Additive-free N-methylation reaction synergistically catalyzed by Pt single atoms and clusters on α-MoC using methanol as a sustainable C1 source

Abstract

Methanol is being actively investigated as a promising C1 reagent to replace conventional C1 reagents in organic synthesis, due to its properties of being economical, abundant, nontoxic and sustainably producible. However, because of the high enthalpy of dehydrogenation, it has not been reported frequently. Herein, we report that Pt single atoms (Pt₁) and Pt clusters (Pt_n) are cooperatively loaded on α-MoC to achieve the conversion of various of unsaturated N-containing compounds into value-added N-methylation compounds simply in methanol aqueous solution, successfully avoiding the use of external hydrogen or any additives. The synergy between coexisting Pt₁ and Pt_n on Pt_1+n/α-MoC is identified as necessary to realize the tandem conversion with superior activity and selectivity. Pt₁/α-MoC is the active site for in situ hydrogen production from aqueous phase methanol reforming, and Pt_n/α-MoC is responsible for the successive hydrogenation and methylation. The partially positive Pt_n^δ+ species are crucial for the reductive N-methylation reaction, as the strong coordination of N-containing compounds to Pt particles (Pt_n) significantly inhibits the catalytic activity. Experimental and DFT results further show that, unlike the traditional hydrogen-borrowing mechanism of methanol via the intermediate formaldehyde, formic acid is found to be a potent intermediate and agent for N-methylation.