Wanzlick's equilibrium in tri- and tetraaminoolefins

Abstract

The dissociation mechanism of electron rich olefins into their parent carbenes has been a controversial topic since Wanzlick’s pioneering work. Herein, we present a combined synthetic and computational study on...

Evidence for Carbene Intermediates in Isocyanide Homologation by Aluminium(I)

“…One is the direct coupling of the carbene B Ph with another equivalent of phenyl isocyanide via TS[B Ph ‐5 Ph ] with an overall barrier of ΔΔ G ≠ =(−39+90) kJ mol −1 =+51 kJ mol −1 . Interestingly, this transition state is with a C−C distance of 2.54 Å similar to that in the Wanzlick‐dimerization of carbenes [62] . Alternatively, carbene B Ph isomerizes to C Ph (Δ G =−109 kJ mol −1 ) via ΔΔ G ≠ =(−43+90) kJ mol −1 =+47 kJ mol −1 , which is only 4 kJ mol −1 lower in energy.…”

“…Interestingly, this transition state is with a CÀ C distance of 2.54 Å similar to that in the Wanzlick-dimerization of carbenes. [62] Alternatively, carbene B Ph isomerizes to C Ph (ΔG = À 109 kJ mol À 1 ) via ΔΔG ‡ = (À 43 + 90) kJ mol À 1 = + 47 kJ mol À 1 , which is only 4 kJ mol À 1 lower in energy. The subsequent coordination of phenyl isocyanide affords IM4 Ph reversibly (ΔG = À 110 kJ mol Subsequently, trimer 5 Ph may convert to the tetramer pre-8 (ΔG = À 290 kJ mol À 1 ) via another association (IM5 Ph ; ΔG = À 199 kJ mol À 1 , ΔG ‡ = (À 189 + 217) kJ mol À 1 = + 28 kJ mol À 1 )-migratory insertion (TS[IM5 Ph -pre-8]; ΔG ‡ = (À 146 + 217) kJ mol À 1 = + 71 kJ mol À 1 ) sequence.…”

In Situ Generation of n‐Type Dopants by Thermal Decarboxylation

“…[35] NHCs are known to reversibly dimerize into their corresponding tetraazafulvalenes, in a process known as the Wanzlick equilibrium, with the position of the equilibrium determined by a variety of factors, such as N-substituents and the singlet-triplet energy gap. [51][52][53][54][55] It is typically these neutral dimeric species that act as electron donors, driven by aromatic stabilization of the oxidized products (Figure 3a). [33] The dimeric form of NHCs has been thoroughly studied in the context of chemical reduction, including the investigation of numerous diimidazolinylidenes and dibenzimidazolinylidene derivatives.…”

Über Carbenintermediate in der AlI vermittelten Homologisierung von Isocyaniden

“…Einerseits kommt es zur direkten Kupplung von B Ph mit einem weiteren Äquivalent Phenylisocyanid via TS[B Ph ‐5 Ph ] mit einer Gesamtbarriere von ΔΔ G ≠ =(−39+90) kJ mol −1 =+51 kJ mol −1 . Auffällig bei diesem Übergangszustand ist der C−C Atomabstand, welcher mit 2.54 Å im Bereich von C−C Atomabständen der Wanzlick‐Dimerisierung von N ‐heterozyklischen Carbenen liegt [62] . Anderseits isomerisiert Carben B Ph zu Verbindung C Ph (Δ G =−109 kJ mol −1 ) mit ΔΔ G ≠ =(−43+90) kJ mol −1 =+47 kJ mol −1 , was energetisch gerade einmal 4 kJ mol −1 niedriger liegt.…”