Bis(allyl)gallium Cation, Tris(allyl)gallium, and Tetrakis(allyl)gallate: Synthesis, Characterization, and Reactivity

A series of cationic, neutral, and anionic allylgallium complexes has been isolated and fully characterized. It includes neutral [Ga(eta(1)-C3H5)(3)(L)] (1, L = THF; 2, L = OPPh3), cationic [Ga(eta(1)-C3H5)(2)(THF)(2)](+)[A](-) (3, [A](-) = [B(C6F5)(4)]; 4, [A]- = [B(C6H3Cl2)(4)](-)), as well as anionic [Cat](+)[Ga(eta(1)-C3H5)(4)](-) (5, [Cat](+) = K+; 6, [Cat](+) = [K(dibenzo-18-c-6](+); 7, [Cat](+) = [PPh4](+)). Binding modes of the allyl ligand in solution and in the solid state have been studied comparatively. Single crystal X-ray analyses revealed a fourcoordinate neutral gallium center in 2, a five-coordinate cationic gallium center in 4 and [4.THF], and a four-coordinate anionic gallium center with a bridging mu(2)-eta(1):eta(2) coordination mode of the allyl ligand in 6. The reactivity of this series of allylgallium complexes toward benzophenone and N-heteroaromatics has been investigated. Counterion effects have also been studied. Reactions of 1 and 5 with isoquinoline revealed the first examples of organogallium complexes reacting under 1,2-insertion with pyridine derivatives.