Multiple Spin‐State Scenarios in Organometallic Reactivity

Dzik, Wojciech I.; Böhmer, Wesley; Bruin, Bas de

doi:10.1002/9781118898277.ch6

“…“Two-state reactivity” emerges when these spin state changes lower the energy of the transition state (Figure ). While extensively investigated in the context of high valent iron oxo chemistry, two-state reactivity has also been proposed for low valent organometallic iron complexes, with the prototypical example being the transient 16-electron species 3 Fe(CO) 4 . Although this species has a triplet ground state, reactions involving ligand binding require spin crossover to the low-lying 1 Fe(CO) 4 state …”

Section: Introductionmentioning

confidence: 99%

Two-State Reactivity in Iron-Catalyzed Alkene Isomerization Confers σ-Base Resistance

Lutz

¹

,

Hickey

²

,

Gao

³

et al. 2020

View full text Add to dashboard Cite

A low-coordinate, high spin (S = 3/2) organometallic iron(I) complex is a catalyst for the isomerization of alkenes. A combination of experimental and computational mechanistic studies supports a mechanism in which alkene isomerization occurs by the allyl mechanism. Importantly, while substrate binding occurs on the S = 3/2 surface, oxidative addition to an η1-allyl intermediate only occurs on the S = 1/2 surface. Since this spin state change is only possible when the alkene substrate is bound, the catalyst has high immunity to typical σ-base poisons due to the antibonding interactions of the high spin state.

show abstract

“…Spin-state changes (spin crossover) can play an important role in chemistry and material research, among others in biochemistry (respiration, enzymatic conversions), 1 development of molecular magnets 2 and spintronics, 3 and as a potential rate-accelerating process in organometallic chemistry and catalysis. 4 Purely metal-centered spin-state changes of coordination complexes can be explained in terms of the coordination and geometry-dependent energy difference between partially filled and empty d-orbitals, as described by the ligand-field splitting parameter Δ. 5…”

Section: Introductionmentioning

confidence: 99%

Ligand-Mediated Spin-State Changes in a Cobalt-Dipyrrin-Bisphenol Complex

Leest

¹

,

Stroek

²

,

Siegler³

et al. 2020

Self Cite

View full text Add to dashboard Cite

The influence of a redox-active ligand on spin-changing events induced by the coordination of exogenous donors is investigated within the cobalt complex [Co II (DPP· 2– )] , bearing a redox-active DPP 2– ligand (DPP = dipyrrin-bis( o , p -di- tert -butylphenolato) with a pentafluorophenyl moiety on the meso -position. This square-planar complex was subjected to the coordination of tetrahydrofuran (THF), pyridine, t BuNH 2 , and AdNH 2 (Ad = 1-adamantyl), and the resulting complexes were analyzed with a variety of experimental (X-ray diffraction, NMR, UV–visible, high-resolution mass spectrometry, superconducting quantum interference device, Evans’ method) and computational (density functional theory, NEVPT2-CASSCF) techniques to elucidate the respective structures, spin states, and orbital compositions of the corresponding octahedral bis-donor adducts, relative to [Co II (DPP· 2– )] . This starting species is best described as an open-shell singlet complex containing a DPP· 2– ligand radical that is antiferromagnetically coupled to a low-spin ( S = 1 / 2 ) cobalt(II) center. The redox-active DPP n – ligand plays a crucial role in stabilizing this complex and in its facile conversion to the triplet THF adduct [Co II (DPP· 2– )(THF) 2 ] and closed-shell singlet pyridine and amine adducts [Co III (DPP 3– )(L) 2 ] (L = py, t BuNH 2 , or AdNH 2 ). Coordination of the weak donor THF to [Co II (DPP· 2– )] changes the orbital overlap between the DPP· 2– ligand radical π-orbitals and the cobalt(II) metalloradical d-orbitals, which results in a spin-flip to the triplet ground state without changing the oxidation states of the metal or DPP· 2– ligand. In contrast, coordination of the stronger donors pyridine, t BuNH 2 , or AdNH 2 induces metal-to-ligand single-electron transfer, resulting in the formation of low-spin ( S = 0) cobalt(III) complexes [Co III (DPP 3– )(L) 2 ] conta...

show abstract

“…The assistance of redox-active ligands in spin changing events during catalysis has already been shown to have enormous effects on product selectivity, reaction feasibility, and rates. 20 , 106 , 114 With further expanding knowledge about redox-active ligands, their characterization, and application, we foresee a focus on the use of these fascinating ligands as tools to control reactivity. Furthermore, (transient) spin states and spin state changes might lead to rational design of spin-controlled reactions.…”

Section: What’s Next?mentioning

confidence: 99%

“…Moreover, changing the absolute amount and relative coupling of unpaired electrons is known to have a tremendous influence on the observed reactivity. 20 Accessing more than one spin state during catalysis (multistate reactivity) can result in lower reaction barriers than reactions that are restricted to a single spin surface. 20 − 22 This is a well-understood paradigm in bioinorganic chemistry, and enzymes selectively oxidize substrates depending on the spin surface accessed during a reaction (spin-selective reactivity), 23 and these concepts have successfully been implemented in catalysis using biomimetic metal complexes.…”

Section: Introductionmentioning

confidence: 99%

Controlling Radical-Type Single-Electron Elementary Steps in Catalysis with Redox-Active Ligands and Substrates

Leest

¹

,

Zwart

²

,

Zhou

³

et al. 2021

JACS Au

Self Cite

View full text Add to dashboard Cite

Advances in (spectroscopic) characterization of the unusual electronic structures of open-shell cobalt complexes bearing redox-active ligands, combined with detailed mapping of their reactivity, have uncovered several new catalytic radical-type protocols that make efficient use of the synergistic properties of redox-active ligands, redox-active substrates, and the metal to which they coordinate. In this perspective, we discuss the tools available to study, induce, and control catalytic radical-type reactions with redox-active ligands and/or substrates, contemplating recent developments in the field, including some noteworthy tools, methods, and reactions developed in our own group. The main topics covered are ( i ) tools to characterize redox-active ligands; ( ii ) novel synthetic applications of catalytic reactions that make use of redox-active carbene and nitrene substrates at open-shell cobalt–porphyrins; ( iii ) development of catalytic reactions that take advantage of purely ligand- and substrate-based redox processes, coupled to cobalt-centered spin-changing events in a synergistic manner; and ( iv ) utilization of redox-active ligands to influence the spin state of the metal. Redox-active ligands have emerged as useful tools to generate and control reactive metal-coordinated radicals, which give access to new synthetic methodologies and intricate (electronic) structures, some of which are yet to be exposed.

show abstract

Multiple Spin‐State Scenarios in Organometallic Reactivity

Cited by 11 publications

References 52 publications

Two-State Reactivity in Iron-Catalyzed Alkene Isomerization Confers σ-Base Resistance

Two-State Reactivity in Iron-Catalyzed Alkene Isomerization Confers σ-Base Resistance

Ligand-Mediated Spin-State Changes in a Cobalt-Dipyrrin-Bisphenol Complex

Controlling Radical-Type Single-Electron Elementary Steps in Catalysis with Redox-Active Ligands and Substrates

Contact Info

Product

Resources

About