Preparation of carbonyl rhodium polyether guanidinium ionic liquids and application in asymmetric hydroformylation based on homogeneous catalysis-biphasic separation system

Four carbonyl rhodium polyether guanidinium ionic liquids (Rh(CO)(4)-PolyGILs) were firstly synthesized by utilizing the ion exchange strategy. This protocol was achieved by introducing polyether guanidinium ionic liquids (PolyGILs) into K[Rh(CO)(4)]. Asymmetric hydroformylation (AHF) of styrene was employed as probe reaction to investigate the catalytic performance of the above obtained four functional ionic liquids. The AHF of styrene provided 79.00% conversion, 73.30% yield and 54% enantiomeric excess for 2-phenylpropionaldehyde ([Me(EO)(16)TMG][Rh(CO)(4)] served as catalyst, (R)-BINAP served as chiral ligand at 60 degrees C and 2.0 MPa for 4 h). In addition, based on the unique solubility properties of the above obtained four ionic liquids, a highly effective homogeneous catalysis-biphasic separation (HCBS) system was established for the AHF. HCBS system with [Me(EO)(16)TMG][Rh[(R)-BINAP](CO)(2)] could be reused four times without significantly decrease in the activity. The structure of [Me(EO)(16)TMG][Rh[(R)BINAP](CO)(2)] was further studied by using the density functional theory (DFT) method, which revealed that the final energy of the molecule was tending to -9460.83 eV and the presence of Ph substituent provided a chiral pocket. The presence of closed rigid chiral pocket could lead to better enantioselectivities. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Four carbonyl rhodium polyether guanidinium ionic liquids were synthesized via ion exchange strategy, and their catalytic performance in asymmetric hydroformylation of styrene was investigated. The unique solubility properties of these ionic liquids led to the establishment of a highly effective homogeneous catalysis-biphasic separation system for the reaction. The reusability of the system was demonstrated up to four times without significant decrease in activity, showcasing potential for practical applications.