136763-65-0Relevant academic research and scientific papers
Synthesis and spectroscopic investigations of alkylaluminum alkoxides derived from optically active alcohols. The first structural identification of an optically active organoaluminum alkoxide
Sierra, Michael L.,Kumar, Rajesh,De Mel, V. Srini J.,Oliver, John P.
, p. 206 - 214 (1992)
The reaction of trialkylaluminum, R3Al (R = Me, Et, i-Bu), with optically active alcohols such as l-menthol and l-borneol in a 1:1 ratio gives high yields of R2AlOR*(OR= l-mentholate, R = Me (1a), Et (1b), i-Bu (1c); OR* = l-borneolate, R = Me (2a), Et (2b), i-Bu (2c)) and the corresponding alkane, RH. The resulting alkoxides have been characterized by 1H and 13C NMR spectroscopy. The single-crystal X-ray structures of 1a,c and 2a established the dimeric structure for these compounds. 1a was assigned to the orthorhombic cell system, space group P212121 (No. 19), with cell constants a = 10.097 (1) ?, b = 10.485 (1) ?, c = 26.920 (4) ?, and Z = 4 (dimers). The structure was refined to a final R = 4.5% (Rw = 3.9%) based on 2669 observed reflections (Fo ≥ 2.5σ(F)). 1c was assigned to the triclinic cell system, space group P1 (No. 1), with cell constants a = 10.838 (4) ?, b = 12.792 (6) ?, c = 15.787 (7) ?, α = 81.56 (4)°, β = 83.04 (4)°, γ = 73.01 (3)°, and Z = 2 (dimers). The structure was refined to a final R = 8.7% (Rw = 8.5%) based on 4213 observed reflections (Fo ≥ 3σ(F)). 2a was assigned to the monoclinic cell system, space group P21 (No. 4), with cell constants a = 7.261 (7) ?, b = 14.494 (8) ?, c = 12.938 (7) ?, β = 93.63 (7)°, and Z = 2 (dimers). The structure was refined to a final R = 5.3% (Rw = 4.4%) based on 1432 observed reflections (Fo ≥ 2.5σ(F)). In 1a,c and 2a, the alkoxide ligands serve as bridging units between the two dialkylaluminum moieties to give stable, planar Al2O2 rings. The behavior of the 1H NMR spectra of 1a-c as a function of temperature has been interpreted in terms of increasing steric interaction of the l-mentholate group with the methyl, ethyl, and isobutyl groups attached to the aluminum. This steric interaction gives rise to restricted rotation of the l-mentholate and/or the alkyl group and leads to nonequivalence of the protons in the ethyl and isobutyl derivatives. This does not occur for the l-borneol derivatives, since the borneol moiety cannot interact with the alkyl groups bound to the aluminum because of its orientation and rigidity.
