Dirhodium Coordination Polymers for Asymmetric Cyclopropanation of Diazooxindoles with Olefins: Synthesis and Spectroscopic Analysis

Abstract A facile approach is reported for the preparation of dirhodium coordination polymers [Rh2(L1)2]n (Rh2-L1) and [Rh2(L2)2]n (Rh2-L2; L1=N,N’-(pyromellitoyl)-bis-L-phenylalanine diacid anion, L2=bis-N,N’-(L-phenylalanyl) naphthalene-1,4,5,8-tetracarboxylate diimide) from chiral dicarboxylic acids by ligand exchange. Multiple techniques including FTIR, XPS, and 1H→13C CP MAS NMR spectroscopy reveal the formation of the coordination polymers. 19F MAS NMR was utilized to investigate the remaining TFA groups in the obtained coordination polymers, and demonstrated near-quantitative ligand exchange. DR-UV-vis and XPS confirm the oxidation state of the Rh center and that the Rh-single bond in the dirhodium node is maintained in the synthesis of Rh2-L1 and Rh2-L2. Both coordination polymers exhibit excellent catalytic performance in the asymmetric cyclopropanation reaction between styrene and diazooxindole. The catalysts can be easily recycled and reused without significant reduction in their catalytic efficiency.