Mechanistic Studies of C-C Bond Cleavage of Nitriles by Dinuclear Metal Cryptates

We previously reported that dinuclear copper(II) cryptate [Cu2L](4+) cleaves the C-C bond of acetonitrile at room temperature to produce a cyano-bridged dinuclear cryptate and methanol, whereby the reaction mechanism has not yet become clear. We have now systemically investigated this reaction, and four cryptates, [Cu2L](ClO4)(4) (1), [Zn2L](ClO4)(4) (2), [Cu2L(H2O)(2)]-(CF3SO3)(4) (5), and [Cu2L(OH)(OH2)]-(ClO4)(3) (6) are reported here. Cryptates 1 and 2 can cleave the C-C bonds of acetonitrile, propionitrile, and benzonitrile at room temperature under open atmospheric conditions to give cyano-bridged cryptates [Cu2L(CN)]-(ClO4)(3) (3) and [Zn2L(CN)](ClO4)(3) (4). respectively, and the corresponding alcohol. In contrast, 5 and 6 do not show any C-C bond activation of nitrites, as the interior axial positions of Cu-II in 5 and 6 are occupied by water/OH-. The C-C bond cleavage of (S)-(+)-2-methylbutyronitrile by 2 produced (R)-(-)-2-butanol only; that is, the cleavage reaction proceeds through an S(N)2 pathway (Walden inversion).