DFT Studies on the Mechanism of Copper-Catalyzed Boracarboxylation of Alkene with CO2 and Diboron

Lin, Shengnan; Lin, Zhenyang

doi:10.1021/acs.organomet.8b00680

Cited by 41 publications

(35 citation statements)

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“…65 However, only inner-sphere CO 2 insertion was considered in the computational evaluations. 36,65 Here we studied the inner-and outer-sphere CO 2 insertion into the Cu−benzyl intermediate formed in the carboxylation of styrene (Scheme 1). 38 Our computations include three different NHCs: the experimentally studied IPr and IMes ligands 38 and the N-methyl analogue IMe, which has a reduced steric environment (Figures 2 and 3).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

To Bind or Not to Bind: Mechanistic Insights into C–CO₂ Bond Formation with Late Transition Metals

2020

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In transition metal-mediated carboxylation reactions, CO2 inserts into a metal–nucleophile bond. At the carboxylation transition state (TS), CO2 may interact with the metal (inner-sphere path) or may insert without being activated by the metal (outer-sphere path). Currently, there is no consensus as to which path prevails. In order to establish general predictions for the insertion of CO2 into metal–carbon bonds, we computationally analyze a series of experimentally reported Cu, Rh, and Pd complexes. Our focus is on carboxylation of aromatic substrates, including Csp3 benzyl and Csp2 aryl and alkenyl nucleophiles. We observe clear trends, where the nature of the nucleophile determines the preferred path: benzylic Csp3 nucleophiles favor outer-sphere and Csp2 systems favor inner-sphere CO2 insertion into the metal–carbon bond. An exception are Cu–benzyl bonds, where inner- and outer-sphere CO2 insertions are found to be competitive, highlighting the need to include both paths in mechanistic studies and in the rationalization of experimental results. For insertion into Pd–Csp2 bonds, we find that the metal–CO2 interactions at the TS are weak and may be beyond 3 Å for sterically congested ligands. Nonetheless, on the basis of a comparison to other TSs, we argue that the CO2 insertion into Pd–Csp2 bonds should be classified as inner-sphere.

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Section: ■ Results and Discussionmentioning

confidence: 99%

To Bind or Not to Bind: Mechanistic Insights into C–CO₂ Bond Formation with Late Transition Metals

2020

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“…This is consistent with conclusions from computational work by Lin showing the importance of the alkoxide base in promoting the salt metathesis step in the boracarboxylation of styrene. 26 Kinetic analysis of carboxylation: Recent computational reports as well as experimental data obtained in our lab suggests that carboxylation serves as the turnover-limiting step of the catalytic boracarboxylation reaction (Scheme 1, Step III). 19,26,27,28 The electronic character of vinyl arene was important in terms of both yield and catalytic efficiency.…”

Section: Characterization and Reactivity Of Spiroboralactonatecopper(i) Complexesmentioning

confidence: 99%

“…26 Kinetic analysis of carboxylation: Recent computational reports as well as experimental data obtained in our lab suggests that carboxylation serves as the turnover-limiting step of the catalytic boracarboxylation reaction (Scheme 1, Step III). 19,26,27,28 The electronic character of vinyl arene was important in terms of both yield and catalytic efficiency. 19 Specifically, higher yields were observed under ambient conditions with more electron-rich vinyl arenes whereas lower yields were observed for a limited group of moderately electron-deficient vinyl arenes (eg., m-fluorostyrene) under heating.…”

Section: Characterization and Reactivity Of Spiroboralactonatecopper(i) Complexesmentioning

confidence: 99%

“…Carboxylation of alkynes, however, has been reported by Hou, following an analogous insertion of the substrate into a Cu I -Bpin bond. 15b Several independent computational studies have detailed specific aspects of the proposed cycle, such as the role of sodium tert-butoxide (NaO t Bu) 26 and the electronic and steric contributions of the ancillary ligand 27 and the boron moiety. 28 Nevertheless, direct experimental evidence in support of the proposed mechanism, remains lacking.…”

Section: Carboxylation (This Work) Salt Metathesismentioning

confidence: 99%

“…40 Computational expense was reduced by replacing IPr and B(pin) with IMe ligand (IMe =1,3-bis(dimethyl)-4,5-dihydroimidazol-2-ylidene) and B(eg) (eg = ethyleneglycato), which is a strategy used in other studies of related Cu I -catalyzed transformations. 26,27,28,41 Para substituents of same or similar electronic character were used to mimic experimental complexes. In a recent publication, we reported that the SE-like carboxylation pathways were disfavored relative to direct insertion (Figure 3).…”

Section: Characterization and Reactivity Of Spiroboralactonatecopper(i) Complexesmentioning

confidence: 99%

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Experimental and Computational Studies of CO2 Addition Reactions Relevant to Copper-Catalyzed Boracarboxylation of Vinyl Arenes: Evidence for a Phosphine-Promoted Mechanism

Baughman¹,

Akhmedov²,

Petersen³

et al. 2020

Preprint

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An experimental and computational mechanistic investigation of the key carboxylation step in copper(I)-catalyzed boracarboxylation of vinyl arenes is presented here. Catalytically relevant intermediates, including a series of CuI-spiroboralactonate complexes, with electronically differentiated vinyl arenes and stabilized by the NHC ligand IPr (IPr = 1,3-Bis(2,6-di-isopropylphenyl)-4,5-dihydroimidazol-2-ylidine), were isolated and characterized. In situ 1H NMR timecourse studies and subsequent Hammett analysis (p) of carbon dioxide addition to (β-borylbenzyl)copper(I) complexes (benzyl = CH2Arp-X) revealed a linear correlation with a negative rho (ρ) value. Density functional theory (DFT) calculations support a direct CO2 insertion as the primary mechanism for electron-rich benzyl-copper carboxylation. Kinetically sluggish carboxylation of electron-poor trifluoromethyl-substituted benzyl-copper complex (benzyl = CH2Arp-CF3) was accelerated upon addition of exogenous PPh3. Conversely, the additive inhibited reactions of electron-rich tert-butyl-substituted benzyl-copper complex (benzyl = CH2Arp-tBu). These kinetic observations implied that a second carboxylation pathway was likely operative. DFT analysis demonstrated that prior binding of the electron-rich phosphine additive at (β-borylbenzyl)copper(I) yields a meta-stable intermediate that precedes an SE-carboxylation mechanism, which is kinetically favorable for electron-deficient benzyl-copper species and circumvents the kinetically challenging direct insertion mechanism. The mechanistic picture that emerges from this complementary experimental/computational study highlights the kinetic complexities and multiple pathways involved in copper-based carboxylation chemistry.

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Asymmetric Boracarboxylation of Styrenes Using Carbon Dioxide

Pettersen,

Dat Do,

Gorantla

et al. 2024

Adv Synth Catal

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The boracarboxylation reaction has potential for production of natural products and drug candidates, but the development of an asymmetric version of this transformation is challenging. We report an enantioselective boracarboxylation of styrenes, enabled by a copper catalyst containing chiral phosphines. Our experimental conditions provide yields between 31‐76% and enantiomeric ratios from 80:20 up to 98:2 for electron‐rich styrenes. Oxidation of a boracarboxylation product provide (S)‐tropic acid, an intermediate towards several tropane alkaloids. A computational analysis of the mechanistic details shows a complex pattern of competing reaction pathways, explaining challenges encountered when developing asymmetric reactions using CO2.

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DFT Studies on the Mechanism of Copper-Catalyzed Boracarboxylation of Alkene with CO₂ and Diboron

Cited by 41 publications

References 81 publications

To Bind or Not to Bind: Mechanistic Insights into C–CO₂ Bond Formation with Late Transition Metals

To Bind or Not to Bind: Mechanistic Insights into C–CO₂ Bond Formation with Late Transition Metals

Experimental and Computational Studies of CO2 Addition Reactions Relevant to Copper-Catalyzed Boracarboxylation of Vinyl Arenes: Evidence for a Phosphine-Promoted Mechanism

Asymmetric Boracarboxylation of Styrenes Using Carbon Dioxide

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DFT Studies on the Mechanism of Copper-Catalyzed Boracarboxylation of Alkene with CO2 and Diboron

Cited by 41 publications

References 81 publications

To Bind or Not to Bind: Mechanistic Insights into C–CO2 Bond Formation with Late Transition Metals

To Bind or Not to Bind: Mechanistic Insights into C–CO2 Bond Formation with Late Transition Metals

Experimental and Computational Studies of CO2 Addition Reactions Relevant to Copper-Catalyzed Boracarboxylation of Vinyl Arenes: Evidence for a Phosphine-Promoted Mechanism

Asymmetric Boracarboxylation of Styrenes Using Carbon Dioxide

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DFT Studies on the Mechanism of Copper-Catalyzed Boracarboxylation of Alkene with CO₂ and Diboron

To Bind or Not to Bind: Mechanistic Insights into C–CO₂ Bond Formation with Late Transition Metals

To Bind or Not to Bind: Mechanistic Insights into C–CO₂ Bond Formation with Late Transition Metals