**2.4 Reduction/hydrogenation**

## *2.4.1 Hydrogenolysis of aryl ethers using Ni-NHC*

Ni-NHC complex in the presence of a suitable base (NaO<sup>t</sup> Bu) could effectively convert C-O bonds in lignin to various useful scaffolds useful in biomass conversion [37]. Hartwig et al. mechanically investigated the reduction of diaryl ethers to corresponding phenols (**Figure 12**) [38].

#### *2.4.2 Transfer hydrogenation using Ir-NHC*

Using water soluble Ir-NHCs proved that glycerol can be exploited as a hydrogen donor to convert a biomass-derived phytochemical, levulinic acid, to selectively produce γ-hydroxyvaleric acid (GHV) and lactic acid (LA) [39].

**Figure 12.** *Hydrogenolysis of diaryl ethers.*

*Late Transition Metal (LTM)-NHC Catalyzed Transformations of Renewable Chemicals… DOI: http://dx.doi.org/10.5772/intechopen.101164*

#### *2.4.3 Iridium-based hydride transfer catalysts*

Lu et al. reported homogeneous Ir-NHC catalysts, which can be utilized for the storage of H2 and fine chemicals through hydride transfer catalysis [40] (**Figure 13**).

**Figure 13.** *Iridium-based hydride transfer catalysts.*

**Figure 14.** *Conversion of sugars into heterocycles.*
