New and robust methodologies have been designed for palladium-catalyzed crosscoupling
reactions involving·a novel·class oftertiary phosphine ligand incorporating a
phospha-adamantane framework. It has been realized that bulky, electron-rich
phosphines, when used as ligands for palladium, allow for cross-coupling reactions
involving even the less reactive aryl halide substrates with a variety of coupling partners.
In an effort to design new ligands suitable for carrying out cross-coupling
transformations, the secondary phosphine, 1,3,5,7-tetramethyl-2,4,8-trioxa-6phosphaadamantane
was converted into a number of tertiary phosphine derivatives. The
ability of these tertiary phosphaadamantanes to act as effective ligands in the palladiumcatalyzed
Suzuki cross-coupling was examined. 1,3,5,7-Tetramethyl-6-phenyl-2,4,8trioxa-
6-phosphaadamantane (PA-Ph) used in combination with Pdz(dba)3permitted the
reaction of an array of aryl iodides, bromides and chlorides with a variety arylboronic
acids to give biaryls in good to excellent yields. Subsequently, palladium complexes of
PA-Ph were prepared and isolated in high yields as air stable palladium bisphosphine
complexes. Two different kinds of crystals were isolated and upon characterization
revealed two complexes, Pd(PA-Ph)z.dba and Pd(PA-Ph)zOz. Preliminary screening for
their catalytic activity indicated that the former is more reactive than the latter. Pd(PAPh)
z.dba was applied as the catalyst for Sonogashira cross-coupling reactions of aryl
iodides and bromides and in the reactions of aryl bromides and chlorides with ketones to
give a-arylated ketones at mild temperatures in high yields
