Sc(OTf)3-catalyzed carbomethoxylation of aliphatic amines with dimethyl carbonate (DMC): DMC activation by η1-O(C=O) coordination to Sc(III) and its relevance to catalysis

The role of metal center in the Sc(OTf)3-catalyzed carbomethoxylation of aliphatic amines with DMC has been investigated. We have shown that the catalytic formation of carbamate ester is promoted by coordination of DMC to scandium(III) ion through the carbonyl oxygen atom. The ability of DMC to coordinate to Sc(III) has been proved by IR and NMR spectroscopy and fully demonstrated also by the isolation, for the first time, of a DMC–metal complex characterized as (η1-O(C=O)–DMC)Sc(OTf)3. A relationship has been shown between the coordination mode of DMC to Sc(III) and the reactivity of coordinated organic carbonate: coordination of DMC to Sc(III) activates both carbonyl group and O–CH3 moieties of the carbonic acid diester and enhances not only the carbomethoxylating but also the methylating activity of the ambident electrophile (DMC), as documented by the different selectivity exhibited by the catalyst in the aminolysis reaction of DMC with benzylamine and aniline, respectively.