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

The bis(oxazolinato)dimethylgallium complexes [{BOX‐Me 2 }GaMe 2 ] ( 2a ) and [{BOX‐( S )‐ i Pr}GaMe 2 ] ( 2b ) are easily obtained in nearly quantitative yield by a methane elimination reaction between GaMe 3 and the corresponding bis(oxazoline) ligands {BOX‐Me 2 }H ( 1a ) and {BOX‐( S )‐ i Pr}H ( 1b ). Compound 2a was also synthesized by a salt metathesis involving the formation of the dichloro complex [{BOX‐Me 2 }GaCl 2 ] by reaction of [(BOX‐Me 2 )Li] with GaCl 3 , followed by its in situ methylation with MeMgBr. The neutral complexes 2a and 2b are rapidly ionized by B(C 6 F 5 ) 3 to cations 3a + and 3b + , respectively, which are either three‐coordinate methylgallium cations or four‐coordinate Ga solvent adducts, as their MeB(C 6 F 5 ) 3 – salts. These cationic species exhibit a limited stability and decompose in solution within several hours at room temperature. However, stable four‐coordinate Ga‐NMe 2 Ph cations ( 4a + and 4b + ) are isolated in good yield when these ionization reactions are performed in the presence of a Lewis base such as NMe 2 Ph. Unlike that of B(C 6 F 5 ) 3 , the reaction of [{BOX‐Me 2 }GaMe 2 ] with[Ph 3 C][B(C 6 F 5 ) 4 ] quantitatively affords an unusual bis(imine)dimethylgallium cation {H 2 C=C(OX‐Me 2 ) 2 }GaMe 2 + ( 5a + ) in a reaction that proceeds via a hydride abstraction 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)