19F NMR Investigations of the Reaction of B(C6F5)3 with Different Tri(alkyl)aluminum Compounds |
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Authors: | Christoph Janiak Paul-Gerhard Lassahn |
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Affiliation: | Institut für Anorganische und Analytische Chemie, Universität Freiburg, Albertstr. 21, D-79104 Freiburg, Germany. Fax (+49) 761 2036147 |
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Abstract: | Tris(pentafluorophenyl)borane, B(C6F5)3 reacts with triethylaluminum, AlEt3 to a mixture of Al(C6F5)3−nEtn and Al2(C6F5)6−nEtn compounds depending on the B/Al ratio. From excess borane to excess AlEt3 the species Al(C6F5)3 → Al(C6F5)2Et Al2(C6F5)4Et2 → Al2(C6F5)3Et3 → Al2(C6F5)2Et4 → Al2(C6F5)Et5 are formed and differentiated by their para-F signal in 19F NMR. The reaction between B(C6F5)3 and the higher aluminum alkyls, tri(iso-butyl)aluminum and tri(n-hexyl)aluminum AlR3 (R = i-Bu, n-C6H13) is slower and requires AlR3 excess to shift the C6F5 R exchange equilibria to almost complete formation of Al(C6F5)R2 and BR3. At equimolar ratio the equilibrium lies on the side of the unchanged borane together with its boranate [B(C6F5)3R]− anion. For tri(n-octyl)aluminum even at large Al(n-C8H17)3 excess no C6F5 alkyl exchange can be observed, but boranate anions form. |
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Keywords: | aluminium alkyl borane cocatalyst 19F NMR perfluorated |
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