Reaction of Me 3Ga and Me 3Al with the tertiary-tetraaza analog of adamantane, hexamethylenetetramine (N 4-Ada). Syntheses and molecular structures of [(Me 3M) n · N 4-Ada] ( n = 1–4, M  Ga or Al)

Abstract

Reaction of Me 3Al or Me 3Ga with hexamethylenetetramine, N 4-Ada (Ada = adamantane), in toluene affords the crystalline addition products [(Me 3M) n · N 4-Ada] ( n = 4, M  Ga ( I); n = 3, M  Ga ( II); n = 3, M  Al ( III); n = 2, M  Ga ( IV); n = 2, M  Al ( V); n = 1, M  Ga ( VI). Compound I crystallizes in the triclinic space group P 1 (no. 2) with unit cell parameters a = 10.365(3), b = 11.814(6), c = 11.991(6), Å, α = 94.16(4), β = 92.56(3), γ = 92.44(3)°, V = 1461(1), Å 3, and D calc. = 1.36 g cm −3 for Z = 2. Least-squares refinement based on 2600 observed reflections converged at R = 0.075, R w = 0.089. Compound III crystallizes in the monoclinic space group P2 1/ c (no. 14) with unit cell parameters a = 7.416(2), b = 16.687(6), c = 19.143(6) Å, β = 91.71(2)° V = 2368(1) Å 3, and D calc. = 1.00 g cm −3 for Z = 4. Least-squares refinement based on 2235 observed reflections converged at R = 0.085, R w = 0.102. The mean GaN bond distance in I is 2.29 (3) Å, while the corresponding AlN distance is 2.11 (1) Å. The GaN distance of 2.318 (9) Å in I is the longest such distance reported. A molecular mechanics study was used to show that the sequential addition of Me 3M (M  Al or Ga) units to N 4-Ada significantly affects the relative Lewis basicities of the nitrogen atoms of the amine.