Heterocyclic Digallanates, Encapsulation of Lithium Cations in Organometallic Cages and C–H Bond Activation

Abstract

Hydrogallation of the dialkynylbenzenes 1,3‐(R2R′Si‐C≡C)2C6H4 (3: R = Me, R′ = Ph; 4: R = Ph, R′ = Me) with dichlorogallane, H‐GaCl2, afforded the corresponding dialkenylbenzenes 5 and 6, with GaCl2 groups geminal to the silyl substituents. Compound 6 was characterised by crystal structure determination, which revealed intramolecular bridging of both gallium atoms by two chlorine atoms as a new structural motif. Treatment of 5 and 6 with six equivalents of ethyllithium gave unprecedented heterocyclic digallanates 7 and 8, in which two four‐coordinate gallium atoms were bridged by two 1,3‐dialkenylbenzene spacer ligands. The obtained large heterocycles encapsulated two lithium counterions in their molecular cavities. The lithium atoms were coordinated in a cryptand‐like fashion and showed a variety of short contacts to aromatic rings, alkenyl groups, and α‐carbon atoms of terminal ethyl groups. They could be removed from the molecular cavity by coordination with chelating 1,2‐dimethoxyethane ligands. Heating of digallanates 7 and 8 in toluene to more than 100 °C over a period of 5 h resulted in fascinating transformations with C–H bond activation and ortho‐metallation. Five‐membered GaC4 metallacycles were formed, which had a terminal R2R′Si‐CH=CH‐ group resulting from the formal protolytic cleavage of an alkenyl–gallium bond by the ortho‐hydrogen atom.

Aluminum and Gallium Hydrazides as Active Lewis Pairs: Cooperative C–H Bond Activation with H–C≡C–Ph and Pentafluorobenzene

“…The second signal may be shifted as a result of close proximity between the H atom and the aromatic ring of the pentafluorobenzene substituents (H···C distances to one ortho -C and two ipso -C atoms 2.68 to 2.79 Å). The methyl group bound to Ga has a chemical shift of δ­( 1 H) = 0.58, which is at a relatively low field compared to other methylgallium compounds or related species with GaCH groups and may be influenced by the electron-withdrawing substituents. As a minor side-product we isolated a few single crystals of 7b , sufficient for an X-ray crystal structure determination, but not for a full characterization.…”

A Sterically Constrained Tricyclic PC3 Phosphine: Coordination Behavior and Insertion of Chalcogen Atoms into P−C Bonds

“…Double hydrogallation of 1,3‐dialkynylbenzene 1 with H‐GaCl 2 afforded the tetrachlordigallium compound 2 in quantitative yield. 2 reacted with nine equivalents of n ‐butyllithium (smaller ratios gave heterocyclic digallanates) in n ‐hexane to afford a solid (Scheme ), which was extracted with hot n ‐hexane in a Soxhlet apparatus for 3 days. Concentration of the extract and cooling to −30 °C yielded an amorphous solid, from which the yellow trilithium compound 3 was extracted with benzene at room temperature.…”

“…Evaporation of the solvent afforded 3 in moderate yields of 25 to 50 % (Scheme ). Li[Ga n Bu 4 ] was formed as a by‐product, which is probably polymeric through Li‐C bridges and insoluble in hot n ‐hexane. 3 results from Ga‐Li exchange and ortho ‐lithiation of the phenylene ring.…”

“…Double hydrogallation of 1,3-dialkynylbenzene 1 [6] with H-GaCl 2 afforded the tetrachlordigallium compound 2 in quantitative yield. 2 reacted with nine equivalents of nbutyllithium (smaller ratios gave heterocyclicd igallanates) [6] in n-hexane to afford asolid (Scheme 1), which was extracted with hot n-hexane in aSoxhlet apparatus for 3days.Concentration of the extract and cooling to À30 8 8Cy ielded an amorphous solid, from which the yellow trilithium compound 3 was extracted with benzene at room temperature.E vaporation of the solvent afforded 3 in moderate yields of 25 to 50 %( Scheme 1). Li[Ga n Bu 4 ]w as formed as ab y-product, which is probably polymeric through Li-C bridges [6] and insoluble in hot n-hexane.…”

Photochemical alkynylation of hydrosilanes by iron catalysis

“…Alkynylsilanes are traditionally prepared from terminal alkynes and silyl electrophiles by using Grignard reagents or strong lithium bases. 5 Clearly, this classic method requires not only harsh reaction conditions but also complicated operation procedures, which might hinder its practical applications. Since the first strategy reported by Voronkov, 6 a number of metal-catalyzed approaches involving cross dehydrogenative coupling between alkynes and hydrosilanes have been developed.…”