Using CO 2 as – CH – and – CH 2 – Sources

In this chapter, we will outline the development of using CO 2 as –CH– and –CH 2 – sources through two-electron or four-electron reductive functionalization of CO 2 , respectively. The main routes of these transformations consist of two/four electrons that reduce CO 2 to C (+2) or C (0) active intermediates and sequent bonding reactions with nucleophiles or transition-metal catalytic process. We focus on the homogeneous reductive transformation of CO 2 with extra coupling partners. The self-reduction of CO 2 to give reductive C1 compounds (CO, HCHO, HCOOH, C, CH 4 , etc.) or construct higher alcohols, aromatics, and the six-electron reduction of CO 2 as methylation reagents will not be discussed here. After a brief introduction of the importance and challenges in using CO 2 as –CH– and –CH 2 – sources by controllable CO 2 reduction, the development of reductive transformations of CO 2 by versatile catalytic systems with different bonding types will be discussed in detail both in reaction scopes and mechanisms. Finally, a summary and outlook of this area will be presented.