Advances in hydroformylation with formaldehyde, formic acid and carbon dioxide as syngas surrogates.

Hydroformylation, a catalytic transformation of alkenes into aldehydes using CO/H2, represents a fundamental route for the valorization of olefins in both industrial and academic settings. To address the safety and sustainability concerns associated with the direct use of carbon monoxide, recent research has increasingly focused on the development of C1-based carbonyl surrogates. In particular, formaldehyde, formic acid, and carbon dioxide have been investigated as viable alternatives capable of releasing CO in situ under appropriate catalytic conditions. These strategies have led to the emergence of "syngas-free" hydroformylation processes, which offer new possibilities for reaction design and system integration. This review provides a comprehensive overview of recent developments in the use of formaldehyde, formic acid, and CO2 as carbonyl surrogates in transition metal-catalyzed hydroformylation, highlighting advances in homogeneous and heterogeneous catalytic systems, substrate scope, and reaction mechanism.