Mechanistic Studies on Rhodium-Catalyzed Chemoselective Cycloaddition of Ene-Vinylidenecyclopropanes: Water-Assisted Proton Transfer

Abstract

Rhodium-catalyzed cycloaddition reactions are a powerful tool for the construction of polycyclic compounds. Combined experimental and DFT studies were used to investigate the temperature-controlled chemoselectivity of cationic rhodium-catalyzed intramolecular cycloaddition reactions of ene-vinylidenecyclopropanes. After a series of mechanistic studies, it was found that trace amounts of water in the reaction system play an important role in generating the product with endo double bond located on a five-membered ring and revealed that trace amounts of water in the reaction system, including the rhodium catalyst, substrate and solvent, were sufficient to promote the formation of the product with endo double bond located on a five-membered ring, and additional water could not further accelerate the reaction. DFT calculation results show that the addition of water indeed significantly lowers the energy barrier of the proton transfer step, making the formation of the product with endo double bond located on a five-membered ring more likely to occur and confirming the rationality of water-assisted proton transfer occurring in the selective access to the product with endo double bond located on a five-membered ring.

N^N^C-Cyclometalated rhodium(iii) complexes with isomeric pyrimidine-based ligands: unveiling the impact of isomerism on structural motifs, luminescence and cytotoxicity

“…In this manuscript we focus on the investigation of the coordination behaviour of HL 2,5 and HL 2,6 toward rhodium(III) chloride and on unveiling the impact of isomerism on structures and properties. Our particular interest to rhodium complexes stems partly from our experience in rhodium chemistry [82][83][84] and partly from appealing properties this metal shows in the C-H bond activation and catalysis, [85][86][87][88][89][90][91] photochemistry [92][93][94][95][96][97][98][99][100][101][102][103][104][105][106][107] and bioinorganic chemistry. Along with the synthesis of HL 2,5 and HL 2,6 and their rhodium(III) complexes [RhL 2,5 (Solv)Cl 2 ]•nEtOH and [RhL 2,6 (Solv)Cl 2 ]•nEtOH, here we report the impact of isomerism on molecular and supramolecular structures of these compounds, on the photophysical properties of the rhodium(III) complexes and on the cytotoxic activity of the ligands and complexes.…”