zwitterionic intermediate II. Proton transfer leads to ketimido intermediate III,
which undergoes elimination to form starting complex 24 and the alkylated benzyl
cyanide (Scheme 25).
The same group also reported the synthesis of the manganese pincer complex 25
based on the same ligand [49]. Interestingly, this catalyst was able to catalyse the
same Michael reaction with lower catalyst loading and at a lower temperature. This
paper mainly focused on fully aliphatic nitriles (Table 12). The effect of α- or
β-substituents on the acrylate substrate was also investigated. Whereas the presence
of an α-methyl group had no deleterious effect, the presence of a β-methyl group led
to formation of the alkylated product in only 18% yield.
More recently, Milstein and co-workers prepared pyridine-based PCP-ruthenium
complexes in which the pyridine is bound via the carbon atom in the 4-position to
Scheme 23 Manganese-catalysed olefination of benzyl cyanides with secondary alcohols
Scheme 24 Activation of nitriles via metal-ligand cooperation (MLC) by Re-pincer complex 24
(
t Bu groups on P atoms omitted for clarity)
346
B. Guo et al.
which undergoes elimination to form starting complex 24 and the alkylated benzyl
cyanide (Scheme 25).
The same group also reported the synthesis of the manganese pincer complex 25
based on the same ligand [49]. Interestingly, this catalyst was able to catalyse the
same Michael reaction with lower catalyst loading and at a lower temperature. This
paper mainly focused on fully aliphatic nitriles (Table 12). The effect of α- or
β-substituents on the acrylate substrate was also investigated. Whereas the presence
of an α-methyl group had no deleterious effect, the presence of a β-methyl group led
to formation of the alkylated product in only 18% yield.
More recently, Milstein and co-workers prepared pyridine-based PCP-ruthenium
complexes in which the pyridine is bound via the carbon atom in the 4-position to
Scheme 23 Manganese-catalysed olefination of benzyl cyanides with secondary alcohols
Scheme 24 Activation of nitriles via metal-ligand cooperation (MLC) by Re-pincer complex 24
(
t Bu groups on P atoms omitted for clarity)
346
B. Guo et al.