The treatment of diethylzinc with (9-BBN)(2)O afforded a tetrameric species [(mu(3)-9-BBN-9-O)ZnEt](4) (1) in high yield due to the selective cleavage of metal-carbon bond whereas (Bu2Zn)-Zn-t was found to be inert toward (9-BBN)(2)O. The reaction of dimethylcadmium with (9-BBN)(2)O resulted in the formation of the analogue [(mu(3)-9-BBN-9-O)CdMe](4) (2). Reactions of tetraethyldiboroxane Et4B2O with Et2Zn, (Bu2Zn)-Zn-t and Me2Cd were also investigated showing its different behavior in each case. The structures of 1 and 2 were determined by X-ray diffraction, and they are the first for group 12 metal boryloxides with a cubane-like M4O4 core. The boron-oxygen interaction affecting deformation of the central core is discussed based on X-ray as well as multinuclear NMR spectroscopy data.