PMe3 Research Articles

Origin and Structural Characteristics of Tri-coordinated Extra-framework Aluminum Species in Dealuminated Zeolites.

Post-synthetic dealumination treatment is a common tactic adopted to improve the catalytic performance of industrialized zeolitic catalysts through enhancements in acidity and stability. However, among the possible extra-framework aluminum (EFAL) species in dealuminated zeolites such as Al3+, Al(OH)2+, Al(OH)2+, AlO+, AlOOH, and Al(OH)3, the presence of tri-coordinated EFAL-Al3+ species, which exhibit large quadrupolar effect due to the lack of hydrogen-bonding species, was normally undetectable by conventional one- and two-dimensional 1H and/or 27Al solid-state nuclear magnetic resonance (SSNMR) techniques. By combining density functional theory (DFT) calculations with experimental 31P SSNMR using trimethylphosphine (TMP) as the probe molecule, we report herein a comprehensive study to certify the origin, fine structure, and possible location of tri-coordinated EFAL-Al3+ species in dealuminated HY zeolite. The spatial proximities and synergies between the Brønsted and various Lewis acid sites were clearly identified, and the origin for the observed EFAL-Al3+ species with ultra-strong Lewis acidity was deduced to be at the expense of adjacent Brønsted acid sites. The excellent performance of such tri-coordinated EFAL species was furthermore confirmed by glucose isomerization reactions.

Me3P-catalyzed addition of hydrogen phosphoryl compounds P(O)H to electron-deficient alkenes: 1 to 1 vs 1 to 2 adducts

Trimethyl phosphine was used as an efficient catalyst for the addition of P(O)-H compounds to electron-deficient alkenes. The addition reactions were generally conducted using a catalytic amount of Me3P under mild reaction conditions. Both 1 to 1 and 1 to 2 adducts were obtained.

Motions of Trimethylphosphine Oxide in Carbon Nanotubes as Revealed by Solid‐state NMR

Trimethylphosphine (TMP) has been adsorbed in carbon nanotubes and oxidized to trimethylphosphine oxide (TMPO). 31P spin–lattice relaxation T1 measurements at temperatures from 203 to 333 K have been employed to investigate the motions of TMPO. The 31P T1 is found to be monoexponential and isotropic. The activation energy is measured as 4.4 ± 0.3 kcal•mol−1, which is comparable to that of TMP adsorbed on Lewis acid sites in zeolites.

Effect of Tunneling Electron Injection on the Dynamic Motion of Confined Molecules in Self-Assembled Molecular Corrals

The dynamic motion of trimethylphosphine (TMP) adsorbates enclosed in self-assembled pyrrole molecular corral structures was observed using scanning tunneling microscopy (STM) techniques. Sequential STM images were obtained under various sample bias and tunneling current conditions to investigate the influence of tunneling conditions on the TMP dynamic motion. It was observed that the TMP adsorbates attempt to move more frequently at lower sample bias conditions, and the TMP movement holds a linear-like relationship with the sample bias. The Si–P antibonding orbitals get stimulated at lower sample bias conditions, which in turn weaken the Si–P bond and force the TMP adsorbates to move. A process can be developed using this attribute to control the dynamic TMP motion such that this molecular system can be utilized as a molecular electronic device.

Trimethylphosphine-Assisted Surface Fingerprinting of Metal Oxide Nanoparticle by (31)P Solid-State NMR: A Zinc Oxide Case Study.

Nano metal oxides are becoming widely used in industrial, commercial and personal products (semiconductors, optics, solar cells, catalysts, paints, cosmetics, sun-cream lotions, etc.). However, the relationship of surface features (exposed planes, defects and chemical functionalities) with physiochemical properties is not well studied primarily due to lack of a simple technique for their characterization. In this study, solid state (31)P MAS NMR is used to map surfaces on various ZnO samples with the assistance of trimethylphosphine (TMP) as a chemical probe. As similar to XRD giving structural information on a crystal, it is demonstrated that this new surface-fingerprint technique not only provides qualitative (chemical shift) but also quantitative (peak intensity) information on the concentration and distribution of cations and anions, oxygen vacancies and hydroxyl groups on various facets from a single deconvoluted (31)P NMR spectrum. On the basis of this technique, a new mechanism for photocatalytic •OH radical generation from direct surface-OH oxidation is revealed, which has important implications regarding the safety of using nano oxides in personal care products.

Synthesis and Reactivity of Group 4 Metal Benzyl Complexes Supported by Carbazolide-Based PNP Pincer Ligands.

This study focuses on the viability of the carbazole-based Cbzdiphos PNP pincer ligand as a stabilizing element for group 4 metal complexes, and both the diphenylphosphino- and di-isopropylphosphino-substituted Cbzdiphos protioligands 1(Ph)H and 1(iPr)H were used. Treatment of the lithiated protioligands with the corresponding chlorido precursor compounds of the metals (titanium, zirconium, and hafnium) afforded the trichlorido complexes [(Cbzdiphos(iPr))MCl3] 2(iPr)M and [(Cbzdiphos(Ph))MCl3] 2(Ph)M (M = Ti, Zr, Hf), which were converted to the corresponding iodido complexes [(Cbzdiphos(iPr))MI3] 3(iPr)M and [(Cbzdiphos(Ph))MI3] 3(Ph)M (M = Ti, Zr, Hf) by reaction with an excess of trimethylsilyl iodide. Reaction of 2(iPr)Ti and 3(Ph)Ti with 1 equiv of dibenzyl magnesium tetrahydrofuran adduct led to the formation of the alkylidene complexes 4(iPr)Ti and 5(Ph)Ti, respectively, while the zirconium and hafnium complexes 2(iPr)Zr and 3(Ph)Zr/Hf formed the cyclometalated monoalkyl compounds [(Cbzdiphos(iPr)-CH)ZrBnCl] 6(iPr)Zr as well as [(Cbzdiphos(Ph)-CH)MBnX] 6(Ph)Hf (X = Cl) and 7(Ph)Zr/Hf (X = I) under analogous reaction conditions. On the other hand, stirring 2(Ph)Zr with 0.25 equiv of tetrabenzyl zirconium afforded [(Cbzdiphos(Ph))ZrBnCl2] (8(Ph)Zr), which contained the PNP ligand intact, while its alkylation with benzyl potassium led to the formation of the cyclometalated monobenzyl complex [(Cbzdiphos(Ph)-CH)ZrBnCl] (6(Ph)Zr). The remaining coordination site occupied by the halogenido ligand in the cyclometalated monobenzyl complexes [(Cbzdiphos-CH)MBnX] 6(iPr)Zr, 6(Ph)Zr/Hf, and 7(Ph)Zr/Hf was readily benzylated by treatment with benzyl potassium to afford the cyclometalated dibenzyl complexes [(Cbzdiphos-CH)MBn2] 9(iPr)Zr and 9(Ph)Zr/Hf. Further reaction of 9(Ph)Zr with an excess of benzyl potassium led to the formation of the anionic tribenzyl zirconium ate complex [(Cbzdiphos-CH)MBn3]K (10(Ph)Zr). Upon heating a solution of 8(Ph)Zr in the presence of 1 mol equiv of trimethyl phosphine, one of the ligand methylene groups was deprotonated, yielding the cyclometalated complex [(Cbzdiphos(Ph)-CH)ZrCl2(PMe3)] 11(Ph)Zr. Finally, reaction of 7(Ph)Zr with methylene triphenylphosphorane produced the ortho-metalated product [(Cbzdiphos(Ph)-CH)Zr(o-C6H4PPh2CH2)I] (12(Ph)Zr), which is characterized by a slightly puckered five-membered Zr-C(48)-P(3)-C(49)-C(50) metallacycle.

ChemInform Abstract: Coupling of Titanacyclopentadienes with a Cp Ligand and Elimination of One Substituent.

AbstractTrisubstituted indenes are formed from alkynes and Cp2TiCl2 via titanacyclopentadienes in the presence of trimethylphosphine and azobenzene.

Dynamic Observation of Confined Molecules in Self-Assembled Molecular Corrals

Molecular corrals self-assembled on a Si(111)-(7 × 7) surface after pyrrole exposure, enclosing silicon adatom sites where trimethylphosphine (TMP) was then datively adsorbed. The phosphine’s dynamic motion was investigated by scanning tunneling microscopy. The TMP was confined by the corral, hopping on adatom sites within it. Density functional theory calculations showed covalent bonding between the pyrroles and surface silicon atoms because of N–H dissociative adsorption. An electropositive potential around the TMP/Si cluster may induce electrostatic repulsion between the adsorbed molecules.

Analysis of the E–E Bond in Group-13 Complexes [(PMe3)2(E2Hn)] (E = B – In, n = 4, 2, 0)

Analysis of the E–E Bond in Group-13 Complexes [(PMe3)2(E2Hn)] (E = B – In, n = 4, 2, 0)

Phosphine-Substituted (η5-Pentadienyl) Manganese Carbonyl Complexes: Geometric Structures, Electronic Structures, and Energetic Properties of the Associative Substitution Mechanism, Including Isolation of the Slipped η3-Pentadienyl Associative Intermediate

The molecule (η5-Me2Pdl)Mn(CO)3 (η5-Me2Pdl = 2,4-dimethyl-η5-pentadienyl) has been prepared by a new method and used as a starting material to prepare the molecules (η5-Me2Pdl)Mn(CO)n(PMe3)3–n (n =...

Intermediate carbene formation in the reaction of thioamides with phosphorus (III) derivatives: Quantum chemical investigation

The reactions of perfluoroalkyl thioamides with trimethyl phosphine, trimethyl phosphite, and tris(dimethylamino)phosphine have been analyzed by means of quantum chemical (DFT and MP2) calculations. The reaction seems to proceed via the nucleophilic attack of the electrophilic carbon atom by the phosphorus lone pair with the formation of cyclic or acyclic adducts. The latter releases the thiophosphate molecule forming perfluoroalkylaminocarbene as the short-lived intermediate. The reaction of the carbene with the second molecule of trialkyl phosphite yields phosphorus ylide. The ylide undergoes a migration of fluorine from carbon to phosphorus. The reactions of perfluoroalkyl thioamides with phosphines and tris(dimethylamino)phosphine probably proceeds differently. Using alkyl thioamides or amides instead of perfluoroalkyl thioamides also makes the reaction less favorable. The only combination of perfluoroalkyl thioamides with trialkyl phosphite fulfills both the kinetic requirements (moderate activation energies and relative energies for intermediates) and the thermodynamic aspects (higher stabilities of the reaction products compared with the starting materials). © 2013 Wiley Periodicals, Inc.

Stereochemical Consequences of Oxygen Atom Transfer and Electron Transfer in Imido/Oxido Molybdenum(IV, V, VI) Complexes with Two Unsymmetric Bidentate Ligands

Two equivalents of the unsymmetrical Schiff base ligand (L(tBu))(-) (4-tert-butyl phenyl(pyrrolato-2-ylmethylene)amine) and MoCl(2)(NtBu)O(dme) (dme = 1,2-dimethoxyethane) gave a single stereoisomer of a mixed imido/oxido Mo(VI) complex 2(tBu). The stereochemistry of 2(tBu) was elucidated using X-ray diffraction, NMR spectroscopy, and DFT calculations. The complex is active in an oxygen atom transfer (OAT) reaction to trimethyl phosphane. The putative intermediate five-coordinate Mo(IV) imido complex coordinates a PMe(3) ligand, giving the six-coordinate imido phosphane Mo(IV) complex 5(tBu). The stereochemistry of 5(tBu) is different from that of 2(tBu) as shown by NMR spectroscopy, DFT calculations, and X-ray diffraction. Single-electron oxidation of 5(tBu) with ferrocenium hexafluorophosphate gave the stable cationic imido phosphane Mo(V) complex [5(tBu)](+) as the PF(6)(-) salt. EPR spectra of [5(tBu)](PF(6)) confirmed the presence of PMe(3) in the coordination sphere. Single-crystal X-ray diffraction analysis of [5(tBu)](PF(6)) revealed that electron transfer occurred under retention of the stereochemical configuration. The rate of OAT, the outcome of the electron transfer reaction, and the stabilities of the imido complexes presented here differ dramatically from those of analogous oxido complexes.

Hydrogenated mesoporous TiO2–SiO2 with increased moderate strong Brönsted acidic sites for Friedel–Crafts alkylation reaction

The acidic properties of mesoporous TiO2–SiO2 mixed oxides were evaluated by 31P magic-angle spinning NMR spectroscopy using trimethylphosphine oxide (TMPO) and trimethylphosphine (TMP) as probe molecules. It confirms that mesoporous TiO2–SiO2 has moderate strong Brönsted acid sites. The number of the Brönsted acidic sites can be increased via a high-temperature hydrogenation process, which subsequently improves their catalytic performance in the Friedel–Crafts reaction of anisole and benzyl alcohol.

Thermal Stability and Acidic Strength of Preyssler‐Type Phosphotungstic Acid, H14[P5W30O110Na] and It's Catalytic Activity for Hydrolysis of Alkyl Acetates

AbstractFull structural analysis of Preyssler‐type phosphotungstic acid, H14[P5W30O110Na], using 183W NMR, 31P NMR, and IR spectroscopy, as well as complete elemental analysis revealed that H14[P5W30O110Na]·44H2O was obtained in pure form. H14[P5W30O110Na] started to decompose by heating at 373 K and was less stable than Keggin‐type phosphotungstic acid, H3PW12O40·6H2O, which was stable even after heating at 673 K. Acidic strength measurements using trimethyl phosphine oxide (Me3P=O) as a probe molecule indicated that the acidic strength of H14[P5W30O110Na] was greater than that of H3PW12O40 on the basis of the amount of acid in an aqueous solution. H14[P5W30O110Na] was less active than H3PW12O40 for hydrolysis of alkyl acetates on the basis of acid amount. However, H14[P5W30O110Na] was more active than H3PW12O40 for hydrolysis of alkyl acetates with small alkyl groups on the basis of catalyst weight because acid amount per weight of H14[P5W30O110Na] was about two times higher than that of H3PW12O40.

Molecular dynamics simulation of liquid trimethylphosphine

Structural and dynamical properties of liquid trimethylphosphine (TMP), (CH(3))(3)P, as a function of temperature is investigated by molecular dynamics (MD) simulations. The force field used in the MD simulations, which has been proposed from molecular mechanics and quantum chemistry calculations, is able to reproduce the experimental density of liquid TMP at room temperature. Equilibrium structure is investigated by the usual radial distribution function, g(r), and also in the reciprocal space by the static structure factor, S(k). On the basis of center of mass distances, liquid TMP behaves like a simple liquid of almost spherical particles, but orientational correlation due to dipole-dipole interactions is revealed at short-range distances. Single particle and collective dynamics are investigated by several time correlation functions. At high temperatures, diffusion and reorientation occur at the same time range as relaxation of the liquid structure. Decoupling of these dynamic properties starts below ca. 220 K, when rattling dynamics of a given TMP molecules due to the cage effect of neighbouring molecules becomes important.

Acidic Strengths of Brønsted and Lewis Acid Sites in Solid Acids Scaled by 31P NMR Chemical Shifts of Adsorbed Trimethylphosphine

The validity of using 31P NMR of adsorbed trimethylphosphine (TMP) as a probe molecule for discerning the types (Brønsted vs Lewis) and strengths of acid sites in solid acid catalysts have been studied by density functional theory (DFT) calculations. Brønsted acid sites with varied acidic strengths covering from weak, strong, to superacid, mimicked by 8T zeolite cluster models having different Si−H bond lengths and hence proton affinities, were examined together with Lewis acid systems having different metallic centers, e.g., BClnF3−n (n = 0−3), AlClnF3−n (n = 0−3), and TiClnF4−n (n = 0−4) and their mixed halides. The theoretical 31P chemical shifts predicted for the hydrogen-bonded TMP···H complex and the TMPH+ adducts were −61 ± 1 and −3 ± 1 ppm, respectively, in good agreement with the experimental data. For the TMP−Lewis acid complex, a linear correlation between the calculated 31P chemical shifts and corresponding binding energies was observed for the B-, Al-, and Ti-containing Lewis acids, respectively, indicating the feasibility of using the 31P chemical shift of adsorbed TMP as a scale for Lewis acidic strength.

Faster oxygen atom transfer catalysis with a tungsten dioxo complex than with its molybdenum analog

The synthesis and characterization of a series of molybdenum ([MoO(2)Cl(L(n))]; L(1) (1), L(2) (3)) and tungsten ([WO(2)Cl(L(n))]; L(1) (2), L(2) (4)) dioxo complexes (L(1) = 1-methyl-4-(2-hydroxybenzyl)-1,4-diazepane and L(2) = 1-methyl-4-(2-hydroxy-3,5-di-tert-butylbenzyl)-1,4-diazepane) of tridentate aminomonophenolate ligands HL(1) and HL(2) are reported. The ligands were obtained by reductive amination of 1-methyl-1,4-diazepane with the corresponding aldehyde. Complexes 3 and 4 were obtained by the reaction of [MO(2)Cl(2)(dme)(n)] (M = Mo, n = 0; W, n = 1) with the corresponding ligand in presence of a base, whereas for the preparation of 1 and 2 the ligands were deprotonated by KH prior to the addition to the metal. They were characterized by NMR and IR spectroscopy, by cyclic voltammetry, mass spectrometry, elemental analysis and by single-crystal X-ray diffraction analysis. Solid-state structures of the molybdenum and tungsten cis-dioxo complexes reveal hexa-coordinate metal centers surrounded by two oxo groups, a chloride ligand and by the tridentate monophenolate ligand which coordinates meridionally through its [ONN] donor set. In the series of compounds 1-4, complexes 3 and 4 have been used as catalysts for the oxygen atom transfer reaction between dimethyl sulfoxide (DMSO) and trimethyl phosphine (PMe(3)). Surprisingly, faster oxygen atom transfer (OAT) reactivity has been observed for the tungsten complex [WO(2)Cl(L(2))] (4) in comparison to its molybdenum analog [MoO(2)Cl(L(2))] (3) at room temperature. The kinetic results are discussed and compared in terms of their reactivity.

Acid properties of solid acid catalysts characterized by solid-state 31P NMR of adsorbed phosphorous probe molecules

A brief review is presented on acidity characterization of solid acid catalysts by means of solid-state phosphor-31 magic-angle-spinning nuclear magnetic resonance ((31)P MAS NMR) spectroscopy using phosphor-containing molecules as probes. It is emphasized that such a simple approach using (31)P MAS NMR of adsorbed phosphorous probe molecules, namely trimethylphosphine (TMP) and trialkylphosphine oxides (R(3)PO), represents a unique technique in providing detailed qualitative and quantitative features, viz. type, strength, distribution, and concentration of acid sites in solid acid catalysts. In particular, it will be shown that when applied with a proper choice of probe molecules with varied sizes and results obtained from elemental analysis, the amounts and locations (intracrystalline vs. extracrystalline) of different types (Brønsted vs. Lewis) of acid sites may be determined. In addition, by incorporating the NMR results with that obtained from theoretical density functional theory (DFT) calculations, correlations between the (31)P chemical shifts (δ(31)P) and acidic strengths of Brønsted and Lewis acid sites may also be derived, facilitating a suitable acidity scale for solid acid catalysts.

Replacement of an Oxo by an Imido Group in Oxotransferase Model Compounds: Influence on the Oxygen Atom Transfer

Treatment of [MoO(N-t-Bu)Cl(2)(dme)] (dme = dimethoxyethane) with 2 equiv of the potassium salts of Schiff base ligands of the type KArNC(CH(3))CHC(CH(3))O afforded oxo imido molybdenum(VI) compounds [MoO(N-t-Bu)L(2)] {1, with Ar = phenyl (L(Ph)), 2 with Ar = 2-tolyl (L(MePh)), 3 with Ar = 2,6-dimethylphenyl (L(Me2Ph)) and 4 with Ar = 2,6-diisopropylphenyl (L(iPr2Ph))}. We have also prepared related bisimido complexes [Mo(N-t-Bu)(2)L(2) (5 with L = L(Ph), 6 with L = L(MePh), and 7 with L = L(Me2Ph)) by treatment of [Mo(N-t-Bu)(2)Cl(2)(dme)] with 2 equiv of the potassium salt of the respective ligand. 1, 3, 5, and 6 were characterized via single crystal X-ray diffraction. The oxo imido complexes exhibit oxygen atom transfer (OAT) reactivity toward trimethyl phosphine. Kinetic data were obtained for 1 and 3 by UV/vis spectroscopy revealing decreased OAT reactivity in comparison to related dioxo complexes with the same Schiff base ligands and decreased reactivity of 1 versus 3. Cyclic voltammetry was used to probe the electronic situation at the molybdenum center showing reversible reduction waves for 3 and [MoO(2)(L(Me2Ph))(2)] at comparable potentials while 1 exhibits a significant lower potential. Density functional theory (DFT) calculations showed a higher electron density on oxygen in the oxo imido complexes.

Computational and experimental approaches to the molecular structure of the HCl adduct of Me3PO.

The reaction of anhydrous HCl(g) with trimethyl phosphane oxide yields trimethylhydroxy phosphonium chloride. A crystal structure analysis showed that the prevalent mesomeric structure in the solid state is the phosphonium chloride ion pair. Ab initio calculations in the gas phase cannot reproduce these findings, whereas higher correlated methods (CISD) and solvation models predict the experimental structure correctly.