The synthesis and coordination chemistry of bulky beta-triketimines and application of their nickel(II) derivatives as ethylene polymerisation catalysts

The reaction of imidoyl chlorides IMC1-9 with lithium β-diketiminates Li(BDKx) (x = iPr, iPr2, tBu, Me3, iPr2/OMe) yields β-triketimines L1-16 which represent a new class of facially-coordinating neutral tridentate nitrogen ligands. The synthetic route is highly modular, allowing for wide variation of substitution patterns and thus fine control over the steric demands of the ligands. In all but two examples (L11 and L12) the β-triketimines exist in solution either solely as their enamine-diimine tautomers, or as equilibrium mixtures of the two. The processes of solution-phase equilibration have been studied by NMR spectroscopy. The molecular structures of L1, L10 and L11 are presented, and for each case a single differing tautomer or isomer is observed exclusively. The majority of the ligands yield fac-(L)M(CO)3 adducts upon reaction with group 6 metal carbonyls, except in cases of extreme steric bulk. The β-triketimines are relatively weak σ-donors, as determined by the CO stretching frequencies in (L)M(CO)3. The molecular structures of the isomorphous pair (L1)M(CO)3 (M = Cr, Mo) reveal porous infinite network arrangements generated by aryl-aryl and CH---OC interactions. The direct reaction of β-triketimines with ZnCl2 in most cases gives [(L)ZnCl]2[Zn2Cl6] complexes, whilst in the presence of either NaBArF4 or AgOTf the corresponding [(L)ZnCl][BArF4] and [(L)ZnCl][OTf] species are obtained. The complexes invariably feature four-coordinate, cationic zinc centres, except in the case of [(η4-L16)ZnCl][BArF4] where a five-coordinate complex is formed by additional coordination of a single ligand methoxy group. The reaction of [(L)ZnCl][BArF4] with TlOEt yielded not the desired zinc alkoxides, but novel [(L)Tl][BArF4] complexes, the solid-state structures of which display thallophilic interactions. The direct reaction of L8 and L10-12 with NiBr2(DME) gives the corresponding four-coordinate [(L)NiBr]2[NiBr4] complexes, whereas the products obtained with weakly-coordinating anions are dependent on the ligand bulk and the size of the anion. With the large BArF4- ion the formation of the five-coordinate dimeric [{(L)Ni(μ-Br)}2][BArF4]2 (L = L1, L3, L5, L7, L8, L12) is strongly favoured, except for the bulkiest ligands where the four-coordinate [(L)NiBr][BArF4] (L = L10, L11) are obtained. The smaller triflate ion generally favours the formation of [(L)NiBr][OTf] (L1, L8, L10-12) except in the case of [{(L)Ni(μ-Br)}2][OTf]2 (L = L3, L5). L15 and L16 act invariably as tetradentate donors to Ni(II), yielding the five-coordinate [(η4-L)NiBr][X] (X = BArF4, OTf) and [(η4-L16)NiBr]2[NiBr4]. The very bulky L6 coordinates in a bidentate mode to Ni(II), giving the four-coordinate [(η2-L6)NiBr(THF)][BArF4] and (η2-L6)NiBr2. [{(L)Ni(μ-Br)}2][BArF4]2 (L = L3, L5, L7), [{(L)Ni(μ-Br)}2][OTf]2 (L = L3, L5), [(η2-L6)NiBr(THF)][BArF4] and (η2-L6)NiBr2 show moderate catalytic activity for the polymerisation of ethylene in combination with MAO. All other complexes tested are inactive, either due to steric factors or the inability of certain β-triketimines to support catalytically active square-planar Ni(II) species. A proposed mechanism for catalyst activation is presented. Elastomeric polyethylene of very low crystallinity is obtained, with branching rates in the range 43-84 branches per 1000 C. 13C NMR spectroscopy reveals the presence of all short-chain branches from methyl to hexyl, as well as longer branches and pairs of branches.EThOS - Electronic Theses Online ServiceEPSRCGBUnited Kingdo

A five-membered PdSbn coordination series

Five complexes of the general formula PdCl2(SbMe2Cl)n (n = 1-5) have been synthesised by combining [PdCl2(MeCN)2] and SbMe2Cl in different molar ratios in toluene. Their solid-state structures have been determined by X-ray crystallography. The complexes display considerable structural diversity: [Pd4Cl8(SbMe2Cl)4] (1, n = 1) is a chloride bridged tetramer, [Pd2Cl4(SbMe2Cl)4] (2, n = 2) is a dimer, [PdCl(SbMe2Cl)2(SbMe2Cl2)] (3, n = 3) is a supramolecular polymer, [Pd2(SbMe2Cl)8]Cl4¬ (4, n = 4) is a loosely associated dimer and [Pd(SbMe2Cl)5]Cl2 (5, n = 5) is a monomer with square pyramidal PdSb5 coordination geometry. Each structure contains secondary interactions between coordinated Sb centres and chloride ligands or anions, resulting in five-coordinate Sb in all cases with a range of Sb∙∙∙Cl bond lengths. The electronic structures of these complexes have been investigated using DFT methods including NBO and Pipek-Mezey localised orbital methods in order to interrogate both the Sb-Pd and secondary Sb∙∙∙Cl bonding

Phase-change memory properties of electrodeposited Ge-Sb-Te thin film

We report the properties of a series of electrodeposited Ge-Sb-Te alloys with various compositions. It is shown that the Sb/Ge ratio can be varied in a controlled way by changing the electrodeposition potential. This method opens up the prospect of depositing Ge-Sb-Te super-lattice structures by electrodeposition. Material and electrical characteristics of various compositions have been investigated in detail, showing up to three orders of magnitude resistance ratio between the amorphous and crystalline states and endurance up to 1000 cycle

Continence for Women: Evaluation of AWHONN's Third Research Utilization Project

To develop an evidence-based protocol for initial evaluation and treatment of urinary incontinence and to design procedures that would facilitate the protocol's implementation into clinical practice. Design : Descriptive report of the Association of Women's Health, Obstetric and Neonatal Nurses (AWHONN) Continence for Women Project. Setting : Twenty-one public, private, and other women's health sites. Participants : Women in ambulatory care settings ( N = 1,474) provided demographic statistics. Methods : The protocol was developed, sites were selected, site coordinator training was provided, data collection was facilitated by project-specific tele-forms, and the overall process was evaluated by the science team. Main Outcome Measures : Site representation, patient representation, site coordinator feedback on the training program, and site coordinator experience during project implementation. Results : The process yielded a representative mix of site and patient diversity appropriate for testing of the protocol. Site coordinators felt well-prepared to implement the protocol and experienced increased professional satisfaction because of therapeutic benefits achieved for patients and positive collaboration with physicians. Conclusions : The Continence for Women Project demonstrated the potential for developing and testing evidence-based protocols for clinical practice when the resources of an organization such as AWHONN and the research community are combined.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74617/1/j.1552-6909.2000.tb02751.x.pd

Continence for Women: Evidence-Based Practice

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72009/1/j.1552-6909.1997.tb02719.x.pd

Revealing important nocturnal and day-to-day variations in fire smoke emissions through a multiplatform inversion

We couple airborne, ground-based, and satellite observations; conduct regional simulations; and develop and apply an inversion technique to constrain hourly smoke emissions from the Rim Fire, the third largest observed in California, USA. Emissions constrainedwithmultiplatform data show notable nocturnal enhancements (sometimes over a factor of 20), correlate better with daily burned area data, and are a factor of 2–4 higher than a priori estimates, highlighting the need for improved characterization of diurnal profiles and day-to-day variability when modeling extreme fires. Constraining only with satellite data results in smaller enhancements mainly due to missing retrievals near the emissions source, suggesting that top-down emission estimates for these events could be underestimated and a multi-platform approach is required to resolve them. Predictions driven by emissions constrained with multi-platform data present significant variations in downwind air quality and in aerosol feedback on meteorology, emphasizing the need for improved emissions estimates during exceptional events

Properties and evolution of biomass burning organic aerosol from Canadian boreal forest fires

Airborne measurements of biomass burning organic aerosol (BBOA) from boreal forest fires reveal highly contrasting properties for plumes of different ages. These measurements, performed using an Aerodyne Research Inc. compact time-of-flight aerosol mass spectrometer (C-ToF-AMS) during the BORTAS (quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites) experiment in the summer of 2011, have been used to derive normalised excess organic aerosol (OA) mass concentrations (ΔOA / ΔCO), with higher average ratios observed closer to source (0.190±0.010) than in the far-field (0.097±0.002). The difference in ΔOA / ΔCO between fresh and aged plumes is influenced by a change in dominant combustion conditions throughout the campaign. Measurements at source comprised 3 plume interceptions during a single research flight and sampled largely smouldering fires. Twenty-three interceptions were made across four flights in the far-field, with plumes originating from fires occurring earlier in the campaign when fire activity had been more intense, creating an underlying contrast in emissions prior to any transformations associated with aging. Changing combustion conditions also affect the vertical distribution of biomass burning emissions, as aged plumes from more flaming-dominated fires are injected to higher altitudes of up to 6000 m. Proportional contributions of the mass-to-charge ratio (<i>m/z</i>) 60 and 44 peaks in the AMS mass spectra to the total OA mass (denoted <i>f</i>₆₀ and <i>f</i>₄₄) are used as tracers for primary and oxidised BBOA, respectively. <i>f</i>₄₄ is lower on average in near-field plumes than those sampled in the far-field, in accordance with longer aging times as plumes are transported a greater distance from source. However, high levels of ΔO₃ / ΔCO and −log(NO_x / NO_y) close to source indicate that emissions can be subject to very rapid oxidation over short timescales. Conversely, the lofting of plumes into the upper troposphere can lead to the retention of source profiles after transportation over extensive temporal and spatial scales, with <i>f</i>₆₀ also higher on average in aged plumes. Evolution of OA composition with aging is comparable to observations of BB tracers in previous studies, revealing a consistent progression from <i>f</i>₆₀ to <i>f</i>₄₄. The elevated levels of oxygenation in aged plumes, and their association with lower average ΔOA / ΔCO, are consistent with OA loss through evaporation during aging due to a combination of dilution and chemical processing, while differences in combustion conditions throughout the campaign also have a significant influence on BBOA production and composition

Programming recognition arrays through double chalcogen-bonding interactions

In this work, we have programmed and synthesized a recognition motif constructed around a chalcogenazolo-pyridine scaffold (CGP) that, through the formation of frontal double chalcogen-bonding interactions, associates into dimeric EX-type complexes. The reliability of the double chalcogen-bonding interaction has been shown at the solid-state by X-ray analysis, depicting the strongest recognition persistence for a Te-congener. The high recognition fidelity, chemical and thermal stability and easy derivatization at the 2-position makes CGP a convenient motif for constructing supramolecular architectures through programmed chalcogen-bonding interactions