1
|
Novotný J, Munzarová M, Marek R. Mechanisms of Ligand Hyperfine Coupling in Transition-Metal Complexes: σ and π Transmission Pathways. Inorg Chem 2024; 63:8580-8592. [PMID: 38690843 PMCID: PMC11094796 DOI: 10.1021/acs.inorgchem.3c04425] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2023] [Revised: 03/27/2024] [Accepted: 03/29/2024] [Indexed: 05/03/2024]
Abstract
Theoretical interpretation of hyperfine interactions was pioneered in the 1950s-1960s by the seminal works of McConnell, Karplus, and others for organic radicals and by Watson and Freeman for transition-metal (TM) complexes. In this work, we investigate a series of octahedral Ru(III) complexes with aromatic ligands to understand the mechanism of transmission of the spin density from the d-orbital of the metal to the s-orbitals of the ligand atoms. Spin densities and spin populations underlying ligand hyperfine couplings are analyzed in terms of π-conjugative or σ-hyperconjugative delocalization vs spin polarization based on symmetry considerations and restricted open-shell vs unrestricted wave function analysis. The transmission of spin density is shown to be most efficient in the case of symmetry-allowed π-conjugative delocalization, but when the π-conjugation is partially or fully symmetry-forbidden, it can be surpassed by σ-hyperconjugative delocalization. Despite a lower spin population of the ligand in σ-hyperconjugative transmission, the hyperfine couplings can be larger because of the direct involvement of the ligand s-orbitals in this delocalization pathway. We demonstrate a quantitative correlation between the hyperfine couplings of aromatic ligand atoms and the characteristics of the metal-ligand bond modulated by the trans substituent, a hyperfine trans effect.
Collapse
Affiliation(s)
- Jan Novotný
- CEITEC
− Central European Institute of Technology, Masaryk University, Kamenice 5, Brno CZ-62500, Czechia
- Department
of Chemistry, Faculty of Science, Masaryk
University, Kamenice
5, Brno CZ-62500, Czechia
| | - Markéta Munzarová
- Department
of Chemistry, Faculty of Science, Masaryk
University, Kamenice
5, Brno CZ-62500, Czechia
| | - Radek Marek
- CEITEC
− Central European Institute of Technology, Masaryk University, Kamenice 5, Brno CZ-62500, Czechia
- Department
of Chemistry, Faculty of Science, Masaryk
University, Kamenice
5, Brno CZ-62500, Czechia
| |
Collapse
|
2
|
Cramer HH, Duchemin C, Kovel CB, Kim J, Pecoraro MV, Chirik PJ. Ligand Field Sensitive Spin Acceleration in the Iron-Catalyzed [2 + 2] Cycloaddition of Unactivated Alkenes and Dienes. J Am Chem Soc 2024; 146:9947-9956. [PMID: 38537152 DOI: 10.1021/jacs.4c00591] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/11/2024]
Abstract
Redox-active pyridine(diimine) (PDI) iron catalysts promote the reversible [2 + 2] cycloaddition of alkenes and dienes to cyclobutane derivatives that have applications ranging from fuels to chemically recyclable polymers. Metallacycles were identified as key intermediates, and spin crossover from the singlet to the triplet surface was calculated to facilitate the reductive coupling step responsible for the formation of the four-membered ring. In this work, a series of sterically and electronically differentiated PDI ligands was studied for the [2 + 2] cycloaddition of ethylene and butadiene to vinylcyclobutane. Kinetic studies revealed that the fastest and slowest turnover were observed with equally electron-deficient supporting ligands that either feature phenyl-substituted imine carbon atoms (MeBPDI) or a pyrazine core (MePZDI). While the oxidative cyclization was comparatively slow for both catalysts, the rate of reductive coupling─determined by stoichiometric 13C2H4 labeling studies─correlated with the turnover frequencies. Two-state density functional theory studies and the distinct electronic structures of related (iPrBPDI) and (iPrPZDI) iron methyl complexes revealed significantly different ligand field strengths due to either diminished ligand σ-donation (MeBPDI) or promoted metal π-backbonding (MePZDI). Spin acceleration, leading to fast reductive coupling and catalytic turnover, was promoted in the case of the weaker ligand field and depends on both the nature and position of the electron-withdrawing group. This study provides strong evidence for the role of two-state reactivity in C(sp3)-C(sp3) bond formation and insights on how ligand design either promotes or inhibits spin acceleration in earth-abundant metal catalysis.
Collapse
Affiliation(s)
- Hanna H Cramer
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
| | - Coralie Duchemin
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
| | - Carli B Kovel
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
| | - Junho Kim
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
| | - Matthew V Pecoraro
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
| | - Paul J Chirik
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
| |
Collapse
|
3
|
Capel Berdiell I, Michaels E, Munro OQ, Halcrow MA. A Survey of the Angular Distortion Landscape in the Coordination Geometries of High-Spin Iron(II) 2,6-Bis(pyrazolyl)pyridine Complexes. Inorg Chem 2024; 63:2732-2744. [PMID: 38258555 PMCID: PMC10848207 DOI: 10.1021/acs.inorgchem.3c04138] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2023] [Revised: 01/04/2024] [Accepted: 01/11/2024] [Indexed: 01/24/2024]
Abstract
Reaction of 2,4,6-trifluoropyridine with sodium 3,4-dimethoxybenzenethiolate and 2 equiv of sodium pyrazolate in tetrahydrofuran at room temperature affords 4-(3,4-dimethoxyphenylsulfanyl)-2,6-di(pyrazol-1-yl)pyridine (L), in 30% yield. The iron(II) complexes [FeL2][BF4]2 (1a) and [FeL2][ClO4]2 (1b) are high-spin with a highly distorted six-coordinate geometry. This structural deviation from ideal D2d symmetry is common in high-spin [Fe(bpp)2]2+ (bpp = di{pyrazol-1-yl}pyridine) derivatives, which are important in spin-crossover materials research. The magnitude of the distortion in 1a and 1b is the largest yet discovered for a mononuclear complex. Gas-phase DFT calculations at the ω-B97X-D/6-311G** level of theory identified four minimum or local minimum structural pathways across the distortion landscape, all of which are observed experimentally in different complexes. Small distortions from D2d symmetry are energetically favorable in complexes with electron-donating ligand substituents, including sulfanyl groups, which also have smaller energy penalties associated with the lowest energy distortion pathway. Natural population analysis showed that these differences reflect greater changes to the Fe-N{pyridyl} σ-bonding as the distortion proceeds, in the presence of more electron-rich pyridyl donors. The results imply that [Fe(bpp)2]2+ derivatives with electron-donating pyridyl substituents are more likely to undergo cooperative spin transitions in the solid state. The high-spin salt [Fe(bpp)2][CF3SO3]2, which also has a strong angular distortion, is also briefly described and included in the analysis.
Collapse
Affiliation(s)
| | - Evridiki Michaels
- School of Chemistry, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, U.K.
| | - Orde Q. Munro
- School of Chemistry, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, U.K.
| | - Malcolm A. Halcrow
- School of Chemistry, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, U.K.
| |
Collapse
|
4
|
Paschelke T, Trumpf E, Grantz D, Pankau M, Grocholski N, Näther C, Sönnichsen FD, McConnell AJ. Tuning the spin-crossover properties of FeII4L 6 cages via the interplay of coordination motif and linker modifications. Dalton Trans 2023; 52:12789-12795. [PMID: 37615965 DOI: 10.1039/d3dt01569f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/25/2023]
Abstract
Despite the increasing number of spin-crossover FeII-based cages, the interplay between ligand modifications (e.g. coordination motif substituents and linker) is not well-understood in these multinuclear systems, limiting rational design. Here, we report a family of FeII4L6 spin-crossover cages based on 2,2'-pyridylbenzimidazoles where subtle ligand modifications lowered the spin crossover temperature in CD3CN by up to 186 K. Comparing pairs of cages, CH3 substituents on either the coordination motif or phenylene linker lowered the spin-crossover temperature by 48 K, 91 K or 186 K, attributed to electronic effects, steric effects and a combination of both, respectively. The understanding of the interplay between ligand modifications gained from this study could be harnessed on the path towards the improved rational design of spin-crossover cages.
Collapse
Affiliation(s)
- Tobias Paschelke
- Otto Diels Institute of Organic Chemistry, Kiel University, Otto-Hahn-Platz 4, Kiel 24098, Germany
| | - Eicke Trumpf
- Otto Diels Institute of Organic Chemistry, Kiel University, Otto-Hahn-Platz 4, Kiel 24098, Germany
| | - David Grantz
- Otto Diels Institute of Organic Chemistry, Kiel University, Otto-Hahn-Platz 4, Kiel 24098, Germany
| | - Malte Pankau
- Otto Diels Institute of Organic Chemistry, Kiel University, Otto-Hahn-Platz 4, Kiel 24098, Germany
| | - Niclas Grocholski
- Otto Diels Institute of Organic Chemistry, Kiel University, Otto-Hahn-Platz 4, Kiel 24098, Germany
| | - Christian Näther
- Institute of Inorganic Chemistry, Kiel University, Max-Eyth-Straße 2, Kiel 24118, Germany
| | - Frank D Sönnichsen
- Otto Diels Institute of Organic Chemistry, Kiel University, Otto-Hahn-Platz 4, Kiel 24098, Germany
| | - Anna J McConnell
- Otto Diels Institute of Organic Chemistry, Kiel University, Otto-Hahn-Platz 4, Kiel 24098, Germany
| |
Collapse
|