Substituted Aluminacyclopent-3-enes

Abstract

Treatment of (Z)-1,4-dilithio-1, 4-bis(trimethylsilyl)but-2-ene and (Z)-1, 4-dilithio-1, 4-bis-(trimethylsilyl)-2, 3-dimethylbut-2-ene adducts of TMEDA (N,N,N′,N′,-tetramethylethylenediamine), [{Li(TMEDA)}2{(Me3SiCHCR)2}], R = H (1a) and Me (1b) with AlC13 in diethyl ether results in stereospecific formation of the corresponding metallacyclopent-3-enes, isolated as [meso-{RC(Me3Si)HC}2Al(Cl)NMe2CH2]2, R = H (2a) and Me (2b); reaction of 1a with MC13, M = Ga and In, results in reduction to the group 13 metal. Assignment of the meso isomer is based on NMR data and an X-ray crystal structure determination. Crystals of 2b are triclinic, space group P1̅, with a = 9.811 (3) Å, b = 15.252 (8) Å, c = 15.266 (9) Å, α = 108.39 (3)°, β = 91.14 (3)°, γ = 95.95 (3)°, V = 2153 (2) Å3, and Z = 2. Ab initio calculations at the 3-21G* level on the model metallacycle [A1C1(C4H6)(NR3)], R = H or Me (Cs symmetry), gives a stabilization energy of 46.11 or 45.82 kcal/mol, R = H or Me, respectively, relative to [AlCl(C4H6)] (C2v) and NR3, and the metallacycle is favored by 33.70 or 35.62 kcal/mol, R = H or Me, relative to the chloro-bridged dimer [{Al(μ-Cl)(C4H6)}2] (D2h), and NR3. Show more