Xantphos doped Rh/POPs-PPh 3 catalyst for highly selective long-chain olefins hydroformylation: Chemical and DFT insights into Rh location and the roles of Xantphos and PPh 3

摘要

Vinyl functionalized Xantphos ligand (denoted as 4v-Xantphos) was newly synthesized and successfully doped into the PPh 3 based porous organic polymers (POPs) through the solvothermal synthesis technique. After proper coordination with Rh precursor, the resultant Xantphos doped Rh/POPs-PPh 3 catalysts exhibited high activity (TOF: 300–500h −1 ), chemoselectivity (87–91%) and regioselectivity (about 90:10) in the hydroformylation of long-chain olefins (C6-C12). As a representative substrate, hydroformylation of 1-octene could be easily realized in a fixed bed reactor for more than 400h with high efficiency employing Xantphos doped Rh/POPs-PPh 3 catalyst, which represented a rare successful example that realized heterogenization of homogeneous hydrofromylation catalysts as well as the regioselectivity-control at the same time without leaching of rhodium. Interestingly, the hydroformylation reaction data indicated that the Rh species tend to coordinate with the exposed P atom from Xantphos rather than that from PPh 3 ligand in the Xantphos doped catalyst frame. More importantly, the HAADF-STEM and EXAFS characterizations indicated that Rh species demonstrated as single site dispersion in Xantphos doped Rh/POPs-PPh 3 catalyst, thus endowed the catalyst with high activity. Detailed DFT calculations revealed that the unique location of single site dispersed Rh species (Rh species coordinated with both of Xantphos and PPh 3 in the catalyst frame simultaneously) was responsible for the high linear regioselectivity and stability of the catalysts, the roles of Xantphos and PPh 3 were further elucidated in details.

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