Hetero-p systems. 18. Highly substituted 2,4-di-tert-butyl-1-boracyclohexadienes.
Boracylohexadienes I (R = OMe, R1 = CHMe2, SiMe3) with three bulky groups should be ideal starting materials for the prepn. of kinetically stabilized borabenzene derivs. I is formed by substitution reactions of anion II, which itself is derived from 2,4-di-tert-butyl-1-methoxy-1-bora-2,5-cyclohexadiene by lithiation. Reaction of II with FeCl2 provides the sandwich-type complex III. As shown by x-ray structure anal., III has C2 sym. with the boron atoms in a syn arrangement in staggered conformation, an unusual feature for borabenzene complexes. Exchange of the methoxy group in the trimethylsilylated substance I (R = OMe, R1 = SiMe3) leads to compds. I (R = Cl, OH, OSiMe3, CH2CH:CH2, R1 = SiMe3). The pyrolyses behavior of I is described.
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