Hypervalent Iodine-Mediated Styrene Hetero- and Homodimerization Initiation Proceeds with Two-Electron Reductive Cleavage

10.26434/chemrxiv.12350879 ◽

2020 ◽

Author(s):

Aqeel A. Hussein ◽

Yumiao Ma ◽

Ahmed Al-Yasari

Keyword(s):

Electron Transfer ◽

Density Functional ◽

Reductive Cleavage ◽

Hypervalent Iodine ◽

Functional Theory ◽

Concerted Mechanism ◽

Bonding Interaction ◽

Reaction Proceeds ◽

Dynamics Simulations ◽

Insight Into

<a>A mechanistic insight into </a>the hetero- and homodimerizations (HETD and HOMD) of styrenes promoted by hypervalent iodine reagents (HVIRs; DMP and PIDA) and facilitated by HFIP to yield all trans cyclobutanes is reported using density functional theory (DFT) calculations. The initialization involving direct bimolecular one-electron transfer is found to be highly unfavored, especially for the PIDA system. At this point, we suggest that the reaction is initiated with an overall two-electron reductive cleavage of two I─O bond cleavages, affording I(III) (iodinane) and I(I) (iodobenzene) product with DMP and PIDA as oxidant, respectively. The resulting acetate groups are stabilized by the solvent HFIP through strong hydrogen bonding interaction, which promotes the electron transfer process. The nature of the electron transfer is studied in detail and found that the overall two-electron transfer occurs within tri-molecular complex organized by π-stacking interactions and as a stepwise and concerted mechanism for I(III) and I(V) oxidants, respectively. The reaction rate is determined by the initialization step: for I(III), the initiation is thermodynamically endergonic, whereas the endergonicity for I(V) is modest. Upon initialization, the reaction proceeds through a stepwise [2+2] pathway, involving a radical-cationic π-π stacked intermediate, either hetero- or homodimerized. DFT results supported by quasiclassical molecular dynamics simulations show that HOMD is dynamically competing pathway to HETD although the latter is relatively faster, in accordance with experimental observations.

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Hypervalent Iodine-Mediated Styrene Hetero- and Homodimerization Initiation Proceeds with Two-Electron Reductive Cleavage

10.26434/chemrxiv.12350879.v8 ◽

2020 ◽

Author(s):

Aqeel A. Hussein ◽

Yumiao Ma ◽

Ahmed Al-Yasari

Keyword(s):

Electron Transfer ◽

Density Functional ◽

Reductive Cleavage ◽

Hypervalent Iodine ◽

Functional Theory ◽

Concerted Mechanism ◽

Bonding Interaction ◽

Reaction Proceeds ◽

Dynamics Simulations ◽

Insight Into

<a>A mechanistic insight into </a>the hetero- and homodimerizations (HETD and HOMD) of styrenes promoted by hypervalent iodine reagents (HVIRs; DMP and PIDA) and facilitated by HFIP to yield all trans cyclobutanes is reported using density functional theory (DFT) calculations. The initialization involving direct bimolecular one-electron transfer is found to be highly unfavored, especially for the PIDA system. At this point, we suggest that the reaction is initiated with an overall two-electron reductive cleavage of two I─O bond cleavages, affording I(III) (iodinane) and I(I) (iodobenzene) product with DMP and PIDA as oxidant, respectively. The resulting acetate groups are stabilized by the solvent HFIP through strong hydrogen bonding interaction, which promotes the electron transfer process. The nature of the electron transfer is studied in detail and found that the overall two-electron transfer occurs within tri-molecular complex organized by π-stacking interactions and as a stepwise and concerted mechanism for I(III) and I(V) oxidants, respectively. The reaction rate is determined by the initialization step: for I(III), the initiation is thermodynamically endergonic, whereas the endergonicity for I(V) is modest. Upon initialization, the reaction proceeds through a stepwise [2+2] pathway, involving a radical-cationic π-π stacked intermediate, either hetero- or homodimerized. DFT results supported by quasiclassical molecular dynamics simulations show that HOMD is dynamically competing pathway to HETD although the latter is relatively faster, in accordance with experimental observations.

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Hypervalent Iodine-Mediated Styrene Hetero- and Homodimerizations Initiation Proceed with Two-Electron Reductive Cleavage

10.26434/chemrxiv.12350879.v7 ◽

2020 ◽

Author(s):

Aqeel A. Hussein ◽

Ahmed Al-Yasari ◽

Yumiao Ma

Keyword(s):

Electron Transfer ◽

Density Functional ◽

Reductive Cleavage ◽

Hypervalent Iodine ◽

Literature Report ◽

Functional Theory ◽

Bonding Interaction ◽

The Difference ◽

Dynamics Simulations ◽

Insight Into

<a>A mechanistic insight into </a>the hetero- and homodimerizations (HETD and HOMD) of styrenes promoted by hypervalent iodine reagents (HVIRs; DMP and PIDA) and facilitated by HFIP to yield all trans cyclobutanes is reported using density functional theory (DFT) calculations. The reaction is initiated with two-electron reductive cleavage of two I─O bond cleavages, affording I(III) (iodinane) and I(I) (iodobenzene) product with DMP and PIDA as oxidant, respectively. The resulting acetate groups are stabilized by the solvent HFIP through strong hydrogen bonding interaction, which promotes the electron transfer process. The initialization involving one-electron transfer was found to be highly unfavored, especially for the PIDA system. At this point, we found that two-electron process is the key initialization process, which is in accordance with literature report on alcohol oxidation. The reaction rate is determined by the initialization step: For I(III), the initiation is thermodynamically endergonic, whereas the endergonicity for I(V) is modest. The difference in reactivity is explained by the difference LUMO energies. Upon initialization, the reaction proceeds through a stepwise [2+2] pathway, involving a radical-cationic π-π stacked intermediate, either hetero- or homodimerized. DFT results supported by quasiclassical molecular dynamics simulations show that HOMD is dynamically competing pathway to HETD although the latter is relatively faster, in accordance with experimental observations.

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Mechanistic Insights on Hypervalent Iodine-Mediated Styrene Hetero- and Homodimerization

10.26434/chemrxiv.12350879.v6 ◽

2020 ◽

Author(s):

Aqeel A. Hussein ◽

Ahmed Al-Yasari ◽

Yumiao Ma

Keyword(s):

Density Functional ◽

Energy Gap ◽

Single Electron ◽

Hypervalent Iodine ◽

Functional Theory ◽

Rate Determining Step ◽

Before And After ◽

Electron Reduction ◽

Dynamics Simulations ◽

Insight Into

A mechanistic insight into the hetero- and homodimerizations (HETD and HOMD) of styrenes promoted by hypervalent iodine reagents (HVIRs; DMP and PIDA) and facilitated by HFIP to yield all trans cyclobutanes is reported using density functional theory (DFT) calculations. The HFIP molecules lower the energy of the single electron oxidation (SEO) or initiation as a result of strong hydrogen bonding interactions that substantially stabilize the frontier orbitals before and after electron addition. The HETD or HOMD is a radically-characterized π-π stacked head-to-head stepwise [2+2] cycloaddition initiated via SEO by DMP or PIDA, respectively. DFT results supported by quasiclassical molecular dynamics simulations show that HOMD is a competing pathway to HETD although the latter is relatively faster, in accordance with experimental observations. The initiation is a rate-determining step as a thermodynamically endergonic and propagation is accomplished by radically-cationic hetero- and homodimerized intermediate as propagation is faster than single electron reduction (SER) or termination by radically-anionic HVIRs. Initiation by DMP found to be faster and less endergonic than by PIDA due to (1) the energy gap of electron transfer in a SEO step by I(V) is lower than I(III) and (2) the SOMO energy of the radical anion I(V) is lower than I(III). Furthermore, the presence of p-methoxy group is essential to underpin the SEO by which the more thermodynamically favorable SEO leads to a successful cycloaddition as the thermodynamic term represents a major contribution in the initiative barrier.

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Thermodynamics Control Reactivity of Hypervalent Iodine-Mediated Styrene Hetero- and Homodimerization: Mechanistic Insights

10.26434/chemrxiv.12350879.v3 ◽

2020 ◽

Author(s):

Aqeel A. Hussein ◽

Ahmed Al-Yasari ◽

Yumiao Ma

Keyword(s):

Density Functional ◽

Energy Gap ◽

Single Electron ◽

Hypervalent Iodine ◽

Functional Theory ◽

Rate Determining Step ◽

Before And After ◽

Electron Reduction ◽

Dynamics Simulations ◽

Insight Into

A mechanistic insight into the hetero- and homodimerizations (HETD and HOMD) of styrenes promoted by hypervalent iodine reagents (HVIRs; DMP and PIDA) and facilitated by HFIP to yield all trans cyclobutanes is reported using density functional theory (DFT) calculations. The HFIP molecules lower the energy of the single electron oxidation (SEO) or initiation as a result of strong hydrogen bonding interactions that substantially stabilize the frontier orbitals before and after electron addition. The HETD or HOMD is a radically-characterized π-π stacked head-to-head stepwise [2+2] cycloaddition initiated via SEO by DMP or PIDA, respectively. DFT results supported by quasiclassical molecular dynamics simulations show that HOMD is a competing pathway to HETD although the latter is relatively faster, in accordance with experimental observations. The initiation is a rate-determining step as a thermodynamically endergonic and propagation is accomplished by radically-cationic hetero- and homodimerized intermediate as propagation is faster than single electron reduction (SER) or termination by radically-anionic HVIRs. Initiation by DMP found to be faster and less endergonic than by PIDA due to (1) the energy gap of electron transfer in a SEO step by I(V) is lower than I(III) and (2) the SOMO energy of the radical anion I(V) is lower than I(III). Furthermore, the presence of p-methoxy group is essential to underpin the SEO by which the more thermodynamically favorable SEO leads to a successful cycloaddition as the thermodynamic term represents a major contribution in the initiative barrier.

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Mechanistic Insights on Hypervalent Iodine-Mediated Styrene Hetero- and Homodimerization

10.26434/chemrxiv.12350879.v5 ◽

2020 ◽

Author(s):

Aqeel A. Hussein ◽

Ahmed Al-Yasari ◽

Yumiao Ma

Keyword(s):

Density Functional ◽

Energy Gap ◽

Single Electron ◽

Hypervalent Iodine ◽

Functional Theory ◽

Rate Determining Step ◽

Before And After ◽

Electron Reduction ◽

Dynamics Simulations ◽

Insight Into

A mechanistic insight into the hetero- and homodimerizations (HETD and HOMD) of styrenes promoted by hypervalent iodine reagents (HVIRs; DMP and PIDA) and facilitated by HFIP to yield all trans cyclobutanes is reported using density functional theory (DFT) calculations. The HFIP molecules lower the energy of the single electron oxidation (SEO) or initiation as a result of strong hydrogen bonding interactions that substantially stabilize the frontier orbitals before and after electron addition. The HETD or HOMD is a radically-characterized π-π stacked head-to-head stepwise [2+2] cycloaddition initiated via SEO by DMP or PIDA, respectively. DFT results supported by quasiclassical molecular dynamics simulations show that HOMD is a competing pathway to HETD although the latter is relatively faster, in accordance with experimental observations. The initiation is a rate-determining step as a thermodynamically endergonic and propagation is accomplished by radically-cationic hetero- and homodimerized intermediate as propagation is faster than single electron reduction (SER) or termination by radically-anionic HVIRs. Initiation by DMP found to be faster and less endergonic than by PIDA due to (1) the energy gap of electron transfer in a SEO step by I(V) is lower than I(III) and (2) the SOMO energy of the radical anion I(V) is lower than I(III). Furthermore, the presence of p-methoxy group is essential to underpin the SEO by which the more thermodynamically favorable SEO leads to a successful cycloaddition as the thermodynamic term represents a major contribution in the initiative barrier.

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Thermodynamics Control Reactivity of Hypervalent Iodine-Mediated Styrene Hetero- and Homodimerization Mechanistic Insights

10.26434/chemrxiv.12350879.v1 ◽

2020 ◽

Author(s):

Aqeel A. Hussein ◽

Ahmed Al-Yasari ◽

Yumaio Ma

Keyword(s):

Density Functional ◽

Energy Gap ◽

Single Electron ◽

Hypervalent Iodine ◽

Functional Theory ◽

Rate Determining Step ◽

Before And After ◽

Electron Reduction ◽

Dynamics Simulations ◽

Insight Into

A mechanistic insight into the hetero- and homodimerizations (HETD and HOMD) of styrenes promoted by hypervalent iodine reagents (HVIRs; DMP and PIDA) and facilitated by HFIP to yield all trans cyclobutanes is reported using density functional theory (DFT) calculations. The HFIP molecules lower the energy of the single electron oxidation (SEO) or initiation as a result of strong hydrogen bonding interactions that substantially stabilize the frontier orbitals before and after electron addition. The HETD or HOMD is a radically-characterized π-π stacked head-to-head stepwise [2+2] cycloaddition initiated via SEO by DMP or PIDA, respectively. DFT results supported by quasiclassical molecular dynamics simulations show that HOMD is a competing pathway to HETD although the latter is relatively faster, in accordance with experimental observations. The initiation is a rate-determining step as a thermodynamically endergonic and propagation is accomplished by radically-cationic hetero- and homodimerized intermediate as propagation is faster than single electron reduction (SER) or termination by radically-anionic HVIRs. Initiation by DMP found to be faster and less endergonic than by PIDA due to (1) the energy gap of electron transfer in a SEO step by I(V) is lower than I(III) and (2) the SOMO energy of the radical anion I(V) is lower than I(III). Furthermore, the presence of p-methoxy group is essential to underpin the SEO by which the more thermodynamically favorable SEO leads to a successful cycloaddition as the thermodynamic term represents a major contribution in the initiative barrier.

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Thermodynamics Control Reactivity of Hypervalent Iodine-Mediated Styrene Hetero- and Homodimerization: Mechanistic Insights

10.26434/chemrxiv.12350879.v2 ◽

2020 ◽

Author(s):

Aqeel A. Hussein ◽

Ahmed Al-Yasari ◽

Yumiao Ma

Keyword(s):

Density Functional ◽

Energy Gap ◽

Single Electron ◽

Hypervalent Iodine ◽

Functional Theory ◽

Rate Determining Step ◽

Before And After ◽

Electron Reduction ◽

Dynamics Simulations ◽

Insight Into

A mechanistic insight into the hetero- and homodimerizations (HETD and HOMD) of styrenes promoted by hypervalent iodine reagents (HVIRs; DMP and PIDA) and facilitated by HFIP to yield all trans cyclobutanes is reported using density functional theory (DFT) calculations. The HFIP molecules lower the energy of the single electron oxidation (SEO) or initiation as a result of strong hydrogen bonding interactions that substantially stabilize the frontier orbitals before and after electron addition. The HETD or HOMD is a radically-characterized π-π stacked head-to-head stepwise [2+2] cycloaddition initiated via SEO by DMP or PIDA, respectively. DFT results supported by quasiclassical molecular dynamics simulations show that HOMD is a competing pathway to HETD although the latter is relatively faster, in accordance with experimental observations. The initiation is a rate-determining step as a thermodynamically endergonic and propagation is accomplished by radically-cationic hetero- and homodimerized intermediate as propagation is faster than single electron reduction (SER) or termination by radically-anionic HVIRs. Initiation by DMP found to be faster and less endergonic than by PIDA due to (1) the energy gap of electron transfer in a SEO step by I(V) is lower than I(III) and (2) the SOMO energy of the radical anion I(V) is lower than I(III). Furthermore, the presence of p-methoxy group is essential to underpin the SEO by which the more thermodynamically favorable SEO leads to a successful cycloaddition as the thermodynamic term represents a major contribution in the initiative barrier.

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Thermodynamics Control Reactivity of Hypervalent Iodine-Mediated Styrene Hetero- and Homodimerization: Mechanistic Insights

10.26434/chemrxiv.12350879.v4 ◽

2020 ◽

Cited By ~ 1

Author(s):

Aqeel A. Hussein ◽

Ahmed Al-Yasari ◽

Yumiao Ma

Keyword(s):

Density Functional ◽

Energy Gap ◽

Single Electron ◽

Hypervalent Iodine ◽

Functional Theory ◽

Rate Determining Step ◽

Before And After ◽

Electron Reduction ◽

Dynamics Simulations ◽

Insight Into

A mechanistic insight into the hetero- and homodimerizations (HETD and HOMD) of styrenes promoted by hypervalent iodine reagents (HVIRs; DMP and PIDA) and facilitated by HFIP to yield all trans cyclobutanes is reported using density functional theory (DFT) calculations. The HFIP molecules lower the energy of the single electron oxidation (SEO) or initiation as a result of strong hydrogen bonding interactions that substantially stabilize the frontier orbitals before and after electron addition. The HETD or HOMD is a radically-characterized π-π stacked head-to-head stepwise [2+2] cycloaddition initiated via SEO by DMP or PIDA, respectively. DFT results supported by quasiclassical molecular dynamics simulations show that HOMD is a competing pathway to HETD although the latter is relatively faster, in accordance with experimental observations. The initiation is a rate-determining step as a thermodynamically endergonic and propagation is accomplished by radically-cationic hetero- and homodimerized intermediate as propagation is faster than single electron reduction (SER) or termination by radically-anionic HVIRs. Initiation by DMP found to be faster and less endergonic than by PIDA due to (1) the energy gap of electron transfer in a SEO step by I(V) is lower than I(III) and (2) the SOMO energy of the radical anion I(V) is lower than I(III). Furthermore, the presence of p-methoxy group is essential to underpin the SEO by which the more thermodynamically favorable SEO leads to a successful cycloaddition as the thermodynamic term represents a major contribution in the initiative barrier.

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N-Heterocyclic Carbene-Catalyzed Synthesis of Ynones via C–H Alkynylation of Aldehydes with Alkynyliodonium Salts

10.26434/chemrxiv.9946925 ◽

2019 ◽

Author(s):

Adam A. Rajkiewicz ◽

Natalia Wojciechowska ◽

Marcin Kalek

Keyword(s):

Density Functional ◽

Bond Formation ◽

Kinetic Studies ◽

Density Functional Theory Calculations ◽

Hypervalent Iodine ◽

Functional Theory ◽

Leaving Group ◽

13C Labelling ◽

Reaction Proceeds ◽

Mechanism Of The Reaction

Alkynylation of aldehydes with alkynyl(aryl)iodonium salts catalyzed by an N-heterocyclic carbene (NHC) has been developed. The application of the organocatalyst and the hypervalent iodine group-transfer reagent allowed for metal-free C–H functionalization and C–C bond formation. The reaction proceeds under exceptionally mild conditions, at –40 ⁰C and in the presence of an amine base, providing access to an array of heteroaryl-propargyl ketones containing various substituents in good to excellent yields. The mechanism of the reaction was investigated by means of both experiments and density functional theory calculations. 13C-labelling and computations determined that the key alkynyl transfer step occurs via an unusual direct SN2 substitution of iodine-based leaving group by Breslow intermediate nucleophile at an acetylenic carbon. Moreover, kinetic studies revealed that the turnover-limiting step of the catalytic cycle is the generation of the Breslow intermediate, whereas the subsequent C–C bond-formation is a fast process. These results were fully reproduced and rationalized by the computed full free energy profile of the reaction, showing that the largest energy span is located between protonated NHC and the transition state for the carbene attack on the aldehyde substrate.

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