PMe3 Research Articles

Characterization of acidity in zeolites and related oxides using trimethylphosphine as a probe

The MAS-NMR spectra of trimethylphosphine (TMP) have been used to study acidity on zeolites, amorphous silica-alumina, sulfated ziconia and other solid materials. Acidic protons react with the strong Lewis base to form [(CH3)3P-H]+ adducts that are characterized by a 31P chemical shift of ca. -3 ppm and a JP-H coupling constant of ca. 500 Hz. Lewis-bound TMP exhibits resonances at considerably higher fields, and if aluminum is involved, a JP-Al coupling of ca. 300 Hz may result in a multiplet of six lines. When excess TMP is present, rapid chemical exchange may occur between the liquid-like molecules and those that are complexed at acid sites. In such cases the distinction between the different forms of TMP is obscured. Attempts to relate Bronsted acid strength to a magnetic parameter such as the scalar coupling constant show promise in those cases where the majority species is of interest. In dealuminated Y zeolites, however, it appears that a small fraction of the protons is responsible for acid-catalyzed reactions, and the value of the JP-H coupling does not adequately reflect the contribution of these centers.

Studies of the electron density in the highest occupied molecular orbitals of PH3, PF3 and P(CH3)3 by electron momentum spectroscopy and Hartree-Fock, MRSD-CI and DFT calculations

The spherically averaged momentum profiles for the highest occupied molecular orbitals of PF3 and P(CH3)3 have been obtained by electron momentum spectroscopy. The measurements provide a stringent test of basis set effects and the quality of ab-initio methods in the description of these larger molecular systems. As in previous work on the methyl-substituted amines, intuitive arguments fail to predict the correct amount of s- and p-type contributions to the momentum profile while delocalized molecular orbital concepts provide a more adequate description of the HOMOs. The experimental momentum profiles have been compared with theoretical momentum profiles calculated at the level of the target Hartree-Fock approximation with a range of basis sets. New Hartree-Fock calculations are also presented for the HOMO of PH3 and compared to previously published experimental and theoretical momentum profiles. The experimental momentum profiles have further been compared to calculations at the level of the target Kohn-Sham approximation using density functional theory with the local density approximation and also with gradient corrected (non-local) exchange correlation potentials. In addition, total energies and dipole moments have been calculated for all three molecules by the various theoretical methods and compared to experimental values. Calculated ‘density difference maps’ show the regions where the HOMO momentum and position electron densities of PF3 and P(CH3)3 change relative to the corresponding HOMO density of PH3. The results suggest that methyl groups have an electron-attracting effect (relative to H) on the HOMO charge density in trimethyl phosphines. These conclusions are supported by a consideration of dipole moments and the 31P NMR chemical shifts for PH3, PF3 and P(CH3)3.

31P Solid State NMR and ESR Investigation of Trimethylphosphane Adsorption on Zirconia and Sulfated Zirconia

31P MAS NMR spectra of trimethylphosphane (TMP) adsorbed on monoclinic zirconia (ZrO2) and on tetragonal sulfated zirconia (ZrO2−S) were measured. The 31P NMR spectra show that protonic acidity, which does not exist on ZrO2, is induced on ZrO2−S. Lewis acid centers on ZrO2−S are stronger than those on ZrO2. The formation of trimethylphosphane oxide was also detected, indicating oxidizing properties of ZrO2−S that sulfate-free ZrO2 does not possess. ESR spectra suggest the formation of SO3- radical anions during TMP oxidation.

Highly site-selective adsorption of trimethylphosphine on a Si(111)-(7 × 7) surface studied by a scanning tunneling microscope (STM)

Adsorption of trimethylphosphine (TMP) on a Si(111)-(7 × 7) surface has been studied using a scanning tunneling microscope (STM). We find that most of the TMP molecules are adsorbed preferably on center adatom sites at the surface. It is observed that the TMP molecule on a corner adatom is moved to a center adatom site at RT. TMP is more stable on the center adatom sites than on the corner adatom sites.

CpMoCl(PMe3)3][BF4] and [Cp*MoCl(PMe3)3][PF6

Chloro(η 5 -cyclopentadienyl)tris (trimethylphosphine)molybdenum(III) tetrafluoroborate, [MoCl(C 5 H 5 )(C 3 H 9 P) 3 ][BF 4 ], was obtained from the oxidation of [MoH(C 5 H 5 )(PMe 3 ) 3 ] by AgBF 4 , followed by crystallization from dichloromethane. Chloro(η 5 -pentamethylcyclopentadienyl)tris(trimethylphosphine)molybdenum(III) hexafluorophosphate, [MoCl(C 10 H 15 )(C 3 H 5 P) 3 ][PF 6 ], was obtained from the reaction of [MoCl 2 -(C 10 H 15 )(C 3 H 9 P) 2 ] with TlPF 6 and PMe 3 in dichloromethane. Both cations adopt a four-legged piano-stool arrangement

31-P NMR study study of acidic sites on Al2O3 and Al2O3-SnO2 after reaction with CCl2F2/H2

The surface acidic properties of two series of samples,γ-Al2O3 andγ-Al2O3-SnO2 after reaction with CCl2F2/H2 (CFC12/H2), have been investigated by solid state high resolution CP/MAS 31-PNMR, using trimethylphosphine (TMP) as a probe molecule. It was found after reaction, that Bronsted acid sites were formed on theγ-Al2O3 surface. The longer the reaction time, the more rigidly TMP bonded to the acid sites. For theγ-Al2O3-SnO2 system, Bronsted acid sites were also found on both the Al2O3 and SnO2 surfaces after reaction of theγ-Al2O3-SnO2 system with CFC12/H2. The signal intensity relevant to these sites, indicates that the SnO2 component is attached to, and therefore covers Bronsted sites ofγ-Al2O3. Two types of Lewis acid site initially present on SnO2 were not observed after reaction with CFC12/H2.

Reaction of W(CPh)X(CO)2(PMe3)2 (X = Cl, Br) with PMe3 To Give W(CPh)X(CO)(PMe3)3: Characterization of a Ketenyltungsten Intermediate

Reaction of W(CPh)X(CO)2(PMe3)2 (X = Cl, Br) with PMe3 To Give W(CPh)X(CO)(PMe3)3: Characterization of a Ketenyltungsten Intermediate

Vibrational absorption intensities in chemical analysis—VIII. Dimethyl sulphide

Abstract The structure and electric dipole moment of dimethyl sulphide have been calculated with a variety of basis sets. It is shown that the force fields computed with the 3-21G, 3-21G and 6-311G** bases are very similar after scaling. The vibrational assignments are discussed. The force field is compared with that of trimethyl phosphine. There is an excellent accord for the CH stretching modes, but the ab initio calculations indicate that the X-C/X-C (X = S,P) interaction terms have opposite signs. This appears to be incompatible with the experimental data. Effective atomic charges and atomic polar tensors (APT) are computed with the above bases and also with bond centred sp functions added to the 3-21G* basis. It is shown that the APT are much more sensitive to the basis set than are the effective atomic charges. The effects of the lone pair electrons on the bond electrical properties are much less than with oxy-ethers, though the overall perturbation of the sulphur atom on the intensities is greater. A number of inadequacies of the SCF calculations are identified.

Motions of Trimethylphosphine on the Surface of Acid Catalysts

On acid surfaces, trimethylphosphine (TMP) forms either Bronsted or Lewis site adducts, TMPH[sup +] or TMP:L, respectively. In TMPH[sup +], the [sup 31]P magnetization decay is practically monoexponential and the [sup 31]P spin-lattice relaxation rate (1/T[sub 1]) is not thermally activated. In TMP:L, the magnetization decay is biexponential and the relaxation rate is thermally activated. Using the known internuclear distances in TMPH or TMPH[sup +], it is shown that the relaxation rates can be accounted for by using the homo- and heteronuclear (intramolecular) contribution rates. The only adjustable parameter is the preexponential factor in the correlation time ([tau][sub 0]). [tau][sub 0] is 10[sup [minus]11] s for the PH vector reorientation and 10[sup [minus]13] s for the H-H (methyl) vector rotation in TMP:L. It is 10[sup [minus]7] s for the PH[sup +] reorientation in TMPH[sup +]. It is observed that the resonance frequency in TMPH[sup +] or TMP:L is temperature independent, ruling out chemical exchange. In one case only, (TMPH[sup +] on dealuminated H-Y zeolite) a change in the isotropic chemical shift with temperature has been observed. 20 refs., 6 figs., 2 tabs.

31P and119Sn high resolution solid state CP/MAS NMR study of Al2O3-SnO2 systems

A series of Al2O3-SnO2 catalysts with the mole ratio of Al2O3 to SnO2 equal to 1:1, 1 ∶ 0.5, 1 ∶ 0.1, 1 ∶ 0.05 and 1 ∶ 0.01 were characterized by31P NMR of adsorbed trimethyl phosphine (TMP) and119Sn MAS NMR spectroscopy. It was found from31P NMR that no Bronsted acid sites exist in these samples. Pure SnO2 shows two different types of Lewis acid sites; in the mixed oxide samples a Lewis peak characteristic of pure Al2O3 is always seen, together with either one or two other Lewis peaks, depending on the Sn concentration.119Sn CP/MAS NMR spectra of the highest Sn-content sample show one narrow line at −603 ppm superimposed on a very broad line, indicating a strong interaction between Al and Sn oxides.

An NMR study of acid sites on chlorided alumina catalysts using trimethylphosphine as a probe

The MAS-NMR spectra of adsorbed trimethylphosphine (TMP) were used to determine the concentration of Bronsted and Lewis acid sites on pure and chlorinatedγ-Al2O3 samples. Chlorination with CHCl3,CCl4 or AlCl3 promoted the formation of Bronsted acid centers, which are characterized by the protonated adduct of TMP. This adduct has a31P chemical shift of ca. −3.8 ppm and a JP−H scalar coupling of 517 Hz. Additional resonances in the −44 to −54 ppm range are attributed to Lewis acid-base pairs. In some cases a partially resolved JP−Al coupling is observed, which confirms the assignment. Upon thermal treatment of a chlorinated sample at temperatures > 200°C, the concentration of Bronsted acid centers decreased; the concentration of one type of Lewis acid increased and another remained almost constant. In a parallel set of experiments the initial conversion ofn-hexane at 150°C and the yields of cracking and isomerization products were determined. Comparable functional relationships were observed between the loss of Bronsted acid sites and the decrease in yields of both cracking and isomerization products. These results suggest that Bransted acidity is responsible for the cracking and isomerization ofn-hexane over chlorided aluminas at 150°C.

Defect density and photoelectrical properties of alternative doped amorphous silicon

Slightly B- and P-doped a-Si:H have been prepared in two different reactors by using Triethylboron (TEB) and Trimethylphosphine (TMP). It is shown that by doping with these agents the Fermi energy E F can be shifted over a wide range within the gap including the region of compensation. The optical parameters are almost constant within the range of doping. The deconvolution of the absorption spectra α( hv) reveals a growing defect peak in the upper half of the gap for p-type (D +-band) and in the lower one for n-type samples (D-band). Remarkable differences between the reactor types were not observed. The data have been successfully analysed on the base of the hydrogen mediated weak bond/dangling bond conversion model. Within the framework of the “defect pool”-model the comparison with the ordinary doping yields only small differences in the pool parameters.

The Synthesis, Reaction and Crystal Structures of Ethyltetramethylcyclopentadienylruthenium Compounds

Pentamethylcyclopentadienyl-trimethylphosphine-metal compounds play an important role in the activation studies of saturated hydrocarbons. A method to synthesize ethyltetramethylruthenium compounds was established, which started from the reaction of RuCl 3 . H 2 O with ethyltetramethylcyclopentadiene to give a dimer compound of 2. When 2 was reacted with different amounts of trimethylphosphine, compounds 3 [C 5 Me 4 EtRu(PMe 3 )Cl 2 ] and 4 [(C 5 Me 4 Et)Ru(PMe 3 ) 2 Cl] were obtained. Compound 3 is a 17-electron species which is in formula similar to Bergman's Ir compound used in hydrocarbon activation reaction, but might be more reactive because of its unsaturated electron structure. The crystal structure analysis of compounds 2, 3 and 4, showed that the ruthenium atom was coordinated in a "threeleg-piano-stool" geometry in all the three compounds. The Ru—Cl bond in 3 and 4 was lengthened, making it labile to other substitution reactions.

Darstellung und struktur von 1-metalla-2,3,4-triazolen des molybdäns und wolframs

The reaction of cyclopentadienyl substituted carbyne complexes of molybdenum and tungsten C 5H 5(CO) 2- n (PMe 3) n MCR (M  Mo, W; R  C 6H 5, C 6H 4CH 3, CH 3, n = 0, 1) ( la–3c) with azides N 3R′ (R′ CO 2CH 3, CH 2CO 2CH 3) results in a [3 + 2]-cycloaddition to the electron-rich metal carbon triple bond, producing neutral 1-metalla-2,3,4-triazole complexes C 5H 5(CO) 2- n (PMe 3) n MC(R)NNN R′(M  MO, W; R  C 6H 5, C 6H 4CH 3, CH 3, n = 0, 1) ( 4a–7c) in high yields.The new compounds were identified by X-ray structure analysis ( 5b), elemental analyses, NMR, IR and mass spectra.

Relationship between the Scaling of the Acid Strength of Lewis Sites by EPR and NMR Probes

While numerous techniques have been successful for scaling the acid strength of Brønsted sites, the situation is not satisfactory at all, for the Lewis acid sites. This is most unfortunate, since Lewis sites are present in most acid catalysts. This contribution aims to show that the simultaneous use of EPR and NMR probes suggests solutions to the problem of scaling the acid strength of Lewis sites. As shown previously, the hyperfine splitting of the EPR spectrum of the aniline radical cation or of the O−2 superoxide ion is a measurement of the strength of the electron acceptor site. Other researchers have suggested the shielding of the 31P nucleus and the shift of its resonance lines in chemisorbed trimethylphosphine (TMP) as a measurement of the Lewis acid strength. The comparison of the scaling obtained on a set of superacids, namely, and in the decreasing order of acidity, the sulfated derivatives of ZrO2, HfO2, Al2O3 and TiO2, by either the EPR or the NMR probes gives interesting information. While very strong Lewis acid centers in sulfated ZrO2 and HfO2 are revealed by 31P downfield shifted resonance lines, no such lines are observed in sulfated Al2O3 or TiO2 or zeolites (such as dealuminated mordenite) which contains strong Lewis acid centers. In the latter samples, the most downfleld shifted line corresponds to that generally assigned to TMPH+. Measurement of 31P relaxation rates suggests that TMP has a more restricted mobility on strong than on weak Lewis sites. They also show that the origin of the relaxation in TMPH+ is ambiguous: either the mobility of TMPH+ is very restricted and/or the extraproton is not as close to the phosphorus as anticipated.

Fluorine-induced chemiluminescence detection of phosphine, alkyl phosphines and monophosphinate esters

Phosphine, alkylated phosphines and monophosphinate esters are detected with high sensitivity in capillary gas chromatography (GC) by their chemiluminescent reactions with molecular fluorine. Detection limits are estimated to be 1.3 pg, 0.5 pg, 8 pg, and 17 pg for phosphine, trimethyl phosphine, trimethyl phosphinate ester, and triethyl phosphine, respectively. As found earlier with alkylated sulfur, selenium and tellurium compounds, the detector exhibits a linear response. For triethyl phosphine, a linear range of greater than three orders of magnitude was demonstrated. Emission spectra were obtained for the trimethyl phosphine and triethyl phosphine systems. Chemiluminescence emitters include electronically excited HCF, vibrationally excited HF, and an unknown species in the trimethyl phosphine system. Banded emission from vibrationally excited HF and a broad continuum were observed for both trimethyl phosphine and triethyl phosphine; however, HCF emission was observed only for TMP. Under the conditions employed, the principal emitter is HCF for trimethyl phosphine and HF and the unknown emitter for triethyl phosphine. This detector may have important applications in investigations of the biogeochemical cycling of phosphorus.

FTIR study of novel palladium trimethylphosphinecarbonyl clusters encaged in zeolite y

Green palladium trimethylphosphinecarbonyl (TMPC) clusters in zeolite Y have been prepared using a “ship-in-a-bottle” method. Trimethylphosphine (TMP) ligands stabilize palladium clusters of small nuclearity; they preferentially coordinate to the corner palladium atoms. Absorption bands of triply-bonded carbonyl (1886 cm −1) are observed only for samples with initially large palladium nuclearity ( n>4). Bands at 1960 and 1950 cm −1, attributed to doubly-bonded carbonyl in a butterfly configuration, dominate the IR spectra. The palladium core in palladium TMPC clusters is electron-rich, in comparison to palladium single crystals, due to electron donation from phosphorus to the palladium. The spectra of the zeolite engaged clusters differ from those reported for Pd TAPC (A  alkyl such as ethyl and butyl) clusters in solution with nuclearity varying from 4 to 38. Zeolite encaged Pd TMPC clusters are stable at 200°C in a flow of H 2+CO. At 3000°C, the TMP ligands decompose and poison the palladium particles.

Proton hyperfine resonance assignments in trimethylphosphine ligated ferrimyoglobin using saturation transfer spectroscopy

1H-NMR saturation transfer spectroscopy and nuclear Overhauser effect (NOE) have been utilized to assign several heme resonances in the low-spin trimethyl phosphine complex of sperm whale metmyoglobin. The two methods permit the location of the heme methyl resonances and the heme 2-vinyl group resonances. A qualitative comparison involving the methyl shift pattern in metMbN 3, metMbCN, imidazole metMb and trimethyl phosphine metMb shows a reverse methyl shift between pyrrole I and pyrrole IV. The different hyperfine shift pattern for metMbPMe 3 is suggested to arise from: (i) a possible reorientation of the proximal histidine plane; (ii) different heme protein contacts in the different ligated proteins, and (iii) a small contribution from high-spin character. The 2-vinyl group is formed in the cis plane orientation.

Bis(trimethylphosphine)-diborane(4) as a reagent for borane framework expansion

Formation de composes d'addition a partir de reactions entre B 4 H 6 , B 2 H 3 et P(CH 3 ) 3

Proton nuclear overhauser effect investigation of the heme pocket expansion in trimethyl phosphine sperm whale myoglobin

Abstract Two-dimensional nuclear magnetic resonance spectroscopy (2D NMR) was used to assign amino acid residues from the distal side of the heme pocket in the 1 H-NMR spectrum of trimethyl phosphine sperm whale myoglobin. The unambiguous assignment of the heme substituents and NOE connectivities from the resonances of trimethyl phosphine protons formed the basis for the identification of amino acid residues. Our results suggest assignment of the aromatic resonances corresponding to Phe-33 (B 14 ), Phe-43 (CD 1 ), Phe-46 (CD 4 ) and His-64 (E 7 ). These assignments provide comparative information on the conformation of the heme pocket in complexes of sperm whale myoglobin with two different ligands CO and PMe 3 . The difference in the spatial disposition of the Val-68 side-chain and the Phe-43 and His-64 rings between the two complexes confirms the greater steric hindrance in MbPMe 3 .