Synthesis and Characterization of Dialkylmetal Boryloxides [(μ-9-BBN-9-O)MMe₂]₂, M = Al, Ga, In

The treatment of trimethylaluminum with 9-hydroxy-9-borabicyclo[3.3.1]nonane 9-(OH)-9-BBN afforded a dimeric species [(μ-9-BBN-9-O)AlMe2]2 (1) in low yield and methylalumoxane (MeAlO)n as well as 9-Me-9-BBN as the major products. When the anhydride (9-BBN)2O was used instead of 9-(OH)-9-BBN, the mixture of (MeAlO)n and 9-Me-9-BBN was formed exclusively. Contrary to this, reactions of (9-BBN)2O with trimethylgallium and trimethylindium proceeded with the cleavage of only one metal−carbon bond. The compounds [(μ-9-BBN-9-O)MMe2]2, where M = Ga (2), In (3), were isolated in high yields. Reactions of tetraethyldiboroxane Et4B2O with trimethyl derivatives of aluminum, gallium, and indium were also studied. The structures of 1−3 were determined by X-ray diffraction showing a significant influence of the metal center on the pp(π) interaction between boron and oxygen. The molecular structure of the similar dimer [(μ-9-BBN-9-O)GaBut2]2 (4) is also reported.