ALKYLSILAZALANES - REACTION OF TRIMETHYLALUMINUM WITH SILAZANES - SYNTHESIS AND MOLECULAR-STRUCTURE OF [AL(CH3)2]2[C12H32N2SI4] AND [AL(CH3)2]2[C8H28N2SI4]

The crystalline product [Al(CH3)2]2[C12H32N2Si4] (I), obtained from reaction of 2,2,5,5-tetramethyl-2,5-disila-1-azacyclopentane with trimethylaluminium in a heptane-chlorobenzene mixture, crystallizes in the orthorhombic space group Pbca (No. 61) with unit-cell parameters a = 15.393(3), b = 12.987(2), c = 13.189(4) Å, V = 2637.4(2) Å3 and Dc = 1.06 g cm-3 for Z = 4. Full-matrix least-squares refinement based on 1549 observed reflections with intensities in the range 4.00 < 2θ < 50.0° converged at R = 0.048 (Rw = 0.064). Compound I resides about a crystallographic centre of symmetry and contains a planar Al2N2 four-membered ring with an Al⋯Al contact of 2.790(3) Å. Reaction of trimethylaluminium with 1,1,3,3-tetramethyldisilazane in heptane affords the crystalline product [Al(CH3)2]2[C8H28N2Si4] (II). Compound II crystallizes in the triclinic space group P1 (No. 2) with unit-cell parameters a = 9.354(2), b = 14.670(3), c = 17.536(4) Å, α = 91.24(2), β = 90.63(2), γ = 99.46(2)°, V = 2372.7(9) Å3 and Dc = 1.06 g cm-3 for Z = 4. Full-matrix least-squares refinement based upon 5033 observed reflections with intensities in the range 3.50 < 2θ < 45.0° converged at R = 0.035 (Rw = 0.048). The mean Al ⋯ Al contact across the Al2N2 four-membered ring in II is 2.813(1) Å. The mean AlN bond distance in I is 2.005(3) Å while the mean AlN bond distance in II is 1.992(3) Å. © 1990.