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Yu S, Bickelhaupt FM, Hamlin TA. Switch From Pauli-Lowering to LUMO-Lowering Catalysis in Brønsted Acid-Catalyzed Aza-Diels-Alder Reactions. ChemistryOpen 2021; 10:784-789. [PMID: 34351072 PMCID: PMC8340067 DOI: 10.1002/open.202100172] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2021] [Revised: 07/20/2021] [Indexed: 12/16/2022] Open
Abstract
Brønsted acid-catalyzed inverse-electron demand (IED) aza-Diels-Alder reactions between 2-aza-dienes and ethylene were studied using quantum chemical calculations. The computed activation energy systematically decreases as the basic sites of the diene progressively become protonated. Our activation strain and Kohn-Sham molecular orbital analyses traced the origin of this enhanced reactivity to i) "Pauli-lowering catalysis" for mono-protonated 2-aza-dienes due to the induction of an asynchronous, but still concerted, reaction pathway that reduces the Pauli repulsion between the reactants; and ii) "LUMO-lowering catalysis" for multi-protonated 2-aza-dienes due to their highly stabilized LUMO(s) and more concerted synchronous reaction path that facilitates more efficient orbital overlaps in IED interactions. In all, we illustrate how the novel concept of "Pauli-lowering catalysis" can be overruled by the traditional concept of "LUMO-lowering catalysis" when the degree of LUMO stabilization is extreme as in the case of multi-protonated 2-aza-dienes.
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Vermeeren P, Tiezza MD, van Dongen M, Fernández I, Bickelhaupt FM, Hamlin TA. Lewis Acid-Catalyzed Diels-Alder Reactions: Reactivity Trends across the Periodic Table. Chemistry 2021; 27:10610-10620. [PMID: 33780068 PMCID: PMC8360170 DOI: 10.1002/chem.202100522] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2021] [Indexed: 12/20/2022]
Abstract
The catalytic effect of various weakly interacting Lewis acids (LAs) across the periodic table, based on hydrogen (Group 1), pnictogen (Group 15), chalcogen (Group 16), and halogen (Group 17) bonds, on the Diels-Alder cycloaddition reaction between 1,3-butadiene and methyl acrylate was studied quantum chemically by using relativistic density functional theory. Weakly interacting LAs accelerate the Diels-Alder reaction by lowering the reaction barrier up to 3 kcal mol-1 compared to the uncatalyzed reaction. The reaction barriers systematically increase from halogen
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Nandi A, Tarannam N, Rodrigues Silva D, Fonseca Guerra C, Hamlin TA, Kozuch S. Boron Tunneling in the "Weak" Bond-Stretch Isomerization of N-B Lewis Adducts. Chemphyschem 2021; 22:1857-1862. [PMID: 34245098 DOI: 10.1002/cphc.202100505] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2021] [Indexed: 11/08/2022]
Abstract
Some nitrile-boron halide adducts exhibit a double-well potential energy surface with two distinct minima: a "long bond" geometry (LB, a van der Waals interaction mostly based on electrostatics, but including a residual charge transfer component) and a "short bond" structure (SB, a covalent dative bond). This behavior can be considered as a "weak" form of bond stretch isomerism. Our computations reveal that complexes RCN-BX3 (R=CH3 , FCH2 , BrCH2 , and X=Cl, Br) exhibit a fast interconversion from LB to SB geometries even close to the absolute zero thanks to a boron atom tunneling mechanism. The computed half-lives of the meta-stable LB compounds vary between minutes to nanoseconds at cryogenic conditions. Accordingly, we predict that the long bond structures are practically impossible to isolate or characterize, which agrees with previous matrix-isolation experiments.
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de Azevedo Santos L, Hamlin TA, Ramalho TC, Bickelhaupt FM. The pnictogen bond: a quantitative molecular orbital picture. Phys Chem Chem Phys 2021; 23:13842-13852. [PMID: 34155488 PMCID: PMC8297534 DOI: 10.1039/d1cp01571k] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2021] [Accepted: 06/03/2021] [Indexed: 02/06/2023]
Abstract
We have analyzed the structure and stability of archetypal pnictogen-bonded model complexes D3PnA- (Pn = N, P, As, Sb; D, A = F, Cl, Br) using state-of-the-art relativistic density functional calculations at the ZORA-M06/QZ4P level. We have accomplished two tasks: (i) to compute accurate trends in pnictogen-bond strength based on a set of consistent data; and (ii) to rationalize these trends in terms of detailed analyses of the bonding mechanism based on quantitative Kohn-Sham molecular orbital (KS-MO) theory in combination with a canonical energy decomposition analysis (EDA) and Voronoi deformation density (VDD) analyses of the charge distribution. We have found that pnictogen bonds have a significant covalent character stemming from strong HOMO-LUMO interactions between the lone pair of A- and σ* of D3Pn. As such, the underlying mechanism of the pnictogen bond is similar to that of hydrogen, halogen, and chalcogen bonds.
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Faltracco M, van de Vrande KNA, Dijkstra M, Saya JM, Hamlin TA, Ruijter E. Palladium-Catalyzed Cascade to Benzoxepins by Using Vinyl-Substituted Donor-Acceptor Cyclopropanes. Angew Chem Int Ed Engl 2021; 60:14410-14414. [PMID: 33822456 PMCID: PMC8251625 DOI: 10.1002/anie.202102862] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2021] [Indexed: 12/18/2022]
Abstract
A palladium-catalyzed intermolecular cascade (4+3) cyclocondensation of salicylaldehydes and vinylcyclopropanes is reported. A key feature of the reaction is the use of a phosphonate group as an acceptor moiety on the cyclopropane, exploiting its propensity to undergo olefination with aldehydes. Subsequent O-allylation enabled the formation of a range of substituted benzoxepinsWith a novel chiral ligand, the products were obtained in generally good yield and with reasonable enantioselectivity.
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Faltracco M, Vrande KNA, Dijkstra M, Saya JM, Hamlin TA, Ruijter E. Palladium‐Catalyzed Cascade to Benzoxepins by Using Vinyl‐Substituted Donor–Acceptor Cyclopropanes. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202102862] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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Yamazaki K, Gabriel P, Di Carmine G, Pedroni J, Farizyan M, Hamlin TA, Dixon DJ. General Pyrrolidine Synthesis via Iridium-Catalyzed Reductive Azomethine Ylide Generation from Tertiary Amides and Lactams. ACS Catal 2021; 11:7489-7497. [PMID: 34306810 PMCID: PMC8291578 DOI: 10.1021/acscatal.1c01589] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Revised: 05/19/2021] [Indexed: 02/06/2023]
Abstract
![]()
An
iridium-catalyzed reductive generation of both stabilized and
unstabilized azomethine ylides and their application to functionalized
pyrrolidine synthesis via [3 + 2] dipolar cycloaddition reactions
is described. Proceeding under mild reaction conditions from both
amide and lactam precursors possessing a suitably positioned electron-withdrawing
or a trimethylsilyl group, using 1 mol% Vaska’s complex [IrCl(CO)(PPh3)2] and tetramethyldisiloxane (TMDS) as a terminal
reductant, a broad range of (un)stabilized azomethine ylides were
accessible. Subsequent regio- and diastereoselective, inter- and intramolecular
dipolar cycloaddition reactions with variously substituted electron-deficient
alkenes enabled ready and efficient access to structurally complex
pyrrolidine architectures. Density functional theory (DFT) calculations
of the dipolar cycloaddition reactions uncovered an intimate balance
between asynchronicity and interaction energies of transition structures,
which ultimately control the unusual selectivities observed in certain
cases.
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Vermeeren P, Hamlin TA, Bickelhaupt FM. Chemical reactivity from an activation strain perspective. Chem Commun (Camb) 2021; 57:5880-5896. [PMID: 34075969 PMCID: PMC8204247 DOI: 10.1039/d1cc02042k] [Citation(s) in RCA: 53] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2021] [Accepted: 05/25/2021] [Indexed: 12/14/2022]
Abstract
Chemical reactions are ubiquitous in the universe, they are at the core of life, and they are essential for industrial processes. The drive for a deep understanding of how something occurs, in this case, the mechanism of a chemical reaction and the factors controlling its reactivity, is intrinsically valuable and an innate quality of humans. The level of insight and degree of understanding afforded by computational chemistry cannot be understated. The activation strain model is one of the most powerful tools in our arsenal to obtain unparalleled insight into reactivity. The relative energy of interacting reactants is evaluated along a reaction energy profile and related to the rigidity of the reactants' molecular structure and the strength of the stabilizing interactions between the deformed reactants: ΔE(ζ) = ΔEstrain(ζ) + ΔEint(ζ). Owing to the connectedness between the activation strain model and Kohn-Sham molecular orbital theory, one is able to obtain a causal relationship between both the sterics and electronics of the reactants and their mutual reactivity. Only when this is accomplished one can eclipse the phenomenological explanations that are commonplace in the literature and textbooks and begin to rationally tune and optimize chemical transformations. We showcase how the activation strain model is the ideal tool to elucidate fundamental organic reactions, the activation of small molecules by metallylenes, and the cycloaddition reactivity of cyclic diene- and dipolarophiles.
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Vermeeren P, van Zeist WJ, Hamlin TA, Fonseca Guerra C, Bickelhaupt FM. Not Carbon s-p Hybridization, but Coordination Number Determines C-H and C-C Bond Length. Chemistry 2021; 27:7074-7079. [PMID: 33513281 PMCID: PMC8248318 DOI: 10.1002/chem.202004653] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Revised: 01/26/2021] [Indexed: 11/26/2022]
Abstract
A fundamental and ubiquitous phenomenon in chemistry is the contraction of both C−H and C−C bonds as the carbon atoms involved vary, in s–p hybridization, along sp3 to sp2 to sp. Our quantum chemical bonding analyses based on Kohn–Sham molecular orbital theory show that the generally accepted rationale behind this trend is incorrect. Inspection of the molecular orbitals and their corresponding orbital overlaps reveals that the above‐mentioned shortening in C−H and C−C bonds is not determined by an increasing amount of s‐character at the carbon atom in these bonds. Instead, we establish that this structural trend is caused by a diminishing steric (Pauli) repulsion between substituents around the pertinent carbon atom, as the coordination number decreases along sp3 to sp2 to sp.
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Vermeeren P, Zeist W, Hamlin TA, Fonseca Guerra C, Bickelhaupt FM. Cover Feature: Not Carbon s–p Hybridization, but Coordination Number Determines C−H and C−C Bond Length (Chem. Eur. J. 24/2021). Chemistry 2021. [DOI: 10.1002/chem.202100494] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Hamlin TA, Bickelhaupt FM, Fernández I. The Pauli Repulsion-Lowering Concept in Catalysis. Acc Chem Res 2021; 54:1972-1981. [PMID: 33759502 DOI: 10.1021/acs.accounts.1c00016] [Citation(s) in RCA: 62] [Impact Index Per Article: 20.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Organic chemistry has undoubtedly had a profound impact on humanity. Day in and day out, we find ourselves constantly surrounded by organic compounds. Pharmaceuticals, plastics, fuels, cosmetics, detergents, and agrochemicals, to name a few, are all synthesized by organic reactions. Very often, these reactions require a catalyst in order to proceed in a timely and selective manner. Lewis acids and organocatalysts are commonly employed to catalyze organic reactions and are considered to enhance the frontier molecular orbital (FMO) interactions. A vast number of textbooks and primary literature sources suggest that the binding of a Lewis acid or an iminium catalyst to a reactant (R1) stabilizes its LUMO and leads to a smaller HOMO(R2)-LUMO(R1) energy gap with the other reactant (R2), thus resulting in a faster reaction. This forms the basis for the so-called LUMO-lowering catalysis concept. Despite the simplicity and popularity of FMO theory, a number of deficiencies have emerged over the years, as a consequence of these FMOs not being the operative factor in the catalysis. LUMO-lowering catalysis is ultimately incomplete and is not always operative in catalyzed organic reactions. Our groups have recently undertaken a concerted effort to generate a unified framework to rationalize and predict chemical reactivity using a causal model that is rooted in quantum mechanics. In this Account, we propose the concept of Pauli repulsion-lowering catalysis to understand the catalysis in fundamental processes in organic chemistry. Our findings emerge from state-of-the-art computational methods, namely, the activation strain model (ASM) of reactivity in conjunction with quantitative Kohn-Sham molecular orbital theory (KS-MO) and a matching energy decomposition analysis (EDA). The binding of the catalyst to the substrate not only leads to a stabilization of its LUMO but also induces a significant reduction of the two-orbital, four-electron Pauli repulsion involving the key molecular orbitals of both reactants. This repulsion-lowering originates, for the textbook Lewis acid-catalyzed Diels-Alder reaction, from the catalyst polarizing the occupied π orbital of the dienophile away from the carbon atoms that form new bonds with the diene. This polarization of the occupied dienophile π orbital reduces the occupied orbital overlap with the diene and constitutes the ultimate physical factor responsible for the acceleration of the catalyzed process as compared to the analogous uncatalyzed reaction. We show that this physical mechanism is generally applicable regardless of the type of reaction (Diels-Alder and Michael addition reactions) and the way the catalyst is bonded to the reactants (i.e., from pure covalent or dative bonds to weaker hydrogen or halogen bonds). We envisage that the insights emerging from our analysis will guide future experimental developments toward the design of more efficient catalytic transformations.
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62
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Azevedo Santos L, Ramalho TC, Hamlin TA, Bickelhaupt FM. Cover Image. J Comput Chem 2021. [DOI: 10.1002/jcc.26515] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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63
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de Azevedo Santos L, Ramalho TC, Hamlin TA, Bickelhaupt FM. Chalcogen bonds: Hierarchical ab initio benchmark and density functional theory performance study. J Comput Chem 2021; 42:688-698. [PMID: 33543482 PMCID: PMC7986859 DOI: 10.1002/jcc.26489] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2020] [Revised: 01/15/2021] [Accepted: 01/18/2021] [Indexed: 12/27/2022]
Abstract
We have performed a hierarchical ab initio benchmark and DFT performance study of D2 Ch•••A- chalcogen bonds (Ch = S, Se; D, A = F, Cl). The ab initio benchmark study is based on a series of ZORA-relativistic quantum chemical methods [HF, MP2, CCSD, CCSD(T)], and all-electron relativistically contracted variants of Karlsruhe basis sets (ZORA-def2-SVP, ZORA-def2-TZVPP, ZORA-def2-QZVPP) with and without diffuse functions. The highest-level ZORA-CCSD(T)/ma-ZORA-def2-QZVPP counterpoise-corrected complexation energies (ΔECPC ) are converged within 1.1-3.4 kcal mol-1 and 1.5-3.1 kcal mol-1 with respect to the method and basis set, respectively. Next, we used the ZORA-CCSD(T)/ma-ZORA-def2-QZVPP (ΔECPC ) as reference data for analyzing the performance of 13 different ZORA-relativistic DFT approaches in combination with the Slater-type QZ4P basis set. We find that the three-best performing functionals are M06-2X, B3LYP, and M06, with mean absolute errors (MAE) of 4.1, 4.2, and 4.3 kcal mol-1 , respectively. The MAE for BLYP-D3(BJ) and PBE amount to 8.5 and 9.3 kcal mol-1 , respectively.
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Rodrigues Silva D, de Azevedo Santos L, Hamlin TA, Fonseca Guerra C, Freitas MP, Bickelhaupt FM. The Gauche Effect in XCH 2 CH 2 X Revisited. Chemphyschem 2021; 22:641-648. [PMID: 33555663 PMCID: PMC8048458 DOI: 10.1002/cphc.202100090] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2021] [Indexed: 11/22/2022]
Abstract
We have quantum chemically investigated the rotational isomerism of 1,2-dihaloethanes XCH2 CH2 X (X = F, Cl, Br, I) at ZORA-BP86-D3(BJ)/QZ4P. Our Kohn-Sham molecular orbital (KS-MO) analyses reveal that hyperconjugative orbital interactions favor the gauche conformation in all cases (X = F-I), not only for X = F as in the current model of this so-called gauche effect. We show that, instead, it is the interplay of hyperconjugation with Pauli repulsion between lone-pair-type orbitals on the halogen substituents that constitutes the causal mechanism for the gauche effect. Thus, only in the case of the relatively small fluorine atoms, steric Pauli repulsion is too weak to overrule the gauche preference of the hyperconjugative orbital interactions. For the larger halogens, X⋅⋅⋅X steric Pauli repulsion becomes sufficiently destabilizing to shift the energetic preference from gauche to anti, despite the opposite preference of hyperconjugation.
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de Azevedo Santos L, van der Lubbe SCC, Hamlin TA, Ramalho TC, Matthias Bickelhaupt F. A Quantitative Molecular Orbital Perspective of the Chalcogen Bond. ChemistryOpen 2021; 10:390. [PMID: 33793082 DOI: 10.1002/open.202100066] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Invited for this month's cover are the groups of Prof. Dr. Teodorico C. Ramalho (Federal University of Lavras and University Hradec Kralove) and Prof. Dr. F. Matthias Bickelhaupt (Vrije Universiteit Amsterdam and Radboud University). The cover picture shows the key message of their work, that is, the covalency of the chalcogen bonds, in an elegantly simple and attractive manner. To that end, the chalcogen bonds are represented by schematic 3D structures of the bond donor D2 Ch and the bond acceptor A- , and their attractive interaction in green. Then, a colorful molecular orbital (MO) diagram where the HOMO-LUMO mixing is represented by the mixing of red (HOMO) and blue (LUMO) into purple (MO) is presented. Read the full text of their Full Paper at 10.1002/open.202000323.
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Azevedo Santos L, Lubbe SCC, Hamlin TA, Ramalho TC, Matthias Bickelhaupt F. Front Cover: A Quantitative Molecular Orbital Perspective of the Chalcogen Bond (4/2021). ChemistryOpen 2021. [DOI: 10.1002/open.202100067] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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67
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de Azevedo Santos L, van der Lubbe SCC, Hamlin TA, Ramalho TC, Matthias Bickelhaupt F. A Quantitative Molecular Orbital Perspective of the Chalcogen Bond. ChemistryOpen 2021; 10:391-401. [PMID: 33594829 PMCID: PMC8015733 DOI: 10.1002/open.202000323] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2020] [Revised: 01/14/2021] [Indexed: 12/18/2022] Open
Abstract
We have quantum chemically analyzed the structure and stability of archetypal chalcogen-bonded model complexes D2 Ch⋅⋅⋅A- (Ch = O, S, Se, Te; D, A = F, Cl, Br) using relativistic density functional theory at ZORA-M06/QZ4P. Our purpose is twofold: (i) to compute accurate trends in chalcogen-bond strength based on a set of consistent data; and (ii) to rationalize these trends in terms of detailed analyses of the bonding mechanism based on quantitative Kohn-Sham molecular orbital (KS-MO) theory in combination with a canonical energy decomposition analysis (EDA). At odds with the commonly accepted view of chalcogen bonding as a predominantly electrostatic phenomenon, we find that chalcogen bonds, just as hydrogen and halogen bonds, have a significant covalent character stemming from strong HOMO-LUMO interactions. Besides providing significantly to the bond strength, these orbital interactions are also manifested by the structural distortions they induce as well as the associated charge transfer from A- to D2 Ch.
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Yu S, Vermeeren P, Hamlin TA, Bickelhaupt FM. Cover Feature: How Oriented External Electric Fields Modulate Reactivity (Chem. Eur. J. 18/2021). Chemistry 2021. [DOI: 10.1002/chem.202100126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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69
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Yu S, Vermeeren P, Hamlin TA, Bickelhaupt FM. How Oriented External Electric Fields Modulate Reactivity. Chemistry 2021; 27:5683-5693. [PMID: 33289179 PMCID: PMC8049047 DOI: 10.1002/chem.202004906] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2020] [Revised: 12/04/2020] [Indexed: 01/27/2023]
Abstract
A judiciously oriented external electric field (OEEF) can catalyze a wide range of reactions and can even induce endo/exo stereoselectivity of cycloaddition reactions. The Diels-Alder reaction between cyclopentadiene and maleic anhydride is studied by using quantitative activation strain and Kohn-Sham molecular orbital theory to pinpoint the origin of these catalytic and stereoselective effects. Our quantitative model reveals that an OEEF along the reaction axis induces an enhanced electrostatic and orbital interaction between the reactants, which in turn lowers the reaction barrier. The stronger electrostatic interaction originates from an increased electron density difference between the reactants at the reactive center, and the enhanced orbital interaction arises from the promoted normal electron demand donor-acceptor interaction driven by the OEEF. An OEEF perpendicular to the plane of the reaction axis solely stabilizes the exo pathway of this reaction, whereas the endo pathway remains unaltered and efficiently steers the endo/exo stereoselectivity. The influence of the OEEF on the inverse electron demand Diels-Alder reaction is also investigated; unexpectedly, it inhibits the reaction, as the electric field now suppresses the critical inverse electron demand donor-acceptor interaction.
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Philippe C, Bui AT, Batsongo-Boulingui S, Pokladek Z, Matczyszyn K, Mongin O, Lemiègre L, Paul F, Hamlin TA, Trolez Y. 1,1,4,4-Tetracyanobutadiene-Functionalized Anthracenes: Regioselectivity of Cycloadditions in the Synthesis of Small Near-IR Dyes. Org Lett 2021; 23:2007-2012. [PMID: 33635667 PMCID: PMC8155560 DOI: 10.1021/acs.orglett.1c00136] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Two small 1,1,4,4-tetracyanobutadiene-functionalized chromophores were obtained by careful leverage of the regioselectivity of the cycloaddition reaction of tetracyanoethylene with anthracene-ynamide derivatives, inducing either a [2 + 2] or a [4 + 2] Diels-Alder process. DFT calculations unraveled the mechanism of the [2 + 2] cycloaddition-retroelectrocyclization reaction sequence with ynamides and elucidated the differing mechanisms in the two substrates. The synthesized dyes presented panchromatic absorption extending into the near-IR and far-red/near-IR photoluminescence in the solid state up to 1550 nm.
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Su G, Thomson CJ, Yamazaki K, Rozsar D, Christensen KE, Hamlin TA, Dixon DJ. A bifunctional iminophosphorane squaramide catalyzed enantioselective synthesis of hydroquinazolines via intramolecular aza-Michael reaction to α,β-unsaturated esters. Chem Sci 2021; 12:6064-6072. [PMID: 33996002 PMCID: PMC8098679 DOI: 10.1039/d1sc00856k] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
An efficient synthesis of enantioenriched hydroquinazoline cores via a novel bifunctional iminophosphorane squaramide catalyzed intramolecular aza-Michael reaction of urea-linked α,β-unsaturated esters is described. The methodology exhibits a high degree of functional group tolerance around the forming hydroquinazoline aryl core and wide structural variance on the nucleophilic N atom of the urea moiety. Excellent yields (up to 99%) and high enantioselectivities (up to 97 : 3 er) using both aromatic and less acidic aliphatic ureas were realized. The potential industrial applicability of the transformation was demonstrated in a 20 mmol scale-up experiment using an adjusted catalyst loading of 2 mol%. The origin of enantioselectivity and reactivity enhancement provided by the squaramide motif has been uncovered computationally using density functional theory (DFT) calculations, combined with the activation strain model (ASM) and energy decomposition analysis (EDA). The activation of both aromatic and aliphatic ureas as N-centered nucleophiles in intramolecular Michael addition reactions to α,β-unsaturated esters was achieved under bifunctional iminophosphorane squaramide superbase catalysis.![]()
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Vermeeren P, Hamlin TA, Bickelhaupt FM, Fernández I. Bifunctional Hydrogen Bond Donor-Catalyzed Diels-Alder Reactions: Origin of Stereoselectivity and Rate Enhancement. Chemistry 2021; 27:5180-5190. [PMID: 33169912 PMCID: PMC8049058 DOI: 10.1002/chem.202004496] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Indexed: 11/11/2022]
Abstract
The selectivity and rate enhancement of bifunctional hydrogen bond donor-catalyzed Diels-Alder reactions between cyclopentadiene and acrolein were quantum chemically studied using density functional theory in combination with coupled-cluster theory. (Thio)ureas render the studied Diels-Alder cycloaddition reactions exo selective and induce a significant acceleration of this process by lowering the reaction barrier by up to 7 kcal mol-1 . Our activation strain and Kohn-Sham molecular orbital analyses uncover that these organocatalysts enhance the Diels-Alder reactivity by reducing the Pauli repulsion between the closed-shell filled π-orbitals of the diene and dienophile, by polarizing the π-orbitals away from the reactive center and not by making the orbital interactions between the reactants stronger. In addition, we establish that the unprecedented exo selectivity of the hydrogen bond donor-catalyzed Diels-Alder reactions is directly related to the larger degree of asynchronicity along this reaction pathway, which is manifested in a relief of destabilizing activation strain and Pauli repulsion.
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Vermeeren P, Hamlin TA, Bickelhaupt FM, Fernández I. Cover Feature: Bifunctional Hydrogen Bond Donor‐Catalyzed Diels–Alder Reactions: Origin of Stereoselectivity and Rate Enhancement (Chem. Eur. J. 16/2021). Chemistry 2021. [DOI: 10.1002/chem.202005344] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Hansen T, Vermeeren P, Yoshisada R, Filippov DV, van der Marel GA, Codée JDC, Hamlin TA. How Lewis Acids Catalyze Ring-Openings of Cyclohexene Oxide. J Org Chem 2021; 86:3565-3573. [PMID: 33538169 PMCID: PMC7901664 DOI: 10.1021/acs.joc.0c02955] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Indexed: 11/29/2022]
Abstract
We have quantum chemically studied the Lewis acid-catalyzed epoxide ring-opening reaction of cyclohexene epoxide by MeZH (Z = O, S, and NH) using relativistic dispersion-corrected density functional theory. We found that the reaction barrier of the Lewis acid-catalyzed epoxide ring-opening reactions decreases upon ascending in group 1 along the series Cs+ > Rb+ > K+ > Na+ > Li+ > H+. Our activation strain and Kohn-Sham molecular orbital analyses reveal that the enhanced reactivity of the Lewis acid-catalyzed ring-opening reaction is caused by the reduced steric (Pauli) repulsion between the filled orbitals of the epoxide and the nucleophile, as the Lewis acid polarizes the filled orbitals of the epoxide more efficiently away from the incoming nucleophile. Furthermore, we established that the regioselectivity of these ring-opening reactions is, aside from the "classical" strain control, also dictated by a hitherto unknown mechanism, namely, the steric (Pauli) repulsion between the nucleophile and the substrate, which could be traced back to the asymmetric orbital density on the epoxide. In all, this work again demonstrates that the concept of Pauli-lowering catalysis is a general phenomenon.
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Vermeeren P, Doppert MT, Bickelhaupt FM, Hamlin TA. How metallylenes activate small molecules. Chem Sci 2021; 12:4526-4535. [PMID: 34163718 PMCID: PMC8179460 DOI: 10.1039/d0sc05987k] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Accepted: 02/02/2021] [Indexed: 11/29/2022] Open
Abstract
We have studied the activation of dihydrogen by metallylenes using relativistic density functional theory (DFT). Our detailed activation strain and Kohn-Sham molecular orbital analyses have quantified the physical factors behind the decreased reactivity of the metallylene on going down Group 14, from carbenes to stannylenes. Along this series, the reactivity decreases due to a worsening of the back-donation interaction between the filled lone-pair orbital of the metallylene and the σ*-orbital of H2, which, therefore, reduces the metallylene-substrate interaction and increases the reaction barrier. As the metallylene ligand is varied from nitrogen to phosphorus to arsenic a significant rate enhancement is observed for the activation of H2 due to (i) a reduced steric (Pauli) repulsion between the metallylene and the substrate; and (ii) less activation strain, as the metallylene becomes increasingly more predistorted. Using a rationally designed metallylene with an optimal Group 14 atom and ligand combination, we show that a number of small molecules (i.e. HCN, CO2, H2, NH3) may also be readily activated. For the first time, we show the ability of our H2 activated designer metallylenes to hydrogenate unsaturated hydrocarbons. The results presented herein will serve as a guide for the rational design of metallylenes toward the activation of small molecules and subsequent reactions.
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