Reactions of trivinylborane with diboron tetrahalides: properties of some dihalogenoboryl(vinylboryl)ethanes

1 : 1 Addition of trivinylborane and diboron tetrachloride gives the adduct 1,2-bis(dichloroboryl)-1-(divinylboryl)-ethane (CH2:CH)2B·CH(BCl2)·CH2BCl2(I), which reacts with BX3(X = Cl, NMe2) to give X2B·CH(BCl2)·CH2BCl2. Dehydroboration of (I) by addition of trimethylamine gives trimethylamine-divinylborane and pyrolysis gives 1,2-bisdichloroborylethylene. Similar 1 : 1 addition using diboron tetrafluoride gives an adduct with properties similar to (I).1 : 2 Addition of trivinylborane and diboron tetrachloride gives (CH2:CH)B[CH(BCl2)·CH2BCl2]2, unstable above –78°C; a similar adduct using diboron tetrafluoride has not been isolated. 1 : 3 addition does not occur with either tetrahalide.