Synthesis of Unsymmetrical Diboranes by Diborane Metathesis

Reactions of readily accessible magnesium‐centered pinacolatoboryl nucleophiles with [(Ph 2 B) 2 O] result in B−O bond activation of the diphenylborinic anhydride. Although [pinBBPh 2 ] is apparently generated when the nucleophilic boron unit is derived in situ from a magnesium diboranate, it cannot be isolated owing to its onward derivatization by a further {Bpin} − equivalent. A reaction with a terminal magnesium boryl species similarly provides a boryloxide byproduct. In this case, however, the unsymmetrical B(sp 2 )−B(sp 3 ) diborane may be intercepted as its DMAP adduct.