Versatile, Cheap, Readily Modifiable Sample Delivery Method for Analysis of Air-/Moisture-Sensitive Samples Using Atmospheric Pressure Solids Analysis Probe Mass Spectrometry.

A cheap, versatile, readily modified, and reusable glass probe system enabling delivery of solid air-/moisture-sensitive samples for mass spectrometric (MS) analysis using an Atmospheric pressure Solids Analysis Probe (ASAP) is described. The simplicity of the design allows quick and easy ASAP MS analyses of sensitive solid and liquid samples without the need for any modifications to commercially available vertically loaded ASAP mass spectrometers. A comparison of ASAP mass spectra obtained for metal complexes under air and an inert atmosphere is given.

Opening the Egg Box: NMR spectroscopic analysis of the interactions between s-block cations and kelp monosaccharides.

The best-known theory accounting for metal-alginate complexation is the so-called "Egg Box" model. In order to gain greater insight into the metal-saccharide interactions that underpin this model, the coordination chemistry of the corresponding monomeric units of alginate, L-guluronate (GulA) and D-mannuronate (ManA) have been studied herein. GulA and ManA were exposed to solutions of different s-block cations and then analysed by 1H and 13C NMR spectroscopy. It was found that the α/ß ratio of the pyranose anomeric equilibria of GulA showed large pertubations from the starting value (α/ß = 0.21 ± 0.01) upon contact with 1.0 M Ca2+, Sr2+, and Ba2+ (α/ß = 1.50 ± 0.03, 1.20 ± 0.02, and 0.58 ± 0.02, respectively) at pD 7.9, but remained almost constant in the presence of Na+, K+, and Mg2+ (α/ß = 0.24 ± 0.01, 0.19 ± 0.01, and 0.26 ± 0.01, respectively). By comparison, no significant changes were observed in the α/ß ratios of ManA and related mono-uronates D-glucuronate (GlcA) and D-galacturonate (GalA) in the presence of all of the metal ions surveyed. Analysis of the 1H and 13C coordination chemical shift patterns indicate that the affinity of α-GulA for larger divalent cations is a consequence of the unique ax-eq-ax arrangement of hydroxyl groups found for this uronate anomer.

Solution-state behaviour of algal mono-uronates evaluated by pure shift and compressive sampling NMR techniques.

Sodium salts of the algal uronic-acids, d-mannuronic acid (HManA) and l-guluronic acid (HGulA) have been isolated and characterised in solution by nuclear magnetic resonance (NMR) spectroscopy. A suite of recently-described NMR experiments (including pure shift and compressive sampling techniques) were used to provide confident assignments of the pyranose forms of the two uronic acids at various pD values (from 7.5 to 1.4). The resulting high resolution spectra were used to determine several previously unknown parameters for the two acids, including their pKa values, the position of their isomeric equilibria, and their propensity to form furanurono-6,3-lactones. For each of the three parameters, comparisons are drawn with the behaviour of the related D-glucuronic (HGlcA) and D-galacturonic acids (HGalA), which have been previously studied extensively. This paper demonstrates how these new NMR spectroscopic techniques can be applied to better understand the properties of polyuronides and uronide-rich macroalgal biomass.

Additives boosting the performance of tungsten imido-mediated ethylene dimerization systems for industrial application.

While activation of tungsten bis(imido) complexes [WCl2(NAr)2(dme)] with EtAlCl2 affords active, and moderately selective ethylene dimerization catalysts, addition of Et3N or Oct4NCl leads to a doubling in productivity and activity, along with increased selectivity (e.g., >93% C4, >99% 1-C4). The performance of the resulting tungsten-based catalyst package is competitive with that of Axens' commercialised Ti-based AlphaButol process and exemplifies the wide potential of similar additives in selective oligomerization.

Species variation in the effects of dewatering treatment on macroalgae.

Seaweeds can be a valuable resource for biorefinery and biotechnology applications, but their high water content is a recurrent problem and one of the key bottlenecks for their sustainable use. Treatments to increase dry matter content of the kelp Laminaria digitata were recently described by the authors. However macroalgae are an extremely diverse group of organisms and compositional variation between species may influence the effects of particular treatments. In this study, potential dewatering treatments including drying, osmotic media, and the application of both organic and mineral acids all followed by screw-pressing have been tested on two other species of kelp (Laminaria hyperborea and Saccharina latissima) and a red seaweed (Palmaria palmata). Conditions that dewatered these species were identified and the data have been combined with the previous results for L. digitata. There were significant differences between species across all the traits of interest. However dewatering was highly dependent on specific interactions with both treatment and season of collection. Nevertheless, the dry matter content of brown seaweeds was widely and successfully increased by air drying or acid treatment followed by screw-pressing. The results for P. palmata were quite different, particularly with regard to juice production. For this species, acid treatment did not result in dewatering, but dry matter content could be increased by screw-pressing immediately after harvest. Together the data presented here demonstrate that dewatering pre-treatments need to be specific for the type of seaweed to be processed; important knowledge for the future use of this sustainable biomass resource.

Biodiesel Production via Trans-Esterification Using Pseudomonas cepacia Immobilized on Cellulosic Polyurethane.

In this work, Pseudomonas cepacia lipase immobilized on cellulosic polyurethane was used as a catalyst for biodiesel production via trans-esterification reactions in order to provide cost-effective methods of enzyme recycling. The efficacy of the immobilized enzyme catalyst at low loading (6.2 wt %) and the effects of temperature, water content, and reaction time in model trans-esterification of glyceryl trioctanoate were investigated extensively. It was found that water was necessary for the reaction of glyceryl trioctanoate with ethanol to proceed. A high conversion of glyceryl trioctanoate (∼70%) was obtained at 35 °C, with only 5.0 wt % of water content over a reaction period of 12 h.

Analysis of air-, moisture- and solvent-sensitive chemical compounds by mass spectrometry using an inert atmospheric pressure solids analysis probe.

A novel method has been developed that enables chemical compounds to be transferred from an inert atmosphere glove box and into the atmospheric pressure ion source of a mass spectrometer whilst retaining a controlled chemical environment. This innovative method is simple and cheap to implement on some commercially available mass spectrometers. We have termed this approach inert atmospheric pressure solids analysis probe ( iASAP) and demonstrate the benefit of this methodology for two air-/moisture-sensitive chemical compounds whose characterisation by mass spectrometry is now possible and easily achieved. The simplicity of the design means that moving between iASAP and standard ASAP is straightforward and quick, providing a highly flexible platform with rapid sample turnaround.

Dewatering treatments to increase dry matter content of the brown seaweed, kelp (Laminaria digitata ((Hudson) JV Lamouroux)).

Macroalgal water content is an on-going problem for the use of readily accessible seaweeds in sustainable biorefining, including fuel production. Silage is a reduced-water, compactable, easily stored, transportable material. Ensiling could establish a non-seasonal supply of preserved algal biomass, but requires high initial dry matter content to mitigate environmental pollution risks from effluent. This study investigated potential dewatering methods for kelp harvested throughout the year. Treatments included air-drying, osmotic media and acids. Significant interactions between treatment and harvest-time were observed for traits of interest. Fresh weight loss during treatment was composed of changes in water and dry matter content. Air-drying gave reliable increase in final dry matter content; in summer and autumn 30% dry matter content was reached after 24h. Dilute hydrochloric acid reduced stickiness and rendered material suitable for dewatering by screw-pressing; it may be possible to use the consequent pH reduction to promote efficient preservation.

Combined DFT and experimental studies of C-C and C-X elimination reactions promoted by a chelating phosphine-alkene ligand: the key role of penta-coordinate Pd(II.).

A combined computational and experimental study of the coordination chemistry of phosphine-alkene ligand L1 (N-diphenylphosphino-7-aza-benzobicyclo[2.2.1]hept-2-ene) with Pd(0) and Pd(II) is presented. Experimentally it is established that ligand L1 promotes direct alkyl-alkyl and indirect alkyl-halide reductive elimination from Pd(II) species, affording the palladium(0) complex [Pd(κ(2)-P,C-L1)2] (2) in each case. The effectiveness of L1 in promoting these reactions is attributed to the initial formation of a penta-coordinate intermediate [PdMe(X)(κ(1)-P-L1)(κ(2)-P,C-L1)] (X = Me, Cl) coupled with the ease with which it transforms to 2. From computation, a lower activation barrier for C(sp(3))-C(sp(3)) coupling and subsequent elimination has been computed for a stepwise associative pathway involving the initial formation of [PdMe2(κ(1)-P-L1)(κ(2)-P,C-L1)], compared to that computed for direct elimination from its parent, cis-[PdMe2(κ(2)-P,C-L1)]. Moreover, the C(sp(3))-C(sp(3)) coupling reaction has been found to be primarily under thermodynamic control. It has also been demonstrated computationally that the methyl group of penta-coordinate [PdCl(Me)(κ(1)-P-L1)(κ(2)-P,C-L1)] is susceptible to nucleophilic attack by the phosphorus lone pair of a further equivalent of ligand L1, which proceeds through an SN2-like transition state. This initiates an unusual, indirect intermolecular reductive elimination process, resulting in the formation of equimolar quantities of the methyl phosphonium chloride salt of L1 and complex 2, in agreement with experimental observations. In contrast to the C(sp(3))-C(sp(3)) coupling, computation shows that this indirect C(sp(3))-Cl reductive elimination process is essentially under kinetic control.

Phosphine-alkene ligand-mediated alkyl-alkyl and alkyl-halide elimination processes from palladium(II).

N-Diphenylphosphino-7-aza-benzobicyclo[2.2.1]hept-2-ene (2) behaves as a chelating phosphine-alkene ligand for Pd(0) and Pd(II), promoting direct alkyl-alkyl and indirect alkyl-halide reductive elimination reactions due to the stabilisation of the resulting bis(phosphine-alkene)Pd(0) complex.

Hydroformylation by Pt-Sn compounds from N-heterocyclic stannylenes.

[(Me(2)Si{NAr}(2))-κ(2)N,N']Sn, reacts with PtCl(2)(L(2)) and [PtCl(µ-Cl)(L)](2) to afford products containing Pt-Sn bonds. In the absence of supporting ligands L, coordination of the stannylene and rearrangement to a structurally unique PtSn(2)N(2)Si metallacycle occurs. The hydroformylation activity of a representative Pt-Sn compound is investigated.

Application of molybdenum bis(imido) complexes in ethylene dimerisation catalysis.

In combination with EtAlCl(2) (Mo : Al = 1 : 15) the imido complexes [MoCl(2)(NR)(NR')(dme)] (R = R' = 2,6-Pr(i)(2)-C(6)H(3) (1); R = 2,6-Pr(i)(2)-C(6)H(3), R' = Bu(t) (3); R = R' = Bu(t) (4); dme = 1,2-dimethoxyethane) and [Mo(NHBu(t))(2)(NR)(2)] (R = 2,6-Pr(i)(2)-C(6)H(3) (5); R = Bu(t) (6)) each show moderate TON, activity, and selectivity for the catalytic dimerisation of ethylene, which is influenced by the nature of the imido substituents. In contrast, the productivity of [MoCl(2)(NPh)(2)(dme)] (2) is low and polymerisation is favoured over dimerisation. Catalysis initiated by complexes 1-4 in combination with MeAlCl(2) (Mo : Al = 1 : 15) exhibits a significantly lower productivity. Reaction of complex 5 with EtAlCl(2) (2 equiv.) gives rise to a mixture of products, while addition of MeAlCl(2) affords [MoMe(2)(N-2,6-Pr(i)(2)-C(6)H(3))(2)]. Treatment of 6 with RAlCl(2) (2 equiv.) (R = Me, Et) yields [Mo({µ-N-Bu(t)}AlCl(2))(2)] (7) in both cases. Imido derivatives 1 and 3 react with Me(3)Al and MeAlCl(2) to form the bimetallic complexes [MoMe(2)(N{R}AlMe(2){µ-Cl})(NR')] (R = R' = 2,6-Pr(i)(2)-C(6)H(3) (8); R = 2,6-Pr(i)(2)-C(6)H(3), R' = Bu(t) (10)) and [MoMe(2)(N{R}AlCl(2){µ-Cl})(NR')] (R = R' = 2,6-Pr(i)(2)-C(6)H(3) (9); R = 2,6-Pr(i)(2)-C(6)H(3), R' = Bu(t) (11)), respectively. Exposure of complex 8 to five equivalents of thf or PMe(3) affords the adducts [MoMe(2)(N-2,6-Pr(i)(2)-C(6)H(3))(2)(L)] (L = thf (12); L = PMe(3) (13)), while reaction with NEt(3) (5 equiv.) yields [MoMe(2)(N-2,6-Pr(i)(2)-C(6)H(3))(2)]. The molecular structures of complexes 5, 9 and 11 have been determined.

Exploring the reactivity of tungsten bis(imido) dimethyl complexes with methyl aluminium reagents: implications for ethylene dimerization.

The reaction of [WCl2(NAr)2(DME)] (1) with excess Me3Al affords the dimethyl complex [WMe2(N{Ar}AlMe2{mu-Cl})(NAr)] (2), which on treatment with THF or MeAlCl2 yields [WMe2(NAr)2(THF)] (3) and [WMe2(N{Ar}AlMe(Cl){mu-Cl})(NAr)] (5), respectively. Complex 3 is unstable in solution dissociating to form [WMe2(NAr)2] (4) that may be isolated as an adduct with PMe3, [WMe2(NAr)2(PMe3)] (6). While complex 2 is inert towards ethylene, complex 3 reacts rapidly to afford a mixture of methane and but-1-ene (1:4). Neither complex 2 nor 3 react with propylene. Reaction of 3 with a C2H4/C2D4 (1:1) affords a mixture of isotopomers that is consistent with complete isotopic scrambling. The structures of complexes 1, 2, and 3 have been determined by X-ray diffraction.

Bridging M-Cl bonds with ambiphilic phosphine-borane ligands.

A combined experimental/theoretical study provides insight into the bridging coordination of M-Cl bonds with the ambiphilic phosphine-borane ligands iPr(2)P-o(C(6)H(4))-BR(2) (PBCy(2): R = Cy; PBMes(2): R = Mes). Reaction of [PdCl(allyl)(PBCy(2))] (3) with HCl affords the related dinuclear complex [PdCl(mu-Cl)(PBCy(2))](2) (5). Subsequent cleavage of the chloride bridge by PPh(3) leads to the heteroleptic mononuclear complex trans-[PdCl(2)(PPh(3))(PBCy(2))] (6). The solid-state structures of complexes 5 and 6 substantiate the propensity of the PBCy(2) ligand to bridge Pd-Cl bonds via P-->Pd--Cl-->B interactions. DFT calculations carried out on both the model mononuclear complexes 3* and 6* reveal that in each system the energy of the linkage isomer with a Cl-->B interaction is very similar to that without. A comparison of the solution and solid-state (11)B NMR spectroscopic data for complexes 3 and 6 suggests the possible interconversion of the bridging and B-pendant forms in solution. Bridging coordination of the PBCy(2) ligand across a Rh-Cl bond is observed in the solid-state structure of the related complex [RhCl(nbd)(PBCy(2))] (7). Replacement of the Cy groups at boron by Mes substituents illustrates the role of steric factors on the participation of the Lewis acid upon coordination, no Cl-->B interaction being observed in the complex [PdCl(allyl)(PBMes(2))] (8).

N-Phosphino-amidines and -guanidines: synthesis, structure and P,N-chelate chemistry.

The syntheses of the cyclic N-phosphino-amidines and -guanidines Ph2PN(Pri)C(NPri2)N(Pri) ( 1) and Ph2PN(c-Hex)C(R)N(c-Hex) [R = piperazino ( 2), morpholino ( 3), Me ( 4), and Ph ( 5)] are reported. DFT studies have identified the preferred structures for compounds 1-5 with the E-configuration being the most stable form for the N-phosphino-amidines, while the Z-conformation is preferred for the N-phosphino-guanidines something that highlights the potential of such systems to act as kappa2-P,N-chelates. The differences in donor characteristics of 2-5 have been probed through the study of their corresponding P(V) selenide derivatives ( 6-9) and their complexes with the cis-RhCl(CO) (10-12) and cis-PdCl2 (13-17) fragments. In line with the DFT studies both the amidines and guanidines are found to coordinate as kappa2-P,N-chelates, with the latter being moderately weaker donor ligands. The molecular structures of compounds 3 and 4, together with those of the Rh and Pd complexes 10 and 15, respectively, have been determined in the solid state by X-ray crystallography, the latter confirming bidentate kappa2-P,N-chelation.

Ambiphilic diphosphine-borane ligands: metal-->borane interactions within isoelectronic complexes of rhodium, platinum and palladium.

Coordination of an ambiphilic diphosphine-borane (DPB) ligand to the RhCl(CO) fragment affords two isomeric complexes. According to X-ray diffraction analysis, each complex adopts a square-pyramidal geometry with trans coordination of the two phosphine buttresses and axial RhB contacts, but the two differ in the relative orientations around the rhodium and boron centres. DFT calculations on the actual complexes provide insight into the influence of the pi-accepting CO co-ligand, compared with previously reported complexes [Rh(mu-Cl)(dpb)]2 and [RhCl(dmap)(dpb)]. In addition, comparison of the nu(CO) frequency of [RhCl(CO)(dpb)] with that of the related borane-free complex [RhCl(CO)(iPr2PPh)2] substantiates the significant electron-withdrawing effect that the sigma-accepting borane moiety exerts on the metal. Valence isoelectronic [PtCl2(dpb)] and [PdCl2(dpb)] complexes have also been prepared and characterized spectroscopically and structurally. The pronounced influence of the transition metal on the magnitude of the M-->B interaction is highlighted by geometric considerations and NBO analyses.