Pure and Applied Chemistry

Dehalogenation of 1,2-dichloro-diborane(4) derivatives with Na/K alloy does not lead to planar cyclo-tetraboranes but to the blue puckered diisopropylamino compound and to the yellow 2,2,6,6-tetramethylpiperidino-tetraboratetrahedrane derivative, respectively. With smaller dialkylamino substituents, the formation of orange-red cyclo-hexaborane (BNMe₂)₆ and the green closo -hexaborane (BNEt₂)₆ is observed. When a 1:1 mixture of Me₂NBCl₂ and [Me₂N(Cl)B]₂ is dehalogenated, a small amount of colorless crystals of the planar diamond-shaped tetrabora-bicyclo-butane [(Me₂N)₂BB -BNMe₂]₂ is obtained. Its MO analysis reveals that eight framework electrons are used to form two 3c,2e sigma bonds, one 4c,2e pi bond, and one 4c,2e sigma bond along the edges.

A new approach to reactive closo-dicarbapentaboranes involves the hydroboration of dichloroboryl-tbutylacetylene with HBCl₂ leading to Me₃CCH₂C(BCl₂)₃. On heating, it is transformed into the closo-dicarbapentaborane (Me₃CCH₂C)₂(BCl)₃, in which the chlorine atoms may be substituted to give new derivatives.

By reacting B₂Cl₄ with C₅Me₅-SiMe₃ the nido-1-borane-2,3,4,5,6-pentacarbahexa- borane(6)is stabilized by the Lewis acid BCl₃ to give (MeC)₅B-BCl₃.

Hydroboration of 3,4-bis(isopropylidene)-1,3-diborolanes leads to the formation of nido-2,3,5-tricarbahexaboranes(7),which may be deprotonated to give the corresponding anions isolobal with C₅H₅^-. Heterotricarbahexaboranes are obtained when a 3,4-bis(dichloroboryl)-2,5-hexadiene derivative is reacted with heptamethyldisilazane and hexamethyl-disilthiane to give the corresponding 1,2,5-azadiborolane and thiadiborolane. Their hydroboration leads to the aza-and thia-nido-dicarbahexaboranes, respectively.