hydrogenation of symmetric urea derivatives gave primary amines and methanol in
excellent yields as displayed in Scheme 22 [41].
2.5 Hydrogenation of Alkenes
The Kirchner group was the first one to report on the hydrogenation of olefins using a
well-defined manganese catalyst in 2019. In contrast to the commonly employed
MLC mode allowing outer-sphere-type hydrogenations, the novel alkyl complexes
employed an inner-sphere mechanism which was initiated by migratory insertion of
the alkyl group into the carbonyl ligand. Within this context, a broad variety of
different mono- and disubstituted alkenes were efficiently reduced. Remarkably, the
hydrogenation of mono- and 1,1-disubstituted alkenes was performed at room
temperature. Apart from that, high functional group tolerance was achieved, while
alcohols, esters, acetals, and even anhydrides were tolerated (Scheme 23) [42].
Scheme 22 Hydrogenation of carbamates and urea derivatives catalyzed by Mn21
Scheme 23 Additive-free hydrogenation of alkenes via inner-sphere mechanism
242
S. Weber and K. Kirchner