Patent Application
20250115535
Effective separation of small gaseous hydrocarbons having comparable sizes and small volatility differences is a challenging endeavor, which is integral to the industrial scale production of high-purity olefins such as ethylene (C2H4) and propylene (C3H6).1-5 It is mainly accomplished by cryogenic distillation under low-temperature and high-pressure conditions, which is capital and energy intensive, and accounts for nearly 0.3% of the global energy consumption just for the purification of ethylene and propylene from their paraffinic counterparts. Alternative methods are clearly desirable to achieve the industrially important olefin-paraffin separation more energy-efficiently and sustainably. Technology based on membranes and porous materials that rely on metal ions such as copper and silver for the selective binding and separation of olefins over paraffins is a promising option and has received significant attention in recent years.
Disclosed herein is a group of non-porous, silver complexes supported by highly fluorinated pyrazolates with ideal features for ethylene-ethane separation.6, 7 Solution chemistry and single crystal X-ray crystallography show that these molecular silver complexes {[4-(R)-3,5-(CF3)2Pz]Ag}3 ([Ag—R]3, R=H, Br, CF3) react with ethylene to form dinuclear silver-ethylene adducts of the type {[4-(R)-3,5-(CF3)2Pz]Ag(C2H4)}2([Ag-R·(C2H4)]2). Gas sorption studies revealed that these processes are reversible and can be utilized to separate ethylene very selectively from an ethylene-ethane mixture.
In some aspects, described herein is a composition including an alkene and a compound of Formula I:
wherein each R is independently chosen from H, CF3, and Br.
In some aspects, the alkene is ethene, propene, butene, or a mixture thereof.
In some aspects, the composition further includes an alkane, wherein the alkane includes one or more of ethane, propane, and butane.
In some aspects, Formula I exhibits a reversible transformation to Formula II:
and/or Formula III:
wherein each R is independently chosen from H, CF3, and Br, and wherein the alkene of the composition is a same alkene of Formula II and Formula III.
In some aspects, Formula II is formed by an alkene adsorption on Formula I when R is H.
In some aspects, Formula III is formed by an alkene adsorption on Formula I when R is CF3, or Br.
In some aspects, an alkene desorption transforms Formula II to Formula I.
In some aspects, an alkene desorption transforms Formula III to Formula I.
In some aspects, the reversible transformation is an exothermic structural rearrangement of Formula 1.
In some aspects, the reversible transformation is a solid-state transformation.
In some aspects, described herein is a method of separating an alkene from a mixture, the method including: contacting the mixture to a compound having Formula I to form a complex having Formula II and/or Formula III; wherein each R is independently chosen from H, CF3, and Br.
In some aspects, the mixture is contacted with the compound having Formula I at a pressure below a partial pressure of the alkene.
In some aspects, the mixture is contacted with the compound having Formula I at a temperature from −75° C. to 25° C.
In some aspects, the mixture is contacted with the compound having Formula I at a pressure from ambient pressure to 100 kPa.
In some aspects, the mixture is contacted with the compound having Formula I at a pressure from 100 kPa to 6,000 kPa.
In some aspects, the mixture is contacted with the compound having Formula I at a pressure from 300 kPa to 1,000 kPa.
In some aspects, the method further includes reducing pressure to ambient pressure or below after forming the complex having Formula II and/or Formula III and collecting the alkene.
In some aspects, the method further includes increasing temperature after forming the complex having Formula II and/or Formula III and collecting the alkene.
In some aspects, the mixture is contacted with the compound having Formula I in the presence of a solvent.
In some aspects, the mixture is a hydrocarbon feed gas mixture.
The present invention can be understood more readily by reference to the following detailed description, examples, drawings, and claims, and their previous and following description. However, before the present compositions, articles, devices, systems, and/or methods are disclosed and described, it is to be understood that this invention is not limited to the specific compositions, articles, devices, systems, and/or methods disclosed unless otherwise specified, as such can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.
The following description of the invention is also provided as an enabling teaching of the invention in its best, currently known aspect. To this end, those of ordinary skill in the relevant art will recognize and appreciate that changes and modifications can be made to the various aspects of the invention described herein, while still obtaining the beneficial results of the present invention. It will also be apparent that some of the desired benefits of the present invention can be obtained by selecting some of the features of the present invention without utilizing other features. Accordingly, those of ordinary skill in the relevant art will recognize that many modifications and adaptations to the present invention are possible and can even be desirable in certain circumstances and are thus also a part of the present invention. Thus, the following description is provided as illustrative of the principles of the present invention and not in limitation thereof.
Various combinations of elements of this disclosure are encompassed by this invention, e.g. combinations of elements from dependent claims that depend upon the same independent claim.
Moreover, it is to be understood that unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps or operational flow; plain meaning derived from grammatical organization or punctuation; and the number or type of aspects described in the specification
All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited.
It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. As used in the specification and in the claims, the term “comprising” may include the aspects “consisting of” and “consisting essentially of” It is further understood that the term “comprise” means “include,” “have,” and “contain,” but is not limited to, and is not intended to exclude, for example, other additives, components, integers, or steps.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined herein.
As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a “complex” or “a composition” includes aspects having two or more complexes or compositions unless the context clearly indicates otherwise.
Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another aspect. By “about” is meant within 5% of the value, e.g. within 4, 3, 2, or 1% of the value. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. It is also understood that each unit between two particular units is also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.
As used herein, the terms “optional” or “optionally” mean that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.
As used herein, the term “substantially,” in, for example, the context “substantially free” refers to a composition having less than about 1% by weight of the stated component. This can include, for example, aspects of less than about 0.5% by weight, less than about 0.1% by weight, less than about 0.05% by weight, or less than about 0.01% by weight of the stated material, based on the total weight of the composition.
It is further understood that the term “substantially,” when used in reference to an amount of composition or a component in a composition, refers at least about 80%, at least about 85%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, or about 100% by weight, based on the total weight of the composition, of a specified feature or component.
As used herein, the term “substantially,” in, for example, the context “substantially identical reference composition” or “substantially identical reference process” refers to a reference composition comprising substantially identical components, or process steps, in the absence of an inventive component. In another exemplary aspect, the term “substantially,” in, for example, the context “substantially identical reference composition,” refers to a reference composition comprising substantially identical components and wherein an inventive component is substituted with a common or conventionally known in the art component. For example, a substantially identical reference composition as described herein can comprise a substantially identical composition comprising an alkene and a compound having the formula: [3,4,5-tris(trifluoromethyl)pyrazolyl)Ag]3, ([(3,4,5-(CF3)3Pz)Ag]3, [Ag—CF3]3).
As used herein, the term “‘step’ pressure,” refers to a pressure value where a steep change in pressure as shown in gas adsorption isotherm occurs. It is understood that the step pressure is been achieved through phase changes induced by osmotic pressure and chemical interaction and is facilitated by flexible ligands, rearrangement of coordination spheres, or spin-crossover. Alternatively, the step pressure can be achieved through intermolecular interactions inducing ordering of the gas (adsorbate) phase such as self-propagating reactions and clathrate formation. It is further understood that the ‘step’ pressure is dependent on a system and can be determined from the system's gas adsorption isotherm.
While aspects of the present invention can be described and claimed in a particular statutory class, such as the system statutory class, this is for convenience only, and one of skill in the art will understand that each aspect of the present invention can be described and claimed in any statutory class. Unless otherwise expressly stated, it is in no way intended that any method or aspect set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not specifically state in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including matters of logic with respect to arrangement of steps or operational flow, plain meaning derived from grammatical organization or punctuation, or the number or type of aspects described in the specification.
The present disclosure may be understood more readily by reference to the following detailed description of various aspects and the examples included therein and to the Figures and their previous and following description.
Due to the current interests and importance of group 11 metals in multiple areas of olefin chemistry, disclosed herein is a group of non-porous, silver complexes supported by highly fluorinated pyrazolates with ideal features for ethylene-ethane separation.6, 7 Solution chemistry and single crystal X-ray crystallography show that these molecular silver(I) complexes {[4-(R)-3,5-(CF3)2Pz]Ag}3 ([Ag—R]3, R=H, Br, CF3) react with ethylene to form dinuclear silver-ethylene adducts of the type {[4-(R)-3,5-(CF3)2Pz]Ag(C2H4)}2 ([Ag-R·(C2H4)]2, R=CF3, Br) and trinuclear silver-ethylene adducts of the type {[4-(R)-3,5-(CF3)2Pz]Ag(C2H4)}3 ([Ag—R·(C2H4)]3, R=H). Gas sorption studies revealed that these processes are reversible and can be utilized to separate ethylene selectively from an ethylene-ethane mixture.
In certain aspects, the present disclosure relates to a compound having Formula I:
wherein each R is independently chosen from H, CF3, and Br. For example, R can be chosen from CF3 and Br. In another example, R can be H.
In other aspects, the present disclosure relates to a composition comprising an alkene and the compound of Formula I. The alkene can be ethene, propene, 1-butene, 2-butene or mixtures thereof. Further the composition can comprise an alkane. The alkanes can be ethane, propane, butane or mixtures thereof.
In further aspects, disclosed herein is a complex having Formula II:
wherein each R is independently chosen from H, CF3, and Br. In an example, Formula I exhibits a reversible transformation to Formula II when R is H.
In still other aspects, alkene can be ethene, propene, 1-butene, 2-butene, or mixtures thereof. Without wishing to be bound by theory, the complexes of Formula II can be present with compounds of Formula I and an alkene, and such compositions are expressly contemplated and disclosed herein.
In yet further aspects, disclosed herein is a complex having Formula III:
wherein each R is independently chosen from H, CF3, and Br. In an example, Formula I exhibits a reversible transformation to Formula III when R is CF3, or Br.
In still other aspects, alkene can be ethene, propene, 1-butene, 2-butene, or mixtures thereof. Without wishing to be bound by theory, the complexes of Formula III can be present with the compound of Formula I and an alkene, and such compositions are expressly contemplated and disclosed herein.
In still other aspects, the complexes of Formula II can be present with the complex of Formula III, compounds of Formula I and an alkene, and such compositions are expressly contemplated and disclosed herein.
It should be noted that while Formula II and Formula III show a solid line between a silver atom and “alkene”, this is not meant to imply a single bond. It is meant merely to illustrate a coordination of the silver to the alkene.
In yet further aspects, the compound having Formula I is in its solid state. Yet in other examples, the composition further comprises a solvent. Examples of suitable solvents include methylene chloride and chloroform.
In still further aspects, disclosed herein are adsorption materials comprising the composition of Formula I and/or Formula II and a substrate. In still further aspects, disclosed herein are adsorption materials comprising the composition of Formula I and/or Formula III and a substrate. The substrate can be a bead, film, particle, or membrane, which can be made of either an inorganic or polymeric substrate. In some examples, the adsorption materials can be in a fixed and/or fluidized bed, e.g., in a fixed and/or fluidized bed temperature and/or pressure swing adsorption process.
In certain aspects, the present disclosure relates to a method of separating an alkene from a mixture. In some aspects, the method comprises contacting the mixture with the compound having Formula I to form a complex having Formula II and/or Formula III, wherein the alkene moiety in the complex is the alkene being separated from the mixture. In some examples, the mixture can be contacted with the compound having Formula I at high pressure and ambient temperature or at low temperatures and ambient pressure. In specific examples, contacting the compound having Formula I with the mixture can occur at pressures at or above ambient pressure.
The alkene can be ethene, propene, 1-butene, 2-butene, or a mixture thereof. While not wishing to be bound by theory, the alkene can be separated from any gas that does not contain a carbon-carbon double bond and/or pi electrons that would interact with the compounds having Formula I. For example, alkenes can be separated from N2, methane, carbon dioxide.
In still further aspects, the mixture is a hydrocarbon feed gas. The hydrocarbon feed gas can be obtained by any methods known in the art. In still further aspects, the hydrocarbon feed gas mixture can comprise one or more alkenes and one or more alkanes. In yet other aspects, the hydrocarbon feed gas mixture can comprise ethylene, propylene, butene, or any combination thereof. It is understood that the hydrocarbon feed gas can be a raw olefin gas or a pretreated olefin gas. In aspects where the hydrocarbon feed gas is a pretreated olefin gas, the gas can be pretreated to remove one or more components depending on the desired application. In some exemplary aspects, the one or more alkenes present in the hydrocarbon feed gas mixture can comprise ethylene. In yet other aspects, the one or more alkanes present in the hydrocarbon feed gas mixture can comprise ethane. In still further exemplary aspects, the disclosed compositions can be used to separate ethylene from ethane. However, it is understood that such aspects are exemplary and non-limiting and the complexes described herein can be also used to separate other alkenes from other alkanes. It is further understood that the processes and the complexes described herein can be used to separate, for example, propylene gas from other components of the hydrocarbon feed gas. It is further understood that in some exemplary aspects, the presence of ethylene in the hydrocarbon feed gas mixture is not required in order to efficiently separate other alkenes from various alkanes. It is understood that in aspects, where ethylene is not present, other alkenes, such as propylene, or butene can adsorb similarly on a trinuclear silver(I) pyrazolate complex to form a specific dinuclear silver(I)-alkene complex and/or trinuclear silver(I)-alkene complex.
The mixture can be contacted with the composition having Formula I at a temperature from −75° C. to 25° C. In some specific examples, the mixture can be contacted with the composition having Formula I at a temperature from −75° C. to −50° C., from −75° C. to −25° C., from −75° C. to 0° C., from −50° C. to −25° C., from −50° C. to 0° C., from −50° C. to 25° C., from −25° C. to 0° C., from −25° C. to 25° C., from 0° C. to 25° C. In further examples, the mixture can be contacted with the composition having Formula I at −70, −60, −50, −40, −30, −20, −10, 0, 10, or 20° C., where any of the stated values can form an upper or lower endpoint of a range.
In still other examples, the mixture can be contacted with the composition of Formula I at pressures from ambient pressure to 100 kPa. In still other examples, the mixture can be contacted with the composition of Formula I at pressures from 100 kPa to 6,000 kPa, e.g., from 300 kPa to 1000 kPa. In specific examples the pressure can be 100 kPa, 200 kPa, 300 kPa, 400 kPa, 500 kPa, 600 kPa, 700 kPa, 800 kPa, 900 kPa, 1000 kPa, 2000 kPa, 3000 kPa, 4,000 kPa, 5,000 kPa, or 6,000 kPa, where any of the stated values can form an upper or lower endpoint of a range.
In other examples, the pressure can be reduced to ambient pressure or below after forming the complex having Formula II and/or Formula III and the alkene can be isolated or recovered. In other examples, the temperature can be increased after forming the complex having Formula II and/or Formula III and the alkene can be isolated or recovered. Still further, the pressure and temperature can be adjusted to conditions that result in the release of the alkene from the complex having Formula II and/or Formula III and the alkene can then be isolated or recovered.
In still further examples, the method can be a solid-state method wherein the compound having Formula I is in its solid state when contacted with the alkene. Yet in other examples, the compound having Formula I can be contacted with the alkene in the presence of a solvent. Examples of suitable solvents include methylene chloride and chloroform.
The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, articles, devices and/or methods claimed herein are made and evaluated and are intended to be purely exemplary and are not intended to limit the disclosure. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in ° C. or is at ambient temperature, and pressure is at or near atmospheric.
Solid-gas reactions and in situ powder X-ray diffraction investigations of trinuclear silver complexes {[3,4,5-(CF3)3Pz]Ag}3 and {[4-Br-3,5-(CF3)2Pz]Ag}3 supported by highly fluorinated pyrazolates reveal that they undergo intricate ethylene-triggered structural transformations in the solid-state producing dinuclear silver-ethylene adducts. Despite the complexity, the chemistry is reversible producing precursor trimers with the loss of ethylene. Less reactive {[3,5-(CF3)2Pz]Ag}3 under ethylene pressure and low-temperature conditions stops at an unusual silver-ethylene complex in the trinuclear state, which could serve as a model for intermediates likely present in more common trimer-dimer reorganizations described above. Complete structural data of three novel silver-ethylene complexes are presented together with a thorough computational analysis of the mechanism.
Trinuclear silver(I) complexes of fluorinated pyrazolates have attracted significant interest because many of them show interesting p-acid properties, luminescence, argentophilic contacts, and useful applications.8-15 For example, {[3,5-(CF3)2Pz]Ag}3 (
In contrast to the aromatic hydrocarbons, the chemistry of industrially relevant gaseous hydrocarbons such as ethylene with silver pyrazolates has not been explored. Silver-ethylene complexes are of particular interest since silver is the metal of choice for partial oxidation of ethylene, which is a major industrial process.23, 24 They are challenging to stabilize and quite labile due to the relatively weak silver(I)-ethylene interactions.25-31 Reversible binding of ethylene to silver, however, is valuable in applications such as the separation of ethylene from ethylene-ethane mixtures using silver complexes and silver-doped materials.32-34 The copper(I) analogs of [Ag—H]3 such as {[4-R-3,5-(CF3)2Pz]Cu}3 ([Cu—R]3, R=H, Br, CF3) are effective in the selective separation of ethylene from ethane containing mixtures.6, 7
Motivated by the fundamental interest and novelty, an in-depth study was conducted of ethylene chemistry of silver(I) pyrazolates {[4-R-3,5-(CF3)2Pz]Ag}3 ([Ag—R]3, R=H, Br, CF3) with different pyrazolyl ring substituents that also utilizes solid-gas35-38 synthesis and in situ powder X-ray diffraction (PXRD) measurements at 17-BM beamline at the Argonne National Laboratory (ANL) advanced photon source. As evident from the following account, this undertaking was successful and led to the stabilization of an unusual trinuclear silver-ethylene complex in a crystalline state. Additionally uncovered were two unprecedented dinuclear silver-ethylene complexes with bridging pyrazolates, of which, only one could be obtained via a traditional solution method.
Traditional solution chemistry. The per-fluorinated silver(I) complex {[3,4,5-(CF3)3Pz]Ag}3 ([Ag—CF3]3) was utilized first for this purpose because it possesses powerful Lewis acidic silver sites and is expected to be more reactive towards ethylene compared to the less-fluorinated analogs. The [Ag—CF3]3 was obtained very conveniently via a reaction between the corresponding pyrazole [3,4,5-(CF3)3Pz]H39 and silver(I) oxide. It is a colorless, air-stable solid and has been characterized by several techniques including NMR spectroscopy, and single crystal and powder X-ray crystallography. It crystallizes with a molecule of dichloromethane in the asymmetric unit (
More importantly, [Ag—CF3]3 reacts with ethylene in CH2Cl2 at low temperatures and produces a product which can be crystallized from the same mixture at −25° C. under an ethylene blanket (Scheme 1). The variable temperature 19F NMR spectroscopic data show that this transformation takes place below −10° C. in CD2Cl2. The analysis of crystalline solid using single crystal X-ray diffraction reveals that it is a dinuclear species [Ag-CF3·(C2H4)]2 (
There are two chemically similar but crystallographically different molecules of [Ag-CF3·(C2H4)]2 in the asymmetric unit. The silver sites are trigonal planar and Ag2N4 cores adopt a boat shape. Although there are no analogous dinuclear silver-ethylene complexes for a direct comparison, a few silver-ethylene complexes such as [PhB(3-(CF3)Pz)3]Ag(C2H4)46 and {[H2C(3,5-(CF3)2Pz)2]Ag(C2H4)}[SbF6]27 with a three coordinate silver sites supported by N-donor ligands are known. The average Ag—N(2.231 Å) and Ag—C(2.282 Å) distances of [Ag-CF3·(C2H4)]2 are similar to those observed in [PhB(3-(CF3)Pz)3]Ag(C2H4) (av. Ag—N and Ag—C are 2.261 and 2.264 Å, respectively).
Next, the related {[3,5-(CF3)2Pz]Ag}3 ([Ag—H]3)16 was studied, which is a molecule based on less fluorinated pyrazolate possessing relatively less electrophilic silver sites. The attempts to observe the silver-ethylene complex from a reaction between [Ag—H]3 and ethylene in CH2Cl2 solution were unsuccessful even at −50° C. It is understandable since ethylene-silver bonds in general are quite weak while the Ag—N bonds in [Ag—H]3 are relatively strong considering that it features a better electron-donating pyrazolate60 than the one present in [Ag—CF3]3.
In situ solid-gas chemistry: Next, these processes were investigated, using solid materials and study the progress of the reaction “live” using in situ PXRD at ANL synchrotron beamline. Recent developments show that in situ and solid-gas chemistry are valuable techniques that enable synthesis and characterization of organometallic species that are difficult or impossible to observe under solution-phase conditions.35-38 Remarkably, crystals of [Ag—CF3]3 upon exposure to ethylene (3-5 bar at 295K,
To see if transient species can be detected, in situ studies of the less reactive [Ag—H]3 with ethylene were conducted. In contrast to [Ag—CF3]3, the reaction of solid [Ag—H]3 with ethylene did not proceed at 295K even under high ethylene pressure up to 60 bar (
The molecular structure of this unprecedented species [Ag-H·(C2H4)]3 is illustrated in
Postulating that this ethylene loaded trimer phase [Ag-H·(C2H4)]3 might be a transition state between unloaded trimer and loaded dimer phases observed for other metal pyrazolates, experiments were carried out at even higher pressures and lower temperatures to see if a further transition to a loaded dimer “[Ag-H·(C2H4)]2” could be observed. First, the in situ PXRD data were collected at 45 bar of C2H4 from room temperature down to 110 K (just above the freezing point of C2H4). The pressure was then increased to 70 bar of ethylene and the sample warmed to room temperature (which led to [Ag—H]3 formation). No evidence of a new crystalline phase was observed under either conditions (see
Encouraged by the success with [Ag—H]3 that led to the characterization of a rare species in the ethylene bound yet pre trimer--dimer transformation stage, the chemistry of [Ag—Br]3 with ethylene was probed. Note that these planar, trinuclear metal adducts displayed different extended structures and therefore, the outcome of solid-state chemistry with ethylene was not necessarily predictable through extrapolation. For example, in contrast to [Ag—H]3 which crystallizes forming zig-zag columns with argentophilic interactions,16, 61 [Ag—Br]3 trimers formed extended structures with inter-trimer Ag⋅⋅⋅Br contacts62 (while [Ag—CF3]3 reported here shows inter-trimer Ag⋅⋅⋅F interactions between trimers).
Traditional solution chemistry with ˜1 bar ethylene did not yield an isolable silver-ethylene complex from [Ag—Br]3 in CH2Cl2. The in situ PXRD data of the solid-gas reaction of polycrystalline [Ag—Br]3 also did not show any phase changes even at 173K under flow of ethylene (˜1 bar). However, at 10 bar of ethylene, a notable change was observed at 220K (
Computational study. In order to further understand ethylene driven molecular reorganization processes described above, a detailed computational study of ethylene reactions of [Ag—CF3]3, [Ag—Br]3 and [Ag—H]3 were conducted (see
Intermediate 2 is a key step prior to the trimer→dimer transformation. After the formation and relaxation of this intermediate, the next step is to release one [Ag-R·(C2H4)]unit (i.e., ethylene bound metal-pyrazolate) given as the second transition state (TS2), which is the rate-determinant step leading to the dimer. Calculations of the bonding energy of Ag2N4—AgN2 for —H, —Br and —CF3, indicate that it is easier to break-up [Ag—CF3]3 and [Ag—Br]3 species (−64.3 and −65.2 kcal/mol, respectively), in comparison to [Ag—H]3 counterpart (−83.8 kcal/mol). From the Gibbs free energy profiles (
In the final step, the loss of a [Ag-R·(C2H4)]unit from [Ag-R·(C2H4)]3, leads to the formation of one dimer species [Ag-R·(C2H4)]2 (TS2), where the released unit further aggregates with another [Ag-R·(C2H4)]fragment from a parallel reaction, resulting in the formation of a second dimer species (3). Calculated Gibbs free energy for step 3 amounts to −30.1, −25.5, and −24.1 kcal/mol for [Ag—CF3]3, [Ag—Br]3 and [Ag—H]3, respectively. Overall, [Ag-H·(C2H4)]2 formation is slightly less energetically favorable process, while [Ag-CF3·(C2H4)]2 formation is the most facile, which is consistent with the experimental observations, and denoted by the slightly less stabilized transition states and activation barriers, in addition to the bonding energy of Ag2N4—AgN2 fragments prior formation of TS2. The formation of trinuclear-tris-ethylene intermediate 2 is favored at lower temperatures but the experimental conditions must be just right to trap this species before it breaks-up to even more energetically favorable dimers 3. The silver(I) and [3,5-(CF3)2Pz]− ligand combination provides the ideal ingredients to trap the elusive species [Ag-H·(C2H4)]3.
In summary, after a careful investigation that involved strategic variations of pyrazolyl ring substituents and solid-gas synthesis under different temperature-pressure combinations, and synchrotron based, in situ PXRD, the trinuclear silver-ethylene complex {[3,5-(CF3)2Pz]Ag(C2H4)}3 ([Ag-H·(C2H4)]3) was trapped and structurally characterized, showing a severely distorted, yet intact Ag3N6 core, that can be viewed as a model for fleeting intermediates likely exist in ethylene driven, trimer-dimer transformations observed in related [Ag—CF3]3 and [Ag—Br]3 systems. Furthermore, this study reveals for the first time, ethylene triggered structural transformations of trinuclear silver(I) pyrazolates in the solid-state leading to dinuclear species {[3,4,5-(CF3)3Pz]Ag(C2H4)}2 ([Ag-CF3·(C2H4)]2) and {[4-Br-3,5-(CF3)2Pz]Ag(C2H4)}2 ([Ag-Br·(C2H4)]2), and molecular structures of two rare dinuclear, silver-ethylene complexes. This investigation also demonstrates the power of in situ synthesis over traditional solution chemistry for the isolation of labile species. Computational studies indicated that the silver(I) and [3,5-(CF3)2Pz]− ligand combination provides the ideal ingredients to stabilize [Ag-H·(C2H4)]3.
General Information. All manipulations were carried out under an atmosphere of purified nitrogen using standard Schlenk techniques or in a MBraun glovebox equipped with a −25° C. refrigerator. Solvents were purchased from commercial sources and purified before use. NMR spectra were recorded at 25° C. on a JEOL Eclipse 500 spectrometer (1H, 500.16 MHz 13C, 125.78 MHz, and 19F, 470.62 MHz) unless otherwise noted. 1H and 13C NMR spectra are referenced to the solvent peak (1H; CDCl3 δ 7.26, 13C; CDCl3 δ 77.16). 1H NMR coupling constants (J) are reported in Hertz (Hz) and multiplicities are indicated as follows: s (singlet), d (doublet), t (triplet), m (multiplet). 19F NMR values were referenced to external CFCl3. Melting points were obtained on a Mel-Temp II apparatus and were not corrected. Elemental analyses were performed using a Perkin-Elmer Model 2400 CHN analyzer. IR spectra were collected at room temperature on a Shimadzu IR Prestige-21 FTIR containing an ATR attachment using pure liquid or solid materials, with instrument resolution at 2 cm−1. Raman data were collected on a Horiba Jobin Yvon LabRAM Aramin Raman spectrometer with a HeNe laser source of 633 nm, by placing pure solid materials on a glass slide. All other reactants and reagents were purchased from commercial sources. Heating was accomplished by either a heating mantle or a silicone oil bath. The 3,4,5-(CF3)3PzH was prepared via reported methods.
Synthesis of {[3,4,5-(CF3)3Pz]Ag}3 ([Ag—CF3]3). Freshly dried 3,4,5-(CF3)3PzH (300 mg, 1.10 mmol) and Ag2O (211 mg, 0.91 mmol) were placed in a Schlenk flask attached to a reflux condenser, slowly heated to 125-130° C. and kept for 4 hours while stirring, or until unreacted pyrazole stops condensing on the walls the flask. A heat gun was used to meltdown the pyrazole condensed on the wall of the Schlenk flask, as needed. Excess 3,4,5-(CF3)3PzH was sublimated off, the product was extracted into dichloromethane and filtered through a bed of Celite. The filtrate was collected, and solvent was removed under reduced pressure to obtain {[3,4,5-(CF3)3Pz]Ag}3 ([Ag—CF3]3) as a white powder. X-ray quality crystals were grown from dichloromethane at −20° C. Yield: 91%. M.p.: 260° C. Anal. Calc. for C18N6F27Ag3: C, 19.02; H, 0.00; N, 7.39. Found: C, 18.98; H, <0.1; N, 7.41. 19F NMR (in CDCl3): δ (ppm) −54.94 (br s), −60.63 (q, 7.2 Hz). 13C{1H}NMR (in CDCl3): δ (ppm) 110.6 (q, 2J(C,F)=42.0 Hz, CCF3), 119.2 (q, 1J(C,F)=270.3 Hz, CF3), 120.7 (q, 1J(C,F)=262.7 Hz, CF3), 143.5 (q, 2J(C,F)=36.0 Hz, CCF3). Raman (cm−1): 3148, 1594, 1536, 1502, 1453, 1349, 1154, 1088, 1000, 985, 845.
Synthesis of {[3,4,5-(CF3)3Pz]Ag(C2H4)}2. {[3,4,5-(CF3)3Pz]Ag}3 (200 mg, 0.18 mmol) was dissolved in 10-12 mL of CH2Cl2, ethylene was bubbled for approximately 10 minutes. The ethylene saturated solution was kept at −25° C. to obtain X-ray quality colorless crystals of {[3,4,5-(CF3)3Pz]Ag(C2H4)}2 ([Ag-CF3·(C2H4)]2). Yield: 96%. 19F NMR (in CDCl3 at −50° C.): δ (ppm) −60.00 (3,5-CF3) and −54.97 (4-CF3). 1H NMR (in CDCl3 at −50° C.): δ (ppm) 5.42.
NMR Studies of solution-state equilibria for the [Ag-CF3·(C2H4)]2 reaction with ethylene. As evident from these spectra, at 20° C. in CDCl3, [Ag-CF3·(C2H4)]2 completely dissociates into [Ag—CF3]3 and free ethylene. Therefore, 19F NMR peaks corresponding to [Ag—CF3]3 species can be observed at 20° C. (−60.64 and −54.98 for 3,5-CF3 and 4-CF3, respectively). Results are shown in
From 0° C. to −20° C. signals for both [Ag-CF3·(C2H4)]2 and [Ag—CF3]3 was observed in various ratios.
From −30° C. to −50° C. only signals corresponding to [Ag-CF3·(C2H4)]2 was observed (−60.00 and −54.97 ppm corresponding to 3,5-CF3 and 4-CF3 groups, respectively).
No clear shift was observable, likely due to highly fluxional Ag-ethylene interaction although the 19F NMR data indicated the formation of [Ag-CF3·(C2H4)]2 from [Ag—CF3]3/ethylene when the temperature is lower than −10° C.
Single crystal X-ray crystallography. A suitable crystal covered with a layer of hydrocarbon/Paratone-N oil was selected and mounted on a Cryo-loop, and immediately placed in the low-temperature nitrogen stream. The X-ray intensity data were measured at 100(2) K on a Bruker D8 Quest with a Photon 100 CMOS detector equipped with an Oxford Cryosystems 700 series cooler, a graphite monochromator, and a Mo Kα fine-focus sealed tube (λ=0.71073 Å). Intensity data were processed using the Bruker Apex program suite. Absorption corrections were applied by using SADABS.63 Initial atomic positions were located by SHELXT,64 and the structures of the compounds were refined by the least-squares method using SHELXL65 within Olex2 GUI.66 All the non-hydrogen atoms were refined anisotropically. There are two molecules of [Ag-CF3·(C2H4)]2 in the asymmetric unit. It was solved and refined in Pna21 space group as an inversion twin. The Pccn space group for [Ag-CF3·(C2H4)]2 was tested, as suggested by the CheckCif but the refinement indicators were significantly poor. The hydrogen atoms of the ethylene groups of [Ag-CF3·(C2H4)]2 was located using difference Fourier maps, included, and refined freely with isotropic displacement parameters. The hydrogen atoms of [Ag—CF3]3·CH2Cl2 were included in their calculated positions and refined as riding on the atoms to which they are joined. X-ray structural figures were generated using Olex2.66 Results of crystal data and structure refinement for [Ag—CF3]3·CH2Cl2 and [Ag-CF3·(C2H4)]2 are shown in
Single crystal X-ray crystallography of [Ag—CF3]3·CH2Cl2. The analysis of the crystal of [Ag—CF3]3 obtained from dichloromethane by single crystal X-ray diffraction show that it crystallizes as [Ag—CF3]3·CH2Cl2 from dichloromethane in P1 space group with chlorine atoms facing silver sites, with Ag—Cl contacts shorter than the van der Waals contact separation of Ag and Cl (3.47 Å). This suggested that the silver sites are quite Lewis acidic even to interact with weakly donating CH2Cl2 which is not surprising considering the number of electron-withdrawing fluorinated substituents on the ligand backbone. The solvent molecules in the crystal lattice, however, can be removed easily under reduced pressure to obtain [Ag—CF3]3, of which structure was confirmed by analyzing the material using powder X-ray diffraction.
In situ synchrotron powder diffraction data collection (PXRD). In situ powder x-ray diffraction data (PXRD) from solid samples in ethylene or helium were collected using the monochromatic X-rays available at the Advanced Photon Source, Argonne National Laboratory, beamline 17-BM. A circular incident beam (300 m diameter) was used a width of approximately 0.45 Å wavelength for experiments in conjunction with a VAREX 4343 amorphous-Si flat panel detector. Samples of were loaded into 1.0 mm quartz capillaries with glass wool on either side. The capillary with sample was then loaded into a gas flow cell,67 to perform in situ PXRD experiments. At one end the gas cell was connected to a two-way valve which allowed changing between a 1 atm helium flow and a high-pressure syringe pump (Teledyne ISCO 500D) which was filled with ethene gas. Pressure was monitored at the other end of the gas flow cell to make sure that there was no blockage or leak during the measurements. Pressures quoted are absolute, so a purge of helium or ethylene is a pressure of 1 bar. Prior to measurements, all samples were activated with supercritical ethylene (295 K, 55 bar) as described.6
The raw images were processed within GSAS-II,68 refining the sample-to-detector distance and tilt of the detector relative to the beam based on data obtained for a LaB6 standard.69 Collected 2D detector images from in situ powder diffraction data sets were reduced to 1D datasets of intensity vs. diffraction angle 2□ with GSAS-II. Plots showing the evolution of the PXRD data were prepared with the same software, in which the diffracted intensity is represented by a color scale. In call cases, time runs from the bottom to the top of the image. Individual scans were analyzed using Topas-Academic software.71 Structures from powder data were determined by simulated annealing, using the single crystal structures as a starting point. The pyrazole groups were incorporated as rigid bodies based on the average geometries from analogous single crystal data, with the CF3 rotations freely refined. Selected bond distances, angles, and torsions were refined as appropriate. The unexpected structure of [Ag-H·(C2H4)]3 was initially hypothesized from the volume of the indexed unit cell and was solved by repeated cycles of model building and refinement.
CIF files (PXRD based and from in situ synthesis) of previously unknown dinuclear [Ag-Br·(C2H4)]2 and trinuclear [Ag-H·(C2H4)]3 silver-ethylene complexes, along with the trinuclear precursor [Ag—CF3]3 for which a single crystal was not available (for the latter, single crystal data have CH2Cl2 as solvents of crystallization), have been deposited at the Cambridge Crystallographic Data Centre with CCDC numbers 2267047, 2266818, and 2266816 respectively.
All calculations were carried out by using relativistic DFT methods employing the ADF code71 with the all-electron triple-ζ Slater basis set plus the double-polarization (STO-TZ2P) basis set in conjunction with the Becke-Perdew (BP86) functional72 within the generalized gradient approximation (GGA). London dispersion corrections were taken into account via the pair-wise Grimme3 approach.73 Such level of theory is denoted as TZ2P/BP86-D3. Geometry optimizations were performed without any symmetry restrain, via the analytical energy gradient method implemented by Versluis and Ziegler,74 with energy convergence criteria set at 10-4 Hartree, gradient convergence criteria at 10-4 Hartree/A and radial convergence of 10-3 Å. Thermodynamic properties were obtained from vibrational analysis. Scalar relativistic effects were considered through the ZORA Hamiltonian.74
The interaction energy is further dissected into several chemically meaningful terms according to the Energy Decomposition Analysis (EDA) of Ziegler and Rauk,75
Where the ΔEPauli term involves the electron repulsion between occupied orbitals from the different fragments. ΔEelstat and ΔEorb are related to the stabilizing electrostatic and covalent character of the interaction, respectively. The contribution from dispersion interaction (ΔEdisp) is evaluated using the pairwise correction of Grimme (D3).
This invention was made with government support under Grant no. CHE-1954456 awarded by the National Science Foundation. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63543386 | Oct 2023 | US |
