ChemInform Abstract: Catalytic Performance of Symmetrical and Unsymmetrical Sulfur‐Containing Pincer Complexes: Synthesis and Tandem Catalytic Activity of the First PCS‐Pincer Palladium Complex.

Abstract

Catalysis O 0020Catalytic Performance of Symmetrical and Unsymmetrical Sulfur-Containing Pincer Complexes: Synthesis and Tandem Catalytic Activity of the First PCS-Pincer Palladium Complex. -A new arene-based unsymmetrical PCS pincer ligand is prepared and tested in the Pd-catalyzed aldol reaction of isocyanoacetate (I) with benzaldehyde (II). The catalytic activity of the new ligand is comparable to that of the corresponding symmetrical SCS ligand as it enters the catalytic cycle as precatalyst, but it behaves different from the symmetrical PCP ligand. The tandem coupling of allylic chlorides (V) and (X) or vinyloxirane (XV) with hexamethyldistannane and aldehyde (VI) or sulfonylimine (VIII) is efficiently catalyzed by the Pd-PCS complex as it catalyzes the formation of an allylstannane as well as its addition to aldehydes/imines. In contrast, the symmetrical PCP ligand is not effective in allylstannane formation. Thus, desymmetrization and electronic fine-tuning of pincer complexes can lead to unexpected synergistic effects and the development of new catalytic domino reactions. -(GAGLIARDO, M.; SELANDER, N.; MEHENDALE, N. C.; VAN KOTEN, G.; KLEIN GEBBINK*, R. J. M.; SZABO, K. J.; Chem. Eur. J. 14 (2008) 16, 4800-4809; Fac. Sci., Chem. Biol. Org. Chem., Utrecht Univ., NL-3584 CH Utrecht, Neth.; Eng.) -Mischke 40-026