Synthesis and Structure of Neutral and Cationic Gallium Complexes Incorporating Bis(oxazolinato) Ligands

The bis(oxazolinato)dimethylgallium complexes [{BOX‐Me2}GaMe2] (2a) and [{BOX‐(S)‐iPr}GaMe2] (2b) are easily obtained in nearly quantitative yield by a methane elimination reaction between GaMe3 and the corresponding bis(oxazoline) ligands {BOX‐Me2}H (1a) and {BOX‐(S)‐iPr}H (1b). Compound 2a was also synthesized by a salt metathesis involving the formation of the dichloro complex [{BOX‐Me2}GaCl2] by reaction of [(BOX‐Me2)Li] with GaCl3, followed by its in situ methylation with MeMgBr. The neutral complexes 2a and 2b are rapidly ionized by B(C6F5)3 to cations 3a+ and 3b+, respectively, which are either three‐coordinate methylgallium cations or four‐coordinate Ga solvent adducts, as their MeB(C6F5)3– salts. These cationic species exhibit a limited stability and decompose in solution within several hours at room temperature. However, stable four‐coordinate Ga‐NMe2Ph cations (4a+ and 4b+) are isolated in good yield when these ionization reactions are performed in the presence of a Lewis base such as NMe2Ph. Unlike that of B(C6F5)3, the reaction of [{BOX‐Me2}GaMe2] with[Ph3C][B(C6F5)4] quantitatively affords an unusual bis(imine)dimethylgallium cation {H2C=C(OX‐Me2)2}GaMe2+ (5a+) in a reaction that proceeds via a hydride ion occurring at the Me group located at the back of the bis(oxazolinato) ligand chelated to the Ga center in 2a. Overall, the reactivity and structural trends observed for the Ga derivatives are closely related to those of the Al analogs, with the Ga compounds being more stable. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)