Synthesis and characterisation of trialkylaluminium–dialkylamine adducts: X-ray diffraction and ¹H NMR studies †

Abstract

Trialkylaluminium–dialkylamine adducts of general formula R¹₃Al·NHR²₂ (R¹ = Me, Et, Prⁱ, Buⁱ or Bu^t; R² = Me, Et, Prⁱ or Buⁱ) were synthesized by reacting R¹₃Al and NHR²₂. at high temperatures these adducts either eliminate alkane, forming dimeric amides, or dissociate. Increase in the bulk of R¹ favours alkane elimination. In the ¹H NMR spectra of the complexes R¹₃Al·NHEt₂ the methylene protons of the ethyl groups exhibited non-equivalence, and the high-temperature coalescence of the methylene proton signals is due to exchange processes involving both the breaking and reforming of the Al–N dative bond, in a unimolecular or a bimolecular step. The free energy of activation for this process has been correlated to the bulk of the groups R¹. The crystal structures of Me₃Al·NHMe₂ and Bu^t₃Al·NHEt₂ were determined and their molecular structures are discussed.

References

1. T. Mole and E. A. Jeffery, Organoaluminium Compounds, Elsevier, Amsterdam, 1972, p. 106.
2. T. Mole, Aust. J. Chem., 1963, 16, 801; 1965, 18, 1183.
3. D. M. Frigo, P. J. Reuvers, D. C. Bradley, H. Chudzynska, H. A. Meinema, J. G. Kraaijkamp and K. Timmer, Chem. Mater., 1991, 3, 1097.
4. K. Gosling and R. E. Bowen, J. Chem. Soc., Dalton Trans., 1974, 1961.
5. K. Haage, K. B. Starowieski and A. Chwojnowski, J. Organomet. Chem., 1979, 174, 149.
6. F. C. Sauls, L. V. Interrante and Z. Jiang, Inorg. Chem., 1990, 29, 2989.
7. C. N. McMahon, S. G. Bott and A. R. Barron, J. Chem. Soc., Dalton Trans., 1997, 3129.
8. N. R. Fetter, B. Bartocha, F. E. Brinckman, Jr. and D. W. Moore, Can. J. Chem., 1963, 41, 1359; J. Chatt, L. A. Duncanson and L. M. Venanzi, J. Chem. Soc., 1956, 2712.
9. L. K. Krannich, C. L. Watkins and D. K. Srivastava, Polyhedron, 1990, 9, 289.
10. D. C. Bradley, I. S. Harding, I. A. Maia and M. Motevalli, J. Chem. Soc., Dalton Trans., 1997, 2969.
11. K. H. Thiele, H. K. Müller and W. Brüser, Z. Anorg. Chem., 1966, 345, 194.
12. J. Sandström, Dynamic NMR Spectroscopy, Academic Press, London, 1982, pp. 84, 96.
13. G. M. Sheldrick, SHELXS 86, Acta Crystallogr., Sect. A, 1990, 46, 467.
14. G. M. Sheldrick, SHELXS 80, University of Göttingen, 1980.
15. L. J. J. Farrugia, ORTEP 3 for Windows, J. Appl. Crystallogr., 1997, 30, 565.