Stable Pd(0) Complexes with Ferrocene Bisphosphanes Bearing Phosphatrioxaadamantyl Substituents Efficiently Catalyze Selective C‐H Arylation of Benzoxazoles by Aryl Chlorides

Abstract

AbstractVersatile applications and unique performance of 1,1’‐bis(diphenylphosphanyl)ferrocene (dppf) in coordination chemistry and catalysis prompted the search for its analogs. This contribution describes the synthesis of the first donor‐unsymmetric dppf congeners bearing bulky and rigid 1,3,5,7‐tetramethyl‐2,4,6‐trioxa‐8‐phosphaadamantyl (CgP) donor groups, viz. Ph2PfcPCg (1) and Ph2PfcCH2PCg (2; fc=ferrocene‐1,1’‐diyl). Bis‐phosphanes 1 and 2 were converted into air‐stable Pd(0) complexes, [Pd(ma)(L^L)] (L^L=1 and 2; ma=maleic anhydride). Together with [Pd(ma)(dppf)], these complexes were applied as catalysts in Pd‐catalyzed C−H arylation of benzoxazoles with aryl chlorides in n‐butanol as an environmentally benign solvent. Among all catalysts tested in this study, complex [Pd(ma)(2)] performed the best, providing a high‐yield and selective synthesis of 2‐arylbenzoxazoles from a range of the generally less reactive chloroarenes at low catalyst loading (typically 1 mol.%). Under similar conditions, the structurally related heterocycles (e. g., 1‐methylbenzimidazole and benzothiazole) did not react.