Chemoselective transfer hydrogenation of α,β-unsaturated carbonyl compounds using potassium formate over amine-grafted Ru/AlO(OH) catalysts†
Yanxiu Gao,Jie Wang,Aijuan Han,Stephan Jaenicke,Gaik Khuan Chuah
Catalysis Science & Technology Pub Date : 12/21/2015 00:00:00 , DOI:10.1039/C5CY01475A
Abstract

Grafting of 3-(2-aminoethylamino)propyltrimethoxysilane onto Ru/AlO(OH) resulted in an active and highly chemoselective heterogeneous catalyst for the transfer hydrogenation of α,β-unsaturated carbonyl compounds to the corresponding allylic alcohols. Potassium formate was used as a sustainable hydrogen donor. A range of substrates including cinnamaldehyde, α-amylcinnamaldehyde, citral, 3-methyl-2-butenal, trans-2-pentenal, and trans-hexenal were selectively hydrogenated at the C[double bond, length as m-dash]O moiety with >96% selectivity. In comparison, the unmodified 1 wt% Ru/AlO(OH) catalyzed hydrogenation of cinnamaldehyde at the C[double bond, length as m-dash]C bond, yielding 3-phenylpropanal as the product. Higher loaded samples with 2–10 wt% Ru exhibited 20–25% selectivity to cinnamyl alcohol. The results show that low coordination sites were more selective to hydrogenation of the internal C[double bond, length as m-dash]C than the terminal C[double bond, length as m-dash]O bond. Immobilization of the amine via chemical bonding with hydroxyl groups of the AlO(OH) support blocks adjacent exposed metal sites, increasing the chemoselective reduction of C[double bond, length as m-dash]O. Optimum results were achieved at an amine/Ru ratio of 6. The catalyst maintained high activity and chemoselectivity even after five cycles.

Graphical abstract: Chemoselective transfer hydrogenation of α,β-unsaturated carbonyl compounds using potassium formate over amine-grafted Ru/AlO(OH) catalysts