiranes are highly strained heterocycles with a small sum of bond angles at the phosphorus (Σ°(P): <260). They act as ligands with interesting properties upon metal complexation due to the unusual electronics they possess as a result of the imposed ring strain; this leads to high s-character at the phosphorus and both lowered HOMO and LUMO energy levels compared to their acyclic counterparts. In Chapter 3 we report the synthesis of chiral binaphthyl-phosphirane ligands 14a,b offering high thermal and air stability, as well as the synthesis and solid state structures of their platinum(II) dichloride complexes. Initial findings for the application of the phosphiranes in the palladium catalysed asymmetric hydrosilylation of styrene are discussed. Furthermore, we were able to synthesise MOP-dimethylphosphine, MOP-bis(dimethylamino) phosphine and MOP-dimethylphosphonite ligands in one-pot reactions from 1a,b. Their peculiar structural and electronic parameters, in addition to those of MOP-phosphiranes 14a,b, are discussed in Chapter 4. The coordination chemistry of these compounds was investigated on platinum(II) and palladium(II) metals elucidating their cis/trans influences III and aryl side-on coordination respectively. We also carried out comparative studies in the allylic alkylation of (rac)-(E)-1,3-diphenylallyl acetate and the hydrosilylation of styrene, utilising palladium complexes of those MOP-type ligands as asymmetric catalysts. In Chapter 5 we report the efficient synthesis of novel MOP-phosphonite hybrid ligands 33a,b and 34a,b which incorporate two binaphthyl groups around the single phosphonite P-donor. We present their methallylpalladium complexes, which were studied in detail both in the solid-state and in solution. The palladium catalysed asymmetric hydrosilylation of styrene was again carried out and the results analysed in view of the molecular structure of the ligands. Furthermore, rhodium complexes of the same ligands were investigated, in particular with a view to examining their binding behaviour towards the metal. An unusual aromatic side-on binding mode was revealed by X-ray crystallography and further elucidated in solution by extended NMR experiments. Solution NMR studies also revealed a dynamic behaviour of these complexes, triggered by the hemilabile binding of the ligands towards the metal centre. Finally, we describe the synthesis of novel MOP-phosphonodichalcogenoite and MOP-phosphaalkene ligands in Chapter 6. Their corresponding gold(I) complexes were prepared and representative examples were characterised by X-ray diffraction. For the MOP-phosphonodiselenoite derivatives we also report the characteristic 77Se NMR data.financial support that was provided by Lee through his EPSRC grant, which allowed me to present my work at the ACS National Meeting 2011 in Anaheim (CA, USA), and the Dalton Transactions Younger Researchers Symposium 2011 at the University of Warwick (UK); I was also able to get funding awarded by PhoSciNet (COST action CM0802) to deliver an oral presentation at the 9th European Workshop on Phosphorus Chemistry 2012 in Rennes (France)

Detection of Chemical Warfare Agents with a Miniaturized High-Performance Drift Tube Ion Mobility Spectrometer Using High-Energetic Photons for Ionization

A growing demand for low-cost gas sensors capable of detecting the smallest amounts of highly toxic substances in air, including chemical warfare agents (CWAs) and toxic industrial chemicals (TICs), has emerged in recent years. Ion mobility spectrometers (IMS) are particularly suitable for this application due to their high sensitivity and fast response times. In view of the preferred mobile use of such devices, miniaturized ion drift tubes are required as the core of IMS-based lightweight, low-cost, hand-held gas detectors. Thus, we evaluate the suitability of a miniaturized ion mobility spectrometer featuring an ion drift tube length of just 40 mm and a high resolving power of Rp= 60 for the detection of various CWAs, such as nerve agents sarin (GB), tabun (GA), soman (GD), and cyclosarin (GF), as well as the blister agent sulfur mustard (HD), the blood agent hydrogen cyanide (AC) and the choking agent chlorine (CL). We report on the limits of detection reaching minimum concentration levels of, for instance, 29 pptvfor sarin (GB) within an averaging time of only 1 s. Furthermore, we investigate the effects of precursors, simulants, and other common interfering substances on false positive alarms

Real‐time remote detection of airborne chemical hazards – an unmanned aerial vehicle (UAV) carrying an ion mobility spectrometer

Rapidly detecting and identifying chemical agents after a chemical release is crucial for a reliable assessment of imminent risks and provides the initial basis for defining an adequate level of protection for first responders. An unmanned / uncrewed aerial vehicle (UAV) equipped with gas detectors may quickly explore the contaminated area without exposing any first responders to the yet unknown threat. However, UAVs possess limitations in their capability concerning payload, operational range, and power requirements. Choosing the appropriate gas sensors for this application, thus, imposes significant technical challenges. In this work, we present a mobile ion mobility spectrometer (IMS) designed for operation with UAVs. The IMS is equipped with a dedicated closed gas loop, high-performance driver electronics, and wireless data transmission capabilities. The resulting performance of the UAV-mounted mobile IMS is characterized in the lab with the chemical warfare agents (CWAs) sarin (GB), tabun (GA), soman (GD), cyclosarin (GF), and sulfur mustard (HD), and further evaluated in three different field-testing scenarios using the simulation compound di(propylene glycol) methyl ether (DPM). It is thereby used to monitor the area near (i) a point source continuously emitting small quantities of a gaseous chemical, (ii) a point source suddenly releasing a limited quantity of a chemical as an aerosol, and (iii) a minor contamination of a liquid chemical on the ground. The results obtained in this work enable a well-founded estimation of the capabilities and limitations of the UAV-mounted mobile IMS concerning the real-time remote detection of chemical hazards such as CWAs

Air-Stable Chiral Primary Phosphines: A Gateway to MOP Ligands with Previously Inaccessible Stereoelectronic Profiles

The air-stable chiral primary phosphines <b>1a</b>,<b>b</b> facilitate the synthesis of previously inaccessible or hard-to-access chiral MOP-type ligands <b>2a</b>,<b>b</b>–<b>5a</b>,<b>b</b>, which can be prepared in one-pot reactions. These derivatives have been prepared to allow for a unique comparison of their differing structural and electronic profiles, determined here by a number of experimental and theoretical studies. Phosphiranes <b>2a</b>,<b>b</b> and phosphonites <b>5a</b>,<b>b</b> are electron-poor compounds, with the former possessing exceptional thermal stability. Conversely, the dimethylarylphosphines <b>3a</b>,<b>b</b> and bis­(dimethylamino)­arylphosphines <b>4a</b>,<b>b</b> are good electron donors, and, in contrast to earlier reports, the dialkylarylphosphines were found to be remarkably air-stable. The ligands were coordinated to platinum­(II), and the weak <i>trans</i>-influence of the highly strained phosphiranes <b>2a</b>,<b>b</b> was revealed both in solution and in the solid state. The steric parameters of the ligands were investigated by the allyl rotation of their methallylpalladium­(II) complexes, which showed subtle differences in exchange rates. Aryl side-on coordination of the MOP-backbone to palladium­(II) was observed for complexes with a non-coordinating counterion and structurally analyzed in the case of ligand <b>4b</b>. The asymmetric induction and catalytic activity of <b>2a</b>,<b>b</b>–<b>5a</b>,<b>b</b> were tested in the hydrosilylation of styrene as well as the allylic alkylation of (<i>rac</i>)-(<i>E</i>)-1,3-diphenylallyl acetate. Major differences in reactivity were related back to the electronic parameters of the ligands

SETTING P-DONOR LIGANDS INTO CONTEXT: AN APPLICATION OF THE LIGAND KNOWLEDGE BASE (LKB) APPROACH

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Synthesis and characterization of chiral phosphirane derivatives of [(μ-H)4Ru4(CO)12] and their application in the hydrogenation of an α,β-unsaturated carboxylic acid

Ruthenium clusters containing the chiral binaphthyl-derived mono-phosphiranes [(S)-([1,1'-binaphthalen]-2-yl)phosphirane] (S)-1a, [(R)-(2'-methoxy-1,1'-binaphthyl-2-yl)phosphirane] (R)-1b, and the diphosphirane [2,2'-di(phosphiran-1-yl)-1,1'-binaphthalene] (S)-1c have been synthesized and characterized. The clusters are [(μ-H)4Ru4(CO)11((S)-1a)] (S)-2, [(μ-H)4Ru4(CO)11((R)-1b)] (R)-3, 1,1-[(μ-H)4Ru4(CO)10((S)-1c)] (S)-4, [(μ-H)4Ru4(CO)11((S)-binaphthyl-P(s)(H)Et)] (S,S p)-5, [(μ-H)4Ru4(CO)11((S)-binaphthyl-P(R)(H)Et)] (S,R p)-6, [(μ-H)4Ru4(CO)11((R)-binaphthyl-P(s)(H)Et)] (R,S p)-7, [(μ-H)4Ru4(CO)11((R)-binaphthyl-P(R)(H)Et)] (R,R p)-8 and the phosphinidene-capped triruthenium cluster [(μ-H)2Ru3(CO)9(PEt)] 9. Clusters 5-8 are formed via hydrogenation and opening of the phosphirane ring in clusters (S)-2 and (R)-3. The phosphirane-substituted clusters were found to be able to catalyze the hydrogenation of trans-2-methyl-2-butenoic acid (tiglic acid), but no enantioselectivity could be detected. The molecular structures of (S)-4, (R,S p)-7 and 9 have been determined and are presented