Merging Tertiary Amine with Palladium Complex on

Graphene Oxide for Promoted Tsuji-Trost Allylation

Qingshan Zhao1, Yang Li1, Guoliang Zhang1, Fengbao Zhang1 and Xiaobin Fan1*
1 School of Chemical Engineering & Technology, Tianjin University, Tianjin, China
Although homogeneous palladium complexes are efficient tools for carbon-carbon bond formation processes, their practical applications are hampered by the problem of separating from the product-containing solutions. Efficient heterogenization strategies with industrial potential are desired to remedy the problem. Herein, we developed a facile strategy of merging an organic amine with palladium complex on graphene oxide (GO) as a cooperative and recyclable catalyst for Tsuji-Trost coupling. Through silylation modification with [3-(diethylamino) propyl] trimethoxysilane (DEAPMS) and
3-(2-aminoethylamino) propyl trimethoxysilane (AEAPMS), followed by a further coordination process, a tertiary amine and palladium-diamine complex were simultaneously immobilized onto the GO support. The immobilized DEAPMS serves as an organic base, and meanwhile AEAPMS provides a tethered ligand for the in situ synthesis of the palladium-diamine complex. GO provides an ideal platform to merge them together. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) mapping and transmission electron microscopy (TEM) confirm the successful preparation of the catalyst. Systematic investigation revealed that the immobilized palladium-diamine complex without amine was effective for Tsuji-Trost allylation of allyl methyl carbonate with ethyl acetoacetate, resulting in a 44.52% conversion in 5 h. The tertiary amine showed a cooperative effect with the palladium complex and could significantly promote the catalytic activity. When the tertiary amine was introduced, the conversion reached up to 91.85% within the same time, with a yield of 87.67% and 4.18% for the monoallylation and diallylation product, respectively. The catalyst could be readily recovered and recycled for at least four times without reduction of catalytic activity. The excellent performance of the catalyst may be ascribed to cooperative dual effect, as well as excellent properties of the GO support and robust immobilization interaction. The developed strategy may open the door to the combination
of transition metal catalysis and organocatalysis in graphene-based heterogenization systems.

Keywords:

Cooperative catalysis; Graphene oxide; Heterogenization; Palladium complex; Tertiary amine; Tsuji-Trost allylation