Reactions of (H(2)AlMes*)(2) (Mes*=2,4,6-(t-Bu)(3)C6H2) with H(2)EAr (E=N,P, or As; Ar=aryl): Characterization of the ring compounds (Mes*AlNPh)(2) and (Mes*AlEPh)(3) (E=P or As)

The reaction between sterically crowded, dimeric, arylalane (H(2)AlMes*)(2) and some aryl amines, phosphines, or arsines are described. Treatment of (H(2)AlMes*)(2) (Mes* = 2,4,6-(t-Bu)(3)C6H2) with the amines H(2)NPh and H(2)NDipp (Dipp = 2,6-(i-Pr)(2)C6H3) affords the monomeric bis(amino)alane products Mes*Al(NHPh)(2) . Et(2)O(1 . Et(2)O) and Mes*Al-(NHDipp)(2) (2) which feature three-coordinate aluminum and nitrogen centers and short Al-N bonds. Heating of a 1:1 mixture of H(2)AlMes* and aniline under carefully controlled conditions affords the dimer (Mes*AlNPh)(2), 3. Reaction of (Mes*AlH2)(2) with H(2)PPh or H(2)AsPh at ca. 160 degrees C gives the trimeric, six-membered-ring compounds (Mes*AlPPh)(3) . Et(2)O (4 . Et(2)O) and (Mes*AlAsPh)(3) . Et(2)O (5 . Et(2)O) which are formal valence analogues of borazine. The structure of 3 features a planar Al2N2 core, which also extends to the ipso carbons of the aryl rings; the Al-N distance is 1.824(2) Angstrom. The structures of 4 and 5 have six-membered rings of alternating aluminum and phosphorus or arsenic atoms arranged in a nonplanar boat conformation. Little or no delocalization of the phosphorus or arsenic lone pairs is evident since the average Al-P and Al-As distances are consistent with single bond lengths. Moreover, pyramidal coordination is observed at all the pnictide centers. The structures of 5 and 4 represent respectively the first and second examples of bonding between three-coordinate aluminum and arsenic or phosphorus, whereas 3 represents a unique instance of an Al2N2 ring with organic substituents. The compounds were characterized by H-1, C-13, and P-31 (4, only) NMR spectroscopy and by X-ray crystallography in the case of 1, 3, 4, and 5. Crystal data with Cu K alpha (lambda = 1.54178 Angstrom) radiation at 130 K: 1, a = 10.255(3) Angstrom, b = 16.733(5) Angstrom, c = 19.267(8) Angstrom, beta = 95.09(3)degrees, V = 3293(2) Angstrom, Z = 4, space group P2(1)/(c), 3070 (I > 2 sigma(I)) data, R = 0.061; 3, a = 8.750(1) Angstrom, beta = 9.326(2) Angstrom, c = 14.025(3) Angstrom, alpha = 101.04(2)degrees, beta = 92.90(1)degrees, gamma = 113.11(1), V = 1088.7(4) Angstrom(3), Z = 1, space group P (1) over bar, 2629 (I > 2 sigma(I)) data, R = 0.053; 4, a = 9.383(5), b = 17.719(7) Angstrom, c = 23.603(14) Angstrom, alpha = 80.86(4)degrees, beta = 82.50(5)degrees, gamma = 75.61 degrees (4), V = 3736(3) Angstrom(3), Z = 2, space group P (1) over bar, 5626 (I > 2 sigma(I)) data, R = 0.084; 5, a = 9.404(7) Angstrom, b = 17.79(2) Angstrom, c = 23.643(10) Angstrom, alpha = 81.01(6)degrees, beta = 83.04(5)degrees, gamma = 75.68(7)degrees, V = 3771(5) Angstrom 3, Z2, space group P (1) over bar, 6363 (I > 2 sigma(I)) data, R = 0.063.