Synthesis of Unsymmetrical Diboranes by Diborane Metathesis

Reactions of readily accessible magnesium-centered pinacolatoboryl nucleophiles with [(Ph₂ B)₂ O] result in B-O bond activation of the diphenylborinic anhydride. Although [pinBBPh₂ ] 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(sp² )-B(sp³ ) diborane may be intercepted as its DMAP adduct.