Hydrosilylation of ketones, imines and nitriles catalysed by electrophilic phosphonium cations: functional group selectivity and mechanistic considerations.

The electrophilic phosphonium salt, [(C6 F5 )3 PF][B(C6 F5 )4 ], catalyses the efficient hydrosilylation of ketones, imines and nitriles at room temperature. In the presence of this catalyst, adding one equivalent of hydrosilane to a nitrile yields a silylimine product, whereas adding a second equivalent produces the corresponding disilylamine. [(C6 F5 )3 PCl][B(C6 F5 )4 ] and [(C6 F5 )3 PBr][B(C6 F5 )4 ] are also synthesised and tested as catalysts. Competition experiments demonstrate that the reaction exhibits selectivity for the following functional groups in order of preference: ketone>nitrile>imine>olefin. Computational studies reveal the reaction mechanism to involve initial activation of the Si-H bond by its interaction with the phosphonium centre. The activated complex then acts cooperatively on the unsaturated substrate.

Olefin isomerization and hydrosilylation catalysis by Lewis acidic organofluorophosphonium salts.

Organofluorophosphonium salts of the formula [(C6F5)(3-x)Ph(x)PF][B(C6F5)4] (x = 0, 1) exhibit Lewis acidity derived from a low-lying σ* orbital at P opposite F. This acidity is evidenced by the reactions of these salts with olefins, which catalyze the rapid isomerization of 1-hexene to 2-hexene, the cationic polymerization of isobutylene, and the Friedel-Crafts-type dimerization of 1,1-diphenylethylene. In the presence of hydrosilanes, olefins and alkynes undergo efficient hydrosilylation catalysis to the alkylsilanes. Experimental and computational considerations of the mechanism are consistent with the sequential activation and 1,2-addition of hydrosilane across the unsaturated C-C bonds.

Combinations of ethers and B(C6F5)3 function as hydrogenation catalysts.

It works ether way: Labile adducts of dialkyl ethers with the electrophilic borane B(C6F5)3 are shown to scramble HD to H2 and D2 and catalyze the hydrogenation of 1,1-diphenylethylene.

Evaluating crude oil distribution tendencies in a multi-phase aquatic system: Effects of oil type, water chemistry, and mineral sediment.

Planning for effective response to crude oil spills into water depends on evidence of oil behavior, including its tendency to become distributed throughout an aquatic system. An improved laboratory method is employed to quantitatively assess crude oil distribution among different layers that form after mixing within a multi-phase system of water and sediment. Mixtures of conventional crude oil or diluted bitumen with different water types in the presence or absence of mineral sediment are first mixed by a standard end-over-end rotary agitation protocol. After a settling period, each mixture's visibly distinct floating, surface oil (e.g., slick or emulsion), subsurface bulk water, and bottom layers are then separated. Finally, the masses of oil, water, and sediment constituting each layer are isolated, quantified, and compared. The novel results reveal how component properties affect oil distribution among layers to inform spill behavior models, risk assessments, and response plans, including applications of spill-treating agents.

Advanced oxidation processes in microreactors for water and wastewater treatment: Development, challenges, and opportunities.

The miniaturization of reaction processes by microreactors offers many significant advantages over the use of larger, conventional reactors. Microreactors' interior structures exhibit comparatively higher surface area-to-volume ratios, which reduce reactant diffusion distances, enable faster and more efficient heat and mass transfer, and better control over process conditions. These advantages can be exploited to significantly enhance the performance of advanced oxidation processes (AOPs) commonly used for the removal of water pollutants. This comprehensive review of the rapidly emerging area of environmental microfluidics describes recent advances in the development and application of microreactors to AOPs for water and wastewater treatment. Consideration is given to the hydrodynamic properties, construction materials, fabrication techniques, designs, process features, and upscaling of microreactors used for AOPs. The use of microreactors for various AOP types, including photocatalytic, electrochemical, Fenton, ozonation, and plasma-phase processes, showcases how microfluidic technology enhances mass transfer, improves treatment efficiency, and decreases the consumption of energy and chemicals. Despite significant advancements of microreactor technology, organic pollutant degradation mechanisms that operate during microscale AOPs remain poorly understood. Moreover, limited throughput capacity of microreactor systems significantly restrains their industrial-scale applicability. Since large microreactor-inspired AOP systems are needed to meet the high-throughput requirements of the water treatment sector, scale-up strategies and recommendations are suggested as priority research opportunities. While microstructured reactor technology remains in an early stage of development, this work offers valuable insight for future research and development of AOPs in microreactors for environmental purposes.

Aqueous naphthenic acids and polycyclic aromatic hydrocarbons in a meso-scale spill tank affected by diluted bitumen analyzed directly by membrane introduction mass spectrometry.

With the increasing use of unconventional, heavy crude oils there is growing interest in potential impacts of a diluted bitumen (DB) spill in marine and freshwater environments. DB has the potential to release several toxic, trace organic contaminants to the water column. Here, the aqueous concentrations and compositions of two classes of organic contaminants, naphthenic acids (NAs) and polycyclic aromatic hydrocarbons (PAHs), are followed over 8 weeks after a simulated spill of DB (10 L) into a freshwater mesocosm (1200 L) with river sediment (2.4 kg). These complex samples contain biogenic dissolved organic matter, inorganic ions, petroleum contaminants, suspended sediments, and oil droplets. We report the first use of condensed phase membrane introduction mass spectrometry (CP-MIMS) as a direct sampling platform in a complex multi-phase mesocosm spill tank study to measure trace aqueous phase contaminants with little to no sample preparation (dilution and/or pH adjustment). CP-MIMS provides complementary strengths to conventional analytical approaches (e.g., gas- or liquid chromatography mass spectrometry) by allowing the entire sample series to be screened quickly. Trace NAs are measured as carboxylates ([M-H]-) using electrospray ionization and PAHs are detected as radical cations (M+•) using liquid electron ionization coupled to a triple quadrupole mass spectrometer. The DB-affected mesocosm exhibits NA concentrations from 0.3 to 1.2 mg/L, which rise quickly over the first 2 - 5 days , then decrease slowly over the remainder of the study period. The NA profile (measured as the full scan in negative-electrospray ionization at nominal mass resolution) shifts to lower m/z with weathering, a process followed by principal component analysis of the normalized mass spectra. We couple CP-MIMS with high-resolution mass spectrometry to follow changes in molecular speciation over time, which reveals a concomitant shift from classical 'O2' naphthenic acids to more oxidized analogues. Concentrations of PAHs and alkylated analogues (C1 - C4) in the DB-affected water range from 0 to 5 µg/L. Changes in PAH concentrations depend on ring number and degree of alkylation, with small and/or lightly alkylated (C0 - C2) PAH concentrations rising to a maximum in the first 4 - 8 days (100 - 200 h) before slowly decaying over the remainder of the study period. Larger and heavily alkylated (C3 - C4) PAH concentrations generally rise slower, with some species remaining below the detection limit throughout the study period (e.g., C20H12 class including benzo[a]pyrene). In contrast, a control mesocosm (without oil) exhibited NA concentrations below 0.05 mg/L and PAHs were below detection limit. Capitalizing on the rapid analytical workflow of CP-MIMS, we also investigate the impacts of sample filtration at the time of sampling (on NA and PAH data) and sample storage time (on NA data only).

Comparison of structure and reactivity of phosphine-amido and hemilabile phosphine-amine chelates of rhodium.

A series of mono- and binuclear rhodium(I) complexes bearing ortho-phosphinoanilido and ortho-phosphinoaniline ligands has been synthesized. Reactions of the protic monophosphinoanilines, Ph(2)PAr or PhPAr(2) (Ar = o-C(6)H(4)NHMe), with 0.5 equiv of [Rh(µ-OMe)(COD)](2) result in the formation of the neutral amido complexes, [Rh(COD)(P,N-Ph(2)PAr(-))] or [Rh(COD)(P,N-PhP(Ar(-))Ar)] (Ar(-) = o-C(6)H(4)NMe(-)), respectively, through stoichiometrically controlled deprotonation of an amine by the internal methoxide ion. Similarly, the binuclear complex, [Rh(2)(COD)(2)(µ-P,N,P',N'-mapm(2-))] (mapm(2-) = Ar(Ar(-))PCH(2)P(Ar(-))Ar), can be prepared by reaction of the protic diphosphinoaniline, mapm (Ar(2)PCH(2)PAr(2)), with 1 equiv of [Rh(µ-OMe)(COD)](2). An analogous series of hemilabile phosphine-amine compounds can be generated by reactions of monophosphinoanilines, Ph(2)PAr' or PhPAr'(2) (Ar' = o-C(6)H(4)NMe(2)), with 1 equiv of [Rh(NBD)(2)][BF(4)] to generate [Rh(NBD)(P,N-Ph(2)PAr')][BF(4)] or [Rh(NBD)(P,N-PhPAr'(2))][BF(4)], respectively, or by reactions of diphosphinoanilines, mapm or dmapm (Ar'(2)PCH(2)PAr'(2)), with 2 equiv of the rhodium precursor to generate [Rh(2)(NBD)(2)(µ-P,N,P',N'-mapm)][BF(4)](2) or [Rh(2)(NBD)(2)(µ-P,N,P',N'-dmapm)][BF(4)](2), respectively. Displacement of the diolefin from [Rh(COD)(P,N-Ph(2)PAr(-))] by 1,2-bis(diphenylphosphino)ethane (dppe) yields [Rh(P,P'-dppe)(P,N-Ph(2)PAr(-))] which, while unreactive to H(2), reacts readily and irreversibly with oxygen to form the peroxo complex, [RhO(2)(P,P'-dppe)(P,N-Ph(2)PAr(-))], and with iodomethane to yield [RhI(CH(3))(P,P'-dppe)(P,N-Ph(2)PAr(-))]. Hemilabile phosphine-amine compounds can also be prepared by reactions of [Rh(P,P'-dppe)(P,N-Ph(2)PAr(-))] with Me(3)OBF(4) or HBF(4)·Et(2)O, resulting in (thermodynamic) additions at nitrogen to form [Rh(P,P'-dppe)(P,N-Ph(2)PAr')][BF(4)] or [Rh(P,P'-dppe)(P,N-Ph(2)PAr)][BF(4)], respectively. The nonlabile phosphine-amido and hemilabile phosphine-amine complexes were tested as catalysts for the silylation of styrene. The amido species do not require the use of solvents in reaction media, can be easily removed from product mixtures by protonation, and appear to be more active than their hemilabile, cationic congeners. Reactions catalyzed by either amido or amine complexes favor dehydrogenative silylation in the presence of excess olefin, showing modest selectivities for a single vinylsilane product. The binuclear complexes, which were prepared in an effort to explore possible catalytic enhancements of reactivity due to metal-metal cooperativity, are in fact somewhat less active than mononuclear species, discounting this possibility.

Direct mass spectrometric analysis of naphthenic acids and polycyclic aromatic hydrocarbons in waters impacted by diluted bitumen and conventional crude oil.

Crude oil spills have well-documented, deleterious impacts on the hydrosphere. In addition to macroscopic effects on wildlife and waterscapes, several classes of petroleum derived compounds, such as naphthenic acids (NAs) and polycyclic aromatic hydrocarbons (PAHs), may be released into the water and present aquatic contamination hazards. The concentrations of these contaminants may be affected by both oil type and water chemistry. We characterize the concentrations of NAs and PAHs in natural and constructed waters, spanning a range of pH and salinity, and directly compare the influence of diluted bitumen (DB) and conventional crude (CC) oil, using condensed-phase membrane introduction mass spectrometry (CP-MIMS) as a direct sampling, on-line technique. The concentration and isomer class profiles of classical NAs in the aqueous phase were assessed using electrospray ionization in negative-ion mode as [M-H]- whereas PAH concentrations were monitored using liquid electron ionization (LEI) in positive-ion mode as [M+•]. NA concentrations (0.03-25 ppm) were highly pH-dependent, and an order of magnitude greater in water samples contaminated with DB than CC. Conversely, concentrations of naphthalene (10-130 ppb) and alkyl-naphthalenes (10-90 ppb) were three to four-fold higher in water samples exposed to CC. We demonstrate that naturally occurring dissolved organic matter does not bias results from the membrane sampling approach employed, and that DB and CC contaminated waters can be differentiated using principal component analysis of the NA isomer class distribution in both constructed and natural waters. Finally, we describe the first demonstration of the concurrent analysis of trace NAs and PAHs in the same water sample by controlling perm-selectivity at the membrane and the ionization mode of the mass spectrometer. The techniques employed here for trace analysis of petroleum derived compounds in water can be applied to rapid screening and real-time monitoring of contamination and remediation processes.

Coordinatively diverse ortho-phosphinoaniline complexes of ruthenium and isolation of a putative intermediate in ketone transfer hydrogenation catalysis.

Amine-functionalized mono- and diphosphines have been used to prepare a series of ruthenium complexes which exhibit a variety of coordination modes depending on the number of donors possessed by the ligands, the degree of amine methylation, the solvent system used, and the oxidation state of the metal. Reactions of the monophosphinoanilines, Ph(2)PAr or Ph(2)PAr' (Ar = o-C(6)H(4)NHMe, Ar' = o-C(6)H(4)NMe(2)), with 0.5 equiv of [RuCl(mu-Cl)(eta(6)-p-cymene)](2) in dichloromethane result in the formation of [RuCl(2)(eta(6)-p-cymene)(P-Ph(2)PAr)] or [RuCl(eta(6)-p-cymene)(P,N-Ph(2)PAr')]Cl, respectively. In refluxing methanol, [RuCl(2)(eta(6)-p-cymene)(P-Ph(2)PAr)] gradually undergoes chloride ion dissociation to afford the P,N-chelate, [RuCl(eta(6)-p-cymene)(P,N-Ph(2)PAr)]Cl. This chelate can then be deprotonated to afford the amido complex, [RuCl(eta(6)-p-cymene)(P,N-Ph(2)PAr(-))] (Ar(-) = o-C(6)H(4)NMe(-)), which is an active ketone transfer hydrogenation catalyst. Reactions of the diphosphines, Ar(2)PCH(2)PAr(2) (mapm) or Ar'(2)PCH(2)PAr'(2) (dmapm) with 0.5 equiv of [RuCl(mu-Cl)(eta(6)-p-cymene)](2) result in the formation of [RuCl(2)(P,P',N,N'-mapm)] or [RuCl(eta(6)-p-cymene)(P,P'-dmapm)]Cl, respectively, in which increased methyl substitution in the latter actually inhibits amine coordination with retention of the p-cymene fragment. Reaction of mapm with 1 equiv of [Ru(CO)(4)(eta(2)-C(2)H(4))] in dichloromethane initially produces [Ru(CO)(4)(P-mapm)] which, over a 24 h period with exposure to ambient light, is completely converted to the P,P'-chelate, [Ru(CO)(3)(P,P'-mapm)], by photodissociation of carbon monoxide. The same reaction with 2 equiv of [Ru(CO)(4)(eta(2)-C(2)H(4))] generates a mixture of [Ru(3)(CO)(10)(mu-P,P'-mapm)] and the mononuclear P,P'-chelate. The trinuclear complex can also be synthesized by direct reaction of mapm with 1 equiv of [Ru(3)(CO)(12)].

Distributions of diluted bitumen and conventional crude oil in a range of water types.

Concern about the impacts that accidental discharge of under-investigated, heavy petroleum products may have on aquatic environments has prompted a comparative examination of the behaviours of diluted bitumen (DB) and light conventional crude (CC) oil in different water types. Distributions of oil among the water column and floating water-in-oil (w/o) emulsion are evaluated by a novel, reproducible procedure involving mixing oil with water, then separating, extracting, and quantifying the total absolute oil content of the water column via gravimetric and gas-chromatographic (high-temperature simulated distillation) analyses. The CC contents of water columns tend to be significantly greater than those of DB under comparable conditions, while the fraction of oil remaining afloat at the water's surface is greater for DB than for CC. The elucidated phase distribution patterns have important implications pertaining to the recoverability of these oils in the event of their release into aquatic environments, which serves to inform best practices for oil spill response. For both DB and CC, oil contents within water columns are the highest in waters of low salinity and high pH. Water contents of buoyant w/DB emulsions are significantly greater than those of w/CC emulsions after 60 min at rest, and are the highest in waters of low salinity and low pH. The effect of crude oil on the pH of water is also studied, and DB is found to have a greater effect than CC on water samples of varying initial pH.

Electrophilic phosphonium cations catalyze hydroarylation and hydrothiolation of olefins.

Electrophilic phosphonium cations (EPCs) are efficient main group catalysts for the hydroarylation of olefins under mild conditions, providing a facile route to substituted aniline, bis-arylamine, phenol, furan, thiophene, pyrrole, and indole derivatives. Similarly, EPCs catalyze the hydrothiolation of aryl olefins with thiophenol affording a series of alkyl aryl thioethers. Experimental data support a mechanism for these reactions that involves initial activation of the olefin.

Synthesis and Lewis acidity of fluorophosphonium cations.

A series of fluorophosphonium salts, [R3PF][X] (R = alkyl or aryl; X = FB(C6F5)3, [B(C6F5)4]), have been prepared by reactions of phosphine/borane frustrated Lewis pairs (FLPs) with XeF2 or difluorophosphoranes with [Et3Si][B(C6F5)4]. As the substituents bound to phosphorus become increasingly electron withdrawing, the corresponding fluorophosphonium salts are shown to be increasingly Lewis acidic. Calculations were also performed to determine the relative fluoride ion affinities (FIA) of these fluorophosphonium cations.

Frustrated Lewis pair-mediated C-O or C-H bond activation of ethers.

Protocols for the FLP-mediated transformation of ethers are presented. Distinct reaction pathways involving either C-O or C-H bond activation occur depending on the application of oxophilic B(C6F5)3 or hydridophilic tritylium ions as the Lewis acid.

The Lewis acidity of fluorophosphonium salts: access to mixed valent phosphorus(III)/(V) species.

Oxidative fluorination of the electron-deficient phosphine Ph(2)P(C(6)F(5)) using XeF(2), followed by fluoride ion abstraction from the resulting difluorophosphorane Ph(2)P(F)(2)(C(6)F(5)), produces electrophilic fluorophosphonium salts [Ph(2)P(F)(C(6)F(5))][X] (X = FB(C(6)F(5))(3) or O(3)SCF(3)). Variable temperature NMR spectroscopic analysis of [Ph(2)P(F)(C(6)F(5))][FB(C(6)F(5))(3)] demonstrates a fluxional process attributed to fluoride ion exchange between B(C(6)F(5))(3) and [Ph(2)P(F)(C(6)F(5))](+), suggesting that these species have comparable Lewis acidities. This exchange can also be illustrated by adding phosphine Ph(3)P to [Ph(2)P(F)(C(6)F(5))][FB(C(6)F(5))(3)] at ambient temperature to produce Ph(2)P(F)(2)(C(6)F(5)) and Ph(3)P-B(C(6)F(5))(3), while heating this mixture results in thermally induced para-substitution of Ph(3)P at the C(6)F(5) group of the phosphonium ion to generate [Ph(3)P(C(6)F(4))P(F)(2)Ph(2)][FB(C(6)F(5))(3)]. Such frustrated Lewis pair reactivity also can be exploited by reacting [Ph(2)P(F)(C(6)F(5))][O(3)SCF(3)] with silylphosphine Ph(2)PSiMe(3) to afford the unique mixed-valent salt [Ph(2)P(C(6)F(4))P(F)Ph(2)][O(3)SCF(3)], which upon the addition of fluoride is converted to Ph(2)P(C(6)F(4))P(F)(2)Ph(2). XeF(2) reacts with [Ph(2)P(C(6)F(4))P(F)Ph(2)][O(3)SCF(3)] at ambient temperature, producing equal proportions of the dicationic salt [Ph(2)P(F)(C(6)F(4))P(F)Ph(2)][O(3)SCF(3)](2) and the bis(difluorophosphorane) Ph(2)P(F)(2)(C(6)F(4))P(F)(2)Ph(2), the latter of which can then be quantitatively converted to the former by adding one equiv of Me(3)SiO(3)SCF(3).

Lewis acidity of organofluorophosphonium salts: hydrodefluorination by a saturated acceptor.

Prototypical Lewis acids, such as boranes, derive their reactivity from electronic unsaturation. Here, we report the Lewis acidity and catalytic application of electronically saturated phosphorus-centered electrophilic acceptors. Organofluorophosphonium salts of the formula [(C6F5)(3-x)Ph(x)PF][B(C6F5)4] (x = 0 or 1; Ph, phenyl) are shown to form adducts with neutral Lewis bases and to react rapidly with fluoroalkanes to produce difluorophosphoranes. In the presence of hydrosilane, the cation [(C6F5)3PF](+) is shown to catalyze the hydrodefluorination of fluoroalkanes, affording alkanes and fluorosilane. The mechanism demonstrates the impressive fluoride ion affinity of this highly electron-deficient phosphonium center.

Mono- and binuclear complexes of rhodium involving a new series of hemilabile o-phosphinoaniline ligands.

Monophosphines of the type Ph(x)PAr(3-x) (x = 0, 1 or 2, Ar = o-N-methylanilinyl) and the diphosphine, Ar(2)PCH(2)PAr(2) (mapm) have been synthesized for use as chelating and/or bridging P,N-ligands within mono- and binuclear rhodium(i) complexes, respectively. The previously prepared phosphines, Ph(x)PAr'(3-x) (x = 0, 1 or 2, Ar' = o-N,N-dimethylanilinyl) and Ar'(2)PCH(2)PAr'(2) (dmapm), have also been used to prepare analogous mono- and binuclear complexes. Variable temperature (1)H NMR spectroscopy of the mononuclear complexes, [RhCl(CO)(L)] (L = PhPAr(2), PhPAr'(2), PAr(3) and PAr'(3)), and line-shape analyses of the resultant spectra indicate the substantially increased lability of the N,N-dimethylanilinyl donors relative to the related monomethylanilinyl groups. X-Ray structural analyses of the mononuclear complexes suggest that the enhanced Type II hemilability in the dimethylanilinyl complexes compared to their monomethyl analogues results from increased steric interactions involving the coordinated dimethylanilinyl substituents. In the case of the binuclear, dmapm-bridged compound [Rh(2)Cl(2)(CO)(2)(micro-dmapm)], there are additional transannular repulsions between the chloro ligand on one metal and the coordinated dimethylanilinyl group on the other, which result in a Rh-Rh separation of over 4.1 A. For the analogous mapm-bridged species, the transannular interactions between the chloro ligands and the amine hydrogens are in fact attractive, resulting in a much closer Rh-Rh separation (3.450 A). The chloride substituents of [Rh(2)Cl(2)(CO)(2)(micro-mapm)] can be replaced to generate the complexes, [Rh(2)(X)(2)(CO)(2)(micro-mapm)] (X = I, CF(3)SO(3), CH(3)CO(2)), the last of which also exhibits pronounced transannular hydrogen-bonding interactions in the solid state.