Heck Catalysts Research Articles

N-Acyl- N, N-dipyridyl and N-acyl- N-pyridyl- N-quinoyl amine based palladium complexes. Synthesis, X-ray structures, heterogenization and use in Heck couplings

A series of homogeneous and heterogeneous palladium(II)-catalysts and their use in Heck-couplings is described. Starting from four different amines, N-pyrid-2-yl- N-(3-methylpyrid-2-yl)amine ( 1), N-pyrid-2-yl- N-(6-methylpyrid-2-yl)amine ( 2), N-(6-methylpyrid-2-yl)- N-(4-methylquinolin-2-yl)amine ( 3) and N-bis(6-methylpyrid-2-yl)amine ( 4), the corresponding acetyl- and norbornene derivatives, N-pyrid-2-yl- N-(3-methylpyrid-2-yl) acetamide ( 5), N-pyrid-2-yl- N-(6-methylpyrid-2-yl) acetamide ( 6), N-(6-methylpyrid-2-yl)- N-(4-methylquinolin-2-yl) acetamide ( 7), N-bis(6-methylpyrid-2-yl)acetamide ( 8) and N-pyrid-2-yl- N-(3-methylpyrid-2-yl)- endo-norborn-2-ene-5-carbamide ( 9), N-pyrid-2-yl- N-(6-methylpyrid-2-yl)- endo-norborn-2-ene-5-carbamide ( 10) and N-(6-methylpyrid-2-yl)- N-(4-methylquinolin-2-yl)- endo-norborn-2-ene-5-carbamide ( 11), respectively, have been prepared. The acetyl derivatives 5– 8 have been used for the preparation of the homogeneous Heck catalysts N-acetyl- N-pyrid-2-yl- N-(3-methylpyrid-2-yl)amine palladium dichloride ( 13), N-acetyl- N-pyrid-2-yl- N-(6-methylpyrid-2-yl)amine palladium dichloride ( 14), N-acetyl- N-(6-methylpyrid-2-yl)- N-(4-methylquinolin-2-yl)amine palladium dichloride ( 15) and N-acetyl- N-bis(6-methylpyrid-2-yl)amine palladium dichloride ( 16). X-ray data were obtained for compounds 9, 11, 13 and 14. Polymer supports 17– 19 were prepared via ring-opening metathesis copolymerization of the norbornene derivatives 9– 11 with 1,4,4a,5,8,8a-hexahydro-1,4,5,8- exo- endo-dimethano-naphthalene (HDMN-6) and subsequently loaded with palladium(II) chloride. Both the homogeneous catalysts 13– 16 and the heterogeneous catalysts are active in the vinylation of aryl iodides and aryl bromides with turn-over numbers (TONs) of up to 220 000. Comparably low yields (=34%) and TONs (=2100) are achieved in the tetrabutylammonium bromide- (TBAB-) assisted vinylation of aryl chlorides as well as in the amination of aryl bromides. Structural data of compounds 9, 11, 13 and 14 were compared with those of the parent systems, N-acetyldipyridylamine palladiumdichloride ( 20) and the poly( N, N-dipyrid-2-yl- endo-norborn-2-ene-5-carbamide)based resin ( 21), respectively. Thus, methyl-substitution leads to a significant perturbation of the almost perfect square planar coordination of Pd found in 20 resulting in lowered stabilities of the corresponding Pd-complexes 13– 16 and consequently lowered coupling yields compared to 20 and 21.

A Pd complex of a tridentate pincer CNC bis-carbene ligand as a robust homogenous Heck catalyst

The bis-carbene precursor, 1, gives a thermally very robust Pd(II) catalyst for Heck coupling that maintains activity even in boiling diethylacetamide (bp 184 °C) in air.

Tridentate SCS Palladium(II) Complexes: New, Highly Stable, Recyclable Catalysts for the Heck Reaction

A new pincer-type SCS ligand containing Pd(II) is a simple, robust catalyst for Heck chemistry using a variety of alkene acceptors and aryl iodides. It is less active with aryl bromides. While certain palladium(II) species insert slowly into the aryl C−H bond of an unsubstituted version of this ligand, the introduction of activating groups into the 5 position of the aromatic ring readily allows quantitative metal insertion. These ligands were synthesized and attached to soluble polymers by simple modification of inexpensive starting materials. For example, both 5-oxy and 5-amido SCS ligands were successfully appended to 5000 Mn poly(ethylene glycol) via ether or amide linkages, respectively. Both the 5-oxo and 5-amido complexes are active as Heck catalysts in DMF solution in air. The PEG-bound 5-amido-SCS−Pd complex was recycled via solvent precipitation three times with no observed catalyst deactivation. While the 5-amido-SCS−Pd complexes are very robust, their 5-oxo counterparts decompose slowly under c...