Three porous polymer networks (PPNs) have been synthesized by the homocoupling of tetrahedral monomers. Like other hyper-cross-linked polymer networks, these materials are insoluble in conventional ...solvents and exhibit high thermal and chemical stability. Their porosity was confirmed by N2 sorption isotherms at 77 K. One of these materials, PPN-3, has a Langmuir surface area of 5323 m2 g−1. Their clean energy applications, especially in H2, CH4, and CO2 storage, as well as CO2/CH4 separation, have been carefully investigated. Although PPN-1 has the highest gas affinity because of its smaller pore size, the maximal gas uptake capacity is directly proportional to their surface area. PPN-3 has the highest H2 uptake capacity among these three (4.28 wt %, 77 K). Although possessing the lowest surface area, PPN-1 shows the best CO2/CH4 selectivity among them.
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Four new di(hydroperoxy)cycloalkane adducts (Ahn adducts) of p-Tol3PO (1) and o-Tol3PO (2), namely, p-Tol3PO·(HOO)2C(CH2)5 (3), o-Tol3PO·(HOO)2C(CH2)5 (4), p-Tol3PO·(HOO)2C(CH2)6 (5), and ...o-Tol3PO·(HOO)2C(CH2)6 (6), have been synthesized and fully characterized. Their single crystal X-ray structures have been determined and analyzed. The 31P NMR data are in accordance with hydrogen bonding of the di(hydroperoxy)alkanes to the PO groups of the phosphine oxides. Due to their high solubility in organic solvents, natural abundance 17O NMR spectra of 1–6 could be recorded, providing the signals for the PO groups and additionally the two different oxygen nuclei in the O–OH groups in the adducts 3–6. The association and mobility of 3–6 were explored by 1H DOSY (diffusion ordered spectroscopy) NMR, which indicated persistent hydrogen bonding of the adducts in solution. Competition experiments with phosphine oxides allowed ranking of the affinities of the di(hydroperoxy)cycloalkanes for the different phosphine oxide carriers. On the basis of variable temperature 31P NMR investigations, the Gibbs energies of activation ΔG ‡ for the adduct dissociation processes of 3–6 at different temperatures, as well as the enthalpy ΔH ‡ and entropy ΔS ‡ of activation, have been determined. IR spectroscopy of 3–6 corroborated the hydrogen bonding, and in the Raman spectra, the ν(O–O) stretching bands have been identified, confirming the presence of peroxy groups in the solid materials. The high solubilities in selected organic solvents have been quantified.
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This review article describes classical and modern solid-state NMR methods that allow to gain insight into catalyst systems where one or two metal complexes are bound to oxide supports via ...bifunctional phosphine linkers, such as (EtO)
3Si(CH
2)
3PPh
2. Many aspects of the immobilized molecular catalysts can be elucidated with the corresponding NMR technique. The bulk of the support can be studied, as well as the interface of the support with the ethoxysilane. With respect to the linkers, their structural integrity and mobility are as easy to investigate by classical CP/MAS and high-resolution magic angle spinning (HRMAS) NMR techniques, as their adsorption behavior. Even electrostatic bonding to the support via phosphonium groups can be proven by solid-state NMR. For the immobilized catalysts, leaching, and even “horizontal” translational mobility effects, as probed by HRMAS NMR under “realistic conditions” in the presence of solvents, are described.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Ferrocene could be adsorbed on activated carbon, carbon nanotube surfaces, graphite, and graphene in the absence of a solvent at room temperature in spite of its high melting point (174 °C). In each ...case only monolayers formed via self-adsorption and the transition to surplus polycrystalline material was abrupt, with no multiple layers occurring. Variable-temperature multinuclear solid-state NMR spectroscopy was applied to study the mobilities of the surface-adsorbed ferrocene molecules. It has been demonstrated that on favorable supports the major anisotropic interactions that usually broaden the solid-state NMR signals of polycrystalline and amorphous materials were reduced or completely eliminated due to the mobility of the adsorbed ferrocene. In favorable cases the chemical shift anisotropy (CSA) and the dipolar and quadrupolar interactions were reduced to a degree that allowed the recording of the spectra of the solid materials on a conventional solution NMR spectrometer.
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When grinding nickelocene with silica in the absence of a solvent at room temperature, it adsorbs on the surface within the pores. This has also been demonstrated visually by adsorbing green ...nickelocene in the pores of a large colorless silica gel specimen. While this dry adsorption and translational mobility of nickelocene within the pores is proven visually, the site-to-site mobility of the nickelocene molecules and their orientation toward the surface are not yet understood. In this contribution, mesoporous silica is used as the support material for a systematic solid-state NMR study of these issues. Paramagnetic 1H VT solid-state NMR and T 1 relaxation times have been powerful tools for studying the dynamics of nickelocene on the silica surface. Herewith, the mobility of the surface-adsorbed nickelocene molecules in the pores could be quantified on the molecular scale. According to the obtained data, the nickelocene molecules move like a liquid on the surface. Isotropically moving molecules exchange places rapidly with surface-attached molecular states of nickelocene in a sample with submonolayer surface coverage. This finding is corroborated by a macroscopic visualization experiment. The states of the surface-attached horizontally oriented nickelocene molecules that are prevalent at temperatures below 200 K have been quantified. The temperature dependencies of the rate k in coordinates of ln(k) versus 1/T and ln(k/T) versus 1/T form ideal straight lines that allow the determination of the kinetic parameters E act = 5.5 kcal/mol, A = 1.1 × 1010, ΔH ‡ = 5.0 kcal/mol, and ΔS ‡ = −15 eu. Investigating a sample with equal amounts of nickelocene and ferrocene in a submonolayer amount of 80% overall surface coverage shows that the different metallocenes mix on the molecular level on the silica surface.
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6.
Hydrogen peroxide adducts of triarylphosphine oxides Arp, Fabian F; Bhuvanesh, Nattamai; Blümel, Janet
Dalton transactions : an international journal of inorganic chemistry,
2019, Volume:
48, Issue:
38
Journal Article
Peer reviewed
Five new hydrogen peroxide adducts of phosphine oxides (
p
-Tol
3
PO·H
2
O
2
)
2
(
1
), (
o
-Tol
3
PO·H
2
O
2
)
2
(
2
), (
o
-Tol
2
PhPO·H
2
O
2
)
2
(
3
), (
p
-Tol
3
PO)
2
·H
2
O
2
(
4
), and (
o
...-TolPh
2
PO)
2
·H
2
O
2
(
5
), and the water adduct (
o
-Tol
2
PhPO·H
2
O)
2
(
6
) have been synthesized and fully characterized. Their single crystal X-ray structures have been determined and analyzed. The IR and
31
P NMR data are in accordance with strong hydrogen bonding of the hydrogen peroxide. The mono-
versus
dimeric nature of the adduct assemblies has been investigated by DOSY NMR experiments. Raman spectroscopy of the symmetric adducts and the
ν
(O-O) stretching bands confirm the presence of hydrogen-bonded hydrogen peroxide in the solid materials. The solubilities in organic solvents have been quantified. Due to the high solubilities of
1-6
in organic solvents their
17
O NMR spectra could be recorded in natural abundance, providing well-resolved signals for the P&z.dbd;O and O-O groups. The adducts
1-5
have been probed regarding their stability in solution at 105 °C. The decomposition of the adduct
1
takes place by loss of the active oxygen atoms in two steps.
Five new safe, solid, and soluble H
2
O
2
adducts of triarylphosphine oxides, including the displayed (
p
-Tol
3
PO·H
2
O
2
)
2
, have been synthesized and characterized.
Ferrocene has been adsorbed on the surface of silica and activated carbon within the pores by dry grinding in the absence of a solvent at room temperature. While the dry adsorption and translational ...mobility of ferrocene within the pores are already established on the centimeter scale, there is little systematic understanding of the surface site-to-site motions of the ferrocene molecules and their orientation with respect to the surface. In this paper, silica and activated carbon, both widely applied in academia and industry as adsorbents, are used as support materials. Using variable-temperature 13C and 2H solid-state NMR and T 1 relaxation time measurements, the dynamics of ferrocene on the surfaces of silica and activated carbon within the pores has been quantitatively characterized on the molecular scale. The obtained data indicate that ferrocene molecules show a liquid-like behavior on the surface. Fast exchange between isotropically moving molecules and surface-attached molecular states of ferrocene has been found in samples with submonolayer surface coverages. The surface-attached molecular states have been characterized by the free energies ΔG ⧧ of 6.1 kcal/mol for silica and ΔG ⧧ of 6.2 kcal/mol for activated carbon at 223 and 263 K, respectively. The horizontally oriented ferrocene molecules are the most thermodynamically stable states on the surfaces of both materials. These molecules exhibit fast C5 rotation of the Cp rings, as established by low-temperature 13C and 2H NMR. The interactions of ferrocene with the pore surfaces have been characterized by adsorption enthalpies measured as −8.4 to −7.0 kcal/mol and −6.7 kcal/mol for activated carbon and silica, respectively. It has been suggested that the ferrocene–surface interactions for both support materials have a polar character.
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Aqueous hydrogen peroxide is widely used as an oxidizing agent in industry and academia. Herein, the hydrogen peroxide adducts of phosphine oxides, tBu3PO⋅H2O22 and Ph3PO⋅H2O22⋅H2O2, are described. ...Additionally, the corresponding di(hydroperoxy)propane adducts R3PO⋅(HOO)2CMe2 (R=Cy, Ph) were synthesized and characterized. All adducts could be obtained as large single crystals suitable for structural characterization by X‐ray crystallography and solid‐state NMR spectroscopy. The di(hydroperoxy)propane adducts are soluble in organic solvents which enables oxidation reactions in one phase. As the adducts are solid and molecular, they can easily be applied stoichiometrically. No loss of oxidizing power occurs upon long‐term storage of the single crystals at room temperature or the powders at −20 °C.
Hydrogen peroxide rocks! Di(hydroperoxy)propane adducts of phosphine oxides, R3PO(HOO)2CMe2 (R=alkyl, aryl), are obtained as very large single crystals. Despite their oxidative power, the long‐term stability of the compounds is high and they are very soluble in organic solvents. These compounds are therefore ideal oxidizing agents that can be applied stoichiometrically in nonaqueous media.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The syntheses of two new representatives of di(hydroperoxy)cycloalkane adducts of phosphine oxides, Cy3PO·(HOO)2C(CH2)4 and Cy3PO·(HOO)2C(CH2)6, and the new hydroperoxy(hydroxy)alkane adduct ...Cy3PO·(HOO)(HO)C(CH2)5 are described. Different synthetic routes were explored. The formation of the adducts proceeds from hydrogen peroxide adducts of phosphine oxides in the presence of cyclic ketones. Additionally, the direct addition of Cy3PO to free di(hydroperoxy)cycloalkanes results in the desired adducts. A mechanism for the formation is proposed, which is supported by generating and identifying the monoperoxy adduct Cy3PO·(HOO)(HO)C(CH2)5. All adducts are fully characterized with single-crystal X-ray crystallography, NMR, and IR spectroscopy. All adducts are safe and solid and have shelf lifetimes of months. They are highly soluble in organic solvents, which allows for homogeneous reactions in nonaqueous media. This was demonstrated by selectively oxidizing Ph2P–PPh2 to the moisture-sensitive Ph2P(O)–P(O)Ph2. All adducts Cy3PO·(HOO)2C(CH2)4–6 perform efficient Baeyer–Villiger oxidations under mild and anhydrous conditions requiring only catalytic amounts of acid.
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Reactions of trans-Fe(CO)3(P((CH2) m CHCH2)3)2 (m = a/4; b/5, c/6, e/8) and Grubbs’ catalyst (12–24 mol %, CH2Cl2, reflux) give the cage-like trienes trans-Fe(CO)3(P((CH2) m CHCH(CH2) m )3 P) ...(3a–c,e, 60–81%). Hydrogenations (ClRh(PPh3)3, 60–80 °C) yield the title compounds trans-Fe(CO)3(P((CH2) n )3 P) (4a–c,e, 74–86%; n = 2m + 2), which have idealized D 3h symmetry. A crystal structure of 4c suggests enough van der Waals clearance for the Fe(CO)3 moiety to rotate within the three P(CH2)14P linkages; structures of E,E,E-3a show rotation to be blocked by the shorter P(CH2)4CHCH(CH2)4P linkages. Additions of NO+BF4 – give the isoelectronic and isosteric cations Fe(CO)2(NO)(P((CH2) n )3 P)+BF4 – (5a–c +BF4 –; 81–98%). Additions of H(OEt2)2+BArf – (BArf = B(3,5-C6H3(CF3)2)4) afford the metal hydride complexes mer,trans-Fe(CO)3(H)(P((CH2) n )3 P)+BArf – (6a–c,e +BArf –; 98–99%). The behavior of the rotators in the preceding complexes is probed by VT NMR. At ambient temperature in solution, 5a,b +BF4 – and 6a +BArf – show two sets of P(CH2) n/2 13C NMR signals (2:1), whereas 5c +BF4 – and 6b,c +BArf – show only one. At higher temperatures, the signals of 5b +BF4 – coalesce; at lower temperatures, those of 5c +BF4 – and 6b +BArf – decoalesce. These data give ΔH ⧧/ΔS ⧧ values (kcal/mol and eu) of 8.3/–28.4 and 9.5/–6.5 for Fe(CO)2(NO)+ rotation (5b,c +) and 6.1/–23.5 for Fe(CO)3(H)+ rotation (6b +). 13C CP/MAS NMR spectra show that the Fe(CO)3 moiety in polycrystalline 4c (but not 4a) undergoes rapid rotation between −60 and 95 °C. Approaches to minimizing these barriers and developing molecular gyroscopes are discussed.
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