C4(BO2Ph)4 and (C2H5)2BOOCC(CH3)3 were stirred and heated at 80°C for 6 h; after cooling pentane was added,; filtered, the colorless solid was thoroughly washed with little portions of pentane. It was sublimed in vac. at 150-170°C; further purifn. by sublimation or by crystn. from a large vol. of toluene; elem. anal.;