The first synthesis of stable palladium(II) PCP-type catalysts supported on silica - application to the Heck reaction

An efficient method for the formation of a silica-immobilized tridentate diphosphinoaryl ligand (PCP-type) palladium(II) complex (11) is described and successfully used as a catalyst for the Heck reaction. Commercially available 5-amino-isophthalic acid dimethyl ester was converted to N-acetyl-3,5-bis(chloromethyl)aniline (4) in three steps, by reduction, acetylation, and chlorination (Scheme 1). Arbuzov reaction of 4 led to the diphosphine oxide (5). Deprotection and functional group manipulations allowed the transformation of 5 into N-[3,5-bis-(diphenyl-phosphinoylmethyl)-phenyl]-succinamic acid (7). Subsequent reduction of 7 with HSiCl3 afforded the diphosphine (8) attached to silica by transforming compound 8 to N-{3,5-bis[(diphenyl-phosphanyl)methyl]-phenyl}-succinamic acid 2,5-dioxo-pyrrolidin-1-yl ester (9). Palladium(II) trifluoroacetate was used to form the PCP-type palladium(II) complex. This complex shows high catalytic activity in the Heck reaction for aryl iodides, and it is also active with aryl bromides. The catalyst is thermally stable and it is also stable towards oxygen and moisture. In addition, it can be recycled by simple filtration in air and reused with moderate loss of activity. (C) 2003 Elsevier Science B.V. All rights reserved.