An NMR Spectroscopic and X-ray Crystalligraphic Study of the Reaction of Tris(dimethylamino)chlorosilane with Aluminium Chloride. A Quest for the Elusive Silicenium Cation

Article abstract of DOI:10.1021/ja00522a030

The reaction of (Me2N)3SiCl with Al2Cl6 in CH2Cl2 has been carried out over a range of stoichiometries in an effort to prepare the <(Me2N)3Si>⁺ ion.In the solid phase the product forms as colorless crystals of (Me2N)3SiCl^.AlCl3 in orthorhombic space group Pbca, with unit cell constants at -35 deg C a = 14.718(14) Angstroem, b = 12.379(7) Angstroem, and c = 33.442(21) Angstroem.The calculated density of 1.441 g cm^-3 is reasonable for 16 molecules of (Me2N)3SiCl^.AlCl3 per unit cell.Full-matrix least-squares refinement of the structure, using the 3646 symmetry-independent reflections for 4 < 2θ < 48 deg which have I₀ > 2.0?(I₀), has converged with a conventional R index (on <*>F<*>) of 0.060.The bonding in each (Me2N)3SiCl^.AlCl3 is such that one of the Me2N groups is involved in a donor-acceptor bond with an AlCl3 unit.In solution the reaction has been investigated by 1H, 13C, 27Al, and 29Si NMR spectroscopy.A preliminary study of the interaction of (Me2N)3SiF with the fluoride ion acceptors PF5 and AsF5 revealed that these reactions are apparently complex and do not result in significant fluoride ion abstraction.