Katalytische C‐F‐Aktivierung und Hydrodefluorierung von Fluoralkylgruppen

Abstract

Effiziente C‐F‐Bindungsspaltung: Das extrem Lewis‐saure Silylkation [Et3Si]+ ist ein aktiver Katalysator der Hydrodefluorierung von Alkylgruppen bei Raumtemperatur. Das Carborat [CHB11H5Cl6]− spielt eine wesentliche Rolle im Katalysezyklus, da es als schwach koordinierendes Anion kationische Intermediate stabilisiert (im Bild unten).

Rare‐Earth Metal Allyl and Hydrido Complexes Supported by an (NNNN)‐Type Macrocyclic Ligand: Synthesis, Structure, and Reactivity toward Biomass‐Derived Furanics

“…The solid‐state structure of the cation 2‐Ce was investigated to understand the effects of the cationic metal center (Figure 6). The compound crystallizes as an ion pair without close interactions between the cation and anion 17. The unit cell contains a cocrystallized THF molecule disordered around a center of symmetry in the lattice.…”

“…To enhance the solubility of the cation, [La(Me 3 TACD)(η 3 ‐C 3 H 5 )(thf) 2 ][B(C 6 F 5 ) 4 ] ( 2 F ‐La ) was synthesized with the Brønsted acid dimethylanilinium tetrakis(pentafluorophenyl)borate. 2 F ‐La provides the same cation as 2‐La combined with a fluorinated anion [B(C 6 F 5 ) 4 ] − , which makes the compound more soluble in less polar solvents such as benzene 17…”

Zirconocene Dichloride Catalyzed Hydrodefluorination of CF bonds

“…[1,2] In the presence of a reductant such as H 2 or a silane, a number of late-transition-metal and main-group catalysts are known to effect the hydrodefluorination of C sp 2 À F and C sp 3 À F bonds. Gates, Andrew J. P. White, and Mark R. Crimmin* In recent years synthetic methods for the activation and functionalization of inert C À F s bonds with organometallic complexes have attracted increased attention.…”

“…Under the catalytic conditions C 6 F 6 was completely consumed after 24 hours at 80 8C and both C 6 F 5 H and p-C 6 F 4 H 2 were observed after protic work up ( Table 1, entry 10). Although the high C À F bond dissociation energy of hexafluorobenzene has meant that it is often employed as a substrate in hydrodefluorination catalysis, [1][2] the stabilization of the {C 6 F 5 H 2 } anion may result in a relatively low activation energy for CÀF bond cleavage by nucleophilic aromatic substitution. A similar argument could not be made for 1-fluoronaphthalene, which underwent hydrodefluorination albeit at a higher temperature of 110 8C and a longer reaction time of 4 days ( Table 1, entry 13).…”

Ein gezähmtes Silyliumion für Diels‐Alder‐Reaktionen bei niedrigen Temperaturen

“…Die Antwort lautet "ja", denn Ozerov et al [9] und auch Müller et al [10] hatten Silyliumionen bereits als reaktive Katalysatoren bei der Aktivierung von C(sp 3 )-F-Bindungen identifiziert. [11] In der Lewis-Säure-Katalyse finden Silyliumionen bisher hingegen kaum Verwendung, [12][13][14][15][16] vermutlich wegen der irreversiblen Bildung von Lewis-Paaren.…”