251912-40-0Relevant academic research and scientific papers
Evidence that SCS pincer Pd(II) complexes are only precatalysts in Heck catalysis and the implications for catalyst recovery and reuse
Yu, Kunquan,Sommer, William,Richardson, John M.,Weck, Marcus,Jones, Christopher W.
, p. 161 - 171 (2005)
SCS-pincer Pd(II) complexes have been covalently immobilized onto porous silica, cross-linked polymer (Merrifield resin) and soluble poly(norbornene) supports via either amide or urea linkages and evaluated in the Heck coupling of iodobenzene with n-butyl acrylate. Kinetic experiments and poisoning studies indicate that in all cases the pincer complexes merely act as precatalysts. Contrary to literature reports, there is no evidence for catalysis by the intact amide-linked SCS-Pd(II) complexes under any conditions studied here.
Tridentate SCS palladium(II) complexes: New, highly stable, recyclable catalysts for the Heck reaction
Bergbreiter, David E.,Osburn, Philip L.,Liu, Yun-Shan
, p. 9531 - 9538 (2007/10/03)
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 certain conditions. These SCS catalysts are analogous to PCP-type catalysts previously reported in the literature but avoid the requirement of an air-sensitive phosphine synthesis.
