Proximity Effect using a Nanocage Structure: Polyhedral Oligomeric Silsesquioxane-Imidazolium Tetrachloro- palladate Salt as a Precatalyst for the Suzuki-Miyaura Reaction in Water

• Published in: ChemCatChem 2016-05, Vol.8 (9), p.1685-1691
• Main Authors: Bivona, Lucia Anna, Giacalone, Francesco, Carbonell, Esther, Gruttadauria, Michelangelo, Aprile, Carmela
• Format: Article
• Language: English
• Subjects: cage compounds; C−C coupling; palladium; phase-transfer catalysis; supported catalysts
• ISSN: 1867-3880; 1867-3899
• DOI: 10.1002/cctc.201600155

A polyhedral oligomeric silsesquioxane‐imidazolium tetrachloropalladate salt (POSS‐Imi‐PdCl4) was prepared by the reaction of a polyhedral oligomeric silsesquioxane‐imidazolium chloride salt (POSS‐Imi‐Cl) with PdCl2 and used as a pre‐catalyst for the Suzuki–Miyaura reaction in water at 100 °C at a low loading (0.08–0.16 mol %). Biphenyl compounds were isolated in high to excellent yields. A comparison of the POSS‐based catalyst with the corresponding catalyst without the nanocage structure (i.e., 1‐butyl‐3‐methylimidazolium tetrachloropalladate) highlighted the role of the POSS structure to reach higher yields in the Suzuki–Miyaura reaction. This result is ascribed to a proximity effect of the imidazolium moieties linked to the nanocage structure. Fresh and used catalytic materials were characterised by using X‐ray photoelectron spectroscopy and TEM. Unity is strength: A fully substituted polyhedral oligomeric silsesquioxane with imidazolium tetrachloropalladate salt displays a higher catalytic activity than the corresponding catalyst without the nanocage structure in the Suzuki–Miyaura reaction in water.