Single atom Bi enables efficient carbonylation of amines on TiO2

MOF-derived catalyst of Bi 1 -TiO 2 was designed for the carbonylation of amines. • Bi 1 -TiO 2 achieved a high space yield of 833 mmol·g cat -1 ·h −1 with 99% selectivity. • Atomic Bi promoted L-acid density to 256 μmol/g cat that benefits carbonylation. • Intermediate DPU activated on Bi 3+ with selective anti-bonding orbits population. The synthesis of N-substituted carbamates through the carbonylation of amines with alkyl carbamates represents a green and promising route, yet it is hindered by insufficient catalytic efficiency and a lack of mechanistic understanding. In this work, a single-atom Bi-doped TiO 2 (Bi 1 -TiO 2 ) catalyst was synthesized using MIL-125(Ti) as the precursor for the carbonylation of amines with ethyl carbamate (EC). The optimized 5% Bi 1 -TiO 2 catalyst demonstrated exceptional performance, achieving a high space–time yield of ethyl propyl carbamate (EPC) at 833 mmol·g cat ⁻ 1 ·h⁻ 1 with 99% selectivity, surpassing most reported catalysts. Mechanistic studies revealed that the 5% Bi 1 -doped TiO 2 possessed a high density of Lewis acid sites of 256 μmol/g cat . Dipropylurea (DPU) was identified as the key reaction intermediate. Both DPU and ethanol were preferentially activated on the Lewis acidic Bi δ+ sites. Further evidence indicated that electrons were populated into the anti-bonding orbitals of DPU from Bi, leading to significant activation of the N-(C=O) bond. This activation dramatically enhanced the carbonylation process by facilitating the alcoholysis of DPU. Additionally, the catalyst exhibited excellent stability for over 250 h and substrate universality across a range of amines for the synthesis of various N-substituted carbamates. Download: Download high-res image (185KB) Download: Download full-size image