title: The influence of halogen substituents on the course of hydrogallation and hydroalumination reactions.
abstract: Treatment of trimethylsilylethynylbenzene derivatives with HGaCl(2) afforded products, [C(6)H(6-x){C(H)=C(SiMe(3))GaCl(2)}(x)], in which by a very fast cis/trans-rearrangement the Ga and H atoms occupied opposite sides of the resulting C=C double bonds. The stability of the cis-forms considerably increased upon application of 1,3-dibromo- and pentafluorophenylalkyne derivatives. Two pairs of cis/trans-isomers could be characterized by crystal structure determinations and allow the direct comparison of structural parameters. For the first time an equilibrium was detected between cis- and trans-forms in solution. Treatment of 1,4-di(tert-butylalkynyl)benzene with HAlR(2) (R = CMe(3), CH(2)CMe(3)) afforded cyclophane-type molecules by the release of AlR(3). Only the neopentyl derivative could be isolated and characterized by crystal structure determination. In contrast, the dibromo compound, 1,4-Br(2)-2,5-(Me(3)CC[triple bond]C)(2)C(6)H(2), yielded the simple addition product, C(6)H(2)Br(2){C(AlR(2))=C(H)CMe(3)}(2) (R = CMe(3)). Condensation was hindered in this case by intramolecular Al-Br interactions. Surprisingly, the simple addition product was also isolated from the reaction of 1,4-(Me(3)CC[triple bond]C)(2)C(6)H(4) with the relatively small hydride HAlEt(2). Solid-state NMR spectra of the product revealed strong intermolecular Al-C interactions involving the negatively charged terminal vinylic carbon atoms, to give one-dimensional coordination polymers.
authors.affiliation: Institut für Anorganische und Analytische Chemie, Universität Münster, D-48149, Münster, Germany. uhlw@uni-muenster.de
authors.forename: Werner
authors.initials: W
authors.lastname: Uhl
authors.forename: Michael
authors.initials: M
authors.lastname: Claesener
authors.forename: Alexander
authors.initials: A
authors.lastname: Hepp
authors.forename: Beate
authors.initials: B
authors.lastname: Jasper
authors.forename: Andrej
authors.initials: A
authors.lastname: Vinogradov
authors.forename: Leo
authors.initials: L
authors.lastname: van Wüllen
authors.forename: Thomas K-J
authors.initials: TK
authors.lastname: Köster