Recoverable cationic Pd-catalyzed Heck reaction under thermomorphic mode

Abstract

The reaction of allylpalladium chloride dimer and 4,4′-bis( R f CH 2OCH 2)-2,2′-bpy, 1a– c, in the presence of AgOT f resulted in the synthesis of cationic complex, [Pd(η 3-allyl)(4,4′-bis-( R f CH 2OCH 2)-2,2′-bpy)](OT f), 2a– c where R f = C 9F 19 ( a), C 10F 21 ( b), C 11F 23 ( c), respectively. The solubility curves of 2a– c which began from virtually zero below −40 °C and increased dramatically at slightly higher temperature were quantitatively measured. Upon changing from −40–90 °C there was several orders of magnitude increase of solubility for 2a– c. The cationic Pd-catalyzed Heck arylation of methyl acrylate was selected to demonstrate the feasibility of recycling usage with 2b, c as the catalyst using DMF as the solvent at 140 °C for 3 h in each run. At the end of each cycle, the product mixtures were cooled to −30 °C, and then catalysts were recovered by decantation. The products were quantified by GC analysis or by the isolated yield. The Heck reaction of C 6H 5I with methyl acrylate could be catalyzed by 2b with good recycling results for a total of 15 times and also with a 100% selectivity favoring the trans product. To our knowledge, this is the first example of cationic Pd-catalyzed Heck reaction under the thermomorphic mode.