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The synthesis and characterization of Fe pincer complexes supported by a bis(phosphino)silyl (PSiP) ligand are described. While four-coordinate species of the type (PSiP)FeX (X = halide) proved challenging to access, examples of five-coordinate (PSiP)Fe(II) and (PSiP)Fe(I) species were prepared and crystallographically characterized. In studying the reactivity of such (PSiP)Fe precursors, a variety of iron hydride species were observed and characterized, and interconversion among such complexes facilitated by the coordination of N2 was noted. The structures and spectroscopic features of several such diamagnetic Fe(II) hydrides were elucidated, including that of a unique and highly stable η2-(Si–H)Fe(II) dihydride complex. A surrogate for a low coordinate (PSiP)FeH species in the form of its bis(dinitrogen) adduct was found to be an effective precatalyst for the direct hydrogenation of alkenes, including various mono- and disubstituted aliphatic alkenes, as well as a trisubstituted example. Esters and ethe...

We describe the results of our combined experimental and computational investigation of structurally analogous (N-phosphinoamidinate)metal(N(SiMe3)2) precatalysts ((PN)M; M = Mn2+, Fe2+, Co2+, and Ni2+; d5–d8) in the isomerization–hydroboration of 1-octene, cis-4-octene, or trans-4-octene (1a–c) with HBPin. As part of this investigation, the synthesis and crystallographic characterization of diamagnetic (PN)Ni, ((PN)NiH)2, (PN)NiH(L) (L = pyridine or DMAP), and (PN)Ni(NHdipp) (dipp = 2,6-iPr2C6H3) are reported. Divergent catalytic reactivity and selectivity was noted for members of the (PN)M series; (PN)Mn and (PN)Ni afforded poor hydroboration yields, whereas the use of (PN)Fe or (PN)Co afforded high conversion and selectivity for the terminal borylation product, (n-octyl)BPin (2a). DFT calculations involving (PN)M as well as stoichiometric reactivity studies featuring (PN)Ni confirmed that (PN)MH intermediates generated upon reaction of (PN)M with HBPin represent viable catalytic species whereby formati...

The synthesis and characterization of group 10 metal pincer complexes supported by a new bis(indolylphosphino)silyl ligand are described, including the synthesis of Ni, Pd, and Pt hydride species. Solution NMR and single-crystal X-ray data revealed that a significant amount of structural variability is possible for such hydride complexes, particularly in the case of Ni, where terminal Ni-H as well as complexes involving η2-SiH coordination are both accessible and may even coexist, in ratios dependent on factors such as the nature of additional coligands, including N2 from the reaction atmosphere, as well as solvent and temperature. Nickel and palladium hydride complexes of this new ligand were found to exhibit divergent selectivity in the catalytic hydroboration of CO2 with pinacolborane (HBPin). While the Pd catalyst exhibited moderate activity for CO2 hydroboration to the formate level, the analogous Ni species exhibited unprecedented selectivity (97%) for hydroboration of CO2 to the formaldehyde level ...

The use of pincer ligands to access non-VSEPR geometries at main-group centers is an emerging strategy for eliciting new stoichiometric and catalytic reactivity. As part of this effort, several different tridentate trianionic substituents have to date been employed at a range of different central elements, providing a patchwork dataset that precludes rigorous structure-function correlation. An analysis of periodic trends in structure (solid, solution, and computation), bonding, and reactivity based on systematic variation of the central element (P, As, Sb, or Bi) with retention of a single tridentate triamide substituent is reported herein. In this homologous series, the central element can adopt either a bent or planar geometry. The tendency to adopt planar geometries increases descending the group with the phosphorus triamide (1) and its arsenic congener (2) exhibiting bent conformations, and the antimony (3) and bismuth (4) analogues exhibiting a predominantly planar structure in solution. This trend has been rationalized using an energy decomposition analysis. A rare phase-dependent dynamic covalent dimerization was observed for 3 and the associated thermodynamic parameters were established quantitatively. Planar geometries were found to engender lower LUMO energies and smaller band gaps than bent ones, resulting in different reactivity patterns. These results provide a benchmark dataset to guide further research in this rapidly emerging area.

The use of pincer ligands to access non-VSEPR geometries at main-group centers is an emerging strategy for eliciting new stoichiometric and catalytic reactivity. As part of this effort, several different tridentate trianionic substituents have to date been employed at a range of different central elements, providing a patchwork dataset that precludes rigorous structure-function correlation. Here we report an analysis of periodic trends in structure (solid, solution, and gas phase), bonding, and reactivity based on systematic variation of the central element (P, As, Sb, or Bi) with retention of a single tridentate triamide substituent. In this homologous series, the central element can adopt either a bent or planar geometry. The tendency to adopt planar geometries increases descending the group with the phosphorus triamide (1) and its arsenic congener (2) exhibiting bent conformations, and the antimony (3) and bismuth (4) analogues exhibiting a predominantly planar structure in solution. This trend has been rationalized using the energy decomposition analysis. A rare phase-dependent dynamic covalent dimerization was observed for 3 and the associated thermodynamic parameters were established quantitatively. Planar geometries were found to engender lower LUMO energies and smaller band gaps as compared to bent ones, resulting in different reactivity patterns. These results provide a benchmark dataset to guide further research in this rapidly emerging area.

To probe ligand-receptor binding at the atomic-level, a frequent approach involves multidimensional nuclear magnetic resonance (NMR) spectroscopy experiments relying on 13C- and/or 15N-enrichment alongside 1H. Alternatively, the lack of fluorine in biomolecules may be exploited through specific incorporation of 19F nuclei into a sample. The 19F nucleus is highly sensitive to environmental changes and allows for one-dimensional NMR spectroscopic study, with perturbation to chemical shift and spin dynamics diagnostic of structural change, ligand binding, and modified conformational sampling. This was applied to the apelinergic system, which comprises a rhodopsin-like G protein-coupled receptor (the apelin receptor (AR)/APJ) and two families of cognate ligands, the apelin and apela (ELABELA/toddler) peptides. Specifically, AR fragments consisting of either the N-terminal tail and first transmembrane (TM) &alpha, helix (AR55) or the first three transmembrane &alpha, helices (TM1-3) were prepared with biosynthetic fluorotryptophan incorporation. Interactions of each AR fragment with a high-affinity, 2,4,5-trifluorophenylalanine labeled apelin analogue were compared by 19F NMR. Distinct ranges of 19F chemical shifts for ligand and receptor provide unambiguous tracking of both species, with distinct binding behaviour observed for each AR fragment implying that AR55 is not sufficient to recapitulate the physiological binding event. Site-specific perturbation was also apparent for the apelin analogue as a function of substitution site, indicating an orientational binding preference. As a whole, this strategy of distinctive 19F labelling for ligand and receptor provides a relatively fast (i.e., employing 1D NMR experiments) and highly sensitive method to simultaneously and definitively track binding in both species.

A new method to determine epoxide concentrations in oxidized oils was developed and validated using (1)H NMR. Epoxides derived from lipid oxidation gave signals between 2.90 and 3.24 ppm, well separated from the signals of other lipid oxidation products. To calibrate, soybean oils with a range of epoxide concentrations were synthesized and analyzed using (1)H NMR by taking the sn-1,3 glycerol protons (4.18, 4.33 ppm) as internal references. The (1)H NMR signals were compared to the epoxide content determined by titration with hydrogen bromide (HBr)-acetic acid solution. As expected, the signal response increased with concentration linearly (R(2) = 99.96%), and validation of the method gave results comparable to those of the HBr method. A study of the oxidative stability of soybean oil was performed by applying this method to monitor epoxides during thermal lipid oxidation. The epoxide content increased over time and showed a different trend compared to peroxide value (PV). A phenomenological model was suggested to model epoxides derived from lipid oxidation.

The physicochemical properties of soft nanoparticles, most notably size, morphology, and ligand interactions, typically depend upon the solution environment in which they are suspended. Comprehensive characterization in a given environment is therefore essential. We have employed high-resolution solution nuclear magnetic resonance (NMR) spectroscopy, nuclear spin relaxation measurements, and diffusion ordered NMR spectroscopy (DOSY) techniques to thoroughly characterize polymeric nanoparticles formed by salt-induced collapse of a methacrylic acid–ethyl acrylate copolymer stabilized by ultraviolet (UV) irradiation. UV-dose-dependent production of new chemical species is apparent from 1H and 13C chemical shift patterns. 1H–13C correlation spectroscopy reveals that cross-linking is likely responsible for nanoparticle structural integrity. Paramagnetic relaxation enhancement (PRE) unambiguously shows protection of photochemically derived moieties from solvent, with a UV-dose-dependent decrease in particle siz...

A new, easily synthesized diphosphine based on a heterocyclic 1,3,2-diazaphospholidine framework has been prepared. Due to the large, sterically encumbering Dipp groups (Dipp = 2,6-diisopropylphenyl) on the heterocyclic ring, the diphosphine undergoes homolytic cleavage of the P-P bond in solution to form two phosphinyl radicals. The diphosphine has been reacted with O(2), S(8), Se, Te, and P(4), giving products that involve insertion of elements between the P-P bond to yield the related phosphinic acid anhydride, sulfide/disulfide, selenide, telluride, and a butterfly-type perphospha-bicyclobutadiene structure with a trans,trans-geometry. All molecules have been characterized by multinuclear NMR spectroscopy, elemental analysis, and single-crystal X-ray crystallography. Variable-temperature EPR spectroscopy was utilized to study the nature of the phosphinyl radical in solution. Electronic structure calculations were performed on a number of systems from the parent diphosphine [H(2)P](2) to amino-substituted [(H(2)N)(2)P](2) and cyclic amino-substituted [(H(2)C)(2)(NH)(2)P](2); then, bulky substituents (Ph or Dipp) were attached to the cyclic amino systems. Calculations on the isolated diphosphine at the B3LYP/6-31+G* level show that the homolytic cleavage of the P-P bond to form two phosphinyl radicals is favored over the diphosphine by ~11 kJ/mol. Furthermore, there is a significant amount of relaxation energy stored in the ligands (52.3 kJ/mol), providing a major driving force behind the homolytic cleavage of the central P-P bond.

Complexes of lead with L-phenylalanine, L-isoleucine, L-valine, or L-arginine have been isolated from reaction mixtures containing lead nitrate and the respective amino acid in acidic aqueous solution. The compounds have been comprehensively characterized using X-ray crystallography, solid state NMR spectroscopy and solution state NMR spectroscopy, IR and Raman spectroscopies, and electrospray ionization mass-spectrometry. The solid state structures of lead-phenylalanine, lead-valine, and lead-valine-isoleucine complexes show a lead center coordinated by two amino acid ligands, while the lead-arginine complex is a cluster involving two lead centers and three arginine molecules. The structural, spectroscopic, and spectrometric characterization of the complexes provides a basis to establish a fundamental understanding of heavy metal-amino acid interactions.

The ability of the coordinatively saturated, 18-electron Cp*(H)Ru═CHR complex 1 to serve as a masked source of the coordinatively unsaturated Cp*Ru-CH2R species 2 via reversible α-hydride elimination was surveyed. The rate constant for this dynamic process (300 K, C6D6) was measured to be 59 ± 1 s−1, on the basis of data obtained from selective inversion NMR experiments. Exposure of 1 to an atmosphere of CO or to an equivalent of either PMe3 or PH2Ph afforded the corresponding 2·L adduct (L = CO, 98%; PMe3, 93%; PH2Ph, 67%). Treatment of 1 with Ph2SiH2, PhSiH3, Ph2SiClH, or PhSiClH2 afforded the corresponding net Si−H addition product, 3a−d (82−94%); an NMR spectroscopic investigation of the analogous reaction of 1 with Ph2SiD2 provided evidence in support of a reaction mechanism involving previously undocumented Si−H addition across the Ru═C unit in 1 in the formation of 3a. Addition of Jutzi’s acid (H(OEt2)2B(C6F5)4) to 1 resulted in the quantitative formation of 4 (the N-C-H cyclometalated variant of [...

A glycosynthase approach was attempted to glycodiversify macrolide antibiotics, using DesR, a family-3 retaining beta-glucosidase involved in the self-resistance mechanism of methymycin production. STD-NMR was used to probe enzyme-substrate interactions. Analysis of competitive STD-NMR experiments between erythromycin A and a chromogenic substrate (pNP-beta-d-glucose) with the hydrolytically inactive nucleophile mutants led us to discover a family of unprecedented glycosidase inhibitors. Analysis of kinetic data with wild-type DesR determined that erythromycin is a competitive inhibitor of the glucosidase (IC50 = 2.8 +/- 0.3 microM and Ki = 2 +/- 0.2 microM) with respect to the hydrolysis of pNP-beta-d-glucose. Comparable inhibitory data was obtained for clarithromycin; however, the inhibitory effect of azithromycin was weak and no significant inhibition was observed with methymycin or d-desosamine. This report documents significant inhibition of glycosidases by macrolide antibiotics and provides insight into the design of novel glycosidase inhibitors based on the macrolactone ring of macrolide antibiotics.

The synthesis and characterization for trifluoromethanesulfonate (triflate) salts of the first definitive examples of cyclotriphosphinophosphonium and cyclodiphosphinophosphonium cations are described, representing new prototypical frameworks in the rational and systematic development of catena-phosphorus chemistry. Addition of methyl triflate (MeOTf) or triflic acid (HOTf) to cyclotetraphosphines (tBuP)4 (1a) or (CyP)4 (1b) gives [(tBuP)3PtBuMe][OTf] (2a[OTf]), [(CyP)3PCyMe][OTf] (2b[OTf]), [(tBuP)3PtBuH][OTf] (3a[OTf]), and [(CyP)3PCyH][OTf] (3b[OTf]), respectively. Cyclotriphosphine (tBuP)3 (4a) reacts with HOTF or Me2PCl/Me3SiOTf to give the ring expanded cations 3a[OTf] and [(tBuP)3PMe2][OTf] (5[OTf]), respectively, but reactions with MeOTf and HCl give cyclic diphosphinophosphonium cation [(tBuP)2PtBuMe][OTf] (6a[OTf]) and ring-opened triphosphine HtBuP-PtBu-PtBuCl (7), respectively. The analogous diphosphinophosphonium cation [(CyP)2PCyMe][OTf] (6b[OTf]) is formed along with 2b[OTf] in reactions of MeOTf with (CyP)3 (4b). Compounds 2a[OTf], 2b[OTf], 3a[OTf], 5[OTf], and 6a[OTf] have been crystallographically characterized. 1H NMR spectra of 2a[OTf], 2b[OTf], 5[OTf], and 6a[OTf] demonstrate that 3JPH coupling is only observed for methyl protons if they are in a cis orientation to the lone pairs on the adjacent phosphine sites.

The micellization process of sodium 8-phenyloctanoate in a deuterated aqueous solution was studied, using 1H NMR spectroscopy and two-dimensional (2D) nuclear Overhauser enhancement spectroscopy (NOESY). 1H NMR spectra, acquired for the sodium 8-phenyloctanoate before and after the critical micelle concentration (CMC) value, showed that large chemical-shift changes were observed for both the aromatic proton peaks and the peaks for the methylene protons near the terminal phenyl group. The plots for the methylene protons near the headgroup do not show these large chemical-shift changes. These observations support the view that the terminal phenyl ring of the surfactant is primarily located in the micellar interior. The 2D NOESY experiments show significant cross-peaks, between the phenyl protons and the methylene protons of the surfactant, that substantiate the conclusions on those drawn from NMR aromatic solute induced shift (ASIS) experiments on the same and similar systems. All these observations are consistent with the Gruen model of the micelle and previous NMR NOESY experiments for other surfactant systems.Key words: surfactants, micelles, NMR, NOESY.

A new method to determine epoxide concentrations in oxidized oils was developed and validated using (1)H NMR. Epoxides derived from lipid oxidation gave signals between 2.90 and 3.24 ppm, well separated from the signals of other lipid oxidation products. To calibrate, soybean oils with a range of epoxide concentrations were synthesized and analyzed using (1)H NMR by taking the sn-1,3 glycerol protons (4.18, 4.33 ppm) as internal references. The (1)H NMR signals were compared to the epoxide content determined by titration with hydrogen bromide (HBr)-acetic acid solution. As expected, the signal response increased with concentration linearly (R(2) = 99.96%), and validation of the method gave results comparable to those of the HBr method. A study of the oxidative stability of soybean oil was performed by applying this method to monitor epoxides during thermal lipid oxidation. The epoxide content increased over time and showed a different trend compared to peroxide value (PV). A phenomenological model was suggested to model epoxides derived from lipid oxidation.

We report the controlled growth of poly(ethylene glycol) methyl ether grafted polymethacrylate (PEGPMA) on nanosized zeolite external surfaces using the atom transfer radical polymerization (ATRP) ...

Nanometer-sized faujasite zeolite (nanoNaX), synthesized with an organic-additive-free approach, was modified with organic functional groups. Raman scattering and solid-state NMR techniques were employed to study the organic components on the zeolites, the structures of the zeolitic frameworks, and the connections between the organosilyl groups and zeolitic silanol groups. Aminopropylsilyl (APS) and vinylsilyl (VS) groups were covalently grafted to the zeolitic surfaces by directly reacting the nanozeolite with corresponding organosilanes. Although the acryloyl group cannot be introduced onto the zeolitic surface by directly reacting nanoNaX with acryloyl chloride, acrylation can be achieved with APS-modified nanozeolite. 29Si solid-state NMR studies clearly indicate the transformation of zeolitic silicate species from Q3 to Q4 with organosilyl modification. This shows that the connections between the organosilyl groups and the zeolitic silanol groups can be represented as RSi(OSizeolite)x. In the APS-nan...

We have successfully synthesized NaX zeolite crystals with controlled sizes from 20 nm to 0.8 μm, using a novel organic-additive-free approach. We show that the NaX crystal size depends on the silicate source and hydrothermal crystallization conditions, especially crystallization temperature and agitation. The physical properties of NaX-nano (20−100 nm) were characterized by X-ray diffraction, high-resolution scanning electron microscopy, FT-IR spectroscopy, 29Si solid-state NMR spectroscopy, and N2 adsorption. The results were compared with those for micrometer-sized NaX crystals, NaX-μ. As expected, the external surface area of NaX-nano was found to be significantly enhanced compared with that of NaX-μ. Porosity analysis indicates that NaX-nano has a broad distribution of mesopores from 2 to 20 nm, associated with interparticle voids. Both FT-IR and 29Si solid-state NMR spectra revealed the presence of Q3 silicon atoms in NaX-nano. All four Q3 species were assigned in the 29Si NMR spectra.

The carbon chemical shift tensors of the carbonyl and thiocarbonyl groups of acetamide, thioacetamide, thioacetanilide, 4′-methoxyacetanilide, and 4′-methoxythioacetanilide have been experimentally determined using dipolar – chemical shift solid-state 13C NMR spectroscopy. The magnitudes of the three principal components of the carbon chemical shift tensors are found to exhibit marked variations between the carbonyl and thiocarbonyl functionalities. However, in contrast to the conclusions of an earlier comparative investigation involving benzophenone and thiobenzophenone, the orientations of the principal axis systems of these chemical shift tensors are found to be similar. These experimental results represent the first complete characterizations of the carbon chemical shift tensor in organic thiocarbonyls. The results of our ab initio GIAO and LORG calculations of carbon chemical shielding tensors in formaldehyde, thioformaldehyde, formamide, and thioformamide as well as in acetamide and thioacetamide are in qualitative agreement with experiment. The findings of the present investigation provide conclusive evidence that the well-known isotropic deshielding of the carbon nucleus in the C=S group relative to C=O is primarily attributable to the decreased energy associated with the σ ↔ π* excitation within the thiocarbonyl fragment. This result is in contrast with the conventional interpretation that the deshielding originates from a red shift in the C=S HOMO–UMO n → π* transition. Keywords: chemical shift tensors, solid-state 13C NMR, carbonyls, thiocarbonyls, ab initio calculations.

Both carbon-13 and nitrogen-15 solid-state NMR spectroscopy have been employed to characterize the carbonyl carbon and nitrogen chemical shift (CS) tensors of the amide fragment of (Z)-acetanilide (I) and (E)-N-methylacetanilide (II). These two related compounds exhibit very different structural features in the solid state, as shown by previous X-ray diffraction studies. The orientation of the principal axis system (PAS) of both the carbon and nitrogen CS tensors has been determined using dipolar-chemical shift NMR spectroscopy in conjunction with IGLO chemical shielding calculations. For I and II, the carbon CS tensors are found to be very similar

Carbon-13 NMR spectra of solid samples of acetanilide- 13 C(CO) have been examined under conditions of cross-polarization (CP) with and without magic-angle spinning (MAS). The 13 C NMR line shapes are perturbed by direct dipolar coupling to the adjacent quadrupolar 14 N nucleus. The 13 C NMR spectra have been fully analyzed employing first-order perturbation theory for 14 N. Residual 13 C, 14 N splittings observed in the 13 C CP/MAS NMR spectra of the carbonyl and C region of acetanilide indicate an upper limit of the 14 N nuclear quadrupolar coupling constant, χ, of -3.2 MHz

Nitrogen-15 NMR spectra have been obtained for spinning and static powder samples of solid cis-azobenzene- 15 N 2 (1). This nitrogen NMR spectra obtained with magic angle spinning exhibited spinning rate-dependent line shapes which are characteristic of dipolar coupled homonuclear spin pairs which have the same inotropic chemical shifts but different orientations of their shift tensors relative to the dipolar vector

The 2-propynyl group in the title compound, C(17)H(22)O(10), adopts an exoanomeric conformation, with the acetylenic group gauche with respect to position C1. Comparison of (13)C NMR chemical shifts from solution and the solid state suggest that the acetylenic group also adopts a conformation anti to C1 in solution. The pyranose ring adopts a (4)C(1) conformation. Of the three secondary O-acetyl groups, that on position O4, flanked by two equatorial groups, adopts a syn conformation, in agreement with recent generalizations [González-Outeiriño, NasserAnderson (2005). J. Org. Chem. 70, 2486-2493]. The acetyl group on position O3 adopts a gauche conformation, also in agreement with the recent generalizations, but that on position O2 adopts a syn conformation, not in agreement with the recent generalizations.

New solid-state NMR (SSNMR) methods and applications continue to blossom such that a diverse array of physical, chemical, and biological problems are now being addressed using a variety of SSNMR experiments. While SSNMR is far from routine for chemists in the manner that a technique such as solution NMR is, there are nevertheless numerous applications of SSNMR which would be beneficial to many “non-specialists”, e.g., synthetic chemists seeking to characterize their materials. This article gathers together practical details for those one-dimensional experiments which, in a broad sense, are considered “routine” in a modern SSNMR laboratory. Emphasis is placed on providing information and over 300 key references in a manner which will be useful for the novice and the non-specialist. For practicing SSNMR spectroscopists, it is hoped that this article will serve as a valuable reference in the laboratory. In addition to providing a brief review of pulsed Fourier transform NMR, the article discusses experimental details relating to the study of solid samples containing spin- 1 nuclei, non-integer quadrupolar nuclei, and deuterium.

Three different benzophospholium salts (benzo-1,3,2-dithiaphospholium (1a), 5-methylbenzo-1,3,2-dithiaphospholium (1b), and benzo-1,3,2-azathiaphospholium (1c)) have been investigated in the solid state using 31 P NMR spectroscopy. The magnitude of the phosphorus chemical shift anisotropy (Δδ) determined for all three derivatives is in excess of 500 ppm. Dipolar-chemical shift 31 P NMR experiments on the thiazaphospholium salt 1c allowed the 31 P chemical shift tensor to be oriented in the molecular frame of reference

Salts of the first crystallographically characterized chlorophosphinophosphonium ions have been prepared, and their reaction with Ph3P results in reductive coupling of the chlorophosphine centers to give the first acyclic 2,3-diphosphino-1,4-diphosphonium ions, representing a key framework in the development of catena-phosphorus chemistry. These new salts of general formula [R3P-PR'-PR'-PR3][OTf]2 are also obtained in a one-pot diastereoselective reaction of a dichlorophosphine, a tertiary phosphine, and trimethylsilyltrifluoromethanesulfonate. The structural and spectroscopic features of the new dications complement those of the known diphosphonium and 2-phosphino-1,3-diphosphonium dications. Quantitative ligand exchange reactions are observed when derivatives of [Ph3P-PR'-PR'-PPh3][OTf]2 are combined with Me3P, demonstrating the coordinative nature of the phosphine-phosphonium P-P bonds and implicating a bonding model involving the diphosphenium dication acceptor. The observed solid state structures have been interpreted in the context of computational studies.

Reaction of a cyclophosphinophosphonium cation with neat MeOTf represents a general and high-yield synthetic approach to dications enabling the isolation of the first derivatives of 2,4,5-triphosphino-1,3-diphosphonium as bis-triflate salts.

The first derivatives of catenated cyclotetraphosphinophosphonium cations, [(PhP)4PPhMe]+ (8a), [(MeP)4PMe2]+ (8b), [(CyP)4PPh2]+ (8d), [(CyP)4PMe2]+ (8e), [(PhP)4PPh2]+ (8f), [(PhP)4PMe2]+ (8g), are synthesized as trifluoromethanesulfonate (triflate, OSO2CF3-) salts through the reaction of cyclopentaphosphines (PhP)5 (4a) or (MeP)5 (4b) with methyl triflate (MeOTf) or by a net phosphenium ion [PR2+, R = Ph, Me; from R2PCl and trimethylsilyltriflate (Me3SiOTf)] insertion into the P-P bond of either cyclotetraphosphine (CyP)4 (3c) or cyclopentaphosphines (PhP)5 (4a) or (MeP)5 (4b). Although more conveniently prepared from 4a, compound 8a[OTf] can also be formed from (PhP)4 (3a) and MeOTf, and derivatives 8f[OTf] and 8g[OTf] are also accessible through reactions of 3a and R2PCl/Me3SiOTf with R = Ph or Me, respectively. A tetrachlorogallate salt of [(PhP)4PPhtBu]+ (8c) has been synthesized by alkylation of 4a with tBuCl/GaCl3. 31P[1H] NMR parameters for all derivatives of 8 have been determined by iterative simulation of experimental data. Derivatives 8a[OTf], 8b[OTf], 8c[GaCl4], 8e[OTf], 8f[OTf], and 8g[OTf] and have been characterized by X-ray crystallography, showing the most favorable all-trans configuration of substituents for the phosphine centers, thus minimizing steric interactions. Each derivative adopts a unique envelope or twist conformation of C1 symmetry. The effective C2 symmetry observed for 8b, d, e, f, and g in solution, signified by their 31P[1H] NMR AA'BB'X spin systems, implies a rapid conformational exchange for derivatives of 8. The core frameworks of the cations in the solid state are viewed as snapshots of different conformational isomers within the solution-phase pseudorotation process.

Fractionation of the hot water extract of Chlorella pyrenoidosa was performed using a combination of ethanol precipitation, size exclusion chromatography, and anion exchange chromatography. One fraction contained a new polysaccharide, and this compound was shown to be a 1-->2-linked beta-d-galactofuranan from its 1D and 2D (1)H and (13)C NMR spectra, with a molecular weight of 15 kDa from DOSY NMR measurements. A number of other fractions were shown to have the same repeating unit as the previously identified arabinogalactan. However, arabinogalactans from different fractions were shown by DOSY NMR to have different molecular weights, which ranged from 27 to 1020 kDa. Agreement with molecular weights measured for some of these fractions by SEC-MALS was very good, further confirming the relationship established by Viel et al. between molecular weights of neutral polysaccharides and self-diffusion coefficients. The smaller molecular weight polysaccharides, the galactofuranan and the 27 and 50 kDa arabinogalactans, were shown to be close to monodisperse by analysis of the distributions of the self-diffusion coefficients for the polymers. The larger arabinogalactans had considerable variation in their molecular weights (188 +/- 109 kDa and 1020 +/- 370 kDa). Only the two larger arabinogalactans showed immunostimulatory activity.

The acyclic tetraphosphorus dication [Ph3P-PPh-PPh-PPh3]2+ has been formed by the reductive coupling of [Ph3P-PPhCl]+, providing a new synthetic method for the systematic development of catena-phosphorus cations. Ligand exchange (Ph3P for Me3P) gives [Me3P-PPh-PPh-PMe3]2+, implicating these dications as bisphosphine-diphosphenium complexes.

Trifluoromethylsulfonyloxy-(2,4,6-tri-tert-butylphenylimino)phosphine, Mes*NPOTf (Mes = 2,4,6-tri-tert-butylphenyl, OTf = trifluoromethanesulfonate, triflate) reacts quantitatively with the multifunctional ligands 2,2'-bipyridine (2,2'-BIPY), N,N,N',N'-tetramethylethylenediamine (TMEDA), 1,2-bis(diethylphosphino)ethane (DEPE), 1,2-bis(diphenylphosphino)ethane (DIPHOS), and N,N,N',N' ',N' '-pentamethyldiethylenetriamine (PMDETA) to give the Lewis acid-base complexes [Mes*NP(2,2'-BIPY)][OTf], [Mes*NP(TMEDA)][OTf], [Mes*NP(DIPHOS)][OTf], [Mes*NP(DEPE)][OTf], and [Mes*NP(PMDETA)][OTf], respectively. Single-crystal X-ray diffraction studies indicate that the closest contact of the ligand donor atoms occurs at phosphorus in all cases, affecting significant displacement of the OTf anion. The resulting cations [Mes*NP(L)]+ are best described as complexes of a neutral chelating ligand on a phosphadiazonium Lewis acceptor, and highlight the potential for electron-rich centers to behave as Lewis acids despite the presence of a lone pair of electrons at the acceptor site. More importantly, the new complexes represent rare examples of systems containing hypervalent, low-coordinate phosphorus(III) centers.

An arabinogalactan was isolated from a hot water extract of freeze-dried cells of the green microalga, Chlorella pyrenoidosa. This hot water extract is a proprietary immunomodulator, with the trademark Respondintrade mark (ONC-107). The arabinogalactan was recovered from the ethanol-soluble fraction of the supernatant resulting from a process that involved controlled ethanol precipitation followed by size exclusion chromatography on Sephadex G-100, then Cetavlon precipitation. Sugar analyses, GC-MS data for (S)-2-octyl glycosides, and 1D and 2D NMR experiments established unambiguously that the repeating unit was -->2)-alpha-L-Araf-(1-->3)-[alpha-L-Araf-(1-->4)]-beta-D-Galp-(1-->. This structure does not fit into any of the known classes of arabinogalactans. SEC/MALS experiments gave a molecular mass for the arabinogalactan isolated as 47 +/- 4 kDa but the original structure was probably larger.

Isolation and characterization of a crystal mixture of iminophosphine 1 and diphosphazane 2 (R = Mes*, X = OTf) is enabled by the steric interactions between bulky substituents implicating monomer/dimer 1/2 equilibria and the conclusion is supported by the observation of a ring-expansion reaction to give a triphosphazane 3 (R = Dipp, X = Cl).

The application of dipolar NMR techniques to the characterization of nitrogen and phosphorus shielding tensors is discussed. After a brief outline of the theoretical basis of the technique, results from the authors’ laboratory are presented. Nitrogen shielding tensors in several compounds containing two-coordinate nitrogen functional groups are characterized and compared to those calculated for related model compounds using the localized orbital-local origin (LORG) method.