Mechanistic insights into the SN2-type reactivity of aryl-Co(<scp>iii</scp>) masked-carbenes for C–C bond forming transformations

Planas, Oriol; Roldán-Gómez, Steven; Martin‐Diaconescu, Vlad; Luis, Josep M.; Company, Anna; Ribas, Xavi

doi:10.1039/c8sc00851e

Cited by 16 publications

(8 citation statements)

References 63 publications

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“…The XANES profile is consistent with a centrosymmetric pseudo-octahedral coordination geometry ( Figure 3C). 23,24 EXAFS analysis supports two coordination shells having 2 N/O scattering atoms at 2.0 Å and 4 N/O scattering atoms at 2.16 Å, which is consistent with the optimized DFT geometry (Figure 3 D and section 3.7 of the SI for details. To study the reduced species under Ar (Eq.…”

Section: Resultssupporting

confidence: 79%

“…The X-ray absorption near edge structure (XANES) profile is consistent with a centrosymmetric pseudo-octahedral coordination geometry for 1 (II) (Figure 3C). 23,24 Extended X-ray absorption fine structure (EXAFS) analysis supports two coordination shells having two N/O scattering atoms at 2.0 Å and four N/O scattering atoms at 2.16 Å, which is consistent with the optimized DFT geometry (Figure 3D and Section 3.7 of the SI for details). To study the reduced species under Ar (eq 1) by XAS and EXAFS, we performed bulk electrolysis at −1.8 V of a solution containing 1 (II) (5 mM, in anhydrous CD 3 CN at −40 °C under argon).…”

Section: Inset)supporting

confidence: 71%

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A Unified Electro- and Photocatalytic CO₂ to CO Reduction Mechanism with Aminopyridine Cobalt Complexes

et al. 2019

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Mechanistic understanding of electro-and photocatalytic CO2 reduction is crucial to develop strategies to overcome catalytic bottlenecks. In this regard, herein it is presented for a new CO2-to-CO reduction cobalt aminopyridine catalyst, a detailed experimental and theoretical mechanistic study toward the identification of bottlenecks and potential strategies to alleviate them. The combination of electrochemistry and in-situ spectroelectrochemistry together with spectroscopic techniques led us to identify elusive key electrocatalytic intermediates derived from complex [L N4 Co(OTf)2] (1) (L N4 =1-[2-pyridylmethyl]-4,7-dimethyl-1,4,7triazacyclononane) such as a highly reactive cobalt (I) (1 (I)) and cobalt (I) carbonyl (1 (I)-CO) species. The combination of spectroelectrochemical studies under CO2, 13 CO2 and CO with DFT disclosed that 1 (I) reacts with CO2 to form the pivotal 1 (I)-CO intermediate at the 1 (II/I) redox potential. However, at this reduction potential, the formation of 1 (I)-CO restricts the electrocatalysis due to the endergonicity of the CO release step. In agreement with the experimentally observed CO2-to-CO electrocatalysis at the Co I/0 redox potential, computational studies suggested that the electrocatalytic cycle involves striking metal carbonyls. In contrast, under photochemical conditions, the catalysis smoothly proceeds at the 1 (II/I) redox potential. Under the latter conditions, it is proposed that the electron transfer to form 1 (I)-CO from 1 (II)-CO is under diffusion control. Then, the CO release from 1 (II)-CO is kinetically favored, facilitating the catalysis. Finally, we have found that visible-light irradiation has a positive impact under electrocatalytic conditions. We envision that light-irradiation can serve as an effective strategy to circumvent the CO poisoning and improve the performance of CO2 reduction molecular catalysts. 1750 1950 2050 2150 Wavenumber (cm-1) Co I-CO Co 0-CO Co II-CO Theoretical 43 cm-1 Experimental under CO 2 Experimental under CO 1910 cm-1 44 cm-1 [L N4 Co I-CO] +

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Section: Resultssupporting

confidence: 79%

Section: Inset)supporting

confidence: 71%

A Unified Electro- and Photocatalytic CO₂ to CO Reduction Mechanism with Aminopyridine Cobalt Complexes

et al. 2019

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“…The XANES profile is consistent with a centrosymmetric pseudo-octahedral coordination geometry ( Figure 3C). 23,24 EXAFS analysis supports two coordination shells having 2 N/O scattering atoms at 2.0 Å and 4 N/O scattering atoms at 2.16 Å, which is consistent with the optimized DFT geometry (Figure 3 D and section 2.6 of the SI for details). To study the reduced species under Ar (Eq.…”

Section: Resultssupporting

confidence: 79%

A Unified Electro- and Photocatalytic CO2 to CO Reduction Mechanism with Aminopyridine Cobalt Complexes

Fernandez¹,

Franco²,

Casadevall³

et al. 2019

Preprint

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Mechanistic understanding of electro- and photocatalytic CO2 reduction is crucial to develop strategies to overcome catalytic bottlenecks. In this regard, herein it is presented a new CO2-to-CO reduction cobalt aminopyridine catalyst, a detailed experimental and theoretical mechanistic study toward the identification of bottlenecks and potential strategies to alleviate them. The combination of electrochemical and in-situ spectroelectrochemical (FTIR/UV-Vis SEC) studies together with spectroscopic techniques (NMR, EXAFS) lead us to identify elusive key electrocatalytic intermediates derived from complex [Co(pyMetacn)(OTf)2] (1) (pyMetacn = 1-[2-pyridylmethyl]-4,7-dimethyl-1,4,7-triazacyclononane) such as a highly reactive cobalt (I) (1(I)) and cobalt (I) carbonyl (1(I)-CO) species. 1(I) was obtained by electrochemical reduction of 1(II), and characterized by NMR, EXAFS and FTIR/UV-Vis SEC. The combination of spectroelectrochemical studies under CO2, 13CO2 and CO with DFT disclosed that 1(I) directly reacts with CO2 to form the pivotal 1(I)-CO intermediate at the 1(II/I) redox potential. At this redox potential the theoretical energy barrier for the C-O bond cleavage was found to be as low as 12.2 kcal·mol-1. However, the catalytic process does not proceed at the 1(II/I) redox potential, due to the formation of 1(I)-CO, which is a thermodynamic sink and the CO release restricts the electrocatalysis. In agreement with the experimental observed CO2-to-CO electrocatalysis at the 1(I/0) redox potential, computational studies suggested that the productive electrocatalytic cycle involves striking metal carbonyl intermediates such as [LN4Co0CO] (LN4 = pyMetacn), [LN4CoII(CO2)CO] and [LN4CoICO)2]. In contrast, under photochemical conditions, the catalytic process smoothly proceeds at the 1(II/I) redox potential. Under the latter conditions, it is proposed that the electron transfer rate is under diffusion control and then the CO release from 1(II)-CO is kinetically favored, facilitating the catalysis. Finally, we have found that visible light irradiation has a positive impact under electrocatalytic conditions. We envision that light irradiation can serve as an effective strategy to improve the CO2 reduction of molecular catalysts, via alleviating bottlenecks, such as the CO poisoning.

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“…The tetradentate cyclophane-based ligand t Bu N3C – ligand was selected as the convenient platform to study C–heteroatom bond formation due to its ability to stabilize high-valent species through chelation thus providing insight into the mechanisms of these reactions. ,− At the same time, amines and pyridine donors resemble common directing groups used in chelation-assisted C–H bond activation . Noninnocent character of such ligands has also been demonstrated by Ribas and co-workers in the corresponding Co complexes. − To access Ar–Mn III complexes, a 1:1 mixture of Mn(CO) 5 Br and t Bu N3CBr was reacted in a dichloroethane solution at room temperature (RT) under Hg lamp irradiation to remove CO (Scheme a). An intense red-colored solution was obtained, from which ( t Bu N3CBr )Mn III Br 2 ( 1 ) was isolated in 58% yield as a deep-red, crystalline solid (Scheme a).…”

Section: Resultsmentioning

confidence: 99%

“…The frontier orbital analysis of the DFT-optimized structure for the proposed intermediate, complex 1 + (Scheme ), shows that three singly occupied molecular orbitals (SOMO’s) have the character of d xy , d xz , and d yz orbitals at the metal (Figure ), consistent with assignment of 1 + as a Mn IV complex (see the Supporting Information for details). Although the possibility of ligand’s noninnocence cannot be fully excluded, the use of t Bu N3C – ligand and analogous chelating N-donor ligands in studying RE from first row TMs (e.g., Cu III , Ag III , and Ni III species) is typically proposed to occur at the high-valent metal center without participation of the ligand. ,− ,− …”

Section: Resultsmentioning

confidence: 99%

Aryl–X Bond-Forming Reductive Elimination from High-Valent Mn–Aryl Complexes

Sarbajna

Dinh

et al. 2019

Organometallics

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C−X bond reductive elimination and oxidative addition are key steps in many catalytic cycles for C−H functionalization catalyzed by precious metals; however, engaging first row transition metals in these overall 2e − processes remains a challenge. Although high-valent Mn aryl species have been implicated in Mn-catalyzed C−H functionalization, the nature and reactivity of such species remain unelucidated. In this work, we report rare examples of stable, cyclometalated monoaryl Mn III complexes obtained through clean oxidative addition of Ar−Br to Mn I (CO) 5 Br. These isolated Mn III −Ar complexes undergo unprecedented 2e − reductive elimination of the Ar−X (X = Br, I, and CN) bond and Mn II induced by 1e − oxidation, presumably via transient reactive Mn IV species. Mechanistic studies suggest a nonradical pathway.

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Mechanistic insights into the S_N2-type reactivity of aryl-Co(iii) masked-carbenes for C–C bond forming transformations

Abstract: Electronic and steric parameters influencing the stability and reactivity of aryl-Co(iii) masked carbenes have been evaluated.

Cited by 16 publications

References 63 publications

A Unified Electro- and Photocatalytic CO₂ to CO Reduction Mechanism with Aminopyridine Cobalt Complexes

A Unified Electro- and Photocatalytic CO₂ to CO Reduction Mechanism with Aminopyridine Cobalt Complexes

A Unified Electro- and Photocatalytic CO2 to CO Reduction Mechanism with Aminopyridine Cobalt Complexes

Aryl–X Bond-Forming Reductive Elimination from High-Valent Mn–Aryl Complexes

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Mechanistic insights into the SN2-type reactivity of aryl-Co(iii) masked-carbenes for C–C bond forming transformations

Abstract: Electronic and steric parameters influencing the stability and reactivity of aryl-Co(iii) masked carbenes have been evaluated.

Cited by 16 publications

References 63 publications

A Unified Electro- and Photocatalytic CO2 to CO Reduction Mechanism with Aminopyridine Cobalt Complexes

A Unified Electro- and Photocatalytic CO2 to CO Reduction Mechanism with Aminopyridine Cobalt Complexes

A Unified Electro- and Photocatalytic CO2 to CO Reduction Mechanism with Aminopyridine Cobalt Complexes

Aryl–X Bond-Forming Reductive Elimination from High-Valent Mn–Aryl Complexes

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Mechanistic insights into the S_N2-type reactivity of aryl-Co(iii) masked-carbenes for C–C bond forming transformations

A Unified Electro- and Photocatalytic CO₂ to CO Reduction Mechanism with Aminopyridine Cobalt Complexes

A Unified Electro- and Photocatalytic CO₂ to CO Reduction Mechanism with Aminopyridine Cobalt Complexes