scholarly journals First Principles Analysis of Ethylene Oligomerization on Single-site Ga3+ Catalysts Supported on Amorphous Silica

2021 ◽  
Author(s):  
Yinan Xu ◽  
Nicole LiBretto ◽  
Guanghui Zhang ◽  
Jeffrey Miller ◽  
Jeffrey Greeley
Keyword(s):  
Amorphous Silica ◽  
First Principles ◽  
Main Group ◽  
Ethylene Oligomerization ◽  
Single Site ◽  
Local Geometry ◽  
Amorphous Oxides ◽  
Rate Determining Step ◽  
Main Group Metal ◽  
Olefin Oligomerization

Amorphous, single site, silica-supported main group metal catalysts have recently been found to promote olefin oligomerization with high activity at moderate temperatures and pressures (~250°C and 1 atm). Herein, we explore the molecular-level relationship between active site structures and the associated oligomerization mechanisms by developing amorphous, silica-supported Ga3+ models from periodic, first-principles calculations. Representative Ga3+ sites, including three- and four-coordinated geometries, are tested for multiple ethylene oligomerization pathways. We show that the three-coordinated Ga3+ site promotes oligomerization through a facile initiation process that generates a Ga-alkyl intermediate, followed by a Ga-alkyl-centered Cossee-Arlman mechanism. The strained geometry of a three-coordinated site enables a favorable free energy landscape with a kinetically accessible ethylene insertion transition state (1.7 eV) and a previously unreported β-hydride transfer step (1.0 eV) to terminate further C-C bond formation. This result, in turn, suggests that Ga3+ does not favor polymerization chemistry, while microkinetic modeling confirms that ethylene insertion is the rate-determining step. The study demonstrates promising flexibility of main group ions for hydrocarbon transformations and, more generally, highlights the importance of the local geometry of metal ions on amorphous oxides in determining catalytic properties.

scholarly journals Olefin Oligomerization by Main Group Ga3+ and Zn2+ Single Site Catalysts

2020 ◽  
Author(s):  
Nicole LiBretto ◽  
Yinan Xu ◽  
Aubrey Quigley ◽  
Ethan Edwards ◽  
Rhea Nargund ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Equilibrium Distribution ◽  
Transition Metal Ions ◽  
Main Group ◽  
Single Site ◽  
Main Group Metal ◽  
Hydride Elimination ◽  
Single Site Catalysts ◽  
Olefin Oligomerization

Abstract In heterogeneous catalysis, olefin oligomerization is typically performed on immobilized transition metal ions, such as Ni2+ and Cr3+. Here we report that silica-supported, single site catalysts containing immobilized, main group Zn2+ and Ga3+ ions catalyze ethylene and propylene oligomerization to an equilibrium distribution of linear olefins with rates similar to that of Ni2+. The molecular weight distribution of products formed on Zn2+ is similar to Ni2+; while Ga3+ forms higher molecular weight olefins. In situ spectroscopic and computational studies suggest that oligomerization unexpectedly occurs by the Cossee-Arlman mechanism via metal hydride and metal alkyl intermediates formed during olefin insertion and β-hydride elimination elementary steps. Initiation of the catalytic cycle is proposed to occur by heterolytic C-H dissociation of ethylene, which occurs at about 250°C where oligomerization is catalytically relevant. This work reports new chemistry for main group metal catalysts with potential for development of new olefin processes.

scholarly journals Olefin oligomerization by main group Ga3+ and Zn2+ single site catalysts on SiO2

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Nicole J. LiBretto ◽  
Yinan Xu ◽  
Aubrey Quigley ◽  
Ethan Edwards ◽  
Rhea Nargund ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Equilibrium Distribution ◽  
Transition Metal Ions ◽  
Main Group ◽  
Single Site ◽  
Main Group Metal ◽  
Hydride Elimination ◽  
Single Site Catalysts ◽  
Olefin Oligomerization

AbstractIn heterogeneous catalysis, olefin oligomerization is typically performed on immobilized transition metal ions, such as Ni2+ and Cr3+. Here we report that silica-supported, single site catalysts containing immobilized, main group Zn2+ and Ga3+ ion sites catalyze ethylene and propylene oligomerization to an equilibrium distribution of linear olefins with rates similar to that of Ni2+. The molecular weight distribution of products formed on Zn2+ is similar to Ni2+, while Ga3+ forms higher molecular weight olefins. In situ spectroscopic and computational studies suggest that oligomerization unexpectedly occurs by the Cossee-Arlman mechanism via metal hydride and metal alkyl intermediates formed during olefin insertion and β-hydride elimination elementary steps. Initiation of the catalytic cycle is proposed to occur by heterolytic C-H dissociation of ethylene, which occurs at about 250 °C where oligomerization is catalytically relevant. This work illuminates new chemistry for main group metal catalysts with potential for development of new oligomerization processes.

scholarly journals Activation and Functionalization of C–C σ-Bonds of Alkylidene Cyclopropanes at Main Group Centers

2020 ◽  
Author(s):  
Mark Crimmin ◽  
Richard Y Kong
Keyword(s):  
Bond Activation ◽  
Substrate Binding ◽  
Oxidative Addition ◽  
Main Group ◽  
Single Site ◽  
Mechanistic Studies ◽  
Metal Bond ◽  
Main Group Metal ◽  
Metal Metal ◽  
Group Center

Aluminum(I) and magnesium(I) compounds are reported for the C–C s-bond activation of strained alkylidene cyclopropanes. These reactions result in the formal addition of the C–C s-bond to main group center either at a single site (Al) or across a metal–metal bond (Mg–Mg). Mechanistic studies suggest that rather than occurring by a concerted oxidative addition, these reactions involve stepwise processes in which substrate binding to the main group metal acts as a precursor to a- or b-alkyl migration steps that break the C–C s-bond. This mechanistic understanding is used to develop the magnesium-catalyzed hydrosilylation of the C–C s-bonds of alkylidene cyclopropanes.

Activation and Functionalization of C–C σ-Bonds of Alkylidene Cyclopropanes at Main Group Centers

2020 ◽  
Author(s):  
Mark Crimmin ◽  
Richard Y Kong
Keyword(s):  
Bond Activation ◽  
Substrate Binding ◽  
Oxidative Addition ◽  
Main Group ◽  
Single Site ◽  
Mechanistic Studies ◽  
Metal Bond ◽  
Main Group Metal ◽  
Metal Metal ◽  
Group Center

Aluminum(I) and magnesium(I) compounds are reported for the C–C s-bond activation of strained alkylidene cyclopropanes. These reactions result in the formal addition of the C–C s-bond to main group center either at a single site (Al) or across a metal–metal bond (Mg–Mg). Mechanistic studies suggest that rather than occurring by a concerted oxidative addition, these reactions involve stepwise processes in which substrate binding to the main group metal acts as a precursor to a- or b-alkyl migration steps that break the C–C s-bond. This mechanistic understanding is used to develop the magnesium-catalyzed hydrosilylation of the C–C s-bonds of alkylidene cyclopropanes.

scholarly journals Activation and Functionalization of C–C σ-Bonds of Alkylidene Cyclopropanes at Main Group Centers

2020 ◽  
Author(s):  
Mark Crimmin ◽  
Richard Y Kong
Keyword(s):  
Bond Activation ◽  
Substrate Binding ◽  
Oxidative Addition ◽  
Main Group ◽  
Single Site ◽  
Mechanistic Studies ◽  
Metal Bond ◽  
Main Group Metal ◽  
Metal Metal ◽  
Group Center

Aluminum(I) and magnesium(I) compounds are reported for the C–C s-bond activation of strained alkylidene cyclopropanes. These reactions result in the formal addition of the C–C s-bond to main group center either at a single site (Al) or across a metal–metal bond (Mg–Mg). Mechanistic studies suggest that rather than occurring by a concerted oxidative addition, these reactions involve stepwise processes in which substrate binding to the main group metal acts as a precursor to a- or b-alkyl migration steps that break the C–C s-bond. This mechanistic understanding is used to develop the magnesium-catalyzed hydrosilylation of the C–C s-bonds of alkylidene cyclopropanes.

To Bend or Not to Bend, the Dilemma of Multiple Bonds

2019 ◽  
Author(s):  
Michele Pizzocchero ◽  
Matteo Bonfanti ◽  
Rocco Martinazzo
Keyword(s):  
First Principles ◽  
2D Materials ◽  
Main Group ◽  
First Principles Calculations ◽  
Group 14 ◽  
Multiple Bonds ◽  
Main Group Elements ◽  
Structural Distortions

The manuscript addresses the issue of the structural distortions occurring at multiple bonds between high main group elements, focusing on group 14. These distortions are known as trans-bending in silenes, disilenes and higher group analogues, and buckling in 2D materials likes silicene and germanene. A simple but correlated \sigma + \pi model is developed and validated with first-principles calculations, and used to explain the different behaviour of second- and higher- row elements.

Reversible Addition of Carbon Dioxide to Main Group Metal Complexes at Temperatures about 0 °C

2021 ◽  
Author(s):  
Tatyana S. Koptseva ◽  
Vladimir G. Sokolov ◽  
Sergey Yu. Ketkov ◽  
Elena A. Rychagova ◽  
Anton V. Cherkasov ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Metal Complexes ◽  
Main Group ◽  
Group Metal ◽  
Reversible Addition ◽  
Main Group Metal

Effect of delocalization of nonbonding electron density on the stability of the M–Ccarbene bond in main group metal-imidazol-2-ylidene complexes: a computational and structural database study

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Samuel Tetteh ◽  
Albert Ofori
Keyword(s):  
Electron Density ◽  
Lone Pair ◽  
Main Group ◽  
Binding Energies ◽  
Electrostatic Model ◽  
Group Metal ◽  
Main Group Metal ◽  
Structural Database ◽  
The Stability ◽  
Lone Pair Electrons

Abstract The M–Ccarbene bond in metal (M) complexes involving the imidazol-2-ylidene (Im) ligand has largely been described using the σ-donor only model with donation of σ electrons from the sp-hybridized orbital of the carbene carbon into vacant orbitals on the metal centre. Analyses of the M–Ccarbene bond in a series of group IA, IIA and IIIA main group metal complexes show that the M-Im interactions are mostly electrostatic with the M–Ccarbene bond distances greater than the sum of the respective covalent radii. Estimation of the binding energies of a series of metal hydride/fluoride/chloride imidazol-2-ylidene complexes revealed that the stability of the M–Ccarbene bond in these complexes is not always commensurate with the σ-only electrostatic model. Further natural bond orbital (NBO) analyses at the DFT/B3LYP level of theory revealed substantial covalency in the M–Ccarbene bond with minor delocalization of electron density from the lone pair electrons on the halide ligands into antibonding molecular orbitals on the Im ligand. Calculation of the thermodynamic stability of the M–Ccarbene bond showed that these interactions are mostly endothermic in the gas phase with reduced entropies giving an overall ΔG > 0.

scholarly journals Cat-CrNP as new material with catalytic properties for 2-chloro-2-propen-1-ol and ethylene oligomerizations

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jacek Malinowski ◽  
Dagmara Jacewicz ◽  
Artur Sikorski ◽  
Mariusz Urbaniak ◽  
Przemysław Rybiński ◽  
...  
Keyword(s):  
Complex Compound ◽  
Atmospheric Pressure ◽  
Room Temperature ◽  
Organometallic Compounds ◽  
Ethylene Oligomerization ◽  
High Catalytic Activity ◽  
New Material ◽  
Activity Requirement ◽  
Olefin Oligomerization ◽  
Xrd Method

AbstractThe contemporary search for new catalysts for olefin oligomerization and polymerization is based on the study of coordinating compounds and/or organometallic compounds as post-metallocene catalysts. However known catalysts are suffered by many flaws, among others unsatisfactory activity, requirement of high pressure or instability at high temperatures. In this paper, we present a new catalyst i.e. the crystalline complex compound possesing high catalytic activity in the oligomerization of olefins, such as 2-chloro-2-propen-1-ol and ethylene under very mild conditions (room temperature, 0.12 bar for ethylene oligomerization, atmospheric pressure for 2-chloro-2-propen-1-ol oligomerization). New material—Cat-CrNP ([nitrilotriacetato-1,10-phenanthroline]chromium(III) tetrahydrate) has been obtained as crystalline form of the nitrilotriacetate complex compound of chromium(III) with 1,10-phenanthroline and characterized in terms of its crystal structure by the XRD method and by multi-analytical investigations towards its physicochemical propeties The yield of catalytic oligomerization over Cat-CrNP reached to 213.92 g · mmol−1 · h−1· bar−1 and 3232 g · mmol−1 · h−1 · bar−1 for the 2-chloro-2-propen-1-ol and ethylene, respectively. Furthemore, the synthesis of Cat-CrNP is cheap, easy to perform and solvents used during preparation are environmentally friendly.

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