Free Phosphine Research Articles

Differences Between Amine- and Phosphine-Boranes: Synthesis, Photoelectron Spectroscopy, and Quantum Chemical Study of the Cyclopropylic Derivatives

Borane complexes of aziridine, phosphirane, cyclopropylamine, cyclopropylphosphine, cyclopropylmethylamine, and cyclopropylmethylphosphine have been prepared by the reaction at low temperatures of a borane complex or diborane on the free phosphine or amine. The products characterized by NMR spectroscopy and mass spectrometry have then been investigated by photoelectron spectroscopy and B3LYP/aug-cc-pVTZ quantum chemical study. The complexation led to rotamers with structures similar to the ones of the corresponding free systems. The main geometry change with the complexation is the P-C bond elongation and the N-C bond shortening, which can be rationalized by the charge transfer attached to the electron donation. The calculated relative stability order of the conformers changes with the complexation only in the case of cyclopropylamine. The calculated complexation energies are higher for the amines, in accord with the differences observed in the flash vacuum thermolysis of methylamine-, methylphosphine-, and aziridine-borane. The photoelectron spectra indicate essential differences between the amines and phosphines toward borane complexation. The dative bond is more stable in the studied amine-boranes than in phosphine-boranes, while the sigma(B-H) orbitals are more stable in the latter compounds. The enthalpy of the hydrogen release reaction of aziridine-borane is almost thermoneutral, indicating the potential of this complex as recyclable hydrogen storage material.

The preparation of multimetallic complexes using sterically bulky N-centred tripodal dialkyl phosphino ligands

Sterically bulky monodentate and bidentate phosphines have been widely used as ligands for metal complexation and catalyst formation. Bulky tridentate phosphine ligands are however much rarer and have not been widely investigated even though they may be considered attractive ligands for coordination chemistry studies and catalysis. Here we report the synthesis of two new N-centred tripodal phosphine ligands bearing bulky cyclohexyl and tert-butyl groups. The coordination chemistry of the cyclohexyl triphosphine ligand N(CH 2PCy 2) 3 ( 4) was investigated and found to react with Mo and W hexacarbonyls preferentially forming bidentate metal tetracarbonyl complexes [Mo(CO) 4{N(CH 2PCy 2) 3-κ 2 P}] ( 6) and [W(CO) 4{N(CH 2PCy 2) 3-κ 2 P}] ( 7) over the expected facial capping tridentate complexes. The steric bulk of the cyclohexyl groups on the phosphorus atoms is sufficient to prevent the third arm of the ligand from coordinating and adopting the required geometry for facial coordination. This ‘steric control’ at the metal centre results in the third arm remaining freely available for further metal coordination. The coordination chemistry of this free phosphine arm on complexes 6 and 7 was investigated further and used to prepare a series of gold, platinum and silver multimetallic complexes. The X-ray crystal structures of the resulting mixed bi and trimetallic complexes [W(CO) 4{N(CH 2PCy 2) 3-κ 2 P}AuCl] ( 8), [[Mo(CO) 4{N(CH 2PCy 2) 3-κ 2 P}] 2(μ-PtCl 2)] ( 9) and [[W(CO) 4{N(CH 2PCy 2) 3-κ 2 P}] 2(μ-Ag)]ClO 4 ( 11) are reported.

Synthesis of 4-Substituted Styrene Compounds via Palladium-Catalyzed Suzuki Coupling Reaction Using Free Phosphine Ligand in Air

The air-stable and easy to prepare nonsymmetric Schiff base ligands have been synthesized and proven to be efficient ligands for Suzuki cross-coupling reaction between aryl bromides and arylboronic acids using PdCl2(CH3CN)2 as palladium source under aerobic conditions. The coupling reaction proceeded smoothly using N-[(3,4-dimethoxyphenyl)methylene]-1,2-benzenediamine (L3) as ligand under mild conditions to provide 4-substituted styrene compounds in good yields.

Dynamic Behavior of Intramolecularly Base-Stabilized Phosphatetrylenes. Insights into the Inversion Processes of Trigonal Pyramidal Geramanium(II) and Tin(II) Centers

The reaction between SnCl2 and either 1 or 2 equiv of the lithium salt [{(Me3Si)2CH}(C6H4-2-CH2NMe2)P]Li gives the heteroleptic compound [{(Me3Si)2CH}(C6H4-2-CH2NMe2)P]SnCl (7) and the homoleptic, intramolecularly base-stabilized diphosphastannylene [{(Me3Si)2CH}(C6H4-2-CH2NMe2)P]2Sn (8), respectively, in good yields. The solid state structure of 8 shows that the tin(II) center is three-coordinate, bound by the N and P atoms of a chelating phosphide ligand and the P atom of a second phosphide ligand. Both 7 and 8 are highly dynamic in solution. Variable-temperature NMR spectra suggest that compound 7 and its germanium analogue 5 are subject to two distinct dynamic processes in polar solvents, which are attributed to the formation of adducts between either 5 or 7 and the free phosphine {(Me3Si)2CH}(C6H4-2-CH2NMe2)PH (9) and interconversion between diastereomers of these adducts. Adduct formation is observed only in polar solvents and may be associated with the formation of weakly bound [[{(Me3Si)2CH}(C6H4-2-CH2NMe2)P]E(L)]+···Cl− ion pairs in solution. The dynamic behavior of 8 has been studied by multielement and variable-temperature NMR experiments; at high temperatures there is rapid equilibrium between diastereomers, but at low temperatures a single diastereomer predominates and exchange between the chelating and terminal phosphide ligands is frozen out. DFT calculations on the model compound {(Me)(C6H4-2-CH2NMe2)P}SnCl (7a) suggest that epimerization occurs either through a vertex-inversion process at phosphorus [Einv = 65.3 kJ mol−1] or an edge-inversion process at tin [Einv = 141.0 kJ mol−1], of which the former is clearly favored. DFT calculations on the model complex {(Me)(C6H4-2-CH2NMe2)P}2Sn (8a) indicate that the lowest energy dynamic process involves exchange between the chelating and terminal phosphide ligands via a pseudotrigonal bipyramidal intermediate [E = −12.6 kJ mol−1]. Inversion at tin in 8a (via an unusual hybrid edge/vertex-inversion process) is calculated to have a barrier of 206.3 kJ mol−1, whereas the barriers to vertex-inversion at phosphorus are 59.4 and 51.0 kJ mol−1 for the chelating and terminal phosphorus atoms, respectively.

Trans influences of Cl−, NCO− and NCS− donors on planar NiS2PN(CO), NiS2PN(CS), NiS2PCl and NiS2P2 chromophores: synthesis, NMR spectral and single crystal X-ray structural studies

Planar [Ni(bedtc)(PPh3)Cl] (1), [Ni(bedtc)(PPh3)(NCO)] (2), [Ni(bedtc)(PPh3)(NCS)] (3), [Ni(bedtc)(PPh3)(CN)] (4) and [Ni(bedtc)(dppe)]ClO4 (5) (where bedtc = N-benzyl-N-(2-hydroxyethyl)dithiocarbamate anion, PPh3 = triphenylphosphine and dppe = 1,2-bis((diphenylphosphino)ethane)) were prepared from [Ni(bedtc)2]. Complexes 1–5 were characterized by elemental analysis, electronic, IR and NMR (1H, 13C, and 31P) spectra. Electronic spectra of the complexes show bands corresponding to dz 2 → dxy/dx 2 − y 2 transitions. The complexes were diamagnetic. IR and 13C NMR studies indicate the mesomeric flow of π-electron density from the dithiocarbamate towards the nickel. In 1H NMR, α-CH2–and β-CH2–protons of–CH2–CH2–OH were equally deshielded. The deshielding for the coordinated phosphorus signals in 31P NMR spectra for all the cases compared with the free phosphine clearly manifests the drift of electron density from the phosphorus toward the metal on complexation. Single crystal X-ray structures of 1–3 indicate that nickel is in a planar environment with short >S2C–N bond distances. In 2, a rare mode of coordination between nickel and cyanate (NCO−) through the nitrogen is observed. Significant asymmetry in Ni–S bond distances were observed for 1–3 clearly supporting the trans influences of Cl−, NCO− and NCS−, respectively, over PPh3.

Synthesis, Characterization, and Electrochemistry of Compounds Containing 1-Diphenylphosphino-1′-(di-tert-butylphosphino)ferrocene (dppdtbpf)

The anodic electrochemistry of 1-di-tert-butylphosphino-1′-diphenylphosphinoferrocene (dppdtbpf) was performed in methylene chloride with tetrabutlylammonium hexafluorophosphate as the supporting electrolyte. The electrochemistry is complicated by a chemical reaction after the oxidation. Three new transition metal complexes of dppdtbpf ([NiCl2(dppdtbpf)], [PtCl2(dppdtbpf)], and [Au2Cl2(dppdtbpf)]) were prepared and characterized. The electrochemistry of the three new compounds and one previously prepared compound ([PdCl2(dppdtbpf)]) was examined. In addition, the reaction of dppdtbpf with sulfur and/or selenium afforded a series of compounds containing a phosphine sulfide (dppSdtbpSf or dppdtbpSf), a phosphine selenide (dppSedtbpSef or dppdtbpSef), or both a phosphine sulfide and a phosphine selenide (dppSedtbpSf or dppSdtbpSef). These compounds were characterized by NMR, and the structures of three of the compounds were determined. Two of the structures are of the isomeric compounds, dppSdtbpSef and dppSedtbpSf, in which the sulfur and selenium atoms are switched between the two different phosphine groups. The anodic electrochemistry of these sulfur- and/or selenium-containing compounds was examined in methylene chloride. The potentials at which oxidation occurs are more positive than those of the free phosphine. Nearly all of the oxidations are complicated by at least one chemical reaction.

Synthesis, photoelectron spectroscopy and quantum chemical study of kinetically unstabilized phosphines complexed by borane

Ethynyl- and allenylphosphine-boranes have been prepared by addition at low temperature of borane on the free phosphine. Purification was performed by selective trapping in vacuo and the complexes were characterized by NMR and infrared spectroscopy and mass spectrometry. A kinetic stability lower than that of the corresponding free systems was observed. A series composed of these compounds and methyl-, vinyl-, allyl- and propargylphosphine-boranes was investigated by photoelectron spectroscopy and B3LYP/aug-cc-pVTZ quantum chemical study in order to define the variation in the electronic effects between the free systems and the corresponding complexes. Although the complexation only led to minor changes in the unsaturated moiety, the P-C bond shortens in all cases because of the charge transfer from phosphorus to boron. Similar rotamers can be found in the complexes and the free systems, and the order of the relative stability is reversed only in the case of the allenyl derivative. The calculated complexation energies are between 80-100 kJ mol(-1) in agreement with flash vacuum thermolysis experiments. The photoelectron spectra can be easily described in the case of alpha,beta-unsaturated compounds by the change of the direct conjugation between the lone electron pair and the pi-bond in the free phosphines to hyperconjugation of the sigma(P-B) bond with the unsaturated moiety in the corresponding complexed derivatives. In the case of beta,gamma-unsaturated derivatives the observed hyperconjugation in phosphines disappears on complexation.

Counterdisproportionation between cationic Ni(II) and phosphine Ni(0) complexes

The interaction of Ni(II) bis-tetrafluoroborate complexes [Ni(Dppe)2](BF4)2 and [Ni(CH3CN)6](BF4)2 (where Dppe = 1,2-bis(diphenylphosphino)ethane)) with Ni(0) phosphine complexes Ni(Dppe)2 and Ni(PPh3)4 in 1 : 1 mixture of toluene-acetonitrile was studied by the EPR method. The counter-disproportionation was shown to occur in a solution between the cationic Ni(II) complexes and the Ni(0) complexes to give Ni(I) complexes almost in quantitative amounts. The structures of the cationic Ni(I) complexes obtained were found to depend on both the solvent nature and the presence of a free phosphine in a solution.

Synthesis and coordination of the bifunctionalized ylides Ph 2P(CH 2) n(Ph) 2P [dbnd]CHCOOMe ( n = 1, 2) and ketenylidene Ph 2P(CH 2) 2(Ph) 2P [dbnd]C [dbnd]C [dbnd]O to Pd and Pt complexes

In this paper it is reported the synthesis of the phosphonium salts [Ph 2P(CH 2) n (Ph) 2PCH 2COOMe]Br ( n = 1 ( 1), 2 ( 2)) and [Ph 2P(CH 2COOMe)(CH 2) n (Ph) 2PCH 2COOMe]Br 2 ( n = 3 ( 3)) derived from the reactions of the diphosphines dppm, dppe and dppp with methyl bromoacetate. By reaction of the monophosphonium salt of dppm and dppe with the strong base Na[N(SiMe 3) 2] the corresponding carbonyl stabilized ylides Ph 2P(CH 2) n (Ph) 2P CHCOOMe ( n = 1 ( 4), 2 ( 5)) were obtained. The Ph 2P(CH 2) 2(Ph) 2P CHCOOMe ( 5) ylide was reacted with Pd(II) and Pt(II) substrates. From these reactions were isolated exclusively complexes in which the ylide was chelated to the metal through the free phosphine group and the ylidic carbon atom. A further reaction of the Ph 2P(CH 2) 2(Ph) 2P CHCOOMe ( 5) ylide with 1.5 equiv. of Na[N(SiMe 3) 2] gives the bifunctionalized ketenylidene Ph 2P(CH 2) 2(Ph) 2P C C O ( 6) system. This cumulenic ylide reacts with Pt(II) complexes to form a chelated derivative in which IR and NMR spectra suggest the breaking of the C C bond of the –C C O group.

The Methoxycarbonylation of Vinyl Acetate Catalyzed by Palladium Complexes of [1,2‐Phenylenebis(methylene)]bis[di(tert‐butyl)phosphine

AbstractPalladium complexes of [1,2‐phenylenebis(methylene)]bis[di(tert‐butyl)phosphine] (1) catalyze the methoxycarbonylation of vinyl acetate (= ethenyl acetate) in the presence of methanesulfonic acid (Scheme 1). High selectivities to ester products can be obtained if free phosphine ligand is in excess over the amount of added acid (Table 1). Selectivities to methyl 2‐acetoxypropanoate, a precursor to lactate esters, can be as high as 3.6 : 1 at low temperature and pressure (Table 2). Replacing tBu by iPr groups leads to less‐active catalysts and lower selectivities to the branched product. Replacing the phenylene moiety by a naphthalenediyl moiety also gives lower activity, but with similar selectivity to the phenylene‐based analogues. Linear hydrocarbon‐chain linkers as the backbone instead of the phenylenebis(methylene) linker leads to poor catalysis, except for a propane‐1,3‐diyl linker, which gives good rates but poor branched selectivity (Table 5). The effect of different reaction conditions on the catalysis is discussed. The syntheses of the new xylene‐based diphosphines 2–5 with one to four iPr groups replacing the tBu groups at the P‐atoms of 1 and of the ligands 6 and 7 based on 1,2‐ and 2,3‐dimethylnaphthalene are also described (Schemes 2 and 3).

Preparation of Half-Sandwich Alkyl−Titanium(IV) Complexes Stabilized by a Cyclopentadienyl Ligand with a Pendant Phosphine Tether and Their Use in the Catalytic Hydroamination of Aliphatic and Aromatic Alkynes

Complex CpPTiCl3 (1; CpP = C5H4CH2CH2PPh2) reacts with 3.0, 2.0, and 1.0 equiv of MeMgCl to give CpPTiMe3 (2), CpPTiMe2Cl (3), and CpPTiMeCl2 (4). In solution the P-donor substituent of the cyclopentadienyl ligand is involved in a coordination−dissociation equilibrium (ΔH° = 7.7 ± 0.1 kcal·mol-1 and ΔS° = 36.9 ± 0.4 cal·mol-1·K-1 for 2, ΔH° = 6.0 ± 0.2 kcal·mol-1 and ΔS° = 22.3 ± 0.6 cal·mol-1·K-1 for 3, and ΔH° = 6.1 ± 0.2 kcal·mol-1 and ΔS° = 24.4 ± 1 cal·mol-1·K-1 for 4). The reaction of 1 with 3.0 equiv of PhCH2MgCl affords CpPTi(CH2Ph)3 (5), containing a free phosphine pendant group between −90 and 20 °C. In contrast to 5, the PPh2 group of {(2,6-iPr2C6H3)NH}CpPTi{N(2,6-iPr2C6H3)} (7), which is formed from the reaction of 2 with 2,6-diisopropylaniline, remains coordinated to the titanium atom between 60 and −60 °C. Complex 2 is an efficient catalyst precursor for the regioselective hydroamination of aliphatic (1-octyne and cyclohexylacetylene) and aromatic (phenylacetylene and 1-phenylpropyne) alkynes with aromatic (2,6-dimethylaniline and 2,6-diisopropylaniline) and aliphatic (tert-butylamine, dodecylamine, and cyclohexylamine) amines. The reactions give imines or imine−enamine mixtures, which are reduced to the corresponding secondary amines. The Markovnikov or anti-Markovnikov nature of the obtained products depends on the aliphatic or aromatic character of both the alkyne and the amine. Markovnikov products with regioselectivities of 100% are formed from the reactions between aliphatic alkynes and aromatic amines, while anti-Markovnikov derivatives with regioselectivies of 100% are obtained from the reactions of aromatic alkynes with all the studied amines and from the reactions of the aliphatic alkynes with tert-butylamine and dodecylamine. The reaction of 1-octyne and cyclohexylacetylene with cyclohexylamine gives mixtures of both types of products. Some considerations about the mechanism of the catalysis are also presented.

Organometallic Complexes Containing 17-Ethynyl-17β-hydroxyandrost-4-en-3-one and Related Ethynyl Steroids

Gold complexes of 17-ethynyl-17β-hydroxyandrost-4-en-3-one, 17-ethynyl-3-methoxyestra-1,3,5(10)-trien-17β-ol, and 17α-ethynylestra-1,3,5(10)-triene-3,17β-diol have been prepared and characterized. The title compounds were prepared by treatment of the parent ethynyl steroid with sodium bis(trimethylsilyl)amide followed by the addition of R3PAuCl. Using a variety of phosphorus donors, a total of 36 gold steroid compounds were readily prepared using this approach. Compounds containing basic low cone angle phosphines such as PMe3 and PEt3 exhibited broad signals in the 13C{1H} NMR spectrum for the alkyne moiety, while compounds containing triarylphosphines or moderately bulky trialkylphosphines exhibited sharp signals. Correlations between common measures of phosphine donor ability with 2 J CP and 3 J CP as well as changes in the 31P chemical shift were made. While the use of low cone angle phosphines was successful, analogous reactions with trimesitylphosphine or tris(2,4,6-trimethoxyphenyl)phosphine resulted in intractable mixtures containing significant amounts of free phosphine. The incorporation of electron-withdrawing groups into the organic fragment of the phosphine donors was tolerated except for P(C6F5)3, where displacement of the phosphine was observed. The molecular structures of five representative examples are presented and discussed. These determinations represent the first structurally characterized examples where the transition metal is σ-bound to the ethynyl fragment of the steroid.

Stabilization of a Dialkylstannylene by Unusual B−H···Sn γ-Agostic-Type Interactions. A Structural, Spectroscopic, and DFT Study

The reaction between SnCl2 and the lithium salt [[{nPr2P(BH3)}(Me3Si)CCH2]Li(THF)2]2 yields the cyclic dialkylstannylene [{nPr2P(BH3)}(Me3Si)CCH2]2Sn (6) as a 1:1 mixture of rac and meso diastereomers. Fractional crystallization from n-hexane gives samples of pure rac-6 and meso-6 which have been studied by X-ray crystallography, UV/visible, infrared, and multi-element NMR spectroscopy. In the solid state, rac-6 exhibits two short agostic-type B−H···Sn contacts, one to each BH3 group, whereas meso-6, in which both BH3 groups lie on the same side of the heterocycle, exhibits a single B−H···Sn contact. Multi-element and variable-temperature NMR spectroscopy suggests that these contacts persist in solution, resulting in unusual 119Sn chemical shifts of 587 and 787 ppm for the rac and meso diastereomers, respectively, significantly upfield in comparison to other dialkylstannylenes. Variable-temperature 1H, 31P{1H}, and 11B{1H} NMR studies reveal dynamic equilibria for the meso diastereomer involving competitive binding of the two BH3 groups to the electron-deficient tin center and restricted rotation about the P−C bond of the free phosphine−borane group. DFT studies confirm that the B−H···Sn contacts are an integral part of the structures; the HOMO and LUMO of both stereoisomers are comprised of an orbital of essentially 5s character on tin and an orbital of predominantly 5p character on tin perpendicular to the plane of the heterocycle, respectively. There is significant donation of electron density from the B−H σ-bonds to the vacant 5p orbital on tin; these B−H···Sn interactions stabilize the electron-deficient Sn(II) center by 30 kcal mol-1 for meso-6 and 40 kcal mol-1 for rac-6.

Functionalisation of the framework of mesoporous organosilicas by rare-earth complexes

A mesoporous hybrid material containing free phosphine oxide ligands in the pore walls was prepared in the presence of a structure-directing agent. The phosphine oxide ligands were proved to operate as templates for further erbium(III) and/or ytterbium(III) ion complexation.

Heats of Formation of Co(CO)2NOPR3, R = CH3 and C2H5, and Its Ionic Fragments

A joint threshold photoelectron photoion coincidence spectrometry (TPEPICO) and collision-induced dissociation (CID) study on the thermochemistry of Co(CO)(2)NOPR(3), R = CH(3) (Me) and C(2)H(5) (Et), complexes is presented. Adiabatic ionization energies of 7.36 +/- 0.04 and 7.24 +/- 0.04 eV, respectively, were extracted from scans of the total ion and threshold electron signals. In the TPEPICO study, the following 0 K onsets were determined for the various fragment ions: CoCONOPMe(3)(+), 8.30 +/- 0.05 eV; CoNOPMe(3)(+), 9.11 +/- 0.05 eV; CoPMe(3)(+) 10.80 +/- 0.05 eV; CoCONOPEt(3)(+), 8.14 +/- 0.05 eV; CoNOPEt(3)(+), 8.92 +/- 0.05 eV; and CoPEt(3)(+), 10.66 +/- 0.05 eV. These onsets were combined with the Co(+)-PR(3) (R = CH(3) and C(2)H(5)) bond dissociation energies of 2.88 +/- 0.11 and 3.51 +/- 0.17 eV, obtained from the TCID experiments, to derive the heats of formation of the neutral and ionic species. Thus, the Co(CO)(2)NOPR(3) (R = CH(3) and C(2)H(5)) 0 K heats of formation were found to be -350 +/- 13 and -376 +/- 18 kJ x mol(-)(1), respectively. These heats of formation were combined with the published heat of formation of Co(CO)(3)NO to determine the substitution enthalpies of the carbonyl to phosphine substitution reactions. Room-temperature values of the heats of formation are also given using the calculated harmonic vibrational frequencies. Analysis of the TCID experimental results provides indirectly the adiabatic ionization energies of the free phosphine ligands, P(CH(3))(3) and P(C(2)H(5))(3), of 7.83 +/- 0.03 and 7.50 +/- 0.03 eV, respectively.

Matrix bound phosphine formation and depletion in eutrophic lake sediment fermentation—simulation of different environmental factors

Closed anaerobic batch-fermentation of eutrophic lake sediment samples was performed under variation of four environmental fermentation factors (pH, temperature, water/sediment ratio and disturbance) to learn how the quantity of phosphine will change and if the quantity of phosphine can increase. The fermentation conditions where matrix bound phosphine (MBP) increased (doubled from 3 193±520 to about 7 982±1003 ng/kg) were: a pH of 8 and of 10 (as compared to 1, 2, 4, 6, 12), a temperature of 20 and 30 °C (as compared to 4 and 40 °C), a water/sediment ratio of 3:1 (as compared to 1:1, 2:1, 5:1) and a disturbance of 100 r/min (as compared to 0 r/min), respectively. Although, over the full time course of fermentation, the balance of phosphine production became negative again or did remain almost unchanged under most conditions. A pH of 1 or disturbance of 150 r/min was significant factors to decrease phosphine over the long term. Free phosphine had been detected but was of minor importance (in the order of 60.9±10.1 ng/m 3). Overall, the fermentation conditions which had been most favorable for microbial life (moderate temperature (20 and 30 °C) and pH 8) were also most favorable for a positive phosphine balance. This is an indication, but no biochemical proof that a natural (biogenic, microbial, biochemical) NET PRODUCTION of phosphine or DE NOVO PRODUCTION of phosphine has occurred. MBP concentrations in lake sediments were discussed as to be strongly dependent on a balance of natural generation and depletion processes, dependent of the simulated parameters.

Steric Effects in Metathesis and Reduction Reactions of Phosphinimines with Catechol- and Pinacolboranes

A series of catecholboryl-phosphinimide complexes with the general formula (mu-(R(3)PN)Bcat)(x)() (cat = O(2)C(6)H(4)) have been synthesized via associative metathetical reactions. For R = Et, n-Bu, Ph, and i-Pr and R(3) = n-Bu t-Bu(2) X-ray crystallography as well as solution NMR spectroscopy and reactivity studies reveal that these species are dimeric. In the case of R = t-Bu, the steric congestion results in the monomeric species, t-Bu(3)PNBcat. Similarly, reactions of R(t-Bu)(2)PNH (R = n-Bu, t-Bu) and i-Pr(3)PNH with pinacolborane (HBO(2)C(2)Me(4) = HBpin) led to the formation of n-Bu(t-Bu(2))PNBpin, t-Bu(3)PNBpin, and i-Pr(3)PNBpin. Analogous reactions of smaller phosphinimines R(3)PNH (R = Et or n-Bu) with pinacolborane (HBpin) generated free phosphine and the boron-containing product HN(Bpin)(2). In the related reactions of R(3)PNPh or R(3)PNAd (R = Et and n-Bu) and HBpin, the white crystalline solids PhHN(Bpin) or AdHN(Bpin) were isolated. HN(Bpin)(2) was also derived from the reaction of Et(3)PNSiMe(3) and HBpin. Kinetic studies showed this reaction is first order in both reagents with a rate constant of 1.3(7) x 10(-4) s(-1). A mechanism involving a 1:1 donor-acceptor interaction of the phosphinimine and borane affording reduction of the phosphinimine to phosphine with concurrent formation of borylamine is proposed. Computational studies were performed to probe the steric effects on these reactions of phosphinimine and borane. Model reactions involving t-Bu(3)PNH showed a lower activation barrier for protonolysis in comparison to phosphinimine reduction. In contrast, for the smaller phosphinimine H(3)PNH, the activation barriers for phosphinimine reduction are lower. The causes of these steric effects are considered.

Phosphine in soils, sludges, biogases and atmospheric implications—a review

This is a review of previously published and unpublished results of research into the occurrence of phosphine (PH 3) in the environment in the form of matrix bound phosphine in soils, aquatic sediments and sludges (range ng kg −1to μg kg −1), free phosphine in formed biogases (range ng m −3 to μg m −3) and in the atmosphere (range pg m −3 to ng m −3). The reviewed data support the hypothesis of the existence of a small gaseous link in the phosphorus cycle, which could become important over the long term. Matrix-bound phosphine in soils can be interpreted as a stationary state concentration of phosphine between production and consumption. This phosphine turnover within the soil may be important even if the stationary state concentration (matrix-bound phosphine) is small. Under such circumstances, a slow migration process of phosphine in the interstitial gas sphere of soils is possible. Such a process would influence the balance of phosphorus in agricultural and wetland soil. The detection of easily oxidizable phosphine as a ubiquitous trace gas in the atmosphere can be interpreted as the residue of an important turnover of phosphine between widely distributed emission sources and sinks such as soils and sediments. The atmosphere can carry gaseous phosphorus to remote places.

Methoxycarbonylation of vinyl acetate catalysed by palladium complexes of bis(ditertiarybutylphosphinomethyl)benzene and related ligands

High selectivities to methyl acetoxypropanoate esters (b : l up to 3.6 : 1) are obtained from the methoxycarbonylation of vinyl acetate catalysed by palladium complexes of bis(ditertiarybutylphosphinomethyl)benzene in the presence of acid, provided that the acid concentration does not exceed that of the free phosphine.

Effect of pH on phosphine production and the fate of phosphorus during anaerobic process with granular sludge

The effect of pH on phosphine formation during anaerobic cultivation of granular sludge was investigated. The sludge was taken from full-scale anaerobic reactors treating brewery wastewater. Acetate and phosphate were used as the carbon source and phosphorus source respectively. After 10 days cultivation in the dark, results showed that acidic conditions were more favorable for free phosphine production. At pH 5, the optimum concentration 86.42 ng PH 3 m −3 of free phosphine was obtained. The level at pH 7 was reduced to 18.53 ng PH 3 m −3, about 1/5 of the maximum. The maximum concentration of matrix-bound phosphine of 3.30 ng PH 3 kg −1 wet sludge was achieved at pH 6. More than 83% of the total phosphine was matrix-bound phosphine, which accounted for 0.003–0.009‰ of the phosphate removal, while free phosphine comprised 0.00002–0.001‰ of the phosphate removal. Most of the phosphorus removal from solution was turned into chemical precipitation or was adsorbed by sludge. The mechanism of the phosphate reduction-step in the formation of phosphine production is still unknown. The promotion of phosphine formation by low pH is compatible with an acidic bio-corrosion mechanism of metal particles in the sludge or of metal phosphides which form phosphine at low pH.