Synthesis, structure, and spectroscopic characterization of unassociated mono-, di-, and triamido derivatives of aluminum and gallium

Article abstract of DOI:10.1021/om00019a040

As part of a study of the possible existence of π-interactions in Al-N or Ga-N bonds, the synthesis and spectroscopic and structural characterization of several unassociated amido derivatives of aluminum and gallium are described. The compounds Mes*GaCl{N(H)Ph}·0.25 (hexane), 1, Mes*₂GaN(H)Ph, 2, MesAl{N(SiMe₃)₂}₂, 3, Mes*Ga(NHPh)₂, 4, and ClGa-{N(SiMe₃)₂}₂, 5 (Mes = 2,4,6-Me₃C₆H₂, Mes* = 2,4,6-t-Bu₃C₆H₂) were synthesized by simple salt elimination procedures and characterized by ¹H and ¹³C NMR and X-ray crystallography. In addition, the X-ray crystal structures of the previously reported triamido compounds Al{N(i-Pr)₂}₃, 6, and Ga{N(SiMe₃)₂}₃, 7, are described. The Al-N and Ga-N distances in 1-7 fall within the narrow limits 1.790(4)-1.809(2) and 1.829(9)-1.874(4) A?, respectively, which are within the previously known range for bonds between three-coordinate nitrogen and three-coordinate aluminum or gallium. Dynamic behavior in the ¹H and ¹³C NMR spectra of 2 and 3 was also observed, with a barrier near 11 kcal mol^-1 being estimated in both molecules. The structural and dynamic NMR data suggest that any π-interactions in the M-N bonds are rather weak and are of the order of 10 kcal mol^-1. Crystal data at 130 K with Mo Kα (4, 6, 7, λ = 0.710 73 A?) or Cu Kα (1-3, 5, λ = 1.541 78 A?) radiation: (1) C_25.5H_38.5ClGaN, a = 9.421(2) A?, b = 14.413(2) A?, c = 18.967(3) A?, α = 87.88(2)°, β = 79.22(2)°, γ = 80.66(2)°, triclinic, space group P1, Z = 4, R = 0.083 for 3867 (I > 3σ(I)) reflections; (2) C₄₂H₆₄GaN, a = 9.945(2) A?, b = 11.245(2) A?, c = 17.825(2) A?, α = 87.28(2)°, β = 85.73(2)°, γ = 79.25(2)°, space group P1, Z = 2, R = 0.054 for 4155 (I > 2σ(I)) reflections; (3) C₂₁H₄₇AlN₂Si₄, a = 13.403(3) A?, b = 16.651(2) A?, c = 26.061(5) A?, β = 91.46(2)°, monoclinic, space group C2/c, Z = 8, R = 0.035 for 2992 (I > 2σ(I)) reflections; (4) C₃₀H₃₀GaN₂, a = 20.346(4) A?, b = 11.696(3) A?, c = 13.565(3) A?, β = 123.17(2)°, monoclinic, space group C2/c, Z = 4, R = 0.066 for 1707 (I > 3σ(I)) reflections; (5) C₁₂H₃₆ClGaN₂Si₄, a = 11.657(3) A?, b = 12.677(2) A?, c = 15.831(3) A?, orthorhombic, space group P2₁2₁2₁, Z = 4, R = 0.040 for 2577 (I > 3σ(I)) reflections; (6) C₁₈H₄₂AlN₃, a = 7.803(6) A?, b = 16.590(12) A?, c = 17.397(14) A?, α = 102.68(5), β = 90.67(5)°, γ = 96.67(5)°, triclinic, space group P1, Z = 4, R = 0.071 for 4311 (I > 2σ(I)) data; (7) C₁₈H₅₄GaN₃Si₆, a = 16.008(3) A?, c = 8.444(2) A?, trigonal, space group P31c, Z = 2, R = 0.059 for 718 (I > 3σ(I)) reflections.