BORA-AROMATIC SYSTEMS .6. DEHALOGENATION OF ORGANOBORON DIHALIDES IN THE SEARCH FOR BORENES

The dehalogenation of various organoboron dihalides (methylboron diiodide, phenylboron dibromide and phenylboron dichloride) by metal reducing agents (potassium, bis(trimethylsilyl)mercury, diethyltin oligomer and hexamethyldistannane) has been examined as a possible approach to the generation of boron(I) or borenoid intermediates. The use of alkynes as a boron(I) trapping agent has been shown to be inadvisable with metals and organoboron dibromides or diiodides. From the reaction of phenylboron dibromide, potassium and diphenylacetylene, none of the previously claimed hexaphenyl-1, 4-dibora-2,5-cyclohexadiene could be detected. The interaction of phenylboron dichloride with various metal agents led to the formation of borenoid intermediates of the type PhBMCl, which showed the tendency to undergo: 1. alpha-elimination (M = Me3SiHg) to generate phenylborene; 2. rearrangement (M = Me3Sn) to yield Ph(Me)BSn(Cl)Me2; and 3. alpha-elimination of PhBMeCl from such latter intermediates to yield Me2Sn. © 1979.