Methyl toluate crystal structure

Based on statistical analyses it may be reasonable to propose that this structure reflects the idealized or low energy mode of coordination to carbonyls for aluminum-centered Lewis acids. It would be interesting to see how distortions away hrom such an arrangement may come about Imposition of steric congestion through bulky substituents is one way to address this question. Ibe crystal suucture of (2,6-di-f-butyl-4-methyl)phenoxydiethylaluminum/methyl toluate was recently reported (Figure 22). ... 

It may be recalled that an opposite stereochemical result is obtained by employing the bulky aluminum reagents MAD and MAT. This observation has been explained by invoking out-of-plane complexation of the Lewis acid in a direction which would prevent equatorial attack (Figure 48). The X-ray crystal structure of methyl toluate complexed with a bulky aluminum Lewis acid is fully consistent with tius model7 However, it is worth mentioning that a six-membered transition state, perhaps involving [Me2( ArO)Al] Li, has not been considered as an alternative mechanism. 

Figure 22 Crystal structure of Et2Al(OAr)/methyl toluate complex...

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