The synthesis and characterization of several hydride derivatives of aluminum and gallium which have bulky aryl substituents are described. The neutral derivatives Mes*2GaH (1), (Trip(2)GaH)(2) (2), and (Trip(2)AlH)(2) (3) (Mes* = 2,4,6-t-Bu(3)C(6)H(2); Trip = 2,4,6-i-Pr3C6H2) were synthesized by the reaction of t-BuLi with the corresponding halide derivatives. The X-ray crystal structures of 1-3 were also determined, and these showed that 1 was monomeric whereas 2 and 3 were dimeric with hydrogen bridging. VT NMR data for 2 indicated that it underwent significant dissociation in solution whereas 3 remains almost completely associated in toluene-d(8) at room temperature. The synthesis and structural characterization of the aluminate species [TriphAlH(3)Li(Et(2)O)(1.5)](2) (4) (Triph = 2,4,6-Ph(3)C(6)H(2)) and [Mes*AlH3Li(THF)(2)](2) (5) and the neutral adduct [2,6-(4-t-BuC(6)H(4))(2)C6H3AlH2-(NMe(3))] (6) are also reported. These compounds are of importance in the synthesis of neutral uncomplexed hydrido derivatives. Crystal data at 130 K with Cu K alpha (1-3, lambda = 1.541 78 Angstrom) or Mo K alpha (4-6, lambda = 0.710 73 Angstrom) radiation : 1, C36H59Ga, a = 9.919(2) Angstrom, b = 29.443(3) Angstrom, c = 11.388(2) Angstrom, beta = 94.72(2)degrees, monoclinic, space group P2(1)/c, Z = 4, R = 0.044 for 3694 (I > 2 sigma(I)) data; 2, C60H94Ga2, a = 14.994(7) Angstrom, b = 10.263(4) Angstrom, c = 37.375(13) Angstrom, beta = 95.56(3)degrees, monoclinic, space group P2(1)/c, Z = 4, R = 0.068 for 6112 (I > 2 sigma(1)) data; 3.PhMe, C67H102Al2, a = 21.254(4) Angstrom, b = 23.318(3) Angstrom, c = 25.197(3) Angstrom, orthorhombic, space group Ibca, Z= 8, R = 0.069 for 3244 (I > 2 sigma(I)) data; 4, C60H70Al2Li2O3, a = 21.960(9) Angstrom, b = 15.835(7) Angstrom, c = 16.363(5) Angstrom, beta = 102.30(3)degrees, monoclinic, space group C2/c, Z = 4, R = 0.073 for 4011 (I > 3 sigma(I)) data; 5, C52H96Al2-Li2O4, a = 13.882(4) Angstrom, b = 19.038(5) Angstrom, c = 10.534(3) Angstrom, beta = 101.02(2)degrees, monoclinic, space group P2(1)/c, Z = 2, R = 0.084 for 2703 (I > 2 sigma(I)) data; 6, C29H40AlN, a = 6.225(2) Angstrom, b = 17.016(2) Angstrom, c = 12.668(3) Angstrom, beta = 102.57(2)degrees, monoclinic, space group P2(1), Z = 2, R = 0.035 for 2883 (I > 2 sigma(I)) data.