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.