SYNTHESIS, STRUCTURE, AND SPECTROSCOPIC CHARACTERIZATION OF UNASSOCIATED MONOAMIDO, DIAMIDO, AND TRIAMIDO DERIVATIVES OF ALUMINUM AND GALLIUM

As part of a study of the possible existence of pi-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 H-1 and C-13 NMR and X-ray crystallography. In addition, the X-ray crystal structures of the previously reported triamido compounds Al{N(iPr)213,6, 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) angstrom, respectively, which are within the previously known range for bonds between three-coordinate nitrogen and three-coordinate aluminum or gallium. Dynamic behavior in the H-1 and C-13 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 pi-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 Kalpha (4, 6, 7, lambda = 0.710 73 angstrom) or Cu Kalpha (1-3, 5, lambda = 1.541 78 angstrom) radiation: (1) C25.5H38.5ClGaN, a = 9.421(2) angstrom, b = 14.413(2) angstrom, c = 18.967(3) angstrom, alpha = 87.88(2)degrees, beta = 79.22(2)degrees, gamma = 80.66(2)degrees, triclinic, space group P1BAR, Z = 4, R = 0.083 for 3867 (I > 3sigma(I)) reflections; (2) C42H64GaN, a = 9.945(2) angstrom, b = 11.245(2) angstrom, c = 17.825(2) angstrom, alpha = 87.28(2)degrees, beta = 85.73(2)degrees, gamma = 79.25(2)degrees, space group P1BAR, Z = 2, R = 0.054 for 4155 (I > 2osigma(I)) reflections; (3) C21H47AlN2Si4, a = 13.403(3) angstrom, b = 16.651(2) angstrom, c = 26.061(5) angstrom, beta = 91.46(2)degrees, monoclinic, space group C2/c, Z = 8, R = 0.035 for 2992 (I > 2sigma(I)) reflections; (4) C30H30GaN2, a = 20.346(4) angstrom, b = 11.696(3) angstrom, c = 13.565(3) A, beta = 123.17(2)degrees, monoclinic, space group C2/c, Z = 4, R = 0.066 for 1707 (I > 3sigma(I)) reflections; (5) C12H36ClGaN2Si4, a = 11.657(3) angstrom, b = 12.677(2) angstrom, c = 15.831(3) angstrom, orthorhombic, space group P2(1)2(1)2(1), Z = 4, R = 0.040 for 2577 (I > 3sigma(I)) reflections; (6) C18H42AlN3, a = 7.803(6) angstrom, b = 16.590(12) angstrom, c = 17.397(14) angstrom, alpha = 102.68(5), beta = 90.67(5)degrees, gamma = 96.67(5)degrees, triclinic, space group P1BAR, Z = 4, R = 0.071 for 4311 (I > 2simga(I)) data; (7) C18H54GaN3Si6, a = 16.008(3) angstrom, c = 8.444(2) angstrom, trigonal, space group P31cBAR, Z = 2, R = 0.059 for 718 (I > 3sigma(I)) reflections.