Using internal electrostatic fields to manipulate the valence manifolds of copper complexes

Weberg, Alexander B.; McCollom, Samuel P.; Thierer, Laura M.; Gau, Michael R.; Carroll, Patrick J.; Tomson, Neil C.

doi:10.1039/d0sc06364a

“… [16] Just recently, Tomson and co‐workers suggested that electrostatic interactions with the d(z 2 )‐orbital might be important for the metal–N(anchor) distance in copper(I) complexes. [17] Our computational analysis (see below) suggests that repulsive electrostatic interactions and negative hyperconjugation cause this structural feature.…”

Section: Resultsmentioning

confidence: 83%

“…This corroborates a formal oxidation state of +IV for the cobalt ion in 4 and suggests a reduced repulsive interaction with the N anchor of the ligand (cf. Figures S63–S68), thus, reducing the Co−N distance in analogy to the previously studied copper complexes [17] and attenuating the p(z)‐character of the nitrogen atom's lone pair of electrons (e.g. TPSSh: 3 , Σ(C−N−C)=358.8°; 4 , Σ(C−N−C)=351.9°).…”

Section: Resultsmentioning

confidence: 89%

A Pair of Cobalt(III/IV) Terminal Imido Complexes

Mao

¹

,

Fehn

²

,

Heinemann

³

et al. 2021

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The reaction of the cobalt(I) complex [(TIMMN mes )Co I ](BPh 4 )(2)(TIMMN mes = tris-[2-(3-mesitylimidazolin-2-ylidene)methyl]amine) with 1-adamantylazide yields the cobalt(III) imido complex [(TIMMN mes )Co III -(NAd)](BPh 4 )( 3)w ith concomitant release of dinitrogen. The N-anchor in diamagnetic 3 features an unusual, planar tertiary amine,w hich results from repulsive electrostatic interaction with the filled d(z 2 )-orbital of the cobalt ion and negative hyperconjugation with the neighboring methylene groups.O ne-electron oxidation of 3 with [FeCp 2 ](OTf) provides access to the rare,h igh-valent cobalt(IV) imido complex [(TIMMN mes )Co IV (NAd)](OTf) 2 (4). Despite ah alflife of less than 1hat room temperature, 4 could be isolated at low temperatures in analytically pure form. Single-crystal Xray diffractometry and EPR spectroscopyc orroborate the molecular structure and the d 5 low-spin, S = 1 = 2 ,e lectron configuration. Ac omputational analysis of 4 suggests high covalency within the Co IV =NAdbond with non-negligible spin density located at the imido moiety,w hicht ranslates into substantial triplet nitrene character.

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“…[16] Just recently,T omson and coworkers suggested that electrostatic interactions with the d(z 2 )-orbital might be important for the metal-N(anchor) distance in copper(I) complexes. [17] Our computational analysis (see below) suggests that repulsive electrostatic interactions and negative hyperconjugation cause this structural feature.…”

Section: Resultsmentioning

confidence: 83%

“…This corroborates aformal oxidation state of + IV for the cobalt ion in 4 and suggests ar educed repulsive interaction with the Nanchor of the ligand (cf. Figures S63-S68), thus,r educing the Co À Nd istance in analogy to the previously studied copper complexes [17] and attenuating the p(z)-character of the nitrogen atomsl one pair of electrons (e.g.TPSSh: 3, S(CÀNÀC) = 358.88 8; 4, S(CÀ NÀC) = 351.98 8). Concomitantly,t he covalencyo ft he pinteraction between the metalsd(xz)-and d(yz)-orbitals with the imido ligand is further enhanced, with each having about 50 %c ontribution.…”

Section: Angewandte Chemiementioning

confidence: 76%

A Pair of Cobalt(III/IV) Terminal Imido Complexes

Mao

¹

,

Fehn

²

,

Heinemann

³

et al. 2021

Angewandte Chemie

6

0

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The reaction of the cobalt(I) complex [(TIMMN mes )Co I ](BPh 4 )(2)(TIMMN mes = tris-[2-(3-mesitylimidazolin-2-ylidene)methyl]amine) with 1-adamantylazide yields the cobalt(III) imido complex [(TIMMN mes )Co III -(NAd)](BPh 4 )( 3)w ith concomitant release of dinitrogen. The N-anchor in diamagnetic 3 features an unusual, planar tertiary amine,w hich results from repulsive electrostatic interaction with the filled d(z 2 )-orbital of the cobalt ion and negative hyperconjugation with the neighboring methylene groups.O ne-electron oxidation of 3 with [FeCp 2 ](OTf) provides access to the rare,h igh-valent cobalt(IV) imido complex [(TIMMN mes )Co IV (NAd)](OTf) 2 (4). Despite ah alflife of less than 1hat room temperature, 4 could be isolated at low temperatures in analytically pure form. Single-crystal Xray diffractometry and EPR spectroscopyc orroborate the molecular structure and the d 5 low-spin, S = 1 = 2 ,e lectron configuration. Ac omputational analysis of 4 suggests high covalency within the Co IV =NAdbond with non-negligible spin density located at the imido moiety,w hicht ranslates into substantial triplet nitrene character.

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“…98 In more recent work, Tomson observed shifts in redox potentials that were attributed to stabilization of a dz 2 orbital, and supported this idea with DFT calculations. 99 Redox potentials were primarily used to probe cation effects in these examples, but incorporation of iron in our complexes enabled us to use Mössbauer spectra that can be directly related to the electronic structure of iron. Through the combination of spectroscopy and DFT, we identified cation-dependent changes in orbital energetics.…”

mentioning

confidence: 99%

Iron Complexes of a Proton-Responsive SCS Pincer Ligand with a Sensitive Electronic Structure

Skubi

¹

,

Hooper

²

,

Mercado

³

et al. 2022

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SCS pincer ligands have an interesting combination of strong-field and weak-field donors that is also present in the nitrogenase active site. Here, we explore the electronic structures of iron(II) and iron(III) complexes with such a pincer ligand, bearing a monodentate phosphine, thiolate S donor, amide N donor, ammonia, or CO. The ligand scaffold features a protonresponsive thioamide site, and the protonation state of the ligand greatly influences the reduction potential of iron in the phosphine complex. The N-H bond dissociation free energy can be quantitated as 56 ± 2 kcal/mol. EPR spectroscopy and SQUID magnetometry measurements show that the iron(III) complexes with S and N as the fourth donors have an intermediate spin (S = 3/2) ground state with large zero field splitting, and X-ray absorption spectra show high Fe-S covalency. The Mössbauer spectrum changes drastically with the position of a nearby alkali metal cation in the iron(III) amido complex, and DFT calculations explain this phenomenon through a change between having the doubly-occupied orbital as dz2 or dyz, as the former is more influenced by the nearby positive charge.

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Using internal electrostatic fields to manipulate the valence manifolds of copper complexes

Abstract: Secondary coordination sphere electrostatic effects tune the valence manifolds of copper centers, impacting molecular geometries, photophysical properties, and redox potentials.

Cited by 22 publications

References 55 publications

A Pair of Cobalt(III/IV) Terminal Imido Complexes

A Pair of Cobalt(III/IV) Terminal Imido Complexes

A Pair of Cobalt(III/IV) Terminal Imido Complexes

Iron Complexes of a Proton-Responsive SCS Pincer Ligand with a Sensitive Electronic Structure

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