On the Thermodynamic Control of Ring Opening of 4-Substituted 1,3,3-Tris-Carbethoxycyclobutene and the Role of the C-3 Substituent in Masking the Kinetic Torquoselectivity. An alternate reaction pathway

<p>The predominant transformations of 4-methyl- and 4-phenyl-1,3,3-<i>tris</i>-carbethoxycyclobutenes to s-<i>trans</i>,<i>trans</i>-1,1,3-<i>tris</i>-carbethoxy-4-methyl- and s-<i>trans</i>,<i>trans</i>-1,1,3-<i>tris</i>-carbethoxy-4-phenyl-1,3-butadienes, respectively, are discussed to proceed through pathways entailing heterolytic cleavage of the s_C3C4 bond rather than the usual conrotatory ring opening following the rules of torquoselectivity. The adventitious or in situ generated halogen acid from CDCl₃ catalyzes the reaction by protonation of the geminal ester group to weaken s_C3C4 bond and allow its S_N2 cleavage by chloride ion. This is followed by cisoid<b>→</b>transoid isomerization and loss of the elements of halogen acid to form the products. In the Lewis acid-catalyzed reaction of 4-phenyl-1,3,3-<i>tris</i>-carbethoxycyclobutene in CH₂Cl₂, coordination of Lewis acid with the geminal ester group is followed by heterolytic cleavage of the s_C3C4 bond. The resultant species subsequently undergoes cisoid<b>→</b>transoid isomerization before losing the Lewis acid to form the products.<br></p>

On the Thermodynamic Control of Ring Opening of 4-Substituted 1,3,3-Tris-Carbethoxycyclobutene and the Role of the C-3 Substituent in Masking the Kinetic Torquoselectivity. An alternate reaction pathway

<p>The predominant transformations of 4-methyl- and 4-phenyl-1,3,3-<i>tris</i>-carbethoxycyclobutenes to s-<i>trans</i>-<i>trans</i>-1,1,3-<i>tris</i>-carbethoxy-4-methyl- and 4-phenyl-1,3-butadienes, respectively, proceed through pathways entailing heterolytic cleavage of the s_C3C4 bond rather than the usual four-electron conrotatory ring opening following the rules of torquoselectivity. The adventitious or in situ generated halogen acid from CDCl₃ catalyzes the reaction of 4-methyl-1,3,3-<i>tris</i>-carbethoxycyclobutene by protonation of one of the two ester groups on C3 and, thereby, weakening the s_C3C4 bond to allow its heterolytic S_N2 cleavage by the chloride ion. This is followed by <i>cisoid</i><b>→</b><i>transoid</i> isomerization and loss of the elements of the halogen acid to form the products. In the Lewis acid-catalyzed reaction of 4-phenyl-1,3,3-<i>tris</i>-carbethoxycyclobutene in CH₂Cl₂, coordination of the Lewis acid with one of two ester groups on C3 is followed by heterolytic cleavage of the s_C3C4 bond. The resultant species subsequently undergoes <i>cisoid</i><b>→</b><i>transoid</i> isomerization before losing the Lewis acid to form the products.<br></p>

Computational Investigation of the Role of Active Site Heterogeneity for a Supported Organovanadium(III) Hydrogenation Catalyst

<div> <div> <p></p><p><a>A crucial consideration for supported heterogeneous catalysts is the non-uniformity of the active sites, particularly for Supported Organometallic Catalysts (SOMCs). Standard spectroscopic techniques, such as X-ray absorption spectroscopy (XAS), reflect the nature of the most populated sites, which are often intrinsically structurally distinct from the most catalytically active sites. With computational models, often only a few representative structures are used to depict catalytic active sites on a surface, even though there are numerous observable factors of surface heterogeneity that contribute to the kinetically favorable active species. A previously reported study on the mechanism of a surface organovanadium(III) catalyst [(SiO)V^III(Mes)(THF)] for styrene hydrogenation yielded two possible mechanisms: heterolytic cleavage and redox cycling. These two mechanistic scenarios are challenging to differentiate experimentally based on the kinetic readouts of the catalyst are identical. To showcase the importance of modeling surface heterogeneity and its effect on catalytic activity, density functional theory (DFT) computational models of a series of potential active sites of [(SiO)V^III(Mes)(THF)] for the reaction pathways are applied in combination with kinetic Monte Carlo (kMC) simulations. Computed results were t then compared to the previously reported experimental kinetic study</a><a>.: 1) DFT free energy reaction pathways indicated the likely active site and pathway for styrene hydrogenation; a heterolytic cleavage pathway requiring a bare tripodal vanadium site. 2) From the kMC simulations, a mixture of the different bond lengths from the support oxygen to the metal center was required to qualitatively describe the experimentally observed kinetic aspects of a supported organovanadium(III) catalyst for olefin hydrogenation. </a>This work underscores the importance of modeling surface heterogeneity in computational catalysis.</p><p></p></div></div>

Computational Investigation of the Role of Active Site Heterogeneity for a Supported Organovanadium(III) Hydrogenation Catalyst

<div> <div> <p></p><p><a>A crucial consideration for supported heterogeneous catalysts is the non-uniformity of the active sites, particularly for Supported Organometallic Catalysts (SOMCs). Standard spectroscopic techniques, such as X-ray absorption spectroscopy (XAS), reflect the nature of the most populated sites, which are often intrinsically structurally distinct from the most catalytically active sites. With computational models, often only a few representative structures are used to depict catalytic active sites on a surface, even though there are numerous observable factors of surface heterogeneity that contribute to the kinetically favorable active species. A previously reported study on the mechanism of a surface organovanadium(III) catalyst [(SiO)V^III(Mes)(THF)] for styrene hydrogenation yielded two possible mechanisms: heterolytic cleavage and redox cycling. These two mechanistic scenarios are challenging to differentiate experimentally based on the kinetic readouts of the catalyst are identical. To showcase the importance of modeling surface heterogeneity and its effect on catalytic activity, density functional theory (DFT) computational models of a series of potential active sites of [(SiO)V^III(Mes)(THF)] for the reaction pathways are applied in combination with kinetic Monte Carlo (kMC) simulations. Computed results were t then compared to the previously reported experimental kinetic study</a><a>.: 1) DFT free energy reaction pathways indicated the likely active site and pathway for styrene hydrogenation; a heterolytic cleavage pathway requiring a bare tripodal vanadium site. 2) From the kMC simulations, a mixture of the different bond lengths from the support oxygen to the metal center was required to qualitatively describe the experimentally observed kinetic aspects of a supported organovanadium(III) catalyst for olefin hydrogenation. </a>This work underscores the importance of modeling surface heterogeneity in computational catalysis.</p><p></p></div></div>

Computational Investigation of the Role of Active Site Heterogeneity for a Supported Organovanadium(III) Hydrogenation Catalyst

<div> <div> <p></p><p><a>A crucial consideration for supported heterogeneous catalysts is the non-uniformity of the active sites, particularly for Supported Organometallic Catalysts (SOMCs). Standard spectroscopic techniques, such as X-ray absorption spectroscopy (XAS), reflect the nature of the most populated sites, which are often intrinsically structurally distinct from the most catalytically active sites. With computational models, often only a few representative structures are used to depict catalytic active sites on a surface, even though there are numerous observable factors of surface heterogeneity that contribute to the kinetically favorable active species. A previously reported study on the mechanism of a surface organovanadium(III) catalyst [(SiO)V^III(Mes)(THF)] for styrene hydrogenation yielded two possible mechanisms: heterolytic cleavage and redox cycling. These two mechanistic scenarios are challenging to differentiate experimentally based on the kinetic readouts of the catalyst are identical. To showcase the importance of modeling surface heterogeneity and its effect on catalytic activity, density functional theory (DFT) computational models of a series of potential active sites of [(SiO)V^III(Mes)(THF)] for the reaction pathways are applied in combination with kinetic Monte Carlo (kMC) simulations. Computed results were t then compared to the previously reported experimental kinetic study</a><a>.: 1) DFT free energy reaction pathways indicated the likely active site and pathway for styrene hydrogenation; a heterolytic cleavage pathway requiring a bare tripodal vanadium site. 2) From the kMC simulations, a mixture of the different bond lengths from the support oxygen to the metal center was required to qualitatively describe the experimentally observed kinetic aspects of a supported organovanadium(III) catalyst for olefin hydrogenation. </a>This work underscores the importance of modeling surface heterogeneity in computational catalysis.</p><p></p></div></div>

Heterolytic cleavage of dihydrogen (HCD) in metal nanoparticle catalysis

Supports, ligands and additives can promote heterolytic H2 splitting by a cooperative mechanism with metal nanoparticles.

Cooperative catalytically active sites for methanol activation by single metal ion-doped H-ZSM-5

Diffraction studies and DFT calculations show the formation of frustrated Lewis pair (FLP) over M-ZSM-5 for heterolytic cleavage of CH3OH.

On the Thermodynamic Control of Ring Opening of 4-Substituted 1,3,3-Tris-Carbethoxycyclobutene and the Role of the C-3 Substituent in Masking the Kinetic Torquoselectivity

<p>The predominant transformations of 4-methyl- and 4-phenyl-1,3,3-<i>tris</i>-carbethoxycyclobutenes to s-<i>trans</i>-<i>trans</i>-1,1,3-<i>tris</i>-carbethoxy-4-methyl- and 4-phenyl-1,3-butadienes, respectively, proceed through pathways entailing heterolytic cleavage of the s_C3C4 bond rather than the usual four-electron conrotatory ring opening following the rules of torquoselectivity. The adventitious or in situ generated halogen acid from CDCl₃ catalyzes the reaction of 4-methyl-1,3,3-<i>tris</i>-carbethoxycyclobutene by protonation of one of the two ester groups on C3 and, thereby, weakening the s_C3C4 bond to allow its heterolytic S_N2 cleavage by the chloride ion. This is followed by <i>cisoid</i><b>→</b><i>transoid</i> isomerization and loss of the elements of the halogen acid to form the products. In the Lewis acid-catalyzed reaction of 4-phenyl-1,3,3-<i>tris</i>-carbethoxycyclobutene in CH₂Cl₂, coordination of the Lewis acid with one of two ester groups on C3 is followed by heterolytic cleavage of the s_C3C4 bond. The resultant species subsequently undergoes <i>cisoid</i><b>→</b><i>transoid</i> isomerization before losing the Lewis acid to form the products.<br></p>

On the Thermodynamic Control of Ring Opening of 4-Substituted 1,3,3-Tris-Carbethoxycyclobutene and the Role of the C-3 Substituent in Masking the Kinetic Torquoselectivity

<p>The predominant transformations of 4-methyl- and 4-phenyl-1,3,3-<i>tris</i>-carbethoxycyclobutenes to s-<i>trans</i>-<i>trans</i>-1,1,3-<i>tris</i>-carbethoxy-4-methyl- and 4-phenyl-1,3-butadienes, respectively, proceed through pathways entailing heterolytic cleavage of the s_C3C4 bond rather than the usual four-electron conrotatory ring opening following the rules of torquoselectivity. The adventitious or in situ generated halogen acid from CDCl₃ catalyzes the reaction of 4-methyl-1,3,3-<i>tris</i>-carbethoxycyclobutene by protonation of one of the two ester groups on C3 and, thereby, weakening the s_C3C4 bond to allow its heterolytic S_N2 cleavage by the chloride ion. This is followed by <i>cisoid</i><b>→</b><i>transoid</i> isomerization and loss of the elements of the halogen acid to form the products. In the Lewis acid-catalyzed reaction of 4-phenyl-1,3,3-<i>tris</i>-carbethoxycyclobutene in CH₂Cl₂, coordination of the Lewis acid with one of two ester groups on C3 is followed by heterolytic cleavage of the s_C3C4 bond. The resultant species subsequently undergoes <i>cisoid</i><b>→</b><i>transoid</i> isomerization before losing the Lewis acid to form the products.<br></p>