Xantphos doped Rh/POPs-PPh3 catalyst for highly selective long-chain olefins hydroformylation: Chemical and DFT insights into Rh location and the roles of Xantphos and PPh3

Vinyl functionalized Xantphos ligand (denoted as 4v-Xantphos) was newly synthesized and successfully doped into the PPh3 based porous organic polymers (POPs) through the solvothermal synthesis technique. After proper coordination with Rh precursor, the resultant Xantphos doped Rh/POPs-PPh3 catalysts exhibited high activity (TOF: 300-500 h(-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 400 h with high efficiency employing Xantphos doped Rh/POPs-PPh3 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 PPh3 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-PPh3 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 PPh3 in the catalyst frame simultaneously) was responsible for the high linear regioselectivity and stability of the catalysts, the roles of Xantphos and PPh3 were further elucidated in details. (C) 2017 Elsevier Inc. All rights reserved.