# Trivalent Metal Lewis Acids Activate CO2 in Transfer Hydrogenations

## TL;DR

Trivalent metal Lewis acids activate CO2 during transfer hydrogenation, enabling efficient synthesis of formamides and azoles from bio-derived hydrogen sources.

## Contribution

This study introduces trivalent metal Lewis acids as catalysts for CO2 activation in transfer hydrogenation, bypassing traditional hydride abstraction mechanisms.

## Key findings

- Trivalent metal MX3 Lewis acids catalyze CO2 hydrogenation to formate with γ-terpinene as a bio-derived H2 surrogate.
- Formate produced via this method yields up to 91% N-formamides and 95% heterocycles like azoles through tandem reactions.
- Density functional theory calculations confirm CO2 directly accepts a hydride from γ-terpinene during formate synthesis.

## Abstract

Using γ‐terpinene as a bio‐derived H2 surrogate, trivalent metal MX3 (M = Al, Ga, In, Yb, X = Cl, OTf) Lewis acids (LAs) catalyze CO2 hydrogenation to formate, yielding p‐cymene as the by‐product. The resulting formate produces up to 91% N‐formamides in tandem hydrogenation‐coupling reactions and up to 95% heterocycles, including azoles, via further in situ transfer formylation to ortho‐substituted anilines and cyclization at 130 °C and 4 bar. But In(OTf)3 and a Lewis base fail to abstract a hydride from γ‐terpinene. Unlike other LAs and transfer hydrogenation catalysts that induce hydride abstraction from 1,4‐cyclohexadiene(s) over B(C6F5)3, alkali earth or noble metals, MX3 LAs activate CO2, so CO2 can directly accept a hydride from γ‐terpinene during formate synthesis, as shown by density functional theory calculations. This triple role of MX3 LAs in promoting (1) CO2 activation, (2) tandem coupling reactions, and (3) transfer formylation at low pressure paves the way for sustainable CO2 hydrogenation processes, leveraging bio‐derived H2 surrogates to develop efficient carbon capture and utilization systems and to synthesize valuable compounds from renewable feedstocks.

Indium(III) triflate and other trivalent metal ions catalyst the transfer hydrogenation of CO2 to formate and a series of in situ tandem reactions to yield formamides or azoles. In contrast to previous reports, the reaction proceeds by CO2 activation instead of hydride abstraction from a transfer hydrogenation source.© 2025 WILEY‐VCH GmbH