Design and Applications of Cyclopropenium Chalcogen Dihalides in Catalysis via C(sp³)–H···X Interactions

Abstract

Noncovalent interactions originated from C­(sp3)–H···X hydrogen bonds frequently appear in different areas such as crystal engineering, protein binding, and supramolecular chemistry. However, employing this class of C­(sp3)–H···X interactions in catalysis is less common because they often offer insufficient catalytic performance due to their relatively weak strength. Herein, we report the use of cyclopropenium chalcogen dihalides as catalysts, in which effective site isolation of the counteranion significantly enhances the availability of the noncovalent interaction donor. The catalytic performance is comparable to those of some typical Lewis acids and much better than those of many common catalysts based on noncovalent interactions. Our mechanistic study suggests that the catalysts activate substrates via multiple C­(sp3)–H···X hydrogen bonds.

Cyclopropenium Sulfide as Lewis Base Catalyst for Chemoselective and Regioselective Electrophilic Selenylation of Phenols

“…In the mixture of 1ah , NPSP, and Cy1 , strong NOE correlations between the methyl groups of 1ah and the cyclohexyl groups in Cy1 were observed, suggesting that the phenolic moiety was brought into close proximity to the cyclopropenium cation to give species E (Figure D, also see SI Figure S2). This hypothesis is also consistent with our recent study in which the C­(sp 3 )-Hs that are in close proximity to the cyclopropenium cation could serve as NCHB donors to interact with electron donors. We had suspected that the Lewis basic selenium in product 2a might promote the reaction and an autocatalysis mechanism might be involved.…”

“…This proposal is also consistent with the results from the control experiments (Figure B,C) in which the reaction is phenol-specific and para -selective, attributed to the formation of phenoxide ion pair in the species G . Since the amount of C­(sp 3 )-Hs in the catalyst appears to correlate to the reaction yield (Figure F), we believe that multiple C–H···O NCHB interactions are playing an important role in the high catalytic performance via site-isolation of the counterions in species F and G (Figure B). In comparison, catalyst Cy2 that has less C­(sp 3 )-Hs gave poorer yield, attributed to the less effective NCHB in stabilizing the counteranion (e.g., species H ).…”

“…The cyclohexyl groups’ C(sp 3 )-Hs that are in close proximity to the cyclopropenium cation were found to be good C–H···O nonclassical hydrogen bond (NCHB) , donors. The phosphate anion could interact with the cyclopropenium cation with multiple NCHB as one of the major interactions and the cross-assembled complex C was found to be a prominent bifunctional catalyst.…”