Chemoselective Change in Hydrogenolysis of Carbonyl Compounds and its Application to Chemical Recycling of Plastic Waste

Date: 4^th November, 2026 (Wednesday)

Time: 5:00 - 6:00 pm (HKT)

 

Venue: Lecture Theatre T5, Meng Wah Complex

 

Kyushu University

Hydrogenation/hydrogenolysis of carbonyl compounds using H₂ is the fundamental chemical transformation in both laboratory and industry. The reactivity of carbonyl compounds is largely affected by two substituents on the carbonyl carbon, obeying an order shown in Fig. 1A.¹ Therefore, the chemoselective transformations of a less reactive carbonyl group in the presence of more reactive ones are highly challenging. We envisioned that catalyst-controlled chemoselectivity change in carbonyl hydrogenolysis serves a game-changing synthetic tool in organic chemistry.

 

Among carbonyl compounds, we initiated our project with the least reactive ureas and found that an Ir complex, Ir/PP, bearing a PN bidentate ligand catalyzes hydrogenolysis of ureas to formamides and amines (Fig. 1B), where not only amides but also esters remained intact.² A similar counterintuitive chemoselectivity was observed in the hydrogenolysis of urethanes using a modified Ir complex, Ir/PB, and CsOt-Bu as catalysts, yielding formamides and alcohols as the products (Fig. 1C).³ Since Milstein’s seminal work,⁴ various transition metal catalysts have been reported, where urethanes are converted into amines, methanol, and alcohols.

 

Next, we focused on selective hydrogenolysis of carboxylic acid derivatives and found that the combined use of Ir/PP with LiOt-Bu enables selective hydrogenolysis of formamides into amines and methanol over esters (Fig. 1D).⁵ We proposed the origin of the chemoselectivity that the pyrrole moiety in Ir/PP undergoes deprotonation by LiOt-Bu, and Lewis acidic Li cation discriminates more Lewis basic amide oxygen to capture amides prior to the addition of Ir-hydride.

 

The present hydrogenolysis catalyst enabled chemical degradation of polymer waste. Polyurethanes (PUs) were degraded under the present catalytic system to afford formamides and polyol monomers. Furthermore, chemoselective degradation of PUs in mixed plastic waste was achieved. For instance, the hydrogenolysis of polyester-PU mixed textile (1.00 g) afforded 0.11 g of degraded PU and 0.87 g of polyester textile without degradation, enabling easy separation of mixed plastic waste by selectively degrading PUs (Fig. 1E).⁶

1. Iwasaki, T.; Nozaki, K. Nat. Rev. Chem. 2024, 8, 518.

2. Iwasaki, T.; Tsuge, K.; Naito, N.; Nozaki, K. Nat. Commun. 2023, 14, 3279.

3. Iwasaki, T.; Yamada, Y.; Naito, N.; Nozaki, K. J. Am. Chem. Soc. 2024, 146, 25562.

4. Milstein, D. et al. Nat. Chem. 2011, 3, 609.

5. Ajiro, S.; Iwasaki, T.; Nozaki, K. ACS Catal. 2026, 16, 11306.

6. Yamada, Y.; Iwasaki, T.; Tanaka, S.; Nozaki, K. Angew. Chem. Int. Ed. 2026, 65, e4288189.