Additional Systems where Metal Ion-Promoted LGA Occurs

4 Additional Systems where Metal Ion-Promoted LGA Occurs 

1 -Catalyzed Cleavage of Methyl Aryl Phosphate Diesters Having ortho-Cf=OjOCHj Groups ° 

30a—h catalyzed by Yb(OTf)3 in methanol at low pH where the catalysis amounted to 10 relative to the background reactions. Because methyl aryl phosphate diesters without the 0-C(=O)OCH3 group do not react under these conditions, we beheve this is a unique example of LGA where we can quantify the rate effect, provide information about how much charge is transferred from the leaving aryloxide to the metal ion, and quantify the catalytic effect of the ring substituents on how they interact with the phenoxy and methoxycarbonyl portions of the LG that bind to the metal ion. 

A few experimental features are of note. Between pH 1 and 3 in methanol, the plot of the rate constant for disappearance of 30a versus Yb(OTf)3 (0.2—2.5 mM) is bowed downward, following apparent saturation kinetics that can be fitted to a standard binding isotherm to provide an average k at 

The only products observed from the reaction of 30 are dimethyl phosphate and the corresponding phenoxides bound tightly to as in 31. 

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