Singlet Diradicals: from Transition States to Crystalline Compounds

Abstract

Singlet diradicals are usually not energy minima. As observed by femtosecond spectroscopy, they readily couple to form final sigma bonds. Substituent effects allow lifetimes to increase into the microsecond range. Taking advantage of the properties of hetero-elements, a diradical has been prepared that is indefinitely stable at room temperature. The availability of diradicals that can be handled under standard laboratory conditions will lead to further insight into their chemical and physical properties, raising the likelihood of practical applications, especially in the field of molecular materials such as electrical conductors and ferromagnets.

Phospha‐Organic Chemistry: Panorama and Perspectives

“…[171] Although somewhat outside the scope of this account, it seems appropriate to mention that another type of stable singlet biradical based on the four-membered P 2 B 2 unit has recently been reported. [172] Quite clearly, phosphorus allows interesting variations from classical closed-shell electronic configurations.…”

[P(μ‐NTer)]2: ein hochtemperaturstabiles Diradikaloid

“…[12] Niecke et al haben Pionierarbeit auf diesem Gebiet geleistet: Sie untersuchten [ClC(m-PMes*)] 2 [13] und verschiedener Derivate, die als isolobale Analoga des intensiv untersuchten S 2 N 2 angesehen werden. [14] Zusätzlich zu diesen Kohlenstoff-ba-sierten 1,3-Diradikaloiden berichteten Bertrand et al [15] [16] und [RGe(m-NSiMe 3 )] 2 (R = 2,6-Dipp 2 C 6 H 3 , Dipp = 2,6-iPr 2 C 6 H 3 )). [17] Kürzlich erweiterten Schnçckel und Mitarbeiter mit [RAl(m-PtBu 2 )] 2 (R = PtBu 2 ) das Gebiet und beschrieben an diesem Intermediat den s-Bindungsbildungsprozess.…”

σ‐Bond Stretching: A Static Approach for a Dynamic Process

“…[9] The groups of Niecke and Yoshifuji have reported the synthesis of 2,4-diphosphacyclobutane-1,3-diyls D, [10,11] confined by a transannular antibonding p overlap, which makes the thermal ring closure into C forbidden. In marked contrast, 1,3-dibora-2,4-diphosphoniocyclobutane-1,3-diyls F [12,13] feature a transannular bonding p overlap, which allows for the thermal ring closure into E (Figure 2). Therefore, a variation of the phosphorus and boron substituents was expected to strongly influence the ground-state structure of compounds E and F and thus offered an opportunity not only to isolate the structural extremes, as reported for C and D, [14] but also to mimic the whole reaction profile for the inversion of E.…”