Ether‐Solvated Sodium Ions in Salts Containing π‐Hydrocarbon Anions: Crystallization, Structures, and Semiempirical Solvation Energies

Abstract

using [2 b] obtained from the extinction coefficient of 2 b and absorbance after the pulse. A half-life ( t l , J of roughly 310 ms was determined for 2 b from the decay curve, while the lifetime based on k, was estimated to be 555 -t 62 ms. Similar measurements for the carbenes 2 a and 2c gave values of k,, k , , and tijz (z) for 2 a of 7.3 +1.5x lo5 M -~s -' , 3.1 0.4s-', and 210 (323 42) ms, respectively, while 2c decayed unimolecularly with k i = 6.9 & 0.5 s -l (z =I45 +10ms).These results indicate that when four methyl groups are introduced at the meta positions of the ortho-methylated diphenylcarbene, the carbenic center is more effectively blocked by the four ortho methyl groups presumably owing to the buttressing effect exerted by the meta substituents. Didurylcarbene is found to be some five orders of magnitude longer lived than the parent diphenylcarbene (2 ps in cyclohexane) .[l4I However, when two more methyl groups are introduced at the para positions, the carbenic center is forced to react with the orlho methyl groups, which are brought much closer to the carbene, and the carbene is shorter lived.Support is lent to this explanation by semiempirical calculations. Optimized geometries calculated for a series of polymethylated phenylcarbenes with the programm PM3-ROHF/ CI (4 x 4)" ' I indicate that the distances between carbenic carbon and o-methyl carbon atom for mesityl-. duryl-, and pentamethylphenylcarbenes are 2.8461, 2.7942, and 2.7778 pm, respectively.The present study reveals that polymethylated diphenylcarbenes are exceptionally long-lived for diarylcarbenes, although they are not persistent enough to be isolable. The buttressing effects effectively strengthen the ortho effect that protects the reactive center. This strategy may prove successful in the preparation of a "bottleable" triplet carbene.

1,2‐Diphenylbenzene Dianion: Alkali‐Metal Salts with Drastically Spread C6 Rings

“…The clearest indication of these effects is the spreading of the phenyl substituents of the polyanions. This formation of contact-ion multiples is a consequence of strong Coulombic interactions M + ···C 6 2À is a general phenomenon, [3,13] covers a multitude of different contact-ion structures, [3][4][5][6] demonstrates essential effects of cation size as well as solvation, [14,15] and provides information on reduction pathways [6] or on promising novel materials. [16] Three examples of C 6 2À dianions illustrate some Angewandte Chemie of these aspects: Lithium-metal reduction of hexakis(trimethylsilyl)benzene (Scheme 4, left) [15] generates at strongly distorted C 6 2À dianion in boat-conformation, which can host two [Li(thf)]…”

Sodium Tetraphenylcyclopentadienide Bis(dimethoxyethane)

“…The coordination sphere of the Na ÷ cation is a distorted pentagonal bipyramid with the Na...O contact distances between 2.388 (2) and 2.513 (2) ~,. Summarizing, the monomeric structure of the title compound provides an additional example of the complex aggregation phenomenon of organometallic compounds, which depends on cation size, steric overcrowding of the anion, charge delocalization and the solvation enthalpy of the specific solvent (Bock, N~ither, Havlas, John & Arad, 1994). Because of the complexity of this multiparameter problem, additional investigations are required.…”

Wechselwirkungen in Kristallen, 176. Mitteilung, Redox-Reaktionen von Hexahydropyren: Kristallstrukturen seiner Radikalanion-Salze sowie von Trihydropyrenylium-tetrachloroaluminat und Dichtefunktionaltheorie-Berechnungen

“…4, a und b). Unter den Reduktionsbedingungen entsteht das 1,2,3,6,7,8-Hexahydropyren-Radikalanion, in welchem die negative Überschussladung weitgehend im Naphthalin-p-System delokalisiert ist, und welches daher bei energetisch günstiger Solvatation des Gegenkations [21] bevorzugt Solvens-getrennte Kontaktionenpaare ausbildet. Im Kristallgitter (Fig.…”