Facile Synthesis of Cyclopropene Analogues of Aluminum and an Aluminum Pinacolate, and the Reactivity of LAlη2-C2(SiMe3)2 toward Unsaturated Molecules (L = HC(CMe)(NAr)2, Ar = 2,6-i-Pr2C6H3)

Reduction of LAlI(2) (1) (L = HC(CMe)(NAr)(2), Ar = 2,6-i-Pr(2)C(6)H(3)) with potassium in the presence of alkynes C(2)(SiMe(3))(2), C(2)Ph(2), and C(2)Ph(SiMe(3)) yielded the first neutral cyclopropene analogues of aluminum LAleta(2)-C(2)(SiMe(3))(2) (3), LAl(eta(2)-C(2)Ph(2)) (4), and LAleta(2)-C(2)Ph(SiMe(3)) (5), respectively, whereas reduction of 1 in the presence of Ph(2)CO gave an aluminum pinacolate LAlO(2)(CPh(2))(2) (6), irrespective of the amount of Ph(2)CO employed. The unsaturated molecules CO(2), Ph(2)CO, and PhCN inserted into one of the Al-C bonds of 3 leading to ring enlargement to give novel aluminum five-membered heterocyclic systems LAlOC(O)C(2)(SiMe(3))(2) (7), LAlOC(Ph)(2)C(2)(SiMe(3))(2) (8), and LAlNC(Ph)C(2)(SiMe(3))(2) (9) in high yields. In contrast, 3 reacted with t-BuCN, 2,6-Trip(2)C(6)H(3)N(3) (Trip = 2,4,6-i-Pr(3)C(6)H(2)), and Ph(3)SiN(3) resulting in the displacement of the alkyne moiety to afford LAlN(2)(Ct-Bu)(2) (10) with an unprecedented aluminum-containing imidazole ring, and the first monomeric aluminum imides LAlNC(6)H(3)-2,6-Trip(2) (11) and LAlNSiPh(3) (12). All compounds have been characterized spectroscopically. The variable-temperature (1)H NMR studies of 3 and ESR measurements of 3 and 4 suggest that the Al-C-C three-membered-ring systems can be best described as metallacyclopropenes. The (27)Al NMR resonances of 2 and 3 are reported and compared. Molecular structures of compounds 3, 4, 6.OEt(2), 8.OEt(2), and 9 were determined by single-crystal X-ray structural analysis.