Is It Possible to Achieve Organic Superbases beyond the Basicity Limit Using Tetrahedrane Scaffolds?

Abstract

Substituted tetrahedranes offer exceptional carbon bases with the gas-phase proton affinities (PAs) up to 356 kcal mol À 1 , due to the strain-induced ring opening upon protonation. Additional tetrahedrane moieties exert a dramatic basicity amplification to PAs reaching 600 kcal mol À 1 , being the strongest organic superbases reported, clearly surpassing the proposed limit of achievable basicities (Angew. Chem. Int. Ed. 2015, 54, 9262). However, because protonation/deprotonation of these compounds is not reversible, PAs of the opened-cage isomers were calculated which were lower than the basiciy limit.

Strong Bases Design: Predicted Limits of Basicity

“…Finally, if protonation is allowed to be irreversible, a metastable structure that literally explodes upon protonation could destroy all of the limits. That might be a large net of tetrahedrane cells, 100 which irreversibly breaks down to a net of cyclobutadiene rings right after protonation.…”

Substituted ketenes offer exceptional carbon bases in gas phase: Computational study by density functional theory method

“…[ 2–5 ] The other organosuperbases that are not naphthalene based were also examined experimentally and computationally. [ 6–17 ] Some of the introduced superbases meet much higher basicity than DMAN, which is mainly due to the unique stability of their conjugate acids. In general, stability and positive charge delocalization in the conjugate acid of the base are provided by the solvation, resonance, IHBs, and use of electron‐donating groups.…”

Dimerization and Cycloaddition Reactions of Transient Tri-tert-butylphosphacyclobutadiene Generated by Lewis Acid Induced Isomerization of Tri-tert-butylphosphatetrahedrane

“…Organic tetrahedranes have long captivated the chemistry community because of their unusual bonding properties and reactivity, as well as their potential applications as organic superbases , and components in high-energy-density materials. , While tetrahedrane is considered the most strained saturated hydrocarbons in terms of Baeyer’s strain theory that was first postulated in 1885, − it was not until 1978 that the first tetrahedrane derivative, tetra- tert -butyltetrahedrane, was successfully isolated . In this seminal study, Maier and co-workers also unveiled the close relationship between tetra- tert -butyltetrahedrane and isomeric tetra- tert -butylcyclobutadiene, by showing their interconversion through thermolysis and photolysis experiments …”

“…O rganic tetrahedranes have long captivated the chemistry community because of their unusual bonding properties and reactivity, 1 as well as their potential applications as organic superbases 2,3 and components in high-energy-density materials. 4,5 While tetrahedrane is considered the most strained saturated hydrocarbons in terms of Baeyer's strain theory that was first postulated in 1885, 6−8 it was not until 1978 that the first tetrahedrane derivative, tetra-tert-butyltetrahedrane, was successfully isolated.…”

“…16 However, reactivity studies were hampered by the low isolated yield of 1 (33 mg, 19% yield). Taking into account that anthracene merely acted as a leaving group in the preparation of the hydro(fluoro)phosphine phosphinidenoid precursor, we wondered whether we could obviate the use of ( t BuC) 3 PA (A = anthracene, C 14 H 10 ) by preparing 1 from ( t BuC) 3 P(SiMe 3 ) 2 (2), which can be prepared on a large scale from P(SiMe 3 ) 3 and [ t Bu 3 C 3 ]-[BF 4 ] (Scheme 1B). 22 Additionally, Niecke and co-workers previously demonstrated that P−SiMe 3 bonds may be cleaved using hexachloroethane to form a P−Cl bond, trimethylsilyl chloride, and tetrachloroethylene.…”