THE X-RAY STRUCTURE DETERMINATION OF THE PYRROLIDES (CH3)(2)AL-C4H3NCH3 AND (CH3)(2)GA-N(CCH3)(4)

N-Methyl-2-dimethylaluminium pyrrolide, (CH3)(2)Al-C4H3NCH3, crystalli zes in the triclinic space group PI with the lattice constants a = 700 .5(1), b = 725.9(1), c = 886.8(1) pm, a = 67.69(1)degrees, P = 70.99(1 )degrees, gamma = 88.48(1)degrees, and Z = 2. This compound is isotypi c with the gallium homologue ill, the shortest metal-ring contact betw een the two molecules of one unit cell decreases to 228.6 pm. N-dimeth ylgallium tetramethylpyrrolide has been synthesized from Li-N(CCH3)(4) and (CH3)(2)GaCl. This ''pi-associate'' crystallizes in the monoclini c space group P 2(1)/c with the lattice parameters a = 989.9(2), b = 1 305.4(3), c = 878.3(2) pm, P = 112.73(1)degrees and 4 units per cell. Again two centrosymmetrically orientated molecules form a dimer by sho rt (224.0 pm) intermolecular ''Ga-pi C'' contacts but the structure di ffers significant from the structure of the indium homologue [1].