Transient Spectroscopy of a Derivative of 2,2-Difluoro-1,3-diphenylcyclopentane-1,3-diylA Persistent Localized Singlet 1,3-Diradical

Adam, Waldemar; Borden, Weston Thatcher; Burda, Clemens; Foster, Heather; Heidenfelder, Thomas; Heubes, Markus; Hrovat, David A.; Kita, Fumio; Lewis, S. B.; Scheutzow, Dieter; Wirz, Jakob

doi:10.1021/ja972977i

Cited by 94 publications

(100 citation statements)

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“…All other factors being equal, 28 polarization of unpaired spin density toward (or away) from the ligating atoms will increase (or decrease) the magnitude of electronic coupling. The notion of altering the magnetic properties of molecules through chemical means has been addressed both computationally [29][30][31][32] and experimentally. [33][34][35] Recent work by Shultz and co-workers, in particular, has clearly demonstrated that spin delocalization contributes to the attenuation of exchange interactions in bridged polynuclear systems.…”

Section: Introductionmentioning

confidence: 99%

Differential Polarization of Spin and Charge Density in Substituted Phenoxy Radicals

Fehir

McCusker

2009

J. Phys. Chem. A

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We have carried out a theoretical study of a series of para-substituted phenoxy radicals in an effort to understand the factors influencing spin and charge density distribution in open-shell systems. The calculations reveal that the distribution of spin and charge are not correlated: cases were found for which spin and charge move together, whereas for other substituents the two quantities exhibit spatially distinct intramolecular polarizations. Charge density variations across the series were found to correlate well with both the Hammett (σ p ) and Hammett-Brown (σ p + ) constants for each substituent, indicating that inductive and/or resonance effects are primarily responsible for the polarization of charge within the molecule. In contrast, the distribution of unpaired spin density could not be adequately accounted for using any of the typical Hammett-type spin delocalization constants cited in the literature. We uncovered an empirical correlation between the polarization of spin density and the R-HOMO-R-LUMO gap of the substituted phenoxy radicals: this led to the development of a simple model based on a three-electron, two-orbital bonding scheme in which mixing between the HOMO of the substituent and the SOMO of the phenoxy moiety serves to define the nature and extent of unpaired spin polarization throughout the molecule. This analysis yielded a correlation coefficient of r > 0.97 for the 15 substituents examined in the study; spin polarization effects in compounds that exhibited the greatest deviation from this correlation could also be readily explained within the context of the model. The underlying reason for the ability to differentially polarize spin and charge likely stems from the fact that net unpaired spin density is completely carried by the unpaired electron (and thus tracks the spatial characteristics of the SOMO), whereas charge density reflects the behavior of all of the electrons of the system. These results could have implications in the field of molecular magnetism, suggesting a means for synthetically tuning the magnitude of intramolecular exchange interactions, as well as providing guidance for the design of catalysts for radical-radical coupling reactions.

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Section: Introductionmentioning

confidence: 99%

Differential Polarization of Spin and Charge Density in Substituted Phenoxy Radicals

Fehir

McCusker

2009

J. Phys. Chem. A

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“…CO ist ein besonders vielversprechendes Molekül für die Aktivierung, da sowohl 1,1-als auch 1,2-Verbrückung von Interesse sind, denn es würde entweder ein [1. [4,5,10,[13][14][15][16] oder auch Cyclopentene nach Gruppenumlagerung [11,17] -isoliert werden. Kleine Moleküle der 15.…”

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Stabile Heterocyclopentan‐1,3‐diyle

2015

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Diphosphadiazandiyl, [(m-NR)P] 2 (R = Ter = 2,6-Dimesitylphenyl), ist für seine Fähigkeit, kleine Moleküle mit Mehrfachbindungen zu aktivieren, bekannt. CO ist ein besonders vielversprechendes Molekül für die Aktivierung, da sowohl 1,1-als auch 1,2-Verbrückung von Interesse sind, denn es würde entweder ein [1. [4,5,10,[13][14][15][16] oder auch Cyclopentene nach Gruppenumlagerung [11,17] -isoliert werden. Kleine Moleküle der 15. Gruppe befinden sich seit einigen Jahren im Zentrum unserer Untersuchungen, aus denen bereits die Isolierung des ersten Cyclo-1,3-diphospha-2,4-diazan-1,3-diyls und dessen schwereren Homologen, Diarsadiazandiyl, hervorging. [18][19][20] Jüngste Berichte über Carbonylierungen mit frustrierten Lewis-Paaren regten unser Interesse an der Aktivierung von CO durch Singulett-Biradikaloide an. [21,22] Für CO kann weder der 1,1-noch der 1,2-verbrückende Bindungsmodus günstig sein, da für den Erstgenannten eine hohe Ringspannung innerhalb des [1.1.1]Bicyclus auftritt, während der Zweitgenannte ein ungewçhnli-ches Carben wäre. Wir berichten hier über die Carbonylierung des Diphosphadiazandiyls, die die Synthese des ersten stabilen Cyclopentan-1,3-diyls durch eine ungewçhnliche Ringerweiterung ermçglichte.Die Umsetzung von [(m-NTer)P] 2 (1; Ter= 2,6-Dimesitylphenyl) erfolgt bereits bei Raumtemperatur mit 1 bar CODruck, wodurch das Biradikaloid 2 gebildet wird (Schema 2).[23] Im Unterschied zur Aktivierung anderer kleiner Moleküle (S 8 , CS 2 , H 2 C = CH 2 , HC CH usw.) mit 1 läuft die Reaktion aber nur sehr langsam ab. Nach 24 h hatte sich die anfangs orangefarbene Lçsung rot gefärbt, obwohl laut 31 P-NMR-spektroskopischen Daten noch 75 % des Ausgangsmaterials vorhanden waren. Daher wurden ein Stahlreaktor eingesetzt und der CO-Druck auf 60 bar erhçht. Nach 48 h konnte vollständiger Umsatz festgestellt werden, und 2 ließ sich in 80 % Ausbeute als kristallines Produkt isolieren.

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“…The direct observation of 2 and, hence, experimental con®r-mation of the prediction of a singlet ground state for this diradical, is consequently, expected to be dicult. However, substitution of phenyl groups at C(1) and C (3) has been found to provide sucient kinetic stabilization for a derivative of 2 to allow its observation [8]. The absence of an EPR signal, the kinetics of disappearance, and the failure to observe trapping by oxygen all point to a singlet ground state for this 1,3-diphenyl derivative of diradical 2.…”

Section: Introductionmentioning

confidence: 93%

Ab initio calculations find 2,2-disilylcyclopentane-1,3-diyl is a singlet diradical with a high barrier to ring closure

Johnson

Hrovat

Skancke

et al. 1999

Theoretical Chemistry Accounts: Theory, Computation, and Modeli

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Ab initio calculations on the lowest singlet and triplet states of 2,2-disilylcyclopentane-1,3-diyl ®nd that the singlet lies well below the triplet. The C 2 singlet diradical is calculated to be a minimum on the potential energy surface with an enthalpic barrier to ring closure of Dr z 298 13.5 kcal/mol at the CASPT2/6-31G* level of theory. The energy of the 1,3-divinyl-substituted singlet diradical is calculated to be only 0.8 kcal/mol higher than that of 5,5-disilyl-1,3-divinylbicyclo[2.1.0]pentane at this level of theory, but the transition state for their equilibration is computed to be 12.8 kcal/mol above the diradical in energy.

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Transient Spectroscopy of a Derivative of 2,2-Difluoro-1,3-diphenylcyclopentane-1,3-diylA Persistent Localized Singlet 1,3-Diradical

Cited by 94 publications

References 30 publications

Differential Polarization of Spin and Charge Density in Substituted Phenoxy Radicals

Differential Polarization of Spin and Charge Density in Substituted Phenoxy Radicals

Stabile Heterocyclopentan‐1,3‐diyle

Ab initio calculations find 2,2-disilylcyclopentane-1,3-diyl is a singlet diradical with a high barrier to ring closure

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