Vinylgallium and alkyllithium compounds: transmetalation and generation of oligolithium cages

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).