A Modular Approach to Structurally Diverse Bidentate Chelate Ligands for Transition Metal Catalysis

摘要

A modular approach to a new class of structurally diverse bidentate P/N. P/P, P/S, adn P/Se chelate ligands has been developed. Starting from hydroquinone, various ligands were synthesized in a divergent manner via orthogonally bis-protected bromohydroquinones as the central building block. The first donor functionality (L~1) is introudced to the backbone either by Pd-catalyzed cross-coupling (Suzuki coupling) with hetero-aryl bromides, by Pd-catalyzed amination, or by lithiation and subsequent treatment with electrophiles (e.g.,chlorophosphanes, disulfides, diselenides, or carbamoyl chlorides). After selective deprotection, the second ligand tooth (L~2) is attached by reaction of the phenolic OH functionality with a chlorophosphane, a chlorophosphite, or a related reagent. Some of the resulting chelate ligands were converted into the respective PdX_2 complexes (X =Cl, I), two of which were characterized by X-ray crsytallography. The methodology developed opens an access to a broad variety of new chiral and achiral transition metal complexes and is generally suited for the solid-phase synthesis of combinatorial libraries, as will be reported separately.