Facile synthesis of cyclopropene analogues of aluminum and an aluminum pinacolate, and the reactivity of LA1[η2-C2(SiMe3)2] toward unsaturated molecules (L = HC[(CMe)(NAr)]2, Ar=2,6-i-Pr2C6H3)

Reduction of LAII(2) (1) (L = HC[(CMe)(NAr)](2), Ar = 2,6-i-Pr2C6H3) with potassium in the presence of alkynes C-2(SiMe3)(2), C2Ph2, and C2Ph(SiMe3) yielded the first neutral cyclopropene analogues of aluminum LAl[eta (2)-C-2(SiMe3)(2)] (3), LAl(eta (2)-C2Ph2) (4), and LAl[eta (2)-C2Ph(SiMe3)] (5), respectively, whereas reduction of 1 in the presence of Ph2CO gave an aluminum pinacolate LAl[O-2(CPh2)(2)] (6), irrespective of the amount of Ph2CO employed. The unsaturated molecules CO2, Ph2CO, and PhCN inserted into one of the Al-C bonds of 3 leading to ring enlargement to give novel aluminum five-membered heterocyclic systems LAI[OC(O)C-2(SiMe3)(2)] (7), LAl[OC(Ph)(2)C-2(SiMe3)(2)] (8), and LAl[NC(Ph)C-2(SiMe3)(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-Pr3C6H2), and Ph3SiN3 resulting in the displacement of the alkyne moiety to afford LAl[N-2(Ct-Bu)(2)] (10) with an unprecedented aluminum-containing imidazole ring and the first monomeric aluminum imides LAlNC6H3-2,6-Trip(2) (11) and LAlNSiPh3 (12). All compounds have been characterized spectroscopically. The variable-temperature H-1 NMR studies of 3 and ESR measurements of 3 and 4 suggest that the Al-C-C three-membered-ring systems can be be,, described a, metallacyclopropenes. The Al-27 NMR resonances of 2 and 3 are reported and compared. Molecular structures of compounds 3, 4, 6.OEt2, 8.OEt2, and 9 were determined by single-crystal X-ray structural analysis.