Vinylgallium and Alkyllithium Compounds: Transmetalation and Generation of Oligolithium Cages

Abstract

Vinylgallium compounds [C(6)H(6-n){(H)C=C(SiR(2) R')-GaR''(2)}(n ] (3, R=Ph, Me; R'=Ph, Me; R''=tBu, Et; n=1, 2) are easily accessible by hydrogallation of the corresponding alkynylbenzene derivatives with H-GaCl(2) and subsequent reaction with alkyllithium derivatives. Treatment of 3 with an excess amount of tert-butyl- or ethyllithium yielded by transmetalation and ortho-deprotonation of the aromatic rings the unprecedented solvent-free oligolithium cluster compounds [{(C(6)H(4)Li)HC=C(SiPh(3))Li}(2)(tBuLi)(2)] (4), [{(C(6)H(4)Li)HC=C(SiPh(2)Me)Li}(4)] (5) and [{(C(6)H(3)Li){HC=C(SiMe(3))Li}(2)}(3)] (6) in moderate yields. Their solid-state structures revealed the presence of unique molecular lithium clusters with 6, 8, or 9 lithium atoms that may be derived from two edge-sharing Li(4) tetrahedra (4), three Li(4) tetrahedra in a chain joined by two common edges (5) or a tricapped trigonal prism of lithium atoms (6).

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

“…The latter distance is in the normal range observed for typical oligomeric alkyllithium compounds such as butyl-or methyllithium, [20] but long-range π-contacts can extend well up to 280 pm. [12,21] In diphenylmethylsilyl derivative 8 (Figure 4), we observe only two relatively short distances to carbon atoms of the bridging phenylene ring [C013Ј and C014Ј; 243.8(5) and 245.1 (5) In an attempt to dissolve compound 8 in organic solvents, we treated the colourless material with DME. Dissolution was only observed under reflux conditions, and only a few single crystals of 8(DME) 6 precipitated upon slow cooling to room temperature.…”

“…Colourless crystals of lithium tetraethylgallanate 9 were obtained by recrystallisation from toluene. The compound and its spectroscopic characterisation are well documented, [12,22] but its molecular structure was previously unknown. It resembles that of Li[AlEt 4 ] [23] and consists of an indefinite chain of alternating lithium and gallium atoms with all α-carbon atoms of the ethyl groups in the bridging …”

“…[12] In this article we report on a continuation of these systematic investigations and on the formation of organometallic digallanates having two lithium cations encapsulated in an organometallic framework and C-H bond activation with ortho-metallation of an aryl group.…”

“…1; Scheme 1), which form interesting structures as a result of oligomerisation through Ga-Cl-Ga bridges and are excellent starting compounds for the generation of various secondary products. [8][9][10][11][12] Addition of H-GaCl 2 to alkynes afforded the trans-addition products with hydrogen and gallium atoms on different sides of the resulting C=C double bonds, whereas dialkylgallium hydrides led, in a first step, to the kinetically controlled cis-addition products via a cyclic transition state. [13] Only rearrangement of sterically less shielded cis-derivatives gave, in a second step, the thermodynamically favoured trans-products.…”

“…[2,3c,14] Dual hydrogallation of alkynes with H-GaCl 2 proceeded easily and gave compounds with aliphatic groups and a geminal arrangement of two gallium atoms. [9][10][11][12] The analogous reactions of dialkylgallium hydrides (and similarly dialkylaluminium hydrides), in contrast, are usually terminated after a single reduction step and the formation of alkene derivatives. Direct twofold hydrogallation was only observed for alkynylgallium compounds, giving gallium-carbon cages by condensation.…”